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  • Articles  (5,717)
  • Wiley  (5,717)
  • American Association for the Advancement of Science (AAAS)
  • American Chemical Society
  • 2015-2019  (4,832)
  • 1980-1984  (885)
  • 1925-1929
  • 2016  (4,832)
  • 1983  (885)
  • Geography  (5,717)
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  • Articles  (5,717)
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  • 2015-2019  (4,832)
  • 1980-1984  (885)
  • 1925-1929
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  • 1
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    Sorted stripes on sub-Antarctic Kerguelen Island (1983)
    Wiley
    Details
    Publication Date: 1983-03-01
    Print ISSN: 0197-9337
    Electronic ISSN: 1096-9837
    Topics: Geography , Geosciences
    Published by Wiley on behalf of British Society for Geomorphology.
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  • 2
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    Flood-related channel change in an arid-region river (1983)
    Wiley
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    Publication Date: 1983-03-01
    Print ISSN: 0197-9337
    Electronic ISSN: 1096-9837
    Topics: Geography , Geosciences
    Published by Wiley on behalf of British Society for Geomorphology.
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  • 3
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    On the estimation of spatial autocorrelation in geomorphology (1983)
    Wiley
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    Publication Date: 1983-01-01
    Print ISSN: 0197-9337
    Electronic ISSN: 1096-9837
    Topics: Geography , Geosciences
    Published by Wiley on behalf of British Society for Geomorphology.
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  • 4
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    Lichenometric dating of debris-flow deposits in the Scottish Highlands (1983)
    Wiley
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    Publication Date: 1983-11-01
    Print ISSN: 0197-9337
    Electronic ISSN: 1096-9837
    Topics: Geography , Geosciences
    Published by Wiley on behalf of British Society for Geomorphology.
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  • 5
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    The effect of Gaussian particle-pair distribution functions in the statistical theory of concentration fluctuations in homogeneous turbulence (1983)
    Wiley
    Details
    Publication Date: 1983-04-01
    Print ISSN: 0035-9009
    Electronic ISSN: 1477-870X
    Topics: Geography , Physics
    Published by Wiley on behalf of Royal Meteorological Society.
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  • 6
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    Turbulent dispersion from an elevated line source: Markov chain simulations of concentration and flux profiles (1983)
    Wiley
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    Publication Date: 1983-07-01
    Print ISSN: 0035-9009
    Electronic ISSN: 1477-870X
    Topics: Geography , Physics
    Published by Wiley on behalf of Royal Meteorological Society.
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  • 7
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    Habitat degradation disrupts neophobia in juvenile coral reef fish (2016)
    Wiley
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    Publication Date: 2016-07-10
    Description: Habitat degradation not only disrupts habitat-forming species, but alters the sensory landscape within which most species must balance behavioural activities against predation risk. Rapidly developing a cautious behavioural phenotype, a condition known as neophobia, is advantageous when entering a novel risky habitat. Many aquatic organisms rely on damage-released conspecific cues (i.e. alarm cues) as an indicator of impending danger and use them to assess general risk and develop neophobia. This study tested whether settlement-stage damselfish associated with degraded coral reef habitats were able to use alarm cues as an indicator of risk and, in turn, develop a neophobic response at the end of their larval phase. Our results indicate that fish in live coral habitats that were exposed to alarm cues developed neophobia, and, in situ , were found to be more cautious, more closely associated with their coral shelters and survived four-times better than non-neophobic control fish. In contrast, fish that settled onto degraded coral habitats did not exhibit neophobia and consequently suffered much greater mortality on the reef, regardless of their history of exposure to alarm cues. Our results show that habitat degradation alters the efficacy of alarm cues with phenotypic and survival consequences for newly settled recruits.
    Print ISSN: 1354-1013
    Electronic ISSN: 1365-2486
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
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  • 8
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    Development and verification of two convection-resolving multi-model ensembles over Western Europe (2016)
    Wiley
    Details
    Publication Date: 2016-07-13
    Description: Three storm-scale ensemble prediction models (AROME-EPS, COSMO-DE-EPS, and MOGREPS-UK) were combined over Western Europe to create two convection-allowing, multi-model ensemble prediction systems (EPSs) with the goal of improving ensemble spread-skill relationships and probabilistic forecasting ability. A shared, uniform grid of _2.2 km resolution was used, containing two regions where model domains overlapped (AROME-EPS/COSMODE-EPS and AROME-EPS/MOGREPS-UK).Verification was conducted over a fivemonth period spanning two years using near-surface observations of wind, temperature, relative humidity and precipitation. Bias correction was also applied to each model in order to remove systematic error and to better assess the added value of the multi-model ensembles. Analyses of EPS errors and ensemble scores are presented, including comparisons between individual EPS and multi-model scores. Verification results show that the multi-model ensembles exhibit generally lower RMSE, increased spread, and improved ROC, ROCA, and Brier scores than the individual EPSs. In addition, a case study was selected to highlight discrepancies in precipitation frequency bias between the AROME-EPS and COSMODE-EPS models, attributable to differences in distribution and intensity of precipitation. When combined as a multi-model EPS, the sixhour precipitation accumulation forecast for this case study matched the observations better than the individual EPS forecasts. Together, these results highlight the potential advantage of using multiple models with differing dynamics and physics parameterizations when developing a convection-allowing EPS.
    Print ISSN: 0035-9009
    Electronic ISSN: 1477-870X
    Topics: Geography , Physics
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  • 9
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    First Assimilation of Temperature Lidar Data into an NWP Model: Impact on the Simulation of the Temperature Field, Inversion Strength, and PBL Depth (2016)
    Wiley
    Details
    Publication Date: 2016-07-13
    Description: The impact of assimilating lower–tropospheric lidar temperature profiles into a numerical weather prediction (NWP) model was investigated. The profiles were measured with the Temperature Rotational Raman Lidar (TRRL) of the University of Hohenheim on 24 April 2013. The day showed the development of a typical daytime planetary boundary layer (PBL) with no optically thick clouds. The Weather Research and Forecasting model was operated with 57 vertical levels covering Central Europe with 3 km horizontal resolution. Three different experiments were carried out with a rapid update cycle with hourly three–dimensional variational data assimilation. The impact run (ALL_DA) was performed with the assimilation of conventional data and the additional assimilation of TRRL profiles between 0900 and 1800 UTC in a height range from about 500 m to 3000 m above ground level with a vertical resolution of about 100 m. In CONV_DA and NO_DA, only conventional data and no data were assimilated, respectively. To consider the representativeness of the TRRL profiles, an observation error of 0.7 K was used for all heights. The assimilation was performed using the radiosonde operator. The TRRL data assimilation corrected the temperature profiles towards the lidar data. In the mean, the boundary layer height was improved by 60 m in ALL_DA compared to the TRRL data and the temperature gradient in the entrainment layer by 0.19 K (100 m) − 1 . While ALL_DA showed a root mean square error (RMSE) of 0.6 K compared to the TRRL data, the RMSE of CONV_DA was twice as large. Compared to data from radiosondes launched at the TRRL site, ALL_DA showed a significantly smaller RMSE than CONV_DA in two out of four times radiosonde data were available. We conclude that the assimilation of TRRL data has great potential to close the critical gap of missing temperature observations in the lower troposphere.
    Print ISSN: 0035-9009
    Electronic ISSN: 1477-870X
    Topics: Geography , Physics
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  • 10
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    Holocene delta evolution and sediment flux of the Pearl River, southern China (2016)
    Wiley
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    Publication Date: 2016-07-15
    Description: ABSTRACT Delta progradation and sediment flux of the Pearl River Delta (PRD), southern China, during the Holocene are presented based on analyses of borehole data on the delta plain. Results indicate that the delta prograded into the drowned valley because of early Holocene inundation from 9 to 6 cal ka BP, as sea-level rise decelerated. The sea level reached its present level at about 6 cal ka BP and, as a consequence, a large portion of the drowned valley was covered by the estuary, with more than 160 rock islands and platforms. The scattered landmasses promoted active deposition and acted as deposition nuclei during deltaic evolution. Consequently, apart from exhibiting a general tendency towards progression, PRD development occurred less regularly over time and space because of deposition around island boundaries. During the last 2 ka, mainly because of significantly increased human activities, which have trapped sediments in the encircled tidal flats along the front of delta plains, the shoreline has advanced rapidly. Estimated sediment fluxes for the three periods (9–6, 6–2 and 2–0 cal ka BP), based on the sediment volume analysis, were 17–25, 22–30 and 44–58 million t a −1 , respectively.
    Print ISSN: 0267-8179
    Electronic ISSN: 1099-1417
    Topics: Geography , Geosciences
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  • 11
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    Spatial statistical network models for stream and river temperature in New England, USA (2016)
    Wiley
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    Publication Date: 2016-07-15
    Description: Watershed managers are challenged by the need for predictive temperature models with sufficient accuracy and geographic breadth for practical use. We described thermal regimes of New England rivers and streams based on a reduced set of metrics for the May to September growing season (July or August median temperature, diurnal rate of change, and magnitude and timing of growing season maximum) chosen through principal component analysis of 78 candidate metrics. We then developed and assessed spatial statistical models for each of these metrics, incorporating spatial autocorrelation based on both distance along the flow network and Euclidean distance between points. Calculation of spatial autocorrelation based on travel or retention time in place of network distance yielded tighter-fitting Torgegrams with less scatter but did not improve overall model prediction accuracy. We predicted monthly median July or August stream temperatures as a function of median air temperature, estimated urban heat island effect, shaded solar radiation, main channel slope, watershed storage (percent lake and wetland area), percent coarse-grained surficial deposits, and presence or maximum depth of a lake immediately upstream, with an overall root-mean-square prediction error of 1.4 and 1.5 ○ C, respectively. Growing season maximum water temperature varied as a function of air temperature, local channel slope, shaded August solar radiation, imperviousness, and watershed storage. Predictive models for July or August daily range, maximum daily rate of change, and timing of growing season maximum were statistically significant but explained a much lower proportion of variance than the above models (5-14% of total) . This article is protected by copyright. All rights reserved.
    Print ISSN: 0043-1397
    Electronic ISSN: 1944-7973
    Topics: Architecture, Civil Engineering, Surveying , Geography
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 12
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    Accurate early and late time modelling of countercurrent spontaneous imbibition (2016)
    Wiley
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    Publication Date: 2016-07-15
    Description: Spontaneous counter-current imbibition into a finite porous medium is an important physical mechanism for many applications, included but not limited to irrigation, CO 2 storage and oil recovery. Symmetry considerations that are often valid in fractured porous media allow us to study the process in a one-dimensional domain. In 1D, the onset of imbibition can be captured by self-similar solutions and the imbibed volume scales with . At later times, the imbibition rate decreases and the finite size of the medium has to be taken into account. This requires numerical solutions. Here, we present a new approach to approximate the whole imbibition process semi-analytically. While the onset is captured by a semi-analytical solution. We also provide an a priori estimate of the time until which the imbibed volume scales with . This time is significantly longer than the time it takes until the imbibition front reaches the model boundary. The remainder of the imbibition process is obtained from a self-similarity solution. We test our approach against numerical solutions that employ parametrizations relevant for oil recovery and CO 2 sequestration. We show that this concept improves common first order approaches that heavily underestimate early-time behaviour and note that it can be readily included into dual porosity models. This article is protected by copyright. All rights reserved.
    Print ISSN: 0043-1397
    Electronic ISSN: 1944-7973
    Topics: Architecture, Civil Engineering, Surveying , Geography
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  • 13
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    Tap water isotope ratios reflect urban water system structure and dynamics across a semiarid metropolitan area (2016)
    Wiley
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    Publication Date: 2016-07-15
    Description: Water extraction for anthropogenic use has become a major flux in the hydrological cycle. With increasing demand for water and challenges supplying it in the face of climate change, there is a pressing need to better understand connections between human populations, climate, water extraction, water use, and its impacts. To understand these connections, we collected and analyzed stable isotopic ratios of more than 800 urban tap water samples in a series of semiannual water surveys (spring and fall, 2013 to 2015) across the Salt Lake Valley (SLV) of northern Utah. Consistent with previous work, we found that mean tap water had a lower 2 H and 18 O concentration than local precipitation, highlighting the importance of nearby montane winter precipitation as source water for the region. However, we observed strong and structured spatiotemporal variation in tap water isotopic compositions across the region which we attribute to complex distribution systems, varying water management practices and multiple sources used across the valley. Water from different sources was not used uniformly throughout the area and we identified significant correlation between water source and demographic parameters including population and income. Isotopic mass balance indicated significant inter- and intra-annual variability in water losses within the distribution network due to evaporation from surface water resources supplying the SLV. Our results demonstrate the effectiveness of isotopes as an indicator of water management strategies and climate impacts within regional urban water systems, with potential utility for monitoring, regulation, forensic and a range of water resource research. This article is protected by copyright. All rights reserved.
    Print ISSN: 0043-1397
    Electronic ISSN: 1944-7973
    Topics: Architecture, Civil Engineering, Surveying , Geography
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  • 14
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    Bed material transport estimate in large gravel-bed rivers using the virtual velocity approach (2016)
    Wiley
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    Publication Date: 2016-07-16
    Description: This paper reports on a first attempt of using the virtual velocity approach to assess sediment mobility and transport in two wide and complex gravel-bed rivers of northern Italy. Displacement length and virtual velocity of spray-painted tracers were measured in the field. Also, the thickness of the sediment active layer during floods was measured using scour chains and post-flood morphological changes as documented by repeated survey of channel cross-sections. The effects of 8 and 7 floods were studied on the Tagliamento and Brenta rivers, where 259 and 277 spray-painted areas were surveyed, respectively. In the Tagliamento Rivers 36 % of the spray-painted areas experienced partial transport, whereas in the Brenta this accounted for 20%. Full removal/gravel deposition was whereas observed on 37 % and 26 % of these areas on the Tagliamento and Brenta rivers, respectively. The mean displacement length of particles, the thickness of the active layer and the extent of partial transport are well correlated with the dimensionless shear stress. The virtual velocity approach allowed calculation of bed material transport over a wide range of flood magnitudes. Annual coarse sediment transport was calculated up to 150 for the Tagliamento, and 30 × 10 3  m 3  yr -1 for the Brenta. The outcomes of this work highlight the relevance of partial transport condition, as it could represent more than 70% of the total bed material transported during low-magnitude floods, and up to 40% for near-bankfull events. Results confirm that bed material load tends to be overestimated by traditional formulas. This article is protected by copyright. All rights reserved.
    Print ISSN: 0197-9337
    Electronic ISSN: 1096-9837
    Topics: Geography , Geosciences
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  • 15
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    Using practical and social information to influence flood adaptation behavior (2016)
    Wiley
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    Publication Date: 2016-07-16
    Description: As the prospect for more frequent and severe extreme weather events gains scientific support, many nations are evaluating mitigation and adaptation options. Insurance and home retrofits could reduce household welfare losses due to flood events. Yet, even after disasters, households often fail to take risk mitigation actions. This paper presents the first randomized field experiment that tests the effect of information provision on household uptake of flood insurance and home retrofits. A sample of 364 flood-prone households in Bangkok was randomly split into treatment and control groups. The treatment group received practical details on home retrofits and flood insurance as well as social information regarding the insurance purchase decisions of peers. Results indicate that the information intervention increased insurance purchases by about five percentage points, while no effect was detected for home retrofits. This effect is nearly equal to the increase in uptake that the national insurance program in Thailand has achieved through all other means since its establishment in 2012. If scaled up to include all uninsured, flood-prone households in Bangkok, nearly 70,000 additional households could be insured. The results suggest that well-designed information interventions could increase uptake of flood insurance, without additional premium subsidies or mandates. This article is protected by copyright. All rights reserved.
    Print ISSN: 0043-1397
    Electronic ISSN: 1944-7973
    Topics: Architecture, Civil Engineering, Surveying , Geography
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 16
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    Integrated surface/subsurface permafrost thermal hydrology: Model formulation and proof-of-concept simulations (2016)
    Wiley
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    Publication Date: 2016-07-16
    Description: The need to understand potential climate impacts and feedbacks in Arctic regions has prompted recent interest in modeling of permafrost dynamics in a warming climate. A new fine-scale integrated surface/subsurface thermal hydrology modeling capability is described and demonstrated in proof-of-concept simulations. The new modeling capability combines a surface energy balance model with recently developed three-dimensional subsurface thermal hydrology models and new models for nonisothermal surface water flows and snow distribution in the microtopography. Surface water flows are modeled using the diffusion wave equation extended to include energy transport and phase change of ponded water. Variation of snow depth in the microtopography, physically the result of wind scour, is modeled phenomenologically with a diffusion wave equation. The multiple surface and subsurface processes are implemented by leveraging highly parallel community software. Fully integrated thermal hydrology simulations on the tilted open book catchment, an important test case for integrated surface/subsurface flow modeling, are presented. Fine-scale 100-year projections of the integrated permafrost thermal hydrological system on an ice wedge polygon at Barrow Alaska in a warming climate are also presented. These simulations demonstrate the feasibility of microtopography-resolving, process-rich simulations as a tool to help understand possible future evolution of the carbon-rich Arctic tundra in a warming climate. This article is protected by copyright. All rights reserved.
    Print ISSN: 0043-1397
    Electronic ISSN: 1944-7973
    Topics: Architecture, Civil Engineering, Surveying , Geography
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  • 17
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    The morphological response of foredunes at a breached barrier system to winter 2013/2014 storms on the southwest coast of Ireland (2016)
    Wiley
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    Publication Date: 2016-07-21
    Description: ABSTRACT Abstract: The level of storminess in Ireland during the winter of 2013/2014 was exceptional, the effects of which cost the Irish state in excess of €260 Million in infrastructure repair and insurance claims. In Ireland, a lack of coastal process data from monitoring programmes means that the response of protective barrier coasts to such events remains largely un-investigated. This study addresses this issue through an examination of the geomorphic impacts of recent storms, including those that occurred during the winter 2013/2014, on a breached barrier on the southwest coast of Ireland. Data from a two-year terrestrial laser scanning (TLS) monitoring campaign shows that the W2013/2014 events caused a major (〉50 m) dune recession at Rossbehy, Co. Kerry. Results from a simple linear regression analysis indicate storm duration plays an important role in the removal of foredunes at the study site. Given the fact that the frequency of intense storms in the vicinity of Ireland is forecast increase within the next century, a scientific understanding of barrier response to such events is critical to inform sound management practices. This article is protected by copyright. All rights reserved.
    Print ISSN: 0197-9337
    Electronic ISSN: 1096-9837
    Topics: Geography , Geosciences
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  • 18
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    Evaluating, predicting and mapping belowground carbon stores in Kenyan mangroves (2016)
    Wiley
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    Publication Date: 2016-07-21
    Description: Despite covering only approximately 138,000 km 2 , mangroves are globally important carbon sinks with carbon density values 3-4 times that of terrestrial forests. A key challenge in evaluating the carbon benefits from mangrove forest conservation is the lack of rigorous spatially resolved estimates of mangrove sediment carbon stocks; most mangrove carbon is stored belowground. Previous work has focused on detailed estimations of carbon stores over relatively small areas, which has obvious limitations in terms of generality and scope of application. Most studies have focused only on quantifying the top 1m of belowground carbon (BGC). Carbon stored at depths beyond 1m, and the effects of mangrove species, location and environmental context on these stores, is poorly studied. This study investigated these variables at two sites (Gazi and Vanga in the south of Kenya) and used the data to produce a country-specific BGC predictive model for Kenya and map BGC store estimates throughout Kenya at spatial scales relevant for climate change research, forest management and REDD+ (Reduced Emissions from Deforestation and Degradation). The results revealed that mangrove species was the most reliable predictor of BGC; Rhizophora muronata had the highest mean BGC with 1485.5t C ha −1 . Applying the species-based predictive model to a base map of species distribution in Kenya for the year 2010 with a 2.5m 2 resolution, produced an estimate of 69.41 Mt C (± 9.15 95% C.I.) for BGC in Kenyan mangroves. When applied to a 1992 mangrove distribution map, the BGC estimate was 75.65 Mt C (± 12.21 95% C.I.); an 8.3% loss in BGC stores between 1992 and 2010 in Kenya. The country level mangrove map provides a valuable tool for assessing carbon stocks and visualising the distribution of BGC. Estimates at the 2.5m 2 resolution provide sufficient detail for highlighting and prioritising areas for mangrove conservation and restoration. This article is protected by copyright. All rights reserved.
    Print ISSN: 1354-1013
    Electronic ISSN: 1365-2486
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
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  • 19
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    Estimation of the functional form of subgrid-scale parameterizations using ensemble-based data assimilation: a simple model experiment (2016)
    Wiley
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    Publication Date: 2016-07-21
    Description: Oceanic and atmospheric global numerical models represent explicitly the large-scale dynamics while the smaller-scale processes are not resolved so that their effects in the large-scale dynamics are included through subgrid-scale parameterizations. These parameterizations represent small-scale effects as a function of the resolved variables. In this work, data assimilation principles are used not only to estimate the parameters of subgrid-scale parameterizations but also to uncover the functional dependencies of subgrid-scale processes as a function of large-scale variables. Two data assimilation methods based on the ensemble transform Kalman filter (ETKF) are evaluated in the two-scale Lorenz ’96 system scenario. The first method is an online estimation that uses the ETKF with an augmented space state composed of the model large-scale variables and a set of unknown global parameters from the parameterization. The second method is an offline estimation that uses the ETKF to estimate an augmented space state composed of the large-scale variables and by a space dependent model error term. Then a polynomial regression is used to fit the estimated model error as a function of the large-scale model variables in order to develop a parameterization of small-scale dynamics. The online estimation shows a good performance when the parameter-state relationship is assumed to be quadratic polynomial function. The offline estimation captures better some of the highly nonlinear functional dependencies found in the subgrid-scale processes. The nonlinear and nonlocal dependence found in an experiment with shear-generated small-scale dynamics is also recovered by the offline estimation method. Therefore, the combination of these two methods could be a useful tool for the estimation of the functional form of subgrid-scale parameterizations.
    Print ISSN: 0035-9009
    Electronic ISSN: 1477-870X
    Topics: Geography , Physics
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  • 20
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    Sensitivity of a continental nighttime stratocumulus-topped boundary layer to varying environmental conditions (2016)
    Wiley
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    Publication Date: 2016-07-21
    Description: Large-eddy simulation of a nocturnal stratocumulus-topped boundary layer in a continental mid-latitude environment has been performed to examine the sensitivity of the cloud to a number of different environmental parameters. The simulations showed that the stratocumulus cloud was strongly affected by the presence of an overlying free tropospheric cirrus cloud (FTC), in agreement with previous studies of marine nighttime stratocumulus. When introducing an FTC with an optical thickness of 2, stratocumulus liquid water path decreased by 30%. Enhancing the optical thickness of the FTC to 8 further decreased the liquid water path by almost 10%. The presence of an FTC decreased the cloud-top radiative cooling which decreased the turbulent mixing in the boundary layer so that the liquid water content and cloud depth were reduced. The sensitivity of the stratocumulus cloud to an overlying FTC was found to be affected by the moisture content in the free troposphere. When a clear positive or negative moisture gradient above the inversion was imposed, and an overlying FTC with an optical thickness of 8 was introduced, the stratocumulus cloud LWP decreased by more than 40%. Furthermore, the effect of changes in free tropospheric moisture content and an overlying FTC on the stratocumulus cloud properties was found to be non-linear, the combined response was in general weaker than the two responses added together. The modeled response to changes in cloud condensation nuclei (CCN) concentrations was found to be non-significant, unless the CCN concentrations were so low that drizzle was induced (r 50 cm −3 ).
    Print ISSN: 0035-9009
    Electronic ISSN: 1477-870X
    Topics: Geography , Physics
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  • 21
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    An Evaluation of Parametric Sensitivities of Different Meteorological Variables Simulated by the WRF Model (2016)
    Wiley
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    Publication Date: 2016-07-21
    Description: ABSTRACT The specification of model parameters in numerical weather prediction (NWP) models has great influence on model performance. However, how to specify model parameters properly is not a trivial task because a typical NWP model like the Weather Research and Forecasting (WRF) model contains many model parameters and many model outputs. This paper presents the results of an investigation into the sensitivities of different WRF model outputs to the specification of its model parameters. Using a global sensitivity analysis method, the sensitivities are evaluated for surface meteorological variables such as precipitation, surface air temperature, humidity and wind speed, as well as for atmospheric variables such as total precipitable water, cloud cover, boundary layer height and outgoing longwave radiation at the top of the atmosphere, all simulated by the WRF model using different model parameters. The goal of this study is to identify the parameters that exert most influence on the skill of short-range meteorological forecasts. The study was performed over the Greater Beijing Region of China. A total of 23 adjustable parameters from seven different physical parameterization schemes were considered. The results indicate that parameter sensitivities vary with different model outputs. However, some of the 23 model parameters considered are shown to be sensitive to all model outputs evaluated, while other parameters may be sensitive to a particular output. The sensitivity results from this research are a basis for further optimizations of the WRF model parameters.
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    Topics: Geography , Physics
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  • 22
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    Oceanic teleconnection for carbon dioxide (2016)
    Wiley
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    Publication Date: 2016-07-23
    Description: Biogeochemical teleconnection links seemingly unrelated chemical/biological anomalies that are geographically separated by large distances. Bronselaer et al propose a new mechanism for an interhemispheric teleconnection of air-sea carbon dioxide fluxes in which the upwelling of the Southern Ocean triggers a series of perturbations leading to the alteration of the carbon uptake in the North Atlantic. The westerly wind over the Southern Ocean has a unique role in the climate system. It energizes the strongest ocean current, Antarctic Circumpolar Current, and it lifts up the carbon- and nutrient-rich deep waters all the way to the surface. It is an end point of the ocean's deep overturning circulation and associated biological carbon storage, where the excess carbon from accumulated decomposition of organic material is finally released back into the atmosphere. It is well established that the Southern Ocean upwelling regionally modulates the de-gassing of carbon dioxide there. However, its global-scale implication is not yet fully understood. What happens to the carbon uptake in the other parts of the oceans? In this volume of Global Biogeochemical Cycles, Bronselaer et al describes the chain of events that link the increased Southern Ocean wind to the ocean carbon uptake in the northern high latitudes. The authors conducted a set of computational experiments, showing that the Southern Ocean is a starting point of the oceanic teleconnection, where the excess nutrient is transported equatorward through the shallow overturning circulation. The stream of macro-nutrient then fertilizes the low-latitude productivity that eventually shifts the carbonate chemistry of the high latitude surface waters. This is an intriguing case of oceanic teleconnection, linking seemingly unrelated biogeochemical anomalies that are geographically separated by large distances. The surprising conclusion is that a stronger Southern Ocean wind increases the de-gassing of carbon dioxide in both northern and southern high latitudes. This happens because more carbon is upwelling into the northern high latitudes due to the increased low-latitude biological pump, approximately doubling the de-gassing intensity relative to the Southern Ocean response alone. There may be more surprises from the Southern Ocean.
    Print ISSN: 0886-6236
    Electronic ISSN: 1944-9224
    Topics: Biology , Chemistry and Pharmacology , Geography , Geosciences , Physics
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    Frequency analysis of nonstationary annual maximum flood series using the time-varying two-component mixture distributions (2016)
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    Publication Date: 2016-07-23
    Description: The most popular practice for analyzing nonstationarity of flood series is to use a fixed single-type probability distribution incorporated with the time-varying moments. However, the type of probability distribution could be both complex because of distinct flood populations and time-varying under changing environments. To allow the investigation of this complex nature, the time-varying two-component mixture distributions (TTMD) method is proposed in this study by considering the time variations of not only the moments of its component distributions but also the weighting coefficients. Having identified the existence of mixed flood populations based on circular statistics, the proposed TTMD was applied to model the annual maximum flood series (AMFS) of two stations in the Weihe River basin (WRB), with the model parameters calibrated by the meta-heuristic maximum likelihood (MHML) method. The performance of TTMD was evaluated by different diagnostic plots and indexes and compared with stationary single-type distributions, stationary mixture distributions and time-varying single-type distributions. The results highlighted the advantages of TTMD with physically-based covariates for both stations. Besides, the optimal TTMD models were considered to be capable of settling the issue of nonstationarity and capturing the mixed flood populations satisfactorily. This article is protected by copyright. All rights reserved.
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    Electronic ISSN: 1099-1085
    Topics: Architecture, Civil Engineering, Surveying , Geography
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    A spatially distributed model for assessment of the effects of changing land use and climate on urban stream quality (2016)
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    Publication Date: 2016-07-23
    Description: While the effects of land use change in urban areas have been widely examined, the combined effects of climate and land use change on the quality of urban and urbanizing streams have received much less attention. We describe a modeling framework that is applicable to the evaluation of potential changes in urban water quality and associated hydrologic changes in response to ongoing climate and landscape alteration. The grid-based spatially distributed model, DHSVM-WQ, is an outgrowth of the Distributed Hydrology-Soil-Vegetation Model (DHSVM) that incorporates modules for assessing hydrology and water quality in urbanized watersheds at a high spatial and temporal resolution. DHSVM-WQ simulates surface runoff quality and in-stream processes that control the transport of nonpoint-source (NPS) pollutants into urban streams. We configure DHSVM-WQ for three partially urbanized catchments in the Puget Sound region to evaluate the water quality responses to current conditions and projected changes in climate and/or land use over the next century. Here we focus on total suspended solids (TSS) and total phosphorus (TP) from nonpoint sources (runoff), as well as stream temperature. The projection of future land use is characterized by a combination of densification in existing urban or partially urban areas, and expansion of the urban footprint. The climate change scenarios consist of individual and concurrent changes in temperature and precipitation. Future precipitation is projected to increase in winter and decrease in summer, while future temperature is projected to increase throughout the year. Our results show that urbanization has a much greater effect than climate change on both the magnitude and seasonal variability of streamflow, TSS and TP loads largely due to substantially increased streamflow, and particularly winter flow peaks. Water temperature is more sensitive to climate warming scenarios than to urbanization and precipitation changes. Future urbanization and climate change together are predicted to significantly increase annual mean streamflow (up to 55%), water temperature (up to 1.9 °C), TSS load (up to 182%), and TP load (up to 74%). This article is protected by copyright. All rights reserved.
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    Topics: Architecture, Civil Engineering, Surveying , Geography
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    How Does DEM Resolution Affect Microtopographic Characteristics, Hydrologic Connectivity, and Modeling of Hydrologic Processes? (2016)
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    Publication Date: 2016-07-23
    Description: The resolution of a digital elevation model (DEM) is a crucial factor in watershed hydrologic and environmental modeling. DEM resolution can cause significant variability in the representation of surface topography, which further affects quantification of hydrologic connectivity and simulation of hydrologic processes. The objective of this study is to examine the effects of DEM resolution on (1) surface microtopographic characteristics, (2) hydrologic connectivity, and (3) the spatial and temporal variations of hydrologic processes. A puddle-to-puddle (P2P) modeling system was utilized for surface delineation and modeling of the P2P overland flow dynamics, surface runoff, infiltration, and unsaturated flow for nine DEM resolution scenarios of a field plot surface. Comparisons of the nine modeling scenarios demonstrated that coarser DEM resolutions tended to eliminate topographic features, reduce surface depression storage, and strengthen hydrologic connectivity and surface runoff. We found that reduction in maximum depression storage and maximum ponding area was as high as 97.56% and 76.36%, respectively, as the DEM grid size increased from 2 cm to 80 cm. The paired t-test and fractal analysis demonstrated the existence of a threshold DEM resolution (10 cm for the field plot), within which the DEM-based hydrologic modeling was effective and acceptable. The effects of DEM resolution were further evaluated for a larger surface in the Prairie Pothole Region (PPR) subjected to observed rainfall events. It was found that simulations based on coarser resolution DEMs (〉10 m) tended to overestimate ponded areas and underestimate runoff discharge peaks. The simulated peak discharge from the PPR surface reduced by approximately 50% as the DEM resolution changed from 2 m to 90 m. Fractal analysis results elucidated scale dependency of hydrologic and topographic processes. In particular, scale analysis highlighted a unique constant-threshold-power relationship between DEM scale and topographic and hydrologic parameters/variables. Not only does this finding allow one to identify threshold DEM, but also further develop functional relationships for scaling to achieve valid topographic characterization as well as effective and efficient hydrologic modeling. This article is protected by copyright. All rights reserved.
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    Land management: data availability and process understanding for global change studies (2016)
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    Publication Date: 2016-07-23
    Description: In light of daunting global sustainability challenges such as climate change, biodiversity loss and food security, improving our understanding of the complex dynamics of the Earth system is crucial. However, large knowledge gaps related to the effects of land management persist, in particular those human-induced changes in terrestrial ecosystems that do not result in land cover conversions. Here we review the current state of knowledge of ten common land management activities for their biogeochemical and biophysical impacts, the level of process-understanding and data availability. Our review shows that ca. one tenth of the ice free land surface is under intense human management, half under medium and one fifth under extensive management. Based on our review, we cluster these ten management activities into three groups: (1) management activities for which datasets are available, and for which a good knowledge base exists (cropland harvest and irrigation); (2) management activities for which sufficient knowledge on biogeochemical and biophysical effects exists but robust global datasets are lacking (forest harvest, tree species selection, grazing and mowing harvest, N-fertilization); and (3) land management practices with severe data gaps concomitant with an unsatisfactory level of process understanding (crop species selection, artificial wetland drainage, tillage and fire management and crop residue management, an element of crop harvest). Although we identify multiple impediments to progress, we conclude that the current status of process understanding and data availability is sufficient to advance with incorporating management in e.g. Earth System or Dynamic Vegetation models in order to provide a systematic assessment of their role in the Earth system. This review contributes to a strategic prioritization of research efforts across multiple disciplines, including land system research, ecological research and Earth system modelling. This article is protected by copyright. All rights reserved.
    Print ISSN: 1354-1013
    Electronic ISSN: 1365-2486
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
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    Estimating runoff from a glacierized catchment using natural tracers in the semi-arid Andes Cordillera (2016)
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    Publication Date: 2016-07-23
    Description: This paper presents a methodology for hydrograph separation in mountain watersheds, which aims at identifying flow sources among ungauged headwater sub-catchments through a combination of observed streamflow and data on natural tracers including isotope and dissolved solids. Daily summer and bi-daily spring season water samples obtained at the outlet of the Juncal River Basin in the Andes of Central Chile were analyzed for all major ions as well as stable water isotopes, δ 18 O and δD. Additionally, various samples from rain, snow, surface streams and exfiltrating subsurface water (springs), were sampled throughout the catchment. A principal component analysis (PCA) was performed in order to address cross-correlation in the tracer dataset, reduce the dimensionality of the problem and to uncover patterns of variability. Potential sources were identified in a two-component U-space that explains 94% of the observed tracer variability at the catchment outlet. Hydrograph separation was performed through an Informative - Bayesian model. Our results indicate that the Juncal Norte Glacier headwater sub-catchment contributed at least 50% of summer flows at the Juncal River Basin outlet during the 2011–12 water year (a hydrologically dry period in the Region), even though it accounts for only 27% of the basin area. Our study confirms the value of combining solute and isotope information for estimating source contributions in complex hydrologic systems, and provides insights regarding experimental design in high-elevation semi-arid catchments. The findings of this study can be useful for evaluating modeling studies of the hydrological consequences of the rapid decrease in glacier cover observed in this region, by providing insights into the origin of river water in basins with little hydrometeorological information.
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    Quantifying Changes of Effective Springshed Area and Net Recharge through Recession Analysis of Spring Flow (2016)
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    Publication Date: 2016-07-24
    Description: The average flow of Silver Springs, one of the largest magnitude springs in central Florida, declined 32% from 2000 to 2012. The average groundwater head in the springshed declined 0.14 m, and the spring pool altitude increased 0.24 m during the same period. This paper presents a novel explanation of the spring flow recession curve for Silver Springs using Torricelli model, which uses the groundwater head at a sentinel well, the spring pool altitude, and the net recharge to groundwater. The effective springshed area and net recharge (defined as recharge minus groundwater pumping and evapotranspiration) were estimated based on the observed recession slopes for spring flow, groundwater head, and spring pool altitude. The results show that the effective springshed area continuously declined since 1989, and the net recharge declined since the 1970s with a significant drop in 2002. Subsequent to 2002, the net recharge increased modestly but not to the levels prior to the 1990s. The reduction in net recharge was caused by changes in hydroclimatic conditions including precipitation and temperature, along with groundwater withdrawals, which contributed to the declined spring flow.
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    Quantification and attribution of errors in the simulated annual gross primary production and latent heat fluxes by two global land surface models (2016)
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    Publication Date: 2016-07-26
    Description: Differences in the predicted carbon and water fluxes by different global land models have been quite large and have not decreased over the last two decades. Quantification and attribution of the uncertainties of global land surface models are important for improving the performance of global land surface models, and are the foci of this study. Here we quantified the model errors by comparing the simulated monthly global gross primary productivity (GPP) and latent heat flux (LE) by two global land surface models with the model-data products of global GPP and LE from 1982-2005. By analyzing model parameter sensitivities within their ranges, we identified about 2 to 11 most sensitive model parameters that have strong influences on the simulated GPP or LE by two global land models, and found that the sensitivities of the same parameters are different among the plant functional types (PFT). Using parameter ensemble simulations, we found that 15% to 60% of the model errors were reduced by tuning only a few (〈4) most sensitive parameters for most PFTs, and that the reduction in model errors varied spatially within a PFT or among different PFTs. Our study shows that future model improvement should optimize key model parameters, particularly those parameters relating to leaf area index, maximum carboxylation rate and stomatal conductance. This article is protected by copyright. All rights reserved.
    Electronic ISSN: 1942-2466
    Topics: Geography , Geosciences
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    Late Quaternary glacial advances in the eastern Qilianshan, north-eastern Tibet, as inferred from luminescence dating of fluvioglacial sediments (2016)
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    Publication Date: 2016-07-27
    Description: ABSTRACT The Qilianshan [ shan means ‘mountain(s)’ in Chinese] are important for understanding the Quaternary glaciations which occurred along the north-eastern margins of the Tibetan Plateau (TP). Two sets of moraines identified in the Gangshika Valley on the southern slopes of the Qilianshan, and in the Jindonggou Valley on the northern slopes of the Lenglongling Ridge in the eastern Qilianshan, were dated using optically stimulated luminescence (OSL) dating. The D e values of the sediments were determined using single aliquot regeneration (SAR) and ‘global standardized growth curve’ (gSGC) procedures. The gSGC method was first applied to glacial sediment and proved to be adaptable. Based on D e distribution analysis, and a comparison between the ages of coarse-grained (90–125 μm) quartz, we concluded that the minimum age model (MAM) OSL age obtained may be closer to the burial age of the sediments. The first set of moraines in the Gangshika Valley was formed at 18.1 ± 1.8 ka. The second set of moraines in both the Gangshika and the Jindonggou valleys was mainly formed at ∼12.5–10.7 ka, consistent with the Younger Drays chronozone, most probably covering the moraines produced at 14.3 ± 1.4 ka. These results indicate that the glaciers along the Lenglongling Ridge were sensitive to abrupt decreases in temperature.
    Print ISSN: 0267-8179
    Electronic ISSN: 1099-1417
    Topics: Geography , Geosciences
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    A glaciogenic sequence from the Early Pleistocene of the Central North Sea (2016)
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    Publication Date: 2016-07-27
    Description: ABSTRACT A depositional sequence bounded by upper and lower erosion surfaces covering a 35-km × 20-km area within the northern embayment of the Early Pleistocene Central North Sea is dated close to the Jaramillo Normal sub-chron at approximately 1.0–1.1 Ma. The basal surface cuts shallow marine clays of the upper Nordland Group and is characterized by furrow incisions, mega-scale glacial lineation textures and bedforms that are all orientated NNW–SSE. The sequence comprises a suite of distinctive bedforms, including a chaotic deposit up to 60 m thick, a series of moulded and lineated depositional bodies and some more complex bedforms, with lithologies shown by petrophysical data to be dominated by overconsolidated clays and thin sand layers. This sequence is considered to represent deposition from the advance and subsequent decay of a marine-terminating ice-sheet. The upper surface of the sequence coincides with the so-called ‘Crenulate Reflection’ and is characterized by a fluvial channel system, representing final retreat of the ice-sheet, which was followed by shallow marine conditions and deposition of the Aberdeen Ground Formation. It is considered that the Aberdeen Ground Formation comprises at least two main sequences spanning the Early to Middle Pleistocene.
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    Electronic ISSN: 1099-1417
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    Spheroidal weathering of granite porphyry with welldeveloped columnar joints by oxidation, iron precipitation, and rindlet exfoliation (2016)
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    Publication Date: 2016-07-27
    Description: ABSTRACT Spheroidal weathering, one of the important rock weathering styles, has been attributed to chemical weathering by the water from joint surfaces, and mechanical aspects of the weathering have not been well addressed. We made an investigation on spheroidal weathering of Miocene granite porphyry with well-developed columnar joints and found that this spheroidal weathering proceeds through chemical processes and accompanying mechanical processes. The investigation of the textures, physical properties, mineralogy, and chemistry of the porphyry revealed the presence of a brown band on the surface margins of corestones, representing the oxidation of pyrite and chlorite, and the precipitation of iron hydroxides, and the consequent generation of micro-cracks within the band. During weathering, oxidation progresses inwards from joints that surround the rindlets, including both high-angle columnar and low-angle planar joints, and causes rounding of the unweathered interior portion of the rock. Microscopic observations of the brown band embedded with fluorescent resin show that pores are first filled with iron hydroxides, and that micro-cracks then form parallel to the oxidation front in the outer portion of the brown band. Iron hydroxide precipitation increases the P-wave velocity in the brown band, while micro-crack formation decreases the tensile strength of the rock. Where the brown band has thickened to ~6 cm, the micro-cracks are connected to one another to create continuous cracks, which separate the rindlets from the corestone. Micro-crack formation parallel to the corestone surface may be attributed to compressive stresses generated by small amounts of volumetric expansion due to the precipitation of iron hydroxides in the brown band. Earth surface is under oxidizing environments so that precipitation of iron hydroxides commonly occurs; the spheroidal weathering in this paper is a typical example of the combination of chemical and mechanical processes under such environments. This article is protected by copyright. All rights reserved.
    Print ISSN: 0197-9337
    Electronic ISSN: 1096-9837
    Topics: Geography , Geosciences
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    Issue Information - TOC (2016)
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    Publication Date: 2016-07-27
    Description: No abstract is available for this article.
    Print ISSN: 0197-9337
    Electronic ISSN: 1096-9837
    Topics: Geography , Geosciences
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    Issue Information - Info Page (2016)
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    Publication Date: 2016-07-27
    Description: No abstract is available for this article.
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    Can channel banks be the dominant source of fine sediment in a UK river?: an example using 137Cs to interpret sediment yield and sediment source. (2016)
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    Publication Date: 2016-07-27
    Description: ABSTRACT Cultivated fields have been shown to be the dominant sources of sediment in almost all investigated UK catchments, typically contributing 85 to 95% of sediment inputs. As a result, most catchment management strategies are directed towards mitigating these sediment inputs. However, in many regions of the UK such as the Nene basin there is a paucity of sediment provenance data. This study used the 137 Cs inventories of lake and floodplain cores as well as the 137 Cs activities of present day sediment to determine sediment provenance. Sediment yields were also reconstructed in a small lake catchment. This article is protected by copyright. All rights reserved. Low 137 Cs inventories were present in the lake and floodplain cores in comparison to the reference inventory and inventories in cores from other UK catchments. 137 Cs activities in the present day sediments were low; falling close to those found in the channel bank catchment samples. It was estimated that 60 to 100% of the sediment in the Nene originated from channel banks. This article is protected by copyright. All rights reserved. Pre 1963 sediment yields were approximately 11.2 t km −2 yr −1 and post 1963 was approximately 11.9 t km −2 yr −1 . The lack of increased sediment yield post 1963 and low sediment yield is unusual for a UK catchment (where a yield of 28 to 51 t km −2 yr −1 is typical for a lowland agricultural catchment), but is explained by the low predicted contribution of sediment from agricultural topsoils. The high channel bank contribution is likely caused by the river being starved of sediment from topsoils, increasing its capacity to entrain bank material. This article is protected by copyright. All rights reserved. The good agreement between the results derived using cores and recently transported sediments, highlight the reliability of 137 Cs when tracing sediment sources. However, care should be taken to assess the potential impacts of sediment particle size, sediment focusing in lakes and the possible remobilisation of 137 Cs from sedimentary deposits. This article is protected by copyright. All rights reserved.
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    Using the Weibull distribution to improve the description of riverine wood loads (2016)
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    Publication Date: 2016-07-27
    Description: ABSTRACT Reporting uncertainty in environmental measurements and estimates is important for cross comparison and inter-comparison of sites and other spatial units. One such measure is the load of large in-stream wood in river systems. In this paper we propose the use of the Weibull distribution to describe the central tendency and variability of wood loads along a river reach. We illustrate the link between the average wood load and the central tendency or scale parameter of the Weibull distribution. The shape of the Weibull distribution is strongly related to the ability of rivers to transport and rearrange the wood in a reach. We use six Victorian rivers to test the fit of the Weibull distribution, showing that the Weibull is a useful and flexible distribution that provides common reporting metrics useful for future studies. Using a common reporting metrics provides a stronger tool for comparisons of wood loads between rivers and with reaches. This article is protected by copyright. All rights reserved.
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    Journal Information (2016)
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    Publication Date: 2016-07-27
    Description: No abstract is available for this article.
    Electronic ISSN: 2054-4049
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geography
    Published by Wiley on behalf of The Royal Geographical Society (with the Institute of British Geographers).
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    Images, imagination and the global environment: towards an interdisciplinary research agenda on global environmental images (2016)
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    Publication Date: 2016-07-27
    Description: Global environmental images have become part of our everyday life experience. We encounter them in news reports, scientific articles and artistic interventions. Yet so far, only the most iconic of these images have received close critical attention from scholars coming mostly from two related fields, science studies and cultural geography. Some of those studies, as for instance research carried out on the famous Apollo photographs, have revealed that the icons of our environmental age do not provide simple readings, that they carry multiple, often contradicting messages, and that they can be vectors of highly ambiguous and even conflicting political beliefs. However, historically informed interdisciplinary research on visual cultures from an environmental perspective is still at its beginning. This essay thus calls for a systematic exploration of the crucial role the visual plays in the creation, circulation, interpretation and adaptation of global environmental knowledge. It is argued that this inquiry cannot be left solely to historians or geographers but calls for a truly interdisciplinary engagement. One central claim is that we need to better understand the constitutive role the visual and associated knowledge practices, conventions and infrastructures play in mediating global environmental phenomena. One possibility, it is argued, is to develop a broader historical framework for understanding how the visual actively shaped scientific and environmental discourse, and how it stimulated the rise of holistic and dynamic understandings of the environment from the nineteenth century onwards. A second important research area that is suggested concerns the crucial role global environmental images play at the interface of science discourse and environmental policy and governance. The essay concludes by suggesting three basic theses which seem particularly promising for future interdisciplinary inquiries into global environmental images. The paper calls for a historically informed interdisciplinary inquiry into global environmental images. e00020
    Electronic ISSN: 2054-4049
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geography
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    Snow hydrology signatures for model identification within a limits-of-acceptability approach (2016)
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    Publication Date: 2016-07-28
    Description: Discharge simulation from snow-dominated catchments seems to be an easy task. Any spatially-explicit precipitation-runoff model coupled to a temperature-index snow model generally yields simulations that mimic well the observed daily discharges. The robustness of such models is, however, questionable: in presence of strong annual discharge cycles, small model residuals do not guarantee high explanatory power of the underlying model. This paper proposes a methodology for snow hydrological model identification within a limits-of-acceptability framework, where acceptable model simulations are the ones that reproduce a set of signatures within an a priori specified range. The signatures proposed here namely include the relationship between the air temperature regime and the discharge regime, a new snow hydrology signature that can be readily transferred to other Alpine settings. The discriminatory power of all analyzed signatures is assessed with a new measure of their discriminatory power in the model prediction domain. The value of the proposed snow hydrology signatures and of the limits-of-acceptability approach is demonstrated for the Dischma river in Switzerland, whose discharge shows a strong temporal variability of hydrologic forcing conditions over the last 30 years. The signature-based model identification for this case study leads to the surprising conclusion that the observed discharge data contains a multi-year period that cannot be reproduced with the model at hand. This model-data mismatch might well result from a yet to be identified problem with the discharge observations, which would have been difficult to detect in a classical residual-based model identification approach. Overall, the detailed results for this case study underline the robustness of the limits-of-acceptability approach in the presence of error-prone observations if it is applied in combination with relatively robust signatures. Future work will show whether snow hydrology signatures and their limits-of-acceptability can be regionalized to ungauged catchments, which would make this model selection approach particularly powerful for Alpine environments. This article is protected by copyright. All rights reserved.
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    Convection generated high frequency gravity waves as observed by MST radar and simulated by WRF model over the Indian tropical station of Gadanki (2016)
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    Publication Date: 2016-07-28
    Description: Using a Mesosphere Stratosphere Troposph e re (MST) radar operating at 53 MHz, the present work reports that during the development of conve c tion over the Indian tropical station of Gadanki at 16:38 – 17:30 UT (Universal time) on 06 June 2011, all these three source mechanisms played important roles in determining the characteristics of high-frequency internal-atmospheric gravity waves generated: (1) latent heating of convection, (2) mechanical oscillation of up and down drafts associated with convection and (3) obstacle effect of wind flows over convective towers near the tropopause level. In general, it is found that while the depth of latent heating determines the vertical wavelength of gravity waves, the oscillation frequency of up and down drafts determines the observed frequency of waves. From the study of vertical structure of vertical wind velocities and phases of three waves (~13, ~17 and ~26 min) generated during this event, it is observed that while the ~13 min and ~26 min oscillations are associated with mechanical oscillator mechanism, the ~17 min oscillation is associated with obstacle effect. Analyses (Fourier, Morlet-wavelet transforms and Maximum Entropy Method (MEM)) of all the three components of wind velocities, measured by the MST radar, show that there is a clear association of gravity waves generated with convection and the vertical propagation characteristics of the gravity waves are found to be in good agreement with theoretical expectations. With the back ground atmospheric information obtained by using the data of GPS radiosondes, ERA-Interim and NCEP-NCAR reanalyses, high-resolution WRF model simulations support the present observations that in turn will help in a large way to the progress of parameterization of convection-generated high-frequency gravity waves in general circulation models. The present work also finds that water molecules induced distinct atmospheric polarized-refractive-index-structures are in existence, which is in accordance with an earlier report on this subject.
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    Impacts of river bank stabilization using riprap on fish habitat in two contrasting environments (2016)
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    Publication Date: 2016-07-29
    Description: Riverbank stabilization using rock riprap is commonly used for protecting road and bridge structures from fluvial erosion. However, little is known about how streams adjust to such perturbation or how this can affect fish habitat in different fluvial environments, particularly for non-salmonid species in small streams. The objective of this study is to assess impacts of riprap on fish habitat quantity and quality through a pairwise comparison of 27 stabilized and non-stabilized stream reaches in two physiographic regions, the St. Lawrence Lowlands and the Appalachian highlands of Montérégie-Est (Quebec, Canada). Both quantitative (hydro-morphological index of diversity, HMID) and qualitative (Qualitative Habitat Evaluation Index , QHEI) fish habitat assessment techniques are applied in order to compare results between methods. For each stream reach depth and velocity were measured to calculate HMID. In-stream cover (woody debris, overhanging vegetation, undercut banks, aquatic macrophytes) and habitat units (pools, riffles, runs, glides) were also documented and used to determine QHEI. Results show that overall bank stabilization using riprap at bridge and stream crossings alters fish habitat characteristics. Loss of in-stream covers and riparian vegetation lower QHEI scores at stabilized reaches, especially in more pristine Appalachian streams, but has less impact on already altered straightened Lowlands streams. In this latter context, some positive alterations of fish habitat were observed in riprapped reaches due to the coarsening of the substrate and an induced increase of slope. The two metrics (HMID and QHEI) revealed similar differences between stabilized and non-stabilized sites for Lowlands sites, but their level of agreement was much less in the Appalachian streams, suggesting caution when interpreting habitat quality results based on a single metric. This article is protected by copyright. All rights reserved.
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    Persistent and pervasive compositional shifts of western boreal forest plots in Canada (2016)
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    Publication Date: 2016-07-29
    Description: Species compositional shifts have important consequences to biodiversity and ecosystem function and services to humanity. In boreal forests, compositional shifts from late-successional conifers to early-successional conifers and deciduous broadleaves have been postulated based on increased fire frequency associated with climate change truncating stand age-dependent succession. However, little is known about how climate change has affected forest composition in the background between successive catastrophic fires in boreal forests. Using 1797 permanent sample plots from western boreal forests of Canada measured from 1958 to 2013, we show that after accounting for stand age-dependent succession, the relative abundances of early-successional deciduous broadleaves and early-successional conifers have increased at the expense of late-successional conifers with climate change. These background compositional shifts are persistent temporally, consistent across all forest stand ages and pervasive spatially across the region. Rising atmospheric CO 2 promoted early-successional conifers and deciduous broadleaves, and warming increased early-successional conifers at the expense of late-successional conifers, but compositional shifts were not associated with climate moisture index. Our results emphasize the importance of climate change on background compositional shifts in the boreal forest and suggest further compositional shifts as rising CO 2 and warming will continue in the 21st century.
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    Modeled ecohydrological responses to climate change at seven small watersheds in the northeastern U.S (2016)
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    Publication Date: 2016-07-30
    Description: A cross-site analysis was conducted on seven diverse, forested watersheds in the northeastern U.S. to evaluate hydrological responses (evapotranspiration, soil moisture, seasonal and annual streamflow, and water stress) to projections of future climate. We used output from four Atmosphere-Ocean General Circulation Models (AOGCMs) (CCSM4, HadGEM2-CC, MIROC5, and MRI-CGCM3) included in Phase 5 of the Coupled Model Intercomparison Project, coupled with two Representative Concentration Pathways (RCP 8.5 and 4.5). The coarse resolution AOGCMs outputs were statistically downscaled using an asynchronous regional regression model to provide finer resolution future climate projections as inputs to the deterministic dynamic ecosystem model PnET-BGC. Simulation results indicated that projected warmer temperatures and longer growing seasons in the northeastern U.S. are anticipated to increase evapotranspiration across all sites, although invoking CO 2 effects on vegetation (growth enhancement and increases in water use efficiency (WUE)) diminish this response. The model showed enhanced evapotranspiration resulted in drier growing season conditions across all sites and all scenarios in the future. Spruce-fir conifer forests have a lower optimum temperature for photosynthesis, making them more susceptible to temperature stress than more tolerant hardwood species, potentially giving hardwoods a competitive advantage in the future. However, some hardwood forests are projected to experience seasonal water stress, despite anticipated increases in precipitation, due to the higher temperatures, earlier loss of snowpacks, longer growing seasons and associated water deficits. Considering future CO 2 effects on WUE in the model alleviated water stress across all sites. Modeled streamflow responses were highly variable, with some sites showing significant increases in annual water yield, while others showed decreases. This variability in streamflow responses poses a challenge to water resource management in the northeastern U.S. Our analyses suggest that dominant vegetation type and soil type are important attributes in determining future hydrologic responses to climate change. This article is protected by copyright. All rights reserved.
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    Numericaldiscretizationandsubgridscalemodele ectson1large-eddysimulationsofastableboundarylayer (2016)
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    Publication Date: 2016-07-29
    Description: Aspects of a large-eddy simulation (LES) model performance are investigated in simulations of a moderately stable boundary layer. The LES utilizes the constant-coefficient Smagorinsky–Lilly subgrid-scale (SGS) closure. Three model parameters are considered: grid spacing, SGS model constant andorder of accuracy (resolving power) of the advection discretization. Second-, fourth- and sixth-orderfully-conservative non-dissipative advection schemes are examined. All three model parameters consid-ered significantly affect the LES results. Depending on the value of the model constant, two main errorproducing mechanisms are identified. For high values of the model constant spurious turbulence collapse,either during the short period of model spin-up, or for the entire simulation duration, is observed. Even though this spurious model characteristic was previously documented, and perhaps expected for low resolution simulations, it depends on the order of the advection discretization implying a significant dis- cretization and SGS closure interaction. For low values of the model constant, numerical discretization errors dominate, leading to accumulation of energy at small scales and over-prediction of the magni- tude of the surface heat flux. Differences in potential temperature profiles are well correlated with the surface heat flux. Overall, the fourth- and sixth-order schemes perform significantly better than the second-order scheme. The differences between the fourth- and sixth-order schemes are relatively small and the increased computational expense of the sixth-order scheme may not be effective in most ap-plications, at least for the low-order statistics considered in this study. Even though the results of the Smagorinsky–Lilly closure show persistent dependence on all model parameters examined, for several pa- rameter combinations the differences with respect to a reference simulation are small. Thus, in contrast to the conclusions of previous studies, the closure can accurately capture moderately stable flows.
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    Large mammal species richness and late Quaternary precipitation change in south-western Australia (2016)
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    Publication Date: 2016-07-30
    Description: ABSTRACT The precipitation history of south-west Australia since the Last Glacial Maximum (LGM) has important implications for understanding southern hemisphere climate dynamics. Previously reported environmental records indicating more open vegetation during the LGM have been interpreted in terms of aridity, but such changes can be explained by alternative mechanisms. To provide new evidence concerning the region's Quaternary precipitation history, we examine temporal changes in large mammal richness at four south-west Australian fossil sites: Devil's Lair, Tunnel Cave, Witchcliffe Rock Shelter and Rainbow Cave. Large mammal richness is correlated strongly with mean annual precipitation across 53 modern Australian communities. Extending this relationship to the fossil record, a steady increase in richness from the LGM to the onset of the Holocene at both Devil's Lair and Tunnel Cave is consistent with increased precipitation through time. This supports previous interpretations of a more arid LGM and implies regional heterogeneity in the position of the southern hemisphere westerlies. A reduction in richness during the last ∼1000 years is unlikely to be the result of precipitation change and may be related to more frequent burning of the landscape by hunter-gatherers in an effort to increase availability of large prey.
    Print ISSN: 0267-8179
    Electronic ISSN: 1099-1417
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    The Effect of Confining Pressure and Water Content on Compressive Strength and Deformation of Ice-Rich Silty Sand (2016)
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    Publication Date: 2016-07-30
    Description: The characteristics of ice-rich frozen soils are important to engineering design in cold-climate regions. Previous work has concentrated on uniaxial strength properties, and limited data exist on triaxial strength and deformation as a function of volumetric ice content and confining pressure. Triaxial compressive tests carried out on ice-rich frozen silty sand indicated that the strength decreases to a minimum and then increases up to that of pure ice for a range of volumetric ice contents. However, the effect of confining pressure on the strength depends on the volumetric ice content itself. The strength was at a nearly constant minimum level when the volumetric ice content was between 48.2 and 65.1 per cent, dominated by the cohesion of the ice matrix. In contrast, at volumetric ice contents of 〉 27.2 to 〈 50.2 per cent and 〉 80.9 per cent, the strength increased with increasing confining pressure. The volumetric ice contents corresponding to maximum failure strain and minimum strength were 50.2 and 61.9 per cent, respectively. Thus, in this range an increase of about 10 per cent in volumetric ice content causes the failure strain to drop to the value for pure ice. The results indicate that there is a transition zone when the volumetric ice content is between 50.2 and 61.9 per cent that separates sample behaviour from that of frozen soil to that of pure ice. Copyright © 2016 John Wiley & Sons, Ltd.
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    Assessing spatial precipitation uncertainties in a convective-scale ensemble (2016)
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    Publication Date: 2016-07-30
    Description: New techniques have recently been developed to quantify the location-dependent spatial agreement between ensemble members, and the spatial spread-skill relationship. In this paper a summer of convection permitting ensemble forecasts are analysed to better understand the factors influencing location-dependent spatial agreement of precipitation fields and the spatial spread-skill relationship over the UK. The aim is to further investigate the agreement scale method, and to highlight the information that could be extracted for a more long-term routine model evaluation. Overall, for summer 2013, the UK 2.2 km-resolution ensemble system was found to be reasonably well spread spatially, although there was a tendency for the ensemble to be over confident in the location of precipitation. For the forecast lead times considered (up to 36 hrs) a diurnal cycle was seen in the spatial agreement and in the spatial spread- skill relationship: the forecast spread and error did not increase noticeably with forecast lead time. Both the spatial agreement, and the spatial spread-skill, were dependent on the fractional coverage and average intensity of precipitation. A poor spread-skill relationship was associated with a low fractional coverage of rain and low average rain rates. The times with a smaller fractional coverage, or lower intensity, of precipitation were found to have lower spatial agreement. The spatial agreement was found to be location dependant, with higher confidence in the location of precipitation to the northwest of the UK.
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    Improving Numerical Experiments of the Persistent Severe Rainfall Events in Southern China using the Spectral Nudging and Filtering Schemes (2016)
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    Publication Date: 2016-07-30
    Description: ABSTRACT Using the inner field spectral nudging (IFSN) and lateral boundary filtering (LBF) methods in the regional Weather Research and Forecasting model, version 3.4 (WRF3.4), the simulation of persistent severe rainfall (PSR) events over South China was investigated. The results showed: (1) Simulation using IFSN improves the forecasting of precipitation, especially for a lead time of greater than 3 days. Meanwhile, simulation with a combination of the IFSN and LBF (IFSN+LBF) methods provides better forecasts at a lead time of 5–7 days. (2) The improvement in precipitation forecasting derives mainly from the reasonable simulation of the large-scale circulation fields and water vapour flux convergence patterns. (3) In terms of large-scale circulation, the anomaly correlation coefficient can be significantly improved for lead times of 1–5 days (7–11 days) by adopting the IFSN (IFSN+LBF) method.
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    Large-scale wind and precipitation extremes in the Mediterranean – dynamical aspects of five selected cyclone events (2016)
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    Publication Date: 2016-07-30
    Description: Cyclones impacting the densely populated Mediterranean region have been a continuous research focus, mainly for investigating either the associated heavy precipitation or the damaging wind gusts. In this study we examine five Mediterranean cyclones with combined large-scale impact of strong 10-m gusts and heavy precipitation. The selected events occurred in (i) December 2003 in the north-eastern Mediterranean; (ii) October 2007 in the central Mediterranean; (iii) January 2009, known as storm ‘Klaus’, in the western Mediterranean; (iv) December 2010 in the eastern Mediterranean; and (v) October 2011 in the central-northern Mediterranean. European Centre for Medium-range Weather Forecasts (ECMWF) reanalyses and 7-km resolution regional model simulations (COSMO) are analysed for each event. A Lagrangian viewpoint is employed to focus on interacting mechanisms that contribute to the joint impact on different spatial and temporal scales. In all cases, widespread strong wind gusts occur in the southwestern parts of the cyclone, while the precipitation field has localized peaks, with variable distribution in the central, southern, eastern and northern parts of the cyclone. Convective precipitation, significant in the cases in 2007, 2010 and 2011, is limited to the southern areas. In all cases, non-convective precipitation is associated with ascent in a warm conveyor belt. Intense gusts are found within unstable air, below a low tropopause in a region with strong vertical wind shear, favouring downward momentum flux by turbulent mixing. Strongly descending dry intrusions are located coherently to the south and west of strong gusts. Much variability exists with regard to the emergence of convection, where strong winds and convective precipitation co-occur: In the 2007 case, the dry intrusion is central in producing shallow convection in the cold frontal region. In the 2010 and 2011 cases, convective activity at high topography and in coastal regions leads to co-location of both types of impact.
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    Internal-BlackBody Calibration (IBBC) Approach and its Operational Application in FY-2 Meteorological Satellites (2016)
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    Publication Date: 2016-07-30
    Description: Fengyun-2 (FY-2) is the first generation geostationary meteorological satellites (GEOMS) in China, two of which, FY-2E and FY-2G, are operating workforce to support the dual-satellite observation mode. The onboard blackbody preliminarily used for stability monitoring of instrument's radiometric response was equipped behind its fore-optics due to the technical limitations in 1990s, which was referred as internal-blackbody (IBB) and operated on the unique preset temperature. In this article, a novel IBB calibration (IBBC) approach is proposed and the radiometric contributions of the main optical elements as well as the IBB itself are modeled and extracted. This is the most distinguishing difference from the traditional full-path blackbody calibration. The IBBC software has been in service for more than two years. Compared with high spectral resolution reference instruments recommended by Global Space-based Inter-Calibration System, the monthly mean calibration biases of long wave infrared band (IR1:10.8 µm) and water vapor band (IR3:6.95 µm) are shown to be lower than 1.5K for FY-2E and lower than 1.0K for FY-2G (for of order 90% of cases). Particularly, the annual mean biases for FY-2G IR3 band can maintain in a good state of 0.4K, which is nearly identical to that of other high class in-orbit satellites, i.e. MTSAT-2 and MSG-1. Likely impacted by ice contamination, the calibration biases of long wave split-window infrared band (IR2:12 µm) of FY-2G could be as large as -2.3K and similar phenomena once occurred in GOES-13 and MSG-1. It is expected to improve this in the near future. In general, the calibration accuracies of FY-2G IR1 and IR3 bands have reached to be lower than 1K, which is significantly superior to those of other 1 st GEOMS, such as GMS-5, Meteosat-7 and GOES-4/7, whose calibration accuracies are around 2-3K. The quality of the data could be greatly enhanced so as to benefit the global observation system.
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    Extracting palaeoflood data from coarse-grained Pleistocene river terrace archives: an example from SE Spain (2016)
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    Publication Date: 2016-07-31
    Description: Field based palaeoflood event reconstruction has the potential to contribute to the development of our understanding of longterm landscape evolution. However the reconstruction of past flow event histories (magnitude and frequency) over long-term (Quaternary) timescales is fraught with difficulties. Here we make a preliminary exploration of some of the practicalities of flood reconstruction from fluvial terrace archives using commonly available sedimentological and geomorphological observations from a field perspective. We utilize Manning and palaeostage indicators to reconstruct historic events that can be used as benchmarks for a lesser used competence based approach (Clarke 1996), which is applied to coarse-grained strath terrace deposits. We evaluate the results against gauged records for extreme and catastrophic events that affected the same region in 1973 and 2012. The findings suggest that the competence approach is most effectively applied to terrace deposits if the channel geometry is taken into account when sampling both in cross section and in longitudinal section and calibrated against the sedimentology for palaeo-flow depth. Problems can arise where constrictive channel geometries allow boulder jams to develop, acting as sediment traps for the coarsest material and leading to downstream ‘boulder starvation’. Useful sites to target for palaeoflood reconstruction, therefore, would be upstream of such constrictive reaches where the coarsest transportable bedload has been effectively trapped. Sites to avoid would be downflow, where the deposited material would poorly represent palaeoflood competence. Underestimation from maximum boulder preservation and limited section exposure issues would appear to outweigh possible overestimation concerns related to fluid density and unsteady flow characteristics such as instantaneous acceleration forces. Flood data derived from river terrace deposits suggests that basal terrace geometries and coarse boulder lags common to many terrace sequences are likely the result of extreme flow events which are subsequently filled by lesser magnitude flood events, in this environmental setting. This article is protected by copyright. All rights reserved.
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    Assessing uncertainties in land cover projections (2016)
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    Publication Date: 2016-07-31
    Description: Understanding uncertainties in land cover projections is critical to investigating land-based climate mitigation policies, assessing the potential of climate adaptation strategies, and quantifying the impacts of land cover change on the climate system. Here we identify and quantify uncertainties in global and European land cover projections over a diverse range of model types and scenarios, extending the analysis beyond the agro-economic models included in previous comparisons. The results from 75 simulations over 18 models are analysed and show a large range in land cover area projections, with the highest variability occurring in future cropland areas. We demonstrate systematic differences in land cover areas associated with the characteristics of the modelling approach, which is at least as great as the differences attributed to the scenario variations. The results lead us to conclude that a higher degree of uncertainty exists in land use projections than currently included in climate or earth system projections. To account for land use uncertainty, it is recommended to use a diverse set of models and approaches when assessing the potential impacts of land cover change on future climate. Additionally, further work is needed to better understand the assumptions driving land use model results and reveal the causes of uncertainty in more depth, to help reduce model uncertainty and improve the projections of land cover. This article is protected by copyright. All rights reserved.
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    Paleogenetic records of Daphnia pulicaria in two North American lakes reveal the impact of cultural eutrophication (2016)
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    Publication Date: 2016-07-31
    Description: Understanding the evolutionary consequences of the Green Revolution, particularly in wild populations, is an important frontier in contemporary biology. Because human impacts have occurred at varying magnitudes or time periods depending on the study ecosystem, evolutionary histories may vary considerably among populations. Paleogenetics in conjunction with paleolimnology enable us to associate microevolutionary dynamics with detailed information on environmental change. We used this approach to reconstruct changes in the temporal population genetic structure of the keystone zooplankton grazer, Daphnia pulicaria , using dormant eggs extracted from sediments in two Minnesota lakes (South Center, Hill). The extent of agriculture and human population density in the catchment of these lakes has differed markedly since European settlement in the late 19 th century, and is reflected in their environmental histories reconstructed here. The reconstructed environments of these two lakes differed strongly in terms of environmental stability and their associated patterns of Daphnia population structure. We detected long periods of stability in population structure and environmental conditions in South Center Lake that were followed by a dramatic temporal shift in population genetic structure after the onset of European settlement and industrialized agriculture in its watershed. In particular, we noted a 24.3-fold increase in phosphorus (P) flux between pre-European and modern sediment P accumulation rates (AR) in this lake. In contrast, no such shifts were detected in Hill Lake, where the watershed was not as impacted by European settlement and rates of change were less directional with a much smaller increase of sediment P AR (2.3-fold). We identify direct and indirect effects of eutrophication proxies on genetic structure in these lake populations, and demonstrate the power of using this approach in understanding the consequences of anthropogenic environmental change on natural populations throughout historic time periods. This article is protected by copyright. All rights reserved.
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    A probabilistic prediction network for hydrological drought identification and environmental flow assessment (2016)
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    Publication Date: 2016-07-30
    Description: A general probabilistic prediction network is proposed for hydrological drought examination and environmental flow assessment. This network consists of three major components. First, we present the joint streamflow drought indicator (JSDI) to describe the hydrological dryness/wetness conditions. The JSDI is established based on a high-dimensional multivariate probabilistic model. In the second part, a drought-based environmental flow assessment method is introduced, which provides dynamic risk-based information about how much flow (the environmental flow target) is required for drought recovery and its likelihood under different hydrological drought initial situations. The final part involves estimating the conditional probability of achieving the required environmental flow under different precipitation scenarios according to the joint dependence structure between streamflow and precipitation. Three watersheds from different countries (Germany, China, and United States) with varying sizes from small to large were used to examine the usefulness of this network. The results show that the JSDI can provide an assessment of overall hydrological dryness/wetness conditions and performs well in identifying both drought onset and persistence. This network also allows quantitative prediction of targeted environmental flow required for hydrological drought recovery and estimation of the corresponding likelihood. Moreover, the results confirm that the general network can estimate the conditional probability associated with the required flow under different precipitation scenarios. The presented methodology offers a promising tool for water supply planning and management and for drought-based environmental flow assessment. The network has no restrictions that would prevent it from being applied to other basins worldwide. This article is protected by copyright. All rights reserved.
    Print ISSN: 0043-1397
    Electronic ISSN: 1944-7973
    Topics: Architecture, Civil Engineering, Surveying , Geography
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    Modeling early in situ wetting of a compacted bentonite buffer installed in low permeable crystalline bedrock (2016)
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    Publication Date: 2016-07-30
    Description: The repository concept for geological disposal of spent nuclear fuel in Sweden and Finland is planned to be constructed in sparsely fractured crystalline bedrock and with an engineered bentonite buffer to embed the waste canisters. An important stage in such a deep repository is the post-closure phase following the deposition and the backfilling operations when the initially unsaturated buffer material gets hydrated by the groundwater delivered by the natural bedrock. We use numerical simulations to interpret observations on buffer wetting gathered during an in situ campaign, the Bentonite Rock Interaction Experiment, in which unsaturated bentonite columns were introduced into deposition holes in the floor of a 417 m deep tunnel at the Äspö Hard Rock Laboratory in Sweden. Our objectives are to assess the performance of state-of-the-art flow models in reproducing the buffer wetting process and to investigate to which extent dependable predictions of buffer wetting times and saturation patterns can be made based on information collected prior to buffer insertion. This would be important for preventing insertion into unsuitable bedrock environments. Field data and modeling results indicate the development of a de-saturated zone in the rock and show that in most cases, the presence or absence of fractures and flow heterogeneity are more important factors for correct wetting predictions than the total inflow. For instance, for an equal open-hole inflow value, homogeneous inflow yields much more rapid buffer wetting than cases where fractures are represented explicitly thus creating heterogeneous inflow distributions. This article is protected by copyright. All rights reserved.
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    Topics: Architecture, Civil Engineering, Surveying , Geography
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    River bank geomorphology controls groundwater arsenic concentrations in aquifers adjacent to the Red River, Hanoi Vietnam (2016)
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    Publication Date: 2016-07-30
    Description: Many aquifers that are highly contaminated by arsenic in South and Southeast Asia are in the floodplains of large river networks. Under natural conditions, these aquifers would discharge into nearby rivers; however large-scale groundwater pumping has reversed the flow in some areas so that rivers now recharge aquifers. At a field site near Hanoi Vietnam, we find river water recharging the aquifer becomes high in arsenic, reaching concentrations above 1000 μg/L, within the upper meter of recently (〈 ∼10 yrs ) deposited riverbed sediments as it is drawn into a heavily pumped aquifer along the Red River. Groundwater arsenic concentrations in aquifers adjacent to the river are largely controlled by river geomorphology. High (〉 50 μg/L) aqueous arsenic concentrations are found in aquifer regions adjacent to zones where the river has recently deposited sediment and low arsenic concentrations are found in aquifer regions adjacent to erosional zones. High arsenic concentrations are even found adjacent to a depositional river reach in a Pleistocene aquifer, a type of aquifer sediment which generally hosts low arsenic water. Using geochemical and isotopic data we estimate the in-situ rate of arsenic release from riverbed sediments to be up to 1000 times the rates calculated on inland aquifer sediments in Vietnam. Geochemical data for riverbed porewater conditions indicate that the reduction of reactive, poorly crystalline iron oxides controls arsenic release. We suggest that aquifers in these regions may be susceptible to further arsenic contamination where riverine recharge drawn into aquifers by extensive groundwater pumping flows through recently deposited river sediments before entering the aquifer. This article is protected by copyright. All rights reserved.
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    Patch-based iterative conditional geostatistical simulation using graph cuts (2016)
    Wiley
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    Publication Date: 2016-07-30
    Description: Training image-based geostatistical methods are increasingly popular in groundwater hydrology even if existing algorithms present limitations that often make real-world applications difficult. These limitations include a computational cost that can be prohibitive for high-resolution 3D applications, the presence of visual artifacts in the model realizations, and a low variability between model realizations due to the limited pool of patterns available in a finite-size training image. In this paper, we address these issues by proposing an iterative patch-based algorithm which adapts a graph cuts methodology that is widely used in computer graphics. Our adapted graph cuts method optimally cuts patches of pixel values borrowed from the training image and assembles them successively, each time accounting for the information of previously stitched patches. The initial simulation result might display artifacts, which are identified as regions of high cost. These artifacts are reduced by iteratively placing new patches in high-cost regions. In contrast to most patch-based algorithms, the proposed scheme can also efficiently address point conditioning. An advantage of the method is that the cut process results in the creation of new patterns that are not present in the training image, thereby increasing pattern variability. To quantify this effect, a new measure of variability is developed, the merging index, quantifies the pattern variability in the realizations with respect to the training image. A series of sensitivity analyses demonstrates the stability of the proposed graph cuts approach, which produces satisfying simulations for a wide range of parameters values. Applications to 2D and 3D cases are compared to state-of-the-art multiple-point methods. The results show that the proposed approach obtains significant speedups and increases variability between realizations. Connectivity functions applied to 2D models transport simulations in 3D models are used to demonstrate that pattern continuity is preserved. This article is protected by copyright. All rights reserved.
    Print ISSN: 0043-1397
    Electronic ISSN: 1944-7973
    Topics: Architecture, Civil Engineering, Surveying , Geography
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    Integrating desalination to reservoir operation to increase redundancy for more secure water supply (2016)
    Wiley
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    Publication Date: 2016-07-30
    Description: ABSTRACT We investigate the potential of integrating desalination to existing reservoir systems to mitigate supply uncertainty. Desalinated seawater and wastewater are relatively reliable but expensive. Water from natural resources like reservoirs is generally cheaper but climate sensitive. We propose combining the operation of a reservoir, and seawater and wastewater desalination plants for an overall system that is less vulnerable to scarcity and uncertainty, while constraining total cost. The joint system is modeled as a multi-objective optimization problem with the double objectives of minimizing risk and vulnerability, subject to a minimum limit on resilience. The joint model is applied to two cases, one based on the climate and demands of a location in India and the other of a location in California. The results for the Indian case indicate it possible for the joint system to reduce risk and vulnerability to zero given a budget increase of 20-120% under current climate conditions and 30-150% under projected future conditions. For the Californian case, this would require budget increases of 20-80% and 30-140% under current and future conditions respectively. Further, our analysis shows a two-way interaction between the reservoir and desalination plants where the optimal operation of the former is just as much affected by the latter as the latter by the former. This highlights the importance of an integrated management approach. This study contributes to a greater quantitative understanding of desalination as a redundancy measure for adapting water supply infrastructures for a future of greater scarcity and uncertainty. This article is protected by copyright. All rights reserved.
    Print ISSN: 0043-1397
    Electronic ISSN: 1944-7973
    Topics: Architecture, Civil Engineering, Surveying , Geography
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    Modeling cosmic-ray neutron field measurements (2016)
    Wiley
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    Publication Date: 2016-07-30
    Description: The cosmic-ray neutron method was developed for intermediate-scale soil moisture detection, but may potentially be used for other hydrological applications. The neutron signal of different hydrogen pools is poorly understood and separating them is difficult based on neutron measurements alone. Including neutron transport modeling may accommodate this shortcoming. However, measured and modeled neutrons are not directly comparable. Neither the scale nor energy ranges are equivalent, and the exact neutron energy sensitivity of the detectors is unknown. Here, a methodology to enable comparability of the measured and modeled neutrons is presented. The usual cosmic-ray soil moisture detector measures moderated neutrons by means of a proportional counter surrounded by plastic, making it sensitive to epithermal neutrons. However, that configuration allows for some thermal neutrons to be measured. The thermal contribution can be removed by surrounding the plastic with a layer of cadmium, which absorbs neutrons with energies below 0.5 eV. Likewise, cadmium-shielding of a bare detector allows for estimating the epithermal contribution. First, the cadmium difference method is used to determine the fraction of thermal and epithermal neutrons measured by the bare and plastic-shielded detectors, respectively. The cadmium difference method results in linear correction models for measurements by the two detectors, and has the greatest impact on the neutron intensity measured by the moderated detector at the ground surface. Next, conversion factors are obtained relating measured and modeled neutron intensities. Finally, the methodology is tested by modeling the neutron profiles at an agricultural field site and satisfactory agreement to measurements is found. This article is protected by copyright. All rights reserved.
    Print ISSN: 0043-1397
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    Topics: Architecture, Civil Engineering, Surveying , Geography
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    Impacts of land use on the hydrological response of tropical Andean catchments (2016)
    Wiley
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    Publication Date: 2016-07-31
    Description: Changes in land use and land cover are major drivers of hydrological alteration in the tropical Andes. However, quantifying their impacts is fraught with difficulties because of the extreme diversity in meteorological boundary conditions, which contrasts strongly with the lack of knowledge about local hydrological processes. Although local studies have reduced data scarcity in certain regions, the complexity of the tropical Andes poses a big challenge to regional hydrological prediction. This study analyses data generated from a participatory monitoring network of 25 headwater catchments covering three of the major Andean biomes ( páramo , jalca , and puna ), and link their hydrological responses to main types of human interventions (cultivation, afforestation and grazing). A paired catchment setup was implemented to evaluate the impacts of change using a “trading space-for-time” approach. Catchments were selected based on regional representativeness and contrasting land use types. Precipitation and discharge have been monitored and analysed at high temporal resolution for a time period between 1 and 5 years. The observed catchment responses clearly reflect the extraordinarily wide spectrum of hydrological processes of the tropical Andes. They range from perennially humid páramos in Ecuador and northern Peru with extremely large specific discharge and baseflows, to highly seasonal, flashy catchments in the drier punas of southern Peru and Bolivia. The impacts of land use are similarly diverse and their magnitudes are a function of catchment properties, original and replacement vegetation, and management type. Cultivation and afforestation consistently affect the entire range of discharges, particularly low flows. The impacts of grazing are more variable, but have the largest effect on the catchment hydrological regulation. Overall, anthropogenic interventions result in increased streamflow variability and significant reductions in catchment regulation capacity and water yield, irrespective of the hydrological properties of the original biome. This article is protected by copyright. All rights reserved.
    Print ISSN: 0885-6087
    Electronic ISSN: 1099-1085
    Topics: Architecture, Civil Engineering, Surveying , Geography
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    Orographic drag on islands in the NWP mountain grey zone (2016)
    Wiley
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    Publication Date: 2016-07-31
    Description: The drag due to resolved and sub-grid flow blocking and gravity waves is examined in simulations of flow over mountainous islands at ‘grey zone’ resolutions, in which the processes are neither well resolved or fully sub-grid-scale. Simulations of flows over narrow (South Georgia) and broad (New Zealand) mountain barriers are used to determine the behaviour of resolved and parametrized pressure drag and gravity-wave momentum fluxes as a function of horizontal grid length. Analysis of the pressure drag in spectral space suggests that contributions from wavelengths shorter than 8–10 grid lengths are poorly resolved and that parametrization schemes should compensate for the missing drag from processes on these scales, rather than strictly the sub-grid scales. The model performance for South Georgia is such that the total (resolved plus parametrized) pressure drag is approximately invariant across a range of resolutions. The parametrized (resolved) drag increases (decreases) as the grid length increases and the resolved and parametrized drag become comparable when the characteristic island wavelength is approximately 8 times the grid length. This is not true when the same tuning of the drag parametrization is applied to New Zealand, in which case the parametrized drag increases too rapidly with increasing grid length. However, satisfactory results are obtained when the scheme is re-tuned and it is shown that the optimal tuning for the two islands is consistent with scaling the sub-grid orographic heights to be representative of the orography on longer length scales, of up to 10 grid lengths. The results suggest that drag schemes require orographic information on these longer scales, rather than only the sub-grid scale. At the coarsest resolutions, where the island wavelength and grid length are similar, the parametrized drag is too small because the grid boxes are increasingly treated as sea points. Possible solutions to this problem are discussed.
    Print ISSN: 0035-9009
    Electronic ISSN: 1477-870X
    Topics: Geography , Physics
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    A Methodology for Simultaneous Retrieval of Ice and Liquid Water Cloud Properties. Part II: Near-global Retrievals and Evaluation against A-Train Products (2016)
    Wiley
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    Publication Date: 2016-07-31
    Description: This paper presents results of a novel methodology capable of simultaneously retrieving optical and microphysical properties of multi-level ice and liquid clouds. The method was introduced in Part I, which theoretically demonstrated its capabilities, and its results are here analysed and evaluated against A-Train operational products. In addition to being robust to multi-layer conditions, another advantage of the method is that rigorous uncertainties and analysis tools are attached to its retrievals. Also, the combined use of shortwave and thermal infrared channels provides a wide range of sensitivity from moderately thin to thick ice cloud layers. Finally, the method is also novel in that the ice water path (IWP) is directly retrieved. These new retrievals should therefore be useful in providing new data for evaluating climate model predictions of IWP. In this study, our methodology has been applied to one year of A-Train measurements, narrowed to daytime conditions over oceanic surfaces. The retrievals and their uncertainties are statistically analysed, after a thorough discussion of the filtering process. It appears that our method is sensitive to IWPs ranging between about 0.5 and 1000 g m − 2 , with uncertainties better than 25% between 5 to 500 g m − 2 . Retrievals of the optical depth and effective radius of liquid layers have uncertainties better than 20%. Our retrievals are then compared to five independent operational A-Train products. Very good agreements, well within a factor of 2, are found by comparisons to products from active and passive instruments. These results overall lead to the validation of our method. Additionally, the robustness of passive operational products to multi-layer conditions is discussed. Preliminary comparisons show a possible overestimation of retrievals obtained under the single-layer approximation. A thorough assessment of this problem will be addressed in a following study.
    Print ISSN: 0035-9009
    Electronic ISSN: 1477-870X
    Topics: Geography , Physics
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    Field techniques for measuring bedrock erosion and denudation (2016)
    Wiley
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    Publication Date: 2016-08-02
    Description: Bedrock erosion rates in natural landscapes are usually slow, of the order of millimeters per year or less, and sophisticated techniques have been developed to measure them. Different techniques have proved to be valuable depending on the spatial and temporal scale on which information is needed, on the environment and on the scientific question that is asked. Here, we give an overview of the various methods that have been developed. We introduce their working principles and outline their advantages and disadvantages. Further, we provide comprehensive references to relevant literature, both on the methods and on scientific examples of their application. This article is protected by copyright. All rights reserved.
    Print ISSN: 0197-9337
    Electronic ISSN: 1096-9837
    Topics: Geography , Geosciences
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    The role of long-term human impact on avulsion and fan development (2016)
    Wiley
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    Publication Date: 2016-08-02
    Description: This study aims to understand (mainly qualitatively) the long-term role of human impact on avulsion processes and the development of fluvial (mega-) fans in semi-arid environments. In this paper we refer to human impact as the direct influences of actions on the river's hydraulics (i.e. flow regulation, flow diversion and channel engineering). In five case-studies drawn from the Khuzestan plains in SW Iran we have analysed the setup and triggering conditions of specific avulsions that occurred in the past (timescale of millennia) and identified the role of human interference in their causation. Our analysis is based on the integration of historical, archaeological, geomorphological and geological data. Through this study we demonstrate that avulsions in the Khuzestan plains are the result of long-term and complex interplay between multiple human-induced and natural causes. In similar ways human-induced actions may play important roles during different phases of avulsion development. The “success” of an avulsion in the post-triggering phase may be defined by human-induced setup causes as well as morphodynamic processes. We suggest that present-day flood events may be partly inherited from long-term human alterations of the natural processes. These finding could have implications for any fluvial system (e.g. distributive fluvial systems, deltas) where avulsion plays a major role in their development and research tends to emphasise on natural mechanisms. This article is protected by copyright. All rights reserved.
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    Topics: Geography , Geosciences
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    Numerical Modelling of Ice-Wedge Polygon Geomorphic Transition (2016)
    Wiley
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    Publication Date: 2016-08-03
    Description: A numerical model is presented to test whether a hillslope diffusion approach can simulate the topographic evolution of some recently developed high-centred ice-wedge polygons south of Prudhoe Bay, Alaska. The polygons are adjacent to a highway whose construction appears to have triggered their geomorphic transition. The model is calibrated using a light detection and ranging data-set that captures both the high-centred polygons and some neighbouring low-centred polygons that appear to be unaffected by thermokarst. The latter are used to represent initial conditions. Model simulations are analysed to estimate potential fluxes of soil from polygon edges into troughs and the loss of depressional water storage during development of the high-centred polygons. Overall, a match between the topography of simulated and observed high-centred polygons suggests that diffusive hillslope processes represent a feasible mechanism driving polygon transition. Rates of soil displacement inferred from optimised simulations, moreover, are within the range previously observed in permafrost terrain with a similar climate. Direct observations of the soil velocity profile in actively transitioning polygons would help resolve whether and to what extent hillslope processes, as opposed to pure thaw-related subsidence at the polygon edges, drive the development of high-centred forms in natural systems. Copyright © 2016 John Wiley & Sons, Ltd.
    Print ISSN: 1045-6740
    Electronic ISSN: 1099-1530
    Topics: Geography , Geosciences
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    Insight into sediment transport processes on saline rangeland hillslopes using three-dimensional soil microtopography changes (2016)
    Wiley
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    Publication Date: 2016-08-03
    Description: ABSTRACT In arid and semi-arid rangeland environments, an accurate understanding of runoff generation and sediment transport processes is key to developing effective management actions and addressing ecosystem response to changes. Yet, many primary processes (namely sheet and splash and concentrated flow erosion, as well as deposition) are still poorly understood due to a historic lack of measurement techniques capable of parsing total soil loss into these primary processes. Current knowledge gaps can be addressed by combining traditional erosion and runoff measurement techniques with image-based 3D soil surface reconstructions. In this study, data (hydrology, erosion and high-resolution surface microtopography changes) from rainfall simulation experiments on twenty-four plots in saline rangelands communities of the Upper Colorado River Basin were used to improve understanding on various sediment transport processes. A series of surface change metrics were developed to quantify and characterize various erosion and transport processes (e.g., plot-wide vs. concentrated flow detachment and deposition) and were related to hydrology and biotic and abiotic land surface characteristics. In general, erosivity controlled detachment and transport processes while factors modulating surface roughness such as vegetation controlled deposition. The extent of the channel network was a positive function of slope, discharge and vegetation. Vegetation may deflect runoff in many flow paths but promoted deposition. From a management perspective, this study suggests that effective runoff soil and salt load reduction strategies should aim to promote deposition of transported sediments rather than reducing detachment which might not be feasible in these resource-limited environments. This article is protected by copyright. All rights reserved.
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    Wildfire effects on road surface erosion, deposition, and road-stream connectivity (2016)
    Wiley
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    Publication Date: 2016-08-03
    Description: High and moderate severity wildfires should increase sediment production from unpaved roads due to the increased surface runoff from upslope, and increase road-stream connectivity due to the decrease in downslope surface roughness as well as the increase in surface runoff and erosion. Because no study has documented these effects, we surveyed road surface erosion features and quantified road-stream connectivity as a function of fire severity and road segment characteristics. The data were collected one year after the High Park wildfire from 141 hydrologically distinct road segments along 6.8 km of an unpaved road west of Fort Collins, Colorado. Road segments below areas burned at high and moderate severity had significantly more rills than road segments below areas that burned at low severity. Road segment slope was an important control on the proportion of segment length with rills, and the strength of the relationship between road segment slope and the amount of rilling increased with burn severity. Flatter road segments tended to capture the sediment eroded from upslope burned areas. In areas burned at high and moderate severity all of the road segments had drainage features extending to a stream, and 78% of the segments in areas burned at low severity also were connected. These exceptionally high rates of road-stream connectivity are attributed to the increased runoff from upslope, the segment-scale collection and funneling of hillslope and road surface runoff to a single drainage point, and the reduced infiltration and trapping capacity of the burned area below the road. The results show the need to either outslope the roads or increase the frequency of constructed drainage features after wildfires, particularly for steeper road segments in areas burned at high or moderate severity. This article is protected by copyright. All rights reserved.
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    Defining the floodplain in hydrologically-variable settings: implications for flood risk management (2016)
    Wiley
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    Publication Date: 2016-08-03
    Description: ABSTRACT Flood risk management is an essential responsibility of state governments and local councils to ensure the protection of people residing on floodplains. Globally, floodplains are under increasing pressure from growing populations. Typically, the engineering-type solutions that are used to predict local flood magnitude and frequency based on limited gauging data are inadequate, especially in settings which experience high hydrological variability. This study highlights the importance of incorporating geomorphological understanding into flood risk management in south-east Queensland (SEQ), an area badly affected by extreme flood events in 2011 and 2013. The major aim of this study is to outline the hydrological and sedimentological characteristics of various ‘inundation surfaces’ that are typical of catchments in the sub-tropics. It identifies four major inundation surfaces; within-channel bench ( Q  ~ 2.33y ARI); genetic floodplain ( Q  = 20y ARI); hydraulic floodplain (20y 〈  Q  ≤ 200y ARI) and terrace ( Q  〉 1000y ARI). These surfaces are considered typical of inundation areas within, and adjacent to, the large macrochannels common to this region and others of similar hydrological variability. An additional area within genetic floodplains was identified where flood surfaces coalesce and produce an abrupt reduction in channel capacity. This is referred to here as a Spill-out zone (SOZ). The associated vulnerability and risk of these surfaces is reviewed and recommendations made based on incorporating this geomorphological understanding into flood risk assessments. These recommendations recognise the importance to manage for risks associated with flow inundation and sediment erosion, delivery and deposition. The increasing availability of high resolution topographic data opens up the possibility of more rapid and spatially extensive assessments of key geomorphic processes which can readily be used to predict flood risk. This article is protected by copyright. All rights reserved.
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    Patch-scale representation of vegetation within hydraulic models (2016)
    Wiley
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    Publication Date: 2016-08-03
    Description: Submerged aquatic vegetation affects flow, sediment and ecological processes within rivers. Quantifying these effects is key to effective river management. Despite a wealth of research into vegetated flows, the detailed flow characteristics around real plants in natural channels are still poorly understood. Here we present a new methodology for representing vegetation patches within computational fluid dynamics (CFD) models of vegetated channels. Vegetation is represented using a Mass Flux Scaling Algorithm (MFSA) and drag term within the Reynolds-Averaged Navier-Stokes Equations, which account for the mass and momentum effects of the vegetation respectively. The model is applied using three different grid resolutions (0.2, 0.1 & 0.05 m) using time-averaged solution methods and compared to field data. The results show that the model reproduces the complex spatial flow heterogeneity within the channel and that increasing the resolution leads to enhanced model accuracy. Future applications of the model to the prediction of channel roughness, sedimentation and key eco-hydraulic variables are presented, likely to be valuable for informing effective river management. This article is protected by copyright. All rights reserved.
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    Cost-Effective Non-Metric Photogrammetry from Consumer-Grade sUAS: Implications for Direct Georeferencing of Structure from Motion Photogrammetry (2016)
    Wiley
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    Publication Date: 2016-08-03
    Description: The declining costs of small Unmanned Aerial systems (sUAS), in combination with Structure from Motion (SfM) photogrammetry have triggered renewed interest in image-based topography reconstruction. However, the potential uptake of sUAS-based topography is limited by the need for ground control acquired with expensive survey equipment. Direct georeferencing (DG) is a workflow that obviates ground control and uses only the camera positions to georeference the SfM results. However, the absence of ground control poses significant challenges in terms of the data quality of the final geospatial outputs. Notably, it is generally accepted that ground control is required to georeference, refine the camera calibration parameters, and remove any artefacts of optical distortion from the topographic model. Here, we present an examination of DG carried out with low-cost consumer-grade sUAS. We begin with a study of surface deformations resulting from systematic perturbations of the radial lens distortion parameters. We then test a number of flight patterns and develop an novel error quantification method to assess the outcomes. Our perturbation analysis shows that there exists families of predictable equifinal solutions of K 1 -K 2 which minimise doming in the output model. The equifinal solutions can be expressed as K 2  =  f (K 1 ) and they have been observed for both the DJI Inspire 1 and Phantom 3 sUAS platforms. This equifinality relationship can be used as an external reliability check of the self-calibration and allow a DG workflow to produce topography exempt of non-affine deformations and with random errors of 0.1% of the flying height, linear offsets below 10 m and off-vertical tilts below 1°. Whilst not yet of survey-grade quality, these results demonstrate that low-cost sUAS are capable of producing reliable topography products without recourse to expensive survey equipment and we argue that direct georeferencing and low-cost sUAS could transform survey practices in both academic and commercial disciplines. This article is protected by copyright. All rights reserved.
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    Irrigating grazed pasture decreases soil carbon and nitrogen stocks (2016)
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    Publication Date: 2016-08-03
    Description: The sustainability of using irrigation to produce food depends not only on the availability of sufficient water, but also on the soils ‘response’ to irrigation. Stocks of carbon (C) and nitrogen (N) are key components of soil organic matter (SOM), which is important for sustainable agricultural production. While there is some information about the effects of irrigation on soil C stocks in cropping systems, there is a paucity of such studies in pastoral food production systems. For this study, we sampled soils from 34 paired, irrigated and unirrigated pasture sites across New Zealand (NZ) and analysed these for total C and N. On average, irrigated pastures had significantly ( P 〈0.05) less soil carbon (C) and nitrogen (N) than adjacent unirrigated pastures, with differences of 6.99 t C ha −1 and 0.58 t N ha −1 in the uppermost 0.3 m. Differences in C and N tended to occur throughout the soil profile, so the cumulative differences increased with depth, and the proportion of the soil C lost from deeper horizons was large. There were no relationships between differences in soil C and N stocks and the length of time under irrigation. This study suggests SOM will decrease when pastures under a temperate climate are irrigated. On this basis, increasing the area of temperate pasture land under irrigation would result in more CO 2 in the atmosphere, and may directly and indirectly increase N leaching to groundwater. Given the large and increasing area of land being irrigated both in NZ and on a global scale, there is an urgent need to determine whether the results found in this study are also applicable in other regions and under different land management systems (e.g. arable). This article is protected by copyright. All rights reserved.
    Print ISSN: 1354-1013
    Electronic ISSN: 1365-2486
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
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    The carbon fertilization effect over a century of anthropogenic CO2 emissions: higher intracellular CO2 and more drought resistance among invasive and native grass species contrasts with increased water use efficiency for woody plants in the US Southwest (2016)
    Wiley
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    Publication Date: 2016-08-03
    Description: From 1890 to 2015, anthropogenic carbon dioxide emissions have increased atmospheric CO 2 concentrations from 270 mol mol −1 to 400 mol mol −1 . The effect of increased carbon emissions on plant growth and reproduction has been the subject of study of Free Air CO 2 Enrichment (FACE) experiments. These experiments have found a) an increase in internal CO 2 partial pressure (c i ) alongside acclimation of photosynthetic capacity, b) variable decreases in stomatal conductance, and c) that increases in yield do not increase commensurate with CO 2 concentrations. Our data set, which includes a 115 year long selection of grasses collected in New Mexico since 1892 is consistent with an increased c i as a response to historical CO 2 increase in the atmosphere; with invasive species showing the largest increase. Comparison with Palmer Drought Sensitivity index (PDSI) for New Mexico indicates a moderate correlation with Δ 13 C (r 2 = 0.32, p 〈 0.01) before 1950, with no correlation (r 2 = 0.00, p = 0.91) after 1950. These results indicate that increased c i may have conferred some drought resistance to these grasses through increased availability of CO 2 in the event of reduced stomatal conductance in response to short term water shortage. Comparison with C 3 trees from arid environments ( Pinus longaeva and Pinus edulis in the US Southwest) as well as from wetter environments ( Bromus and Poa grasses in New Mexico) suggest differing responses based on environment; arid environments in New Mexico see increased intrinsic water use efficiency (WUE) in response to historic elevated CO 2 while wetter environments see increased c i . The present study suggests that a) the observed increases in c i in FACE experiments are consistent with historical CO 2 increases and b) the CO 2 increase influences plant sensitivity to water shortage, through either increased WUE or c i in arid and wet environments, respectively. This article is protected by copyright. All rights reserved.
    Print ISSN: 1354-1013
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    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
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    Comment on ‘Anav et al. (2016) Comparing concentration-based (AOT40) and stomatal uptake (PODY) metrics for ozone risk assessment to European forests’ Global Change Biology, 22(4), 1608–1627, doi:10.1111/gcb.13138 (2016)
    Wiley
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    Publication Date: 2016-08-03
    Print ISSN: 1354-1013
    Electronic ISSN: 1365-2486
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
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    Fluvial sediment supply and pioneer woody seedlings as a control on bar-surface topography (2016)
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    Publication Date: 2016-08-04
    Description: Plants influence river channel topography, but our understanding of the interaction among plants, flow, and sediment is limited, especially when sediment supply is variable. Using laboratory experiments in a recirculating flume with live seedlings in a mobile sand bed, we demonstrate how varying the balance between sediment supply and transport capacity shifts the relationship between plants and bar-surface topography. Each experimental trial contrasted two sediment conditions, in which initially supply was maintained in equilibrium with transport via sediment recirculation, followed by sediment deficit, in which transport capacity exceeded supply, which was set to zero. For both sediment balances, the topographic response was sensitive to plant size, with larger plants inducing greater aggradation relative to a baseline condition. During sediment equilibrium, the positive relationship between plant size and topographic change also depended on species morphology (multi-stemmed shrubs versus single-stemmed plants). Plant morphology effects disappeared when the sediment balance shifted to a deficit, but the presence of plants had a greater impact on the magnitude of change compared to the topographic response under sediment equilibrium. Our results suggest that the interactions among sediment supply, plants, and topography may be strongest on rivers with a balance in sediment supply and transport capacity. Because of the large variability in fluvial sediment supply resulting from natural and anthropogenic influences, these interactions will differ spatially (e.g. longitudinally through a watershed) and at different temporal scales, from single flood events to longer time periods. This article is protected by copyright. All rights reserved.
    Print ISSN: 0197-9337
    Electronic ISSN: 1096-9837
    Topics: Geography , Geosciences
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    A regime analysis of Atlantic winter jet variability applied to evaluate HadGEM3-GC2 (2016)
    Wiley
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    Publication Date: 2016-08-04
    Description: The behaviour of the eddy-driven jet over the Atlantic sector during the winter season is analysed for the ERA-Interim reanalysis and the coupled and atmosphere-only configuration of HadGEM3-GC2 - the climate model in use at the Met Office. The tri-modal distribution that characterises the jet-stream structure in terms of its preferred locations is reproduced with good accuracy by the model, although a distinct bias towards the high-latitude position is observed. Two different scenarios are found to contribute to this bias. One occurs when the jet shifts from its southern regime, whereby it settles too far north and for too long compared to the reanalysis. The other is associated with the exit from the central latitude regime, with too many events shifting poleward rather than equatorward. Excessively large lower tropospheric eddy heat fluxes during these transitions may account for the jet errors, even though the heat fluxes do not exhibit a climatological bias. Interestingly, these biases are weaker when the atmosphere model is forced with observed SSTs, suggesting that either it is vital to have the correct SST distribution or that ocean-atmosphere coupling plays a key role in the biases . Additional analysis revealed that the Pacific jet exit is biased south in the coupled model and that this contributes to the Atlantic bias. Anomalously warm SSTs in the Gulf Stream region may be acting together with the Pacific bias in fostering the anomalous activity in the low level eddy heat fluxes.
    Print ISSN: 0035-9009
    Electronic ISSN: 1477-870X
    Topics: Geography , Physics
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    Informing climate models with rapid chamber measurements of forest carbon uptake (2016)
    Wiley
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    Publication Date: 2016-08-05
    Description: Models predicting ecosystem carbon dioxide (CO 2 ) exchange under future climate change rely on relatively few real-world tests of their assumptions and outputs. Here we demonstrate a rapid and cost-effective method to estimate CO 2 exchange from intact vegetation patches under varying atmospheric CO 2 concentrations . We find that net ecosystem CO 2 uptake (NEE) in a boreal forest rose linearly by 4.7 ± 0.2% of the current ambient rate for every 10 ppm CO 2 increase, with no detectable influence of foliar biomass, season or nitrogen (N) fertilization. The lack of any clear short-term NEE response to fertilization in such an N-limited system is inconsistent with the instantaneous down-regulation of photosynthesis formalized in many global models. Incorporating an alternative mechanism with considerable empirical support – diversion of excess carbon to storage compounds – into an existing earth system model brings the model output into closer agreement with our field measurements. A global simulation incorporating this modified model reduces a long-standing mismatch between the modeled and observed seasonal amplitude of atmospheric CO 2 . Wider application of this chamber approach would provide critical data needed to further improve modeled projections of biosphere-atmosphere CO 2 exchange in a changing climate. This article is protected by copyright. All rights reserved.
    Print ISSN: 1354-1013
    Electronic ISSN: 1365-2486
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
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    Spatial and temporal variability of temperature, precipitation, and streamflow in upper Sang-kan basin, China (2016)
    Wiley
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    Publication Date: 2016-08-05
    Description: Temporal streamflow variability in an inland hydrologic station and temporal trends and frequency changes at three weather stations in a semiarid river basin located in Loess Plateau, China were detected using linear regression, Mann-Kendall (MK) analysis, and wavelet transform methods. Double Cumulative Curve and Ordered Clustering were used to identify the hydrological periods of upper Sang-kan (USK) basin between 1957 and 2012. The results indicate that: (1) precipitation in the USK basin over the study period did not show any trend while the temperature showed a significant increase; (2) streamflow flowing out of the USK basin indicated a significant decrease; (3) two distinct hydrological periods; the “natural period” from 1957 to 1984 and the “human impact period” from 1985 to 2012 were present; and (4) the contribution of climate change and human activities to reduce the streamflow was 36.9% and 63.1%, respectively. The results indicate that human activities may be contributing to a decrease in streamflow in the USK basin. This article is protected by copyright. All rights reserved.
    Print ISSN: 0885-6087
    Electronic ISSN: 1099-1085
    Topics: Architecture, Civil Engineering, Surveying , Geography
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    Improving spatial localisation in 4DEnVar (2016)
    Wiley
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    Publication Date: 2016-08-05
    Description: The 4DEnVar is a credible alternative to the 4D-Var formulation, especially for Numerical Weather Prediction centres that have invested a lot in this latter formulation during the last decades. First implementations of this technique however rely on a simplified form for the localisation of the 4D covariances inside the assimilation period. It is shown in this paper that the use of a unique localisation for all the cross-covariances between perturbations at different times can be a crude approximation especially in areas where the mean flow speed is large. To overcome this problem a Lagrangian advection of the localisation is proposed. It is first tested in the simplified Burgers’ model and then introduced in the real size system associated with the French global model ARPEGE. The test of this advection in both environments shows a significative positive impact in regions where the advection is large. The possibility to use such a Lagrangian advection to evolve the static initial covariance matrix in a flow-dependent way inside the assimilation period, in a hybrid 4DEnVar formulation, is also investigated. Copyright c 2015 Royal Meteorological Society
    Print ISSN: 0035-9009
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    Calibration induced uncertainty of the EPIC model to estimate climate change impact on global maize yield (2016)
    Wiley
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    Publication Date: 2016-08-06
    Description: Understanding the interactions between agricultural production and climate is necessary for sound decision-making in climate policy. Gridded and high-resolution crop simulation has emerged as a useful tool for building this understanding. Large uncertainty exists in this utilization, obstructing its capacity as a tool to devise adaptation strategies. Increasing focus has been given to sources of uncertainties for climate scenarios, input-data, and model, but uncertainties due to model parameter or calibration are still unknown. Here, we use publicly available geographical datasets as input to the Environmental Policy Integrated Climate model (EPIC) for simulating global gridded maize yield. Impacts of climate change are assessed up to the year 2099 under a climate scenario generated by HadEM2-ES under RCP 8.5. We apply five strategies by shifting one specific parameter in each simulation to calibrate the model and understand the effects of calibration. Regionalizing crop phenology or harvest index appears effective to calibrate the model for the globe, but using various values of phenology generates pronounced difference in estimated climate impact. However, projected impacts of climate change on global maize production are consistently negative regardless of the parameter being adjusted. Different values of model parameter results in a modest uncertainty at global level, with difference of the global yield change less than 30% by the 2080s. The uncertainty subjects to decrease if applying model calibration or input data quality control. Calibration has a larger effect at local scales, implying the possible types and locations for adaptation. This article is protected by copyright. All rights reserved.
    Electronic ISSN: 1942-2466
    Topics: Geography , Geosciences
    Published by Wiley on behalf of American Geophysical Union (AGU).
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    The role of cloud radiative heating within the atmosphere on the high cloud amount and top-of-atmosphere cloud radiative effect (2016)
    Wiley
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    Publication Date: 2016-08-06
    Description: The effect of cloud radiation interactions on cloud properties is examined in the context of a limited domain cloud-resolving model. The atmospheric cloud radiative effect (ACRE) influences the areal extent of tropical high clouds in two distinct ways. The first is through direct radiative destabilization of the elevated cloud layers, mostly as a result of longwave radiation heating the cloud bottom and cooling the cloud top. The second effect is radiative stabilization, whereby cloud radiative heating of the atmospheric column stabilizes the atmosphere to deep convection. In limited area domain simulations, the stabilizing (or indirect) effect is the dominant role of the cloud radiative heating, thus reducing the cloud cover in simulations where ACRE is included compared to those where it is removed. Direct cloud radiative heating increases high cloud fraction, decreases mean cloud optical depth, and increases cloud top temperature. The indirect cloud radiative heating decreases high cloud fraction, but also decreases mean cloud optical depth and increases cloud top temperature. The combination of these effects increases the top-of-atmosphere cloud radiative effect. In mock-Walker circulation experiments, the decrease in high cloud amount owing to radiative stabilization tends to cancel out the increase in high cloud amount owing to the destabilization within the cloud layer. The changes in cloud optical depth and cloud top pressure, however, are similar to those produced in the limited area domain simulations. This article is protected by copyright. All rights reserved.
    Electronic ISSN: 1942-2466
    Topics: Geography , Geosciences
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    Modern pollen assemblages from surface lake sediments and their environmental implications on the southwestern Tibetan Plateau (2016)
    Wiley
    In: Boreas
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    Publication Date: 2016-08-06
    Description: The relationships amongst modern pollen assemblages, vegetation, climate and human activity are the basis for reconstructing palaeoenvironmental changes using pollen records. It is important to determine these relationships at regional scales due to the development of vegetation under different climatic conditions and human activities. In this paper, we report on an analysis of modern pollen assemblages of 31 surface lake samples from 31 lakes (one sample per lake) on the southwestern Tibetan Plateau where the knowledge of modern pollen and their relationships with vegetation, climate and human activities is insufficient. The region includes five vegetation zones: sub-alpine shrub steppe, alpine steppe, alpine meadow and steppe ecotone, mountain desert and alpine desert. The lakes span a wide range of mean annual precipitation (50–500 mm) and mean annual temperature (−8 to 6 °C). Modern pollen assemblages from our samples mainly consist of herb taxa ( Artemisia , Cyperaceae, Poaceae, Chenopodiaceae, etc.) and some tree taxa ( Pinus , Fagaceae, Alnus , etc.). The results indicate that modern pollen assemblages are able to reflect the main vegetation distribution. Redundancy analysis for the main pollen types and environmental variables shows that precipitation is the leading factor that influences the pollen distribution in the study area with the first axis capturing 13.7% of the variance in the pollen data set. The Artemisia /Chenopodiaceae ratio is valid for separating the desert component (〈2) from the steppe and other vegetation zones (〉2) but is unable to distinguish moisture variations. The Artemisia /Cyperaceae ratio is able to identify meadows (〈1) and steppes (〉1) and can be used as a moisture index on the southwestern Tibetan Plateau. Our results show that an appropriate range is needed for a modern pollen data set in order to perform pollen-based quantitative climate reconstructions in one region. It is essential to perform modern studies before using pollen ratios to reconstruct palaeovegetation and palaeoclimate at a regional scale.
    Print ISSN: 0300-9483
    Electronic ISSN: 1502-3885
    Topics: Geography , Geosciences
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    Chronology and stratigraphy of the Magdalen Islands archipelago from the last glaciation to the early Holocene: new insights into the glacial and sea-level history of eastern Canada (2016)
    Wiley
    In: Boreas
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    Publication Date: 2016-07-10
    Description: The Magdalen Islands (Québec, Canada) are a key location for unravelling the glacial and sea-level history of the Maritime Provinces of eastern Canada. Although many sedimentary sequences have been described in the literature, absolute ages are lacking, impeding an accurate interpretation of the deposits and the establishment of a precise chronological framework. This study provides a detailed description of 21 stratigraphical sequences located throughout the archipelago, as well as the first comprehensive luminescence chronology from the Last Glacial Maximum (LGM) to c.  10 ka. In addition to the five samples collected for age control purposes, 34 luminescence samples were taken from 17 different sites in glacial, periglacial and coastal deposits. The stratigraphical and chronological data reveal that the islands were at the crossroads of two icecaps during the LGM; the southern islands were glaciated by the Escuminac icecap located in the western Gulf of St. Lawrence whereas the northern archipelago was glaciated at the end of the LGM by an ice flow from Newfoundland. The glacial deposit covering the northern Magdalen Islands was associated with the Newfoundland icecap; here it is named the Grande-Entrée till and is dated to c.  20 ka. OSL ages between c.  23 and 17 ka acquired from cryopediment and coastal deposits on the southern islands indicate that this part of the archipelago was deglaciated shortly after the LGM and was affected by a high sea level and periglacial processes. Around 15 ka, the entire archipelago was deglaciated and partially submerged until c.  10 ka. This data set is the first major contribution to a detailed chronology of the Magdalen Islands and constitutes the first step towards interpreting the glacial and sea-level history of the central area of the Gulf of St. Lawrence; this new understanding will provide input to regional marine and glacial modelling.
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    Microsedimentology of ice stream tills from the Eastern Alps, Austria – a new perspective on till microstructures (2016)
    Wiley
    In: Boreas
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    Publication Date: 2016-07-10
    Description: This study of tills from the Eastern Alps, Austria, illustrates the insights obtained using microsedimentology on subglacial tills in the context of palaeogeographical reconstructions of glacier advances. Investigations of several sites with tills derived from both local glaciers and the ice-sheet streaming of the Inn Glacier during the Last Glacial Maximum and its termination reveal a detailed picture of subglacial sedimentology that provides evidence of soft sediment subglacial deformation under polythermal conditions. All the tills exhibit microstructures that are proxy evidence of significant changes in till rheology. The tills originate from multiple sources, incorporating older tills and other deposits picked up by the subglacial deformation within a polythermal but dominantly warm temperate subglacial thermal regime. The analyses of till microstructures reveal a direct relationship between basal ice strain conditions and their development. A hypothesis is derived, from the various microstructures observed in these Austrian tills formed under soft sediment deforming basal ice conditions, that suggests that with basal thermal changes and fluctuations in clay content, pore-water content and pressure, microstructures form in a non-random manner. It is postulated that in clay-deficient sediments, edge-to-edge events are most likely to occur first; and where clay content increases, grain stacks, rotation structures, deformation bands and, finally, shear zones are likely to evolve in an approximate sequential manner. After repeated transport, emplacement, reworking and, probably, further shearing and deformation events, an emplaced ‘till’, as observed in these Austrian tills, will form that carries most, if not all of these microstructures, in varying percentages. Finally, the impact of the Inn Glacier Ice Stream on these tills is not easily detected and/or differentiated, but indications of high pore water and probable dilatant events leading to reductions in the number of edge-to-edge events point to the impact of fast or thick ice upon these subglacial tills.
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    Extinct or still out there? Disentangling influences on extinction and rediscovery helps to clarify the fate of species on the edge (2016)
    Wiley
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    Publication Date: 2016-07-12
    Description: Each year, two or three species that had been considered to be extinct are rediscovered. Uncertainty about whether or not a species is extinct is common, because rare and highly threatened species are difficult to detect. Biological traits such as body size and range size are expected to be associated with extinction. However, these traits, together with the intensity of search effort, might influence the probability of detection and extinction differently. This makes statistical analysis of extinction and rediscovery challenging. Here we use a variant of survival analysis known as cure rate modelling to differentiate factors that influence rediscovery from those that influence extinction. We analyse a global dataset of 99 mammals that have been categorised as extinct or possibly extinct. We estimate the probability that each of these mammals is still extant, and thus estimate the proportion of missing (presumed extinct) mammals that are incorrectly assigned extinction. We find that body mass and population density are predictors of extinction, and body mass and search effort predict rediscovery. In mammals, extinction rate increases with body mass and population density, and these traits act synergistically to greatly elevate extinction rate in large species that also occurred in formerly dense populations. However, when they remain extant, larger-bodied missing species are rediscovered sooner than smaller species. Greater search effort increases the probability of rediscovery in larger species of missing mammals, but has a minimal effect on small species, which take longer to be rediscovered, if extant. By separating the effects of species characteristics on extinction and detection, and using models with the assumption that a proportion of missing species will never be rediscovered, our new approach provides estimates of extinction probability in species with few observation records and scant ecological information. This article is protected by copyright. All rights reserved.
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    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
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    Grazing intensity significantly affects belowground carbon and nitrogen cycling in grassland ecosystems: a meta-analysis (2016)
    Wiley
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    Publication Date: 2016-07-15
    Description: Livestock grazing activities potentially alter ecosystem carbon (C) and nitrogen (N) cycles in grassland ecosystems. Despite the fact that numerous individual studies and a few meta-analyses had been conducted, how grazing, especially its intensity, affects belowground C and N cycling in grasslands remains unclear. In this study, we performed a comprehensive meta-analysis of 115 published studies to examine the responses of 19 variables associated with belowground C and N cycling to livestock grazing in global grasslands. Our results showed that, on average, grazing significantly decreased belowground C and N pools in grassland ecosystems, with the largest decreases in microbial biomass C and N (21.62 and 24.40%, respectively). In contrast, belowground fluxes, including soil respiration, soil net N mineralization and soil N nitrification increased by 4.25%, 34.67 and 25.87%, respectively in grazed grasslands compared to ungrazed ones. More importantly, grazing intensity significantly affected the magnitude (even direction) of changes in the majority of the assessed belowground C and N pools and fluxes, and C:N ratio as well as soil moisture. Specifically,light grazing contributed to soil C and N sequestration whereas moderate and heavy grazing significantly increased C and N losses. In addition, soil depth, livestock type and climatic conditions influenced the responses of selected variables to livestock grazing to some degree. Our findings highlight the importance of the effects of grazing intensity on belowground C and N cycling, which may need to be incorporated into regional and global models for predicting effects of human disturbance on global grasslands and assessing the climate- biosphere feedbacks. This article is protected by copyright. All rights reserved.
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    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
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    A meta-analysis of soil salinization effects on nitrogen pools, cycles and fluxes in coastal ecosystems (2016)
    Wiley
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    Publication Date: 2016-07-15
    Description: Salinity intrusion caused by land subsidence resulting from increasing groundwater abstraction, decreasing river sediment loads and increasing sea level because of climate change has caused widespread soil salinization in coastal ecosystems. Soil salinization may greatly alter nitrogen (N) cycling in coastal ecosystems. However, a comprehensive understanding of the effects of soil salinization on ecosystem N pools, cycling processes and fluxes is not available for coastal ecosystems. Therefore, we compiled data from 551 observations from 21 peer-reviewed papers and conducted a meta-analysis of experimental soil salinization effects on 19 variables related to N pools, cycling processes and fluxes in coastal ecosystems. Our results showed that the effects of soil salinization varied across different ecosystem types and salinity levels. Soil salinization increased plant N content (18%), soil NH 4 + (12%) and soil total N (210%), although it decreased soil NO 3 - (2%) and soil microbial biomass N (74%). Increasing soil salinity stimulated soil N 2 O fluxes as well as hydrological NH 4 + and NO 2 - fluxes more than three-fold, although it decreased the hydrological dissolved organic nitrogen (DON) flux (59%). Soil salinization also increased the net N mineralization by 70%, although salinization effects were not observed on the net nitrification, denitrification and dissimilatory nitrate reduction to ammonium in this meta-analysis. Overall, this meta-analysis improves our understanding of the responses of ecosystem N cycling to soil salinization, identifies knowledge gaps and highlights the urgent need for studies on the effects of soil salinization on coastal agro-ecosystem and microbial N immobilization. Additional increases in knowledge are critical for designing sustainable adaptation measures to the predicted intrusion of salinity intrusion so that the productivity of coastal agro-ecosystems can be maintained or improved and the N losses and pollution of the natural environment can be minimized. This article is protected by copyright. All rights reserved.
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    Tracking lags in historical plant species’ shifts in relation to regional climate change (2016)
    Wiley
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    Publication Date: 2016-07-15
    Description: Can species shift their distributions fast enough to track changes in climate? We used abundance data from the 1950s and the 2000s in Wisconsin to measure shifts in the distribution and abundance of 78 forest-understory plant species over the last half-century and compare these shifts to changes in climate. We estimated temporal shifts in the geographic distribution of each species using vectors to connect abundance-weighted centroids from the 1950s and 2000s. These shifts in distribution reflect colonization, extirpation, and changes in abundance within sites, separately quantified here. We then applied climate analog analyses to compute vectors representing the climate change that each species experienced. Species shifted mostly to the northwest (mean: 49 ± 29 km) primarily reflecting processes of colonization and changes in local abundance. Analog climates for these species shifted even further to the northwest, however, exceeding species’ shifts by an average of 90 ± 40 km. Most species thus failed to match recent rates of climate change. These lags decline in species that have colonized more sites and those with broader site occupancy, larger seed mass, and higher habitat fidelity. Thus, species’ traits appear to affect their responses to climate change, but relationships are weak. As climate change accelerates, these lags will likely increase, potentially threatening the persistence of species lacking the capacity to disperse to new sites or locally adapt. However, species with greater lags have not yet declined more in abundance. The extent of these threats will likely depend on how other drivers of ecological change and interactions among species affect their responses to climate change. This article is protected by copyright. All rights reserved.
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    Representing model uncertainty in the Met Office convection permitting ensemble prediction system and its impact on fog forecasting (2016)
    Wiley
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    Publication Date: 2016-07-15
    Description: Representing model uncertainty in convection-permitting ensemble prediction systems is a developing area of research. While methods for including variability to account for model uncertainty at the global scales are quite mature, it is not clear that these methods will necessarily be applicable at the convective-scale. One such method is the Random Parameter (RP) scheme, where parameters from the physics parametrizations are perturbed at regular intervals throughout the forecast. In this work, we adapt the RP scheme to represent model uncertainty in the Met Office's convection permitting ensemble prediction system for the UK (MOGREPS-UK). The revised version of the RP scheme is applied to a sub-set of model parameters, chosen to target specific physical processes relevant to the UK forecast. Objective verification scores from two one-month trials show particular improvements for visibility and surface temperature when the RP scheme is used. Application of the RP scheme results in a modest increase in the ensemble spread for all surface parameters. The results of low visibility case studies show that applying the RP scheme enables the ensemble to capture observed fog events otherwise missed by the forecast. Overall, the RP scheme has a positive effect on MOGREPS-UK, and demonstrates the benefit of schemes that target known areas of model uncertainty.
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    Assessment and Tuning of Data Assimilation Systems Using Passive Observations (2016)
    Wiley
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    Publication Date: 2016-07-15
    Description: Independent observations can be used to diagnose and tune a data assimilation (DA) system. Analysis increments generally improve the model state nearby assimilated observations but degrade it further away. High-resolution aircraft observations from Mode-S EHS are used as an independent data source to verify increment degradation as a function of distance from assimilated observations. An adaptation of the inherently imperfect gain matrix in DA is proposed such that resulting analyses better fit the independent data source and as such draw model simulations closer to the true atmospheric state. It is found that the structure functions of the background error covariance matrix of the experimental mesoscale HARMONIE model are appropriate but too much weight is given to observations relative to the model background. The ECMWF model is well tuned with a slight overestimation of temperature information in the upper troposphere. Finally, a caveat is highlighted when comparing model forecasts from different experiments against observations. It is common practice to use the same observing system both in the analysis and for forecast verification. However, forecast verification is prone to sampling errors yielding less favourable scores when using an independent data source. To avoid biased conclusions on the impact of observing systems, e.g., in observing system experiments (OSE), requires an independent data source (best practice) or a data source used in all experiments (best pragmatic practice) for verification of forecasts from different experiments.
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    Gust factor based on research aircraft measurements: a new methodology applied to the Arctic marine boundary layer (2016)
    Wiley
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    Publication Date: 2016-07-15
    Description: There is as yet no standard methodology for measuring wind gusts from a moving platform. To address this, we have developed a method to derive gusts from research aircraft data. First we evaluated four different approaches, including Taylor's hypothesis of frozen turbulence, to derive the gust length scales that correspond to the gust time scales, namely, the gust duration (seconds) and the sample period (typically 10 min). The novelty of our method is in using peak factors (deviation of the gust from the mean wind speed normalized by the local turbulence) to convert between the scales. After devising a way to derive the gust length scales, we calculated the gust factors from aircraft observations and tested them against those from four parameterizations originally developed for weather stations. Three of them performed well ( R 2  = 0.66 or higher), while the fourth overestimated the gust factors in unstable conditions ( R 2  = 0.52). The mean errors for all methods were low, from −0.02 to 0.05, indicating that wind gust factors can indeed be measured from research aircraft. Moreover, we showed that aircraft can provide gust measurements within the whole boundary layer, if horizontal legs are flown at multiple levels over the same track. This is a significant advance, as gust measurements are usually limited to heights reached by weather masts. In unstable conditions over the open ocean the gust factor was nearly constant with height throughout the boundary layer, the near-surface values only slightly exceeding those at upper levels. Furthermore, we found gust factors to be strongly dependent on surface roughness conditions, which differed between the open ocean and sea ice in the Arctic marine environment. The roughness effect on the gust factor was stronger than the effect of boundary-layer stability.
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    Indirect Forcing of Black carbon on Clouds over North East India (2016)
    Wiley
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    Publication Date: 2016-07-15
    Description: Black Carbon (BC) induced indirect radiative forcing and cloud albedo effect has been studied for the first time over Northeast India. Measurements of BC and Cloud microphysical parameters were carried out during Phase-I of Cloud Aerosol Interaction and Precipitation Enhancement Experiment (CAIPEEX) over North East India (Guwahati) in 2009. Liquid water path (LWP) in the cloud layers coherent with BC on different experimental days was found to be 206 to 327 gm -2 over the region. Black carbon aerosol Indirect effect (BCIE) for fixed LWP is found to be 0.32 to 0.48 on different days of observations. The indirect forcing corresponding to this BCIE has been estimated using a radiative transfer model for fixed LWP by altering the derived BC-AOD (from measured BC profiles) and cloud effective radius (R e ) combinations. The estimated average BC induced indirect forcing (BCIF) was -24 to -37.1Wm -2 at the surface and +2.5 to +14.8 Wm -2 at Top Of the Atmosphere (TOA). The average albedo due to BCIF at TOA was 0.49 to 0.61. BCIF is found to reduce the cloud reflection by 1.5 to 2% over the region. The sensitivity of cloud parameters to BCIF and albedo effect are illustrated.
    Print ISSN: 0035-9009
    Electronic ISSN: 1477-870X
    Topics: Geography , Physics
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    Spatial Verification Using Wavelet Transforms: A Review (2016)
    Wiley
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    Publication Date: 2016-07-15
    Description: Due to the emergence of new high resolution numerical weather prediction (NWP) models and the availability of new or more reliable remote sensing data, the importance of efficient spatial verification techniques is growing. Wavelet transforms offer an effective framework to decompose spatial data into separate (and possibly orthogonal) scales and directions. Most wavelet based spatial verification techniques have been developed or refined in the last decade and concentrate on assessing forecast performance (i.e. forecast skill or forecast error) on distinct physical scales. Particularly during the last five years, a significant growth in meteorological applications could be observed. However, a comparison with other scientific fields such as feature detection, image fusion, texture analysis, or facial and biometric recognition, shows that there is still a considerable, currently unused potential to derive useful diagnostic information. In order to tab the full potential of wavelet analysis, we revise the state-of-the art in one- and two-dimensional wavelet analysis and its application with emphasis on spatial verification. We further use a technique developed for texture analysis in the context of high-resolution quantitative precipitation forecasts, which is able to assess structural characteristics of the precipitation fields and allows efficient clustering of ensemble data.
    Print ISSN: 0035-9009
    Electronic ISSN: 1477-870X
    Topics: Geography , Physics
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    Model simulations of flood and debris flow timing in steep catchments after wildfire (2016)
    Wiley
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    Publication Date: 2016-07-16
    Description: Debris flows are a typical hazard on steep slopes after wildfire, but unlike debris flows that mobilize from landslides, most post-wildfire debris flows are generated from water runoff. The majority of existing debris-flow modeling has focused on landslide-triggered debris flows. In this study we explore the potential for using process-based rainfall-runoff models to simulate the timing of water flow and runoff-generated debris flows in recently burned areas. Two different spatially distributed hydrologic models with differing levels of complexity were used: the full shallow water equations and the kinematic wave approximation. Model parameter values were calibrated in two different watersheds, spanning two orders of magnitude in drainage area. These watersheds were affected by the 2009 Station Fire in the San Gabriel Mountains, CA, USA. Input data for the numerical models were constrained by time series of soil moisture, flow stage, and rainfall collected at field sites, as well as high-resolution lidar-derived digital elevation models. The calibrated parameters were used to model a third watershed in the burn area, and the results show a good match with observed timing of flow peaks. The calibrated roughness parameter (Manning's $n$) was generally higher when using the kinematic wave approximation relative to the shallow water equations, and decreased with increasing spatial scale. The calibrated effective watershed hydraulic conductivity was low for both models, even for storms occurring several months after the fire, suggesting that wildfire-induced changes to soil-water infiltration were retained throughout that time. Overall the two model simulations were quite similar suggesting that a kinematic wave model, which is simpler and more computationally efficient, is a suitable approach for predicting flood and debris flow timing in steep, burned watersheds. This article is protected by copyright. All rights reserved.
    Print ISSN: 0043-1397
    Electronic ISSN: 1944-7973
    Topics: Architecture, Civil Engineering, Surveying , Geography
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    A combined field, laboratory and numerical study of the forces applied to, and the potential for removal of, bar top vegetation in a braided river. (2016)
    Wiley
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    Publication Date: 2016-07-19
    Description: Vegetation can have an important role in controlling channel planform, through its effects on channel roughness, and root-reinforcement of bank and bar materials. Along the Platte River in central Nebraska, USA, The Platte River Recovery Implementation Program (PRRIP) has been tasked with managing the planform of the river to benefit endangered species. To investigate the potential use of planned Short Duration High Flow events (SDHFs) to manage bar vegetation, this study combined several approaches to determine whether flows of up to 227 m 3 s -1 through the central Platte River, could remove cottonwood, Phragmites and reed canarygrass stands of various ages and densities from in-channel bars. First, fieldwork was carried out to measure the uprooting resistance, and resistance to bending for each species. Second, a set of flume experiments was carried out to measure the forces exerted on the three species of interest under different flow conditions. Finally, a numerical study compared drag forces (driving) measured in the flume study, with uprooting forces (resisting) measured in the field, was carried out for each species to determine the likelihood of plant removal by SDHFs. Results showed that plants with more than a year of root growth, likely cannot be removed through drag and local scour alone, even at the 100-year recurrence interval discharge. At most, a few cottonwood seedlings could be removed from bars through drag, scour and undercutting, where rooting depths are still small. The results presented here help us further understand the positive feedbacks that lead to the creation of permanent, vegetated bars rather than mobile braided channels. As such, the findings could help inform management decisions for other braided rivers, and the combined field, flume and modelling techniques used in this study could be applied to other fluvial systems where vegetation and planform dynamics are of interest. This article is protected by copyright. All rights reserved.
    Print ISSN: 0197-9337
    Electronic ISSN: 1096-9837
    Topics: Geography , Geosciences
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    Exploiting Maximum Entropy method and ASTER data for assessing debris flow and debris slide susceptibility for the Giampilieri catchment (north-eastern Sicily, Italy). (2016)
    Wiley
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    Publication Date: 2016-07-19
    Description: This study aims at evaluating the performance of the Maximum Entropy method in assessing landslide susceptibility, exploiting topographic and multispectral remote sensing predictors. We selected the catchment of the Giampilieri stream, which is located in the north-eastern sector of Sicily (southern Italy), as test site. On 1/10/2009, a storm rainfall triggered in this area hundreds of debris flow/avalanche phenomena causing extensive economical damage and loss of life. Within this area a presence-only-based statistical method was applied to obtain susceptibility models capable of distinguish future activation sites of debris flow and debris slide, which where the main source failure mechanisms for flow or avalanche type propagation. The set of predictors used in this experiment comprised primary and secondary topographic attributes, derived by processing a high resolution digital elevation model, CORINE land cover data and a set of vegetation and mineral indices obtained by processing multispectral ASTER images. All the selected data sources are dated before the disaster. A spatially random partition technique was adopted for validation, generating fifty replicates for each of the two considered movement typologies in order to assess accuracy, precision and reliability of the models. The debris slide and debris flow susceptibility models produced high performances with the first type being the best fitted. The evaluation of the probability estimates around the mean value for each mapped pixel shows an inverted relation, with the most robust models corresponding to the debris flows. With respect to the role of each predictor within the modelling phase, debris flows appeared to be primarily controlled by topographic attributes whilst the debris slides were better explained by remotely sensed derived indices, particularly by the occurrence of previous wildfires across the slope. The overall excellent performances of the two models suggest promising perspectives for the application of presence-only methods and remote sensing derived predictors. This article is protected by copyright. All rights reserved.
    Print ISSN: 0197-9337
    Electronic ISSN: 1096-9837
    Topics: Geography , Geosciences
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    Oxygen utilization rate (OUR) underestimates ocean respiration – a model study (2016)
    Wiley
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    Publication Date: 2016-07-19
    Description: We use a simple 1D model representing an isolated density surface in the ocean and 3D global ocean biogeochemical models to evaluate the concept of computing the subsurface oceanic oxygen utilization rate (OUR) from the changes of apparent oxygen utilization (AOU) and water age. The distribution of AOU in the ocean is not only the imprint of respiration in the ocean's interior, but is strongly influenced by transport processes and eventually loss at the ocean surface. Since AOU and water age are subject to advection and diffusive mixing, it is only when they are affected both in the same way that OUR represents the correct rate of oxygen consumption. This is the case only when advection prevails or with uniform respiration rates, when the proportions of AOU and age are not changed by transport. In experiments with the 1D-tube model, OUR underestimates respiration when maximum respiration rates occur near the outcrops of isopycnals, and overestimates when maxima occur far from the outcrops. Given the distribution of respiration in the ocean, i.e. elevated rates near high latitude outcrops of isopycnals and low rates below the oligotrophic gyres, underestimates are the rule. Integrating these effects globally in three coupled ocean biogeochemical and circulation models we find that AOU-over-age based calculations underestimate true model respiration by a factor of three. Most of this difference is observed in the upper 1000 m of the ocean with the discrepancies increasing towards the surface where OUR underestimates respiration by as much as factor of four.
    Print ISSN: 0886-6236
    Electronic ISSN: 1944-9224
    Topics: Biology , Chemistry and Pharmacology , Geography , Geosciences , Physics
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    Aquifer Heterogeneity Controls on Adverse Human Health Effects and the Concept of the Hazard Attenuation Factor (2016)
    Wiley
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    Publication Date: 2016-07-19
    Description: We analyze the probability distribution of the hazard attenuation factor for a non-carcinogenic reactive compound captured by a well in heterogeneous porous formations. The hazard attenuation factor is defined as the ratio between the hazard index HI at a detection well and at the source. Heterogeneity of the aquifer is represented through the Multi-Indicator Model (a collection of blocks of independent permeability) while flow and transport are solved by the means of the Self-Consistent Approach, that is able to deal with any degree of heterogeneity. Due to formation heterogeneity, HI is a random variable and similar for hazard attenuation index. The latter can be fully characterized by its cumulative distribution function (CDF), which in turn can be related to the statistics of the travel time of solute particles, from the source to the detection well. The approach is applied to the case of a solute which undergoes decay and a well with a screen much smaller than the correlation scale of hydraulic conductivity. The results show that the probability of exceeding a given acceptable threshold of the hazard index is significantly affected by the level of heterogeneity comparable to the one observed for the MADE site, and the distance between the source and the well. This article is protected by copyright. All rights reserved.
    Print ISSN: 0043-1397
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    Topics: Architecture, Civil Engineering, Surveying , Geography
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    Global-change drivers of ecosystem functioning modulated by natural variability and saturating responses (2016)
    Wiley
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    Publication Date: 2016-07-21
    Description: Humans are altering global environment at an unprecedented rate through changes in biodiversity, climate, nitrogen cycle, and land-use. In order to address their effects on ecosystem functioning, experiments most frequently explore one driver at a time and control as many confounding factors as possible. Yet, which driver exerts the largest influence on ecosystem functioning and whether their relative importance changes among systems remain unclear. We analyzed experiments in the Patagonian steppe that evaluated the aboveground net primary production (ANPP) response to manipulated gradients of species richness, precipitation, temperature, nitrogen fertilization (N) and grazing intensity. We compared the effect on ANPP relative to ambient conditions considering intensity and direction of manipulations for each driver. The ranking of responses to drivers with comparable manipulation intensity was: biodiversity〉grazing〉precipitation〉N. For a similar intensity of manipulation, the effect of biodiversity loss was 4.0, 3.6, and 1.5, times larger than N deposition, decreased precipitation, and increased grazing intensity. We interpreted our results considering two hypotheses. First, the response of ANPP to changes in precipitation and biodiversity is saturating, so we expected larger effects when the driver was reduced, relative to ambient conditions, than when it was increased. Experimental manipulations that reduced ambient levels had larger effects than those that increased them. Second, the sensitivity of ANPP to each driver is inversely related to the natural variability of the driver. In Patagonia, the ranking of natural variability of drivers is: precipitation〉grazing〉temperature〉biodiversity〉N. So, in general, the ecosystem was most sensitive to drivers that varied the least. Comparable results from Cedar Creek (MN) support both hypotheses and suggest that sensitivity to drivers varies among ecosystem types. Given the importance of understanding ecosystem sensitivity to predict global-change impacts, it is necessary to design new experiments located in regions with contrasting natural variability and that include the full range of drivers. This article is protected by copyright. All rights reserved.
    Print ISSN: 1354-1013
    Electronic ISSN: 1365-2486
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
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    Stomatal response to humidity and CO2 implicated in recent decline in U.S. evaporation (2016)
    Wiley
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    Publication Date: 2016-07-21
    Description: Evapotranspiration, defined as the total flux of water from the land surface to the atmosphere, is a major component of the hydrologic cycle and surface energy balance. Although evapotranspiration is expected to intensify with increasing temperatures, long-term, regional trends in evapotranspiration remain uncertain due to spatially and temporally limited direct measurements. In this study, we utilize an emergent relation between the land surface and atmospheric boundary layer to infer daily evapotranspiration from historical meteorological data collected at 236 weather stations across the U.S. Our results suggest a statistically significant ( α = 0.05) decrease in evapotranspiration of approximately 6% from 1961 to 2014, with a significant ( α = 0.05) sharp decline of 13% from 1998 to 2014. We attribute the decrease in evapotranspiration mostly to declines in surface conductance, but also to offsetting changes in longwave radiation, wind speed, and incoming solar radiation. Using an established stomatal conductance model, we explain the changes in inferred surface conductance as a response to increases in carbon dioxide and, more recently, to an abrupt decrease in atmospheric humidity. This article is protected by copyright. All rights reserved.
    Print ISSN: 1354-1013
    Electronic ISSN: 1365-2486
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
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    An ecoregion assessment of projected tree species vulnerabilities in western North America through the 21st century (2016)
    Wiley
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    Publication Date: 2016-07-21
    Description: Forest ecosystems across western North America will likely see shifts in both tree species dominance and composition over the rest of this century in response to climate change. Our objective in this paper is to identify which ecological regions might expect the greatest changes to occur. We used the process-based growth model 3-PG, to provide estimates of tree species responses to changes in environmental conditions and to evaluate the extent that species are resilient to shifts in climate over the rest of this century. We assessed the vulnerability of 20 tree species in western North America using the Canadian global circulation model under three different emission scenarios. We provided detailed projections of species shifts by including soil maps that account for the spatial variation in soil water availability and soil fertility as well as by utilizing annual climate projections of monthly changes in air temperature, precipitation, solar radiation, vapor pressure deficit and frost at a spatial resolution of 1 km. Projected suitable areas for tree species were compared to their current ranges based on observations at 〉40,000 field survey plots. Tree species were classified as vulnerable if environmental conditions projected in the future appear outside that of their current distribution ≥70% of the time. We added a migration constraint that limits species dispersal to 〈200 m year −1 to provide more realistic projections on species distributions. Based on these combinations of constraints, we predicted the greatest changes in the distribution of dominant tree species to occur within the Northwest Forested Mountains and the highest number of tree species stressed will likely be in the North American Deserts. Projected climatic changes appear especially unfavorable for species in the subalpine zone, where major shifts in composition may lead to the emergence of new forest types. This article is protected by copyright. All rights reserved.
    Print ISSN: 1354-1013
    Electronic ISSN: 1365-2486
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
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