ALBERT

Beschreibung: Snow availability in Alpine catchments plays an important role in water resources management. In this paper we propose a method for an optimal estimation of snow depth (areal extension and thickness) in Alpine systems from point data and satellite observations by using significant explanatory variables deduced from a digital terrain model. It is intended to be a parsimonious approach that may complement physical-based methodologies. Different techniques (multiple regression, multi-criteria analysis and kriging) are integrated to address the following issues: We identify the explanatory variables that could be helpful based on a critical review of the scientific literature. We study the relationship between ground observations and explanatory variables using a systematic procedure for a complete multiple regression analysis. Multiple regression models are calibrated combining all suggested model structures and explanatory variables. We also propose an evaluation of the models (using indices to analyze the goodness of fit) and select the best approaches (models and variables) based on multi-criteria analysis. Estimation of the snow depth is performed with the selected regression models. The residual estimation is improved by applying kriging in cases with spatial correlation. The final estimate is obtained by combining regression and kriging results, and constraining the snow domain in accordance with satellite data. The method is illustrated using the case study of the Sierra Nevada mountain range (Southern Spain). A cross validation experiment has confirmed the efficiency of the proposed procedure. Finally, although it is not the scope of this work, the snow depth is used to asses a first estimation of snow water equivalent (SWE) resources.

Beschreibung: Impact of icebergs on net primary productivity in the Southern Ocean Shuang-Ye Wu and Shugui Hou The Cryosphere, 11, 707-722, doi:10.5194/tc-11-707-2017, 2017 The primary productivity in the Southern Ocean (SO) is limited by the amount of iron available for biological activities. Recent studies show that icebergs could be a main source of iron to the SO. Based on remote sensing data, our study shows that iceberg presence is associated with elevated levels of ocean productivity, particularly in iron-deficient regions. This impact could serve as a negative feedback to the climate system.

Beschreibung: Bromine, iodine and sodium in surface snow along the 2013 Talos Dome–GV7 traverse (northern Victoria Land, East Antarctica) Niccolò Maffezzoli, Andrea Spolaor, Carlo Barbante, Michele Bertò, Massimo Frezzotti, and Paul Vallelonga The Cryosphere, 11, 693-705, doi:10.5194/tc-11-693-2017, 2017 Sea ice is a crucial parameter within Earth's climate system. Understanding its dynamics and its response to other climatic variables is therefore of primary importance in view of a warming climate and sea ice decline. In this work we investigate some features of a chemical parameter in ice cores, bromine enrichment, which is linked to sea ice and can therefore be used to reconstruct sea ice in the past.

Beschreibung: Application of a two-step approach for mapping ice thickness to various glacier types on Svalbard Johannes Jakob Fürst, Fabien Gillet-Chaulet, Toby J. Benham, Julian A. Dowdeswell, Mariusz Grabiec, Francisco Navarro, Rickard Pettersson, Geir Moholdt, Christopher Nuth, Björn Sass, Kjetil Aas, Xavier Fettweis, Charlotte Lang, Thorsten Seehaus, and Matthias Braun The Cryosphere Discuss., doi:10.5194/tc-2017-30,2017 Manuscript under review for TC (discussion: open, 0 comments) For the large majority of glaciers and ice caps, there is no information on the thickness of the ice cover. Any attempt to predict glacier demise under climatic warming and to estimate the future contribution to sea-level rise is limited as long as the glacier thickness is not well constrained. Here, we present a two-step mass-conservation approach for mapping ice thickness. Measurements are naturally reproduced. The reliability is readily assessible from a complementary map of error estimates.

Beschreibung: The urban environment modifies the hydrologic cycle resulting in increased runoff rates, volumes and peak flows. Green Infrastructure, which uses best management practices (BMPs), is a natural system approach used to mitigate the impacts of urbanization onto stormwater runoff. Patterns of stormwater runoff from urban environments are complex and it is unclear how efficiently green infrastructure will improve the urban water cycle. These challenges arise from issues of scale, the merits of BMPs depend on changes to small scale hydrologic processes aggregated up from the neighborhood to the urban watershed. Here, we use a hyper-resolution (1 m), physically-based hydrologic model of the urban hydrologic cycle with explicit inclusion of the built environment. This model represents the changes to hydrology at the BMP scale (~1 m), represents each individual BMP explicitly to represent response over the urban watershed. Our study varies both the percentage of BMP emplacement and their spatial location for storm events of increasing intensity in an urban watershed. We develop a metric of effectiveness that indicates a nonlinear relationship is seen between percent BMP emplacement and storm intensity. Results indicate that BMP effectiveness varies with spatial location and that type and emplacement within the urban watershed may be more important than overall percent.

Beschreibung: A number of extensive droughts and destructive floods have occurred in Poland in the last 25 years, hence projections of low and high river flows are of considerable interest and importance. In the first part of this paper, projections of low and high flows in the rivers of the Vistula and the Odra basins (VOB region), for two future time horizons, are presented. Projections are based on the SWAT hydrological model simulations driven by results of the EURO-CORDEX experiment under Representative Concentration Pathways 4.5 and 8.5. The VOB region covers most of Poland and parts of five neighboring countries, giving this study an international relevance. In the second part of the paper a review of projections of low and high flows in rivers in Central and Eastern Europe is presented. Despite a substantial spread of flow projections, the main message of the modelling part is that increases of both low and high flows are dominating. The magnitude of increase of low flow is considerably higher than that of high flow. In other words, future streamflow droughts are projected to be less severe, while, in contrast, river floods are projected to increase, which is a challenge for flood risk reduction, water management and climate change adaptation. There is an overall agreement of our findings for the VOB region with projections of hydrological extremes from large-scale models forced by EURO-CORDEX results in the European-scale studies.

Beschreibung: Transformations of precipitation into groundwater and streamflow are fundamental hydrological processes, critical to irrigated agriculture, hydroelectric power generation and ecosystem health. Our understanding of the timing of groundwater recharge and streamflow generation remains incomplete, limiting our ability to predict fresh water, nutrient, and contaminant fluxes, especially in large basins. Here we analyze thousands of rain, snow, groundwater and streamflow δ 18 O and δ 2 H values in the Nelson River basin, which covers 1.2 million km 2 of central Canada. We show that the fraction of precipitation that recharges aquifers is ~1.3-5 times higher for precipitation falling during cold months with subzero mean monthly temperatures than for precipitation falling during warmer months. The near-ubiquity of cold-season-biased groundwater recharge implies that changes to winter water balances may have disproportionate impacts on annual groundwater recharge rates. We also show that young streamflow—defined as precipitation that enters a river in less than ~2.3 months—comprises ~27 % of annual streamflow, but varies widely among tributaries in the Nelson River basin (1-59 %). Young streamflow fractions are lower in steep catchments, and higher in flatter catchments such as the transboundary Red River basin. Our findings imply that flat, lower-permeability, heavily-tiled landscapes favor more rapid transmission of precipitation into rivers, possibly mobilizing excess soluble fertilizers and exacerbating eutrophication events in Lake Winnipeg.

Beschreibung: Ice-shelf damming in the glacial Arctic Ocean: dynamical regimes of a basin-covering kilometre thick ice shelf Johan Nilsson, Martin Jakobsson, Chris Borstad, Nina Kirchner, Göran Björk, Raymond T. Pierrehumbert, and Christian Stranne The Cryosphere Discuss., doi:10.5194/tc-2017-37,2017 Manuscript under review for TC (discussion: open, 0 comments) Recent data suggest that a one-kilometre thick ice shelf extended over the glacial Arctic Ocean during MIS 6, about 140 000 years ago. Here, we theoretically analyse the development and equilibrium features of such an ice shelf. The ice shelf was effectively dammed by the Fram Strait and the mean ice-shelf thickness was controlled primarily by the horizontally-integrated mass balance. Our results can aid to resolve some outstanding questions of the state of the glacial Arctic Ocean.

Beschreibung: Saturation-excess runoff is the major runoff mechanism in humid well-vegetated areas where infiltration rates often exceed rainfall intensity. While the Soil and Water Assessment Tool (SWAT) is one of the most widely used models, it predicts runoff based mainly on soil and land use characteristics, and is implicitly an infiltration-excess runoff type of model. Previous attempts to incorporate the saturation-excess runoff mechanism in SWAT fell short due to the inability to distribute water from one Hydrological Response Unit (HRU) to another. This paper introduces a modified version of SWAT, referred to as SWAT-Hillslope (SWAT-HS). This modification improves the simulation of saturation-excess runoff by redefining HRUs based on wetness classes, and by introducing a surface aquifer with the ability to route interflow from “drier” to “wetter” wetness classes. Mathematically, the surface aquifer is a non-linear reservoir that generates rapid subsurface stormflow as the water table in the surface aquifer rises. The SWAT-HS model was tested in the Town Brook watershed in the upper reaches of the West Branch Delaware River in the Catskill region of New York, USA. SWAT-HS predicted discharge well with a Nash-Sutcliffe Efficiency of 0.68 and 0.87 for daily and monthly time steps. Compared to the original SWAT model, SWAT-HS predicted less surface runoff and groundwater flow and more lateral flow. The saturated areas predicted by SWAT-HS were concentrated in locations with a high topographic index and were in agreement with field observations. With the incorporation of topographic characteristics and the addition of the surface aquifer, SWAT-HS improved streamflow simulation and gave a good representation of saturated areas on the date that measurements were available. SWAT-HS is expected to improve water quality model predictions where the location of the surface runoff matters.

Beschreibung: Precipitation and temperature time series suffer from many problems, such as short time period, inadequate spatial coverage, missing data and biases from various causes, which is particularly critical in remote areas such as Northern Canada. The development of alternative datasets for using as proxies for inadequate/missing weather data represents a key research area. In this paper, the performance of six alternative datasets is evaluated for hydrological modeling over 12 watersheds located across Canada and the contiguous United States. The datasets can be classified into three distinct categories: (1) interpolated gridded data, (2) reanalysis data, and (3) climate model outputs. Hydrological simulations were carried out using a lumped conceptual hydrological model calibrated using standard weather data, and compared against results using a calibration specific to each alternative dataset. Prior to the hydrological simulations, the alternative datasets were all evaluated with respect to their ability to reproduce gridded daily precipitation and temperature characteristics over North America. The results show that both the reanalysis data and climate model data adequately represent the spatial pattern of daily precipitation and temperature over North America. The North American Regional Reanalysis (NARR) dataset consistently shows the best performance. With respect to hydrological modeling, the observed discharges are accurately represented by both the gridded and NARR datasets, and more so for the NARR data. The National Centers for Environmental Prediction (NCEP) dataset consistently performs worst as it is unable to even capture the seasonal pattern of observed streamflow for three out of the 12 watersheds. These results indicate that the NARR dataset could be used as a proxy for gauged precipitation and temperature for hydrological modeling over watersheds where observational datasets are deficient. The results also illustrate the ability of climate model data to be used for performing hydrological modeling when driven by reanalysis data at their boundaries, and especially so for high-resolution models.

Beschreibung: Flat terrain and soils with variable permeability make it difficult to assess the relative importance of surface and subsurface runoff in the Canadian Prairies, especially in riparian areas that are critical for water transmission and solute transport. The main objective of this study is therefore to determine whether patterns of hydrologic state variables, namely near-surface soil moisture (SM), soil electrical conductivity (SEC) and soil temperature (ST), can help infer riparian-to-stream soil water movement in Prairie landscapes. Focus is on the near-level Catfish Creek Watershed (south-eastern Manitoba, Canada) where three riparian sites were monitored: a naturally vegetated grassland site, a headwater forested site, and a highly impacted grassed site adjacent to an engineered drainage dyke and a man-made drainage channel. Data from nine to twelve SM, SEC and ST surveys completed at each site in 2015 using a 75-point grid are matched with riparian water table data, surface water level data from adjacent drainage channels and indicators of antecedent moisture conditions. Pattern characteristics, in the form of descriptive statistics and variogram parameters, are estimated for each state variable and then correlated to indicators of antecedent moisture conditions (AMCs), stream and subsurface water level data to infer soil water movement. Results show that potential evapotranspiration, depth to water table and antecedent precipitation have a significant yet variable impact on SM, SEC and ST patterns. A switching behaviour, between dry and wet conditions, is present in riparian areas characterized by grassland vegetation and well-drained soils. The occurrence of shallow subsurface flow is inferred during the wettest conditions. While riparian SM conditions are useful for predicting streamflow response in adjacent channels, such is not the case for riparian SEC and ST. Further investigations are however necessary to confirm the usefulness of SM spatial patterns for predicting streamflow response in other landscapes across the Canadian Prairies.

Beschreibung: Bioretention cells, which are generally effective in controlling surface runoff and recharging groundwater, have been widely adopted as low impact development practices. However, shallow groundwater has limited their implementation in some locations due to the potential problems of a reduction in surface runoff control, groundwater pollution, and continuous groundwater drainage through the underdrain. Many guidelines have established minimum requirements for the groundwater depth below bioretention cells, but they may not be optimized for certain environmental conditions and bioretention cell designs. This study made use of a variably saturated flow model to examine the hydrologic performance of a single bioretention cell in shallow groundwater with event-based simulations, considering a wide range of initial groundwater depths, media and in situ soil types, surface runoff loads, and underdrain sizes. Performance indicators (e.g., runoff reduction, time for infiltrated water to reach the bioretention cell bottom and the groundwater table, height and dissipation time of groundwater mound) were evaluated to examine the processes of runoff generation, the formation and dissipation of groundwater mounds, and the bioretention cell's performance in a shallow groundwater environment. The most influential factors were the initial groundwater depth, the hydraulic conductivity of the media soil, and the rainfall runoff load. With a deeper initial groundwater table, infiltrated water took longer to reach the bioretention cell bottom and groundwater table. Groundwater mounds, however, took longer to dissipate even though they were smaller. The groundwater quality can be better protected if relatively less-permeable soil types (e.g., sandy loam) are used as the media, although it may compromise the performance in runoff quantity control. However, only very high surface runoff loads would cause concerns regarding a reduction in runoff quantity control and possible groundwater contamination due to the shallow groundwater. A distance of 1.5-3 m between the bioretention cell bottom and the groundwater table is generally sufficient. The results of this study could help to guide the planning and design of bioretention cells in areas of shallow groundwater.

Beschreibung: Northern peatlands are a vital component of the global carbon cycle, containing large stores of soil organic carbon and acting as a long-term carbon sink. Moss productivity is an important factor in determining whether these wetlands will retain this function under future climatic conditions. Research on unsaturated water flow in peatlands, which controls moss productivity during periods of evaporative stress, has focused on relatively deep bog systems. However, shallower peatlands and marginal connective wetlands can be essential components of many landscape mosaics. In order to better understand factors influencing moss productivity, water balance simulations using Hydrus 1-D were run for different soil profile depths, compositions and antecedent moisture conditions. Our results demonstrate a bimodal distribution of peatland realizations; either primarily conserving water by limiting evapotranspiration or, maximizing moss productivity. For sustained periods of evaporative stress, both deep water storage and a shallow initial water table delay the onset of high vegetative stress, thus maximizing moss productivity. A total depth of sand and peat of 0.8 m is identified as the threshold above which increasing peat depth has no effect on changing vegetative stress response. In contrast, wetlands with shallow peat deposits (less than 0.5 m thick) are least able to buffer prolonged periods of evaporation due to limited labile water storage, and will thus quickly experience vegetative stress and so limit evaporation and conserve water. With a predicted increase in the frequency and size of rain events in continental North America the moss productivity of shallow wetland systems may increase, but also greater moisture availability will increase the likelihood they remain as wetlands in a changing climate.

Beschreibung: Shallow aquifers typically have greater hydrologic connectivity and response to recharge and changes in surface water management practices than deeper aquifers, and are therefore often managed to reduce the risk of flooding. Quantification of the water table elevation response under different management scenarios provides valuable information in shallow aquifer systems to assess indirect influences of such modifications. The Episodic Master Recession method was applied to the 15-min water table elevation and NEXRAD rainfall data for six wells to identify water table response and individual rainfall events. The objectives of this study were to evaluate the effects of rainfall, water table elevation, canal stage, site specific characteristics, and canal structure modification/ water management practice on the fluctuations in water table elevations using multiple/stepwise multiple linear regression techniques. With the modification of canal structure and operation adjustment, significant difference existed in water table response in the southern wells due to its relative downstream position regarding the general groundwater flow direction and the structural modification locations. On average, water table response height and flood risk were lower after than before the structure modification to canals. The effect of rainfall event size on the height of water table response was greater than the effect of antecedent water table elevation and canal stage on the height of water table response. Other factors including leakance of the canal bed sediment, specific yield, and rainfall on i-1 day had significant effects on the height of water table response as well. Antecedent water table elevation and canal stage had greater and more linear effects on the height of water table response after the management changes to canals. Variation in water table response height/rainfall event size ratio was attributed to difference in S y , antecedent soil water content, hydraulic gradient, rainfall size and runoff ratio. After the structure modification, water table response height/rainfall event size ratio demonstrated more linear and proportional relationship with antecedent water table elevation and canal stage.

Beschreibung: The proper management of coastal aquifers commonly requires an understanding of regional mass flow and complete seawater-freshwater circulation. In this study, time series observations of seawater intrusion and refreshing were conducted using a column experiment based on natural flow conditions in coastal groundwater and a sampled medium from a coastal sandy aquifer without chemical treatment. Ranges of hydrodynamical and hydrochemical variables were tested and analyzed. The results showed that the zeta potential of suspended colloids in aqueous solution in an aquifer polluted with 0.5 g/kg of heavy metals exhibited an isoelectric point for pH values ranging from 5.70 to 6.07 when freshwater or seawater completely occupied the aquifer pores, which is representative of natural hydrochemical conditions. In this scenario, a high background concentration of heavy metals induced colloidal immobilization. Otherwise, seawater-freshwater circulation enabled colloid mobilization due to ionic strength and pH fluctuations. The migration of multiple heavy metals occurred at a characteristic time of approximately 1 pore volume after each intrusion stage began and when the peak rate of colloid release was reached. At these times, the colloid behavior determined the quantity and pathway of heavy metal transport. Based on the influences of seawater and freshwater interactions, the quantity of mobilized particles generally decreased and was uniformly distributed in each fraction due to particle loss and decreased porous connectivity. We speculate that the decrease in the total surface area of the migratory colloids may cause colloid-associated heavy metal transport to decrease. The experimental results provide a useful basis for testing coastal groundwater flow and mass transport models because these phenomena require full characterization to precisely evaluate the associated fluxes from the field scale to the microscopic dimension.

Beschreibung: The Natural Resources Conservation Service Curve Number model (NRCS CN) is one of the most recognizable procedures in the field of rainfall-runoff estimation. It has been widely applied for different purposes in hydrological models. In spite of its widespread use, some uncertainties have not even clarified, and must be examined for its proper application. Particularly, choosing the most representative rainfall-runoff events, and the coefficient λ which relates the parameters of the model (curve number CN and initial abstraction I a ). In this research, an advanced analysis is developed to evaluate the influence of λ for a set of representative watersheds of the ARS-USDA (Agricultural Research Service of the United Stated Department of Agriculture). They are characterized by different soil properties, land uses and climatic conditions. Finally, two novel methodologies for the selection of the most representative rainfall-runoff events and for the adaptation of coefficient λ are included, based on the pattern of rainfall distribution.

Beschreibung: Modeling nutrient transport during snowmelt in cold regions remains a major scientific challenge. A key limitation of existing nutrient models for application in cold regions is the inadequate representation of snowmelt, including hydrological and biogeochemical processes. This brief period can account for more than 80% of the total annual surface runoff in the Canadian Prairies and Northern Canada and processes such as atmospheric deposition, over-winter redistribution of snow, ion exclusion from snow crystals, frozen soils, and snowcovered area depletion during melt influence the distribution and release of snow and soil nutrients, thus affecting the timing and magnitude of snowmelt runoff nutrient concentrations. Research in cold regions suggests that nitrate (NO3) runoff at the field scale can be divided into five phases during snowmelt. In the first phase, water and ions originating from ion-rich snow layers travel and diffuse through the snowpack. This process causes ion concentrations in runoff to gradually increase. The second phase occurs when this snow ion meltwater front has reached the bottom of the snowpack and forms runoff to the edge-of-the-field (EOF). During the third and fourth phases, the main source of NO3 transitions from the snowpack to the soil. Finally, the fifth and last phase occurs when the snow has completely melted, and the thawing soil becomes the main source of NO3 to the stream. In this research, a process-based model was developed to simulate hourly export based on this five-phase approach. Results from an application in the Red River Basin of southern Manitoba, Canada shows that the model can adequately capture the dynamics and rapid changes of NO3 concentrations during this period at relevant temporal resolutions. This is a significant achievement to advance the current nutrient modeling paradigm in cold climates, which is generally limited to satisfactory results at monthly or annual resolutions. The approach can inform catchment-scale nutrient models to improve simulation of this critical snowmelt period. Nutrient exports Winter Snow Nitrate Agriculture Nutrient model

Beschreibung: Upland agricultural land management activities such as grazing, vegetation burning and bare ground restoration impact hydrological elements of headwater catchments, many of which may be important for downstream flood peaks (e.g. overland flow and soil water storage). However, there is poor understanding of how these management practices affect river flow peaks during high magnitude rainfall events. Using the distributed TOPMODEL, spatial configurations of land management were modelled to predict flood response in an upland catchment which contains different regions operating subsidised agricultural stewardship schemes. Heavy grazing leading to soil compaction and loss of vegetation cover in stewardship regions covering 79.8% of the catchment gave a 42 min earlier flow peak which was 82.2% higher (under a 1-hr 15 mm storm) than the current simulated hydrograph. Light grazing over the same regions of the catchment had much less influence on river flow peaks (18 min earlier and 32.9% increase). Rotational burning (covering 8.8% of the catchment), most of which is located in the headwater areas, increased the peak by 3.2% in the same rainfall event. Vegetation restoration with either Eriophorum or Sphagnum (higher density) in bare areas (5.8%) of the catchment provided a reduction of flood peak (3.9% and 5.2% in the 15 mm storm event); while, the same total area revegetated with Sphagnum in riparian regions delivered a much larger decrease (15.0%) in river flow peaks. We show that changes of vegetation cover in highly-sensitive areas (e.g. near-stream zones) generate large impacts on flood peaks. Thus it is possible to design spatially distributed management systems for upland catchments which reduce flood peaks while at the same time ensuring economic viability for upland farmers.

Beschreibung: Fluvial organic carbon (OC) transformations are an important component of carbon cycling and greenhouse gas production in inland waters resulting in considerable recent interest in the fate of fluvial OC exported from carbon rich soils such as peatlands. Additionally, peatland catchments are important drinking water collection areas, where high OC concentrations in runoff have water treatment implications. This analysis presents the results from a year-round intensive study within a water treatment catchment draining an area of peatland, considering carbon transformations along a continuum from headwater river, through a storage reservoir and pipe, to a water treatment works. The study uses a unique combination of methods (colourmetric, ultrafiltration and 14 C radiocarbon dating) to assess catchment wide changes in fluvial carbon composition (colour, size and age) alongside concentration measures. The results indicate clear patterns of carbon transformations in the river and reservoir, and dissolved Low Molecular Weight (LMW) coloured carbon to be most subject to change, with both loss and replacement within the catchment residence time. Whilst the evidence suggests Dissolved OC (DOC) gains are from Particulate OC (POC) breakdown, the mechanisms of DOC loss are less certain and may represent greenhouse gas losses or conversions to POC. The transformations presented here appear to have minimal impact on the amount of harder to treat (〈10 kDa) dissolved carbon, although they do have implications for total DOC loading to water treatment works. This paper has shown that reservoirs in peatland systems are not passive receptors of particulate and dissolved organic carbon from headwater systems but that this fluvial carbon load is actively cycled in the reservoir system with implications for understanding peatland carbon cycling and water treatment in peatland catchments.

Beschreibung: Soil pipes, continuous macropores parallel to the soil surface, are an important factor in hillslope hydrological processes. However, the water flow dynamics in soil pipes, especially closed soil pipes, is not well understood. In this study, the water and air dynamics within closed soil pipes have been investigated in a bench-scale laboratory experiment by using a soil box with an artificial acrylic soil pipe. In order to grasp the state of water and air within the soil pipe, the existing soil pipe flow and air pressure in the soil pipe were directly measured. The laboratory experiment showed that air in the soil pipe had an important role in the water flow in the closed soil pipe. When air entrapment occurred in the soil pipe before the soil matrix around the soil pipe was saturated with water, water intrusion in the soil pipe was prevented by air entrapped in the pipe, which inhibited the soil pipe flow. This air entrapment in the soil pipe was controlled by the soil water and air flow. Moreover, after the soil pipe flow started, the soil pipe was not filled completely with water even when the soil pipe was completely submerged under the groundwater table. The entrapped air in the soil pipe prevented further water intrusion in the soil pipe.

Beschreibung: It is often assumed that the net groundwater flow direction is toward the channel in headwater streams in humid climates, with magnitudes dependent on flow state. However, studies that characterize stream-groundwater interactions in ephemeral and intermittent streams in humid landscapes remain sparse. Here, we examined seasonally-driven stream-groundwater interactions in response to temporary streamflow based on field observations of streamflow and groundwater on an adjacent hillslope. The direction of hydraulic head gradients between the stream and groundwater shifted seasonally. The stream gained water (head gradients were toward the stream) when storage state was high. During this period, streamflow was persistent. The stream lost water to the groundwater system (head gradients were away from the stream) when storage state was low. During this period, streamflow only occurred in response to precipitation events and head gradients remained predominantly away from the stream during events. This suggested mechanisms other than deep groundwater contributions produced runoff when storage was low, such as surface and perched subsurface flowpaths above the water table. Analysis of the annual water balance for the study period showed that the residual between precipitation inputs and streamflow and evapotranspiration outputs, which were attributed to the loss of water to the deeper, regional groundwater system, was similar in magnitude to streamflow. This, coupled with results that showed bi-directionality in stream-groundwater head gradients, indicated that headwaters comprised of temporary (e.g. ephemeral and intermittent) streams can be important focal areas for regional groundwater recharge and both contribute to and receive water, solutes, and materials from the groundwater system.

Beschreibung: To understand the moisture regime at the southern slopes of Mt. Kilimanjaro, we analyzed the isotopic variability of oxygen (δ 18 O) and hydrogen (δD) of rainfall, throughfall and fog from a total of 2,140 samples collected weekly over two years at nine study sites along an elevation transect ranging from 950 m a.s.l. to 3,880 m a.s.l.. Precipitation in the Kilimanjaro tropical rainforests consists of a combination of rainfall, throughfall and fog. We defined Local Meteoric Water Lines (LMWL) for all three precipitation types individually and the overall precipitation (δD prec = 7.45(± 0.05) x δ 18 O prec + 13.61(± 0.20) ( n = 2,140; R 2 = 0.91, p 〈 0.001). We investigated the precipitation type specific stable isotope composition and analyzed effects of amount, altitude and temperature. Aggregated annual mean values revealed isotope composition of rainfall as most depleted and fog water as most enriched in heavy isotopes at the highest elevation research site. We found an altitude effect of δ 18 O rain = -0.11 ‰ * 100 m -1 , which varied according to precipitation type and season. The relatively weak isotope/altitude gradient may reveal two different moisture sources in the research area: (i) local moisture recycling and (ii) regional moisture sources. Generally, the seasonality of δ 18 O rain values follows the bimodal rainfall distribution under the influences of south- and northeasterly trade winds. These seasonal patterns of isotopic composition were linked to different regional moisture sources by analyzing HYSPLIT backward trajectories. Seasonality of d excess values revealed evidence of enhanced moisture recycling after the onset of the rainy seasons. This comprehensive dataset is essential for further research using stable isotopes as a hydrological tracer of sources of precipitation that contribute to water resources of the Kilimanjaro region.

Beschreibung: In this paper, we addressed a sensitivity analysis of the snow module of the GEOtop2.0 model at point and catchment scale in a small high-elevation catchment in the Eastern Italian Alps (catchment size: 61 km 2 ). Simulated snow depth and snow water equivalent at the point scale were compared with measured data at four locations from 2009–2013. At the catchment scale, simulated snow covered area was compared with binary snow cover maps derived from MODIS and Landsat satellite imagery. Sensitivity analyses were used to assess the effect of different model parameterisations on model performance at both scales and the effect of different thresholds of simulated snow depth on the agreement with MODIS data. Our results at point scale indicated that modifying only the snow correction factor resulted in substantial improvements of the snow model and effectively compensated inaccurate winter precipitation by enhancing snow accumulation. SCA inaccuracies at catchment scale during accumulation and melt period were affected little by different snow depth thresholds when using calibrated winter precipitation from point scale. However, inaccuracies were strongly controlled by topographic characteristics and model parameterisations driving snow albedo ( snow aging coefficient and extinction of snow albedo ) during accumulation and melt period. While highest accuracies (OA = 1 in 86% of the catchment area) were observed during winter, lower accuracies (OA 〈 0.7) occurred during the early accumulation and melt period (in 29% and 23%, respectively), mostly present in areas with grassland and forest, slopes of 20°– 40°, areas exposed NW or areas with a roughness index of -0.25 to 0 m. These findings may give recommendations for defining more effective model parameterisation strategies and guide future work, in which simulated and MODIS SCA may be combined to generate improved products for SCA monitoring in Alpine catchments.

Beschreibung: The seasonally-dry climate of Northern California imposes significant water stress on ecosystems and water resources during the dry summer months. Frequently during summer, the only water inputs occur as non-rainfall water, in the form of fog and dew. However, due to spatially heterogeneous fog interaction within a watershed, estimating fog water fluxes to understand watershed-scale hydrologic effects remains challenging. In this study, we characterized the role of coastal fog, a dominant feature of Northern Californian coastal ecosystems, in a San Francisco Peninsula watershed. To monitor fog occurrence, intensity, and spatial extent, we focused on the mechanisms through which fog can affect the water balance: throughfall following canopy interception of fog, soil moisture, streamflow, and meteorological variables. A stratified sampling design was used to capture the watershed's spatial heterogeneities in relation to fog events. We developed a novel spatial averaging scheme to upscale local observations of throughfall inputs and evapotranspiration suppression and make watershed-scale estimates of fog water fluxes. Inputs from fog water throughfall (10–30 mm/year) and fog suppression of evapotranspiration (125 mm/year) reduced dry season water deficits by 25% at watershed scales. Evapotranspiration suppression was much more important for this reduction in water deficit than were direct inputs of fog water. The new upscaling scheme was analyzed to explore the sensitivity of its results to the methodology (data type and interpolation method) employed. This evaluation suggests that our combination of sensors and remote sensing allows an improved incorporation of spatially-averaged fog fluxes into the water balance than traditional interpolation approaches.

Beschreibung: ABSTRACT The occurrence of water ponding on soil surfaces during and after heavy rainfall produces surface runoff or surface water accumulation in low-lying areas, which might reduce the water supply to soils and result in a reduction of the soil water that plants can use, especially in arid climates. On Mongolian rangeland, we observed ponded water on the surface of a specific soil condition subjected to a heavy rainfall of 30 mm/h. By contrast, ponded water was not observed for the same type of soil where livestock grazing had been removed for 6 years via a fence or for nearby soil containing less clay. We measured the infiltration rate (the saturated hydraulic conductivity of the surface soil; K s ) of the three sites by applying ponded water on the soil surface (an intake rate test). The results showed that K s in the rangeland was lower than the rainfall intensity in the site where water ponded on the soil surface; however, K s of the soil inside of the fence has recovered to three times that of the soil outside of the fence to exceed the rainfall intensity. Heavy rainfall that exceeds the infiltration rate occurs several times a year at the livestock-grazing site where we observed ponded water. Slight water repellency of the soil reduces rain infiltration to increase the possibility of surface ponding for the soil.

Beschreibung: Although it has been increasingly acknowledged that groundwater flow pattern is complicated in the three-dimensional (3-D) domain, two-dimensional (2-D) water table-induced flow models are still widely used to delineate basin-scale groundwater circulation. However, the validity of 2-D cross-sectional flow field induced by water table has been seldom examined. Here, we derive the analytical solution of 3-D water table-induced hydraulic head in a Tóthian basin and then examine the validity of 2-D cross-sectional models by comparing the flow fields of selected cross sections calculated by the 2-D cross-sectional model with those by the 3-D model, which represents the “true” cases. For cross sections in the recharge or discharge area of the 3-D basin, even if head difference is not significant, the 2-D cross-sectional models result in flow patterns absolutely different from the true ones. For the cross section following the principal direction of groundwater flow, although 2-D cross-sectional models would overestimate the penetrating depth of local flow systems and underestimate the recharge/discharge flux, the flow pattern from the cross-sectional model is similar to the true one and could be close enough to the true one by adjusting the decay exponent and anisotropy ratio of permeability. Consequently, to determine whether a 2-D cross-sectional model is applicable, a comparison of hydraulic head difference between 2-D and 3-D solutions is not enough. Instead, the similarity of flow pattern should be considered to determine whether a cross-sectional model is applicable. This study improves understanding of groundwater flow induced by more natural water table undulations in the 3-D domain and the limitations of 2-D models accounting for cross-sectional water table undulation only.

Beschreibung: Some conceptual models suggest that baseflow in agriculturally-fragmented watersheds may contain little, if any, groundwater. This has critical implications for stream quality and ecosystem functioning. Here we: 1) identify the sources and flowpaths contributing to baseflow using 222 Rn and 87 Sr/ 86 Sr, and 2) quantify mean apparent ages of groundwater and baseflow using multiple isotopic tracers (CFC, SF 6 , 36 Cl, and 3 H) in four small (0.08 to 0.64 km 2 ) tributary catchments to the Wabash River in Indiana, USA. 222 Rn activities and 87 Sr/ 86 Sr ratios indicate that baseflow in three catchments is sourced primarily from groundwater; baseflow in the fourth is dominated by a source similar to agricultural runoff. CFC-12 data indicate that springs in one catchment are discharging significant proportions of water that recharged between 1974 (42 +/- 2 years) and 1961 (55 +/- 2 years). Those same springs have 36 Cl/Cl ratios between 1381.08 +/- 29.37 (x 10 -15 ) and 1530.64 +/- 27.65 (x 10 -15 ) indicating that a substantial proportion of the discharge likely recharged between 1975 (41 years) and 1950 (66 years). Groundwater collected from streambed mini-piezometers in a separate catchment have CFC-12 concentrations indicating that a large proportion of the recharge occurred between 1948 (68 +/- 2 years) to 1950 (66 +/- 2 years). Samples collected in September 2015 after above-average summer rainfall did not show significant decreases in mean apparent age. The relatively old ages observed in three of the catchments can be explained by geological complexities which are likely present in all four catchments, but overwhelmed by flow from the shallow phreatic aquifer in the fourth catchment.

Beschreibung: With high spatiotemporal resolution and wide coverage, satellite-based precipitation products can potentially fill the deficiencies of traditional in situ gauge precipitation observations and provide an alternative data source for ungauged areas. However, due to the relatively poor accuracy and high uncertainty of satellite-based precipitation products, it remains necessary to assess the quality and applicability of the products for each investigated area. This study evaluated the accuracy and error of the latest Tropical Rainfall Measuring Mission (TRMM) Multi-satellites Precipitation Analysis (TMPA) 3B42-V7 satellite-based precipitation product and validated the applicability of the product for the Beijiang and Dongjiang River Basin, downstream of the Pearl River Basin in China. The study first evaluated the accuracy, error, and bias of the 3B42-V7 product during 1998-2006 at daily and monthly scale via comparison with in situ observations. The study further validated the applicability of the product via hydrologic simulation using the Variable Infiltration Capacity (VIC) hydrological model for three hydrological stations in the Beijiang River Basin, considering two scenarios: a streamflow simulation with gauge-calibrated parameters (scenario I) and a simulation after recalibration with the 3B42-V7 product (scenario II). The results revealed that: 1) the 3B42-V7 product produced acceptable accuracy both at the daily scale and high accuracy at the monthly scale, while generally tending to overestimate precipitation; 2) the product clearly overestimated the frequency of no rainfall events at the gridcell-scale and light rainfall (〈 1 mm/day) events at the region-scale, and also overestimated the amount of heavy rain (25-50 mm/day) and hard rain (≥ 50 mm/day) events; 3) under scenario I, the 3B42-V7 product performed poorly at three stations with gauge-calibrated parameters; under scenario II, the recalibrated model provided significantly improved performance of streamflow simulation with the 3B42-V7 product; 4) the VIC model has the ability to reveal the hydrological characteristics of the karst landform in the Beijiang Basin when using the 3B42-V7 product.

Beschreibung: Over a four-month summer period, we monitored how forest ( Pinus sylvestris ) and heather moorland ( Calluna spp. and Erica spp.) vegetation canopies altered the volume and isotopic composition of net precipitation (NP) in a southern boreal landscape in northern Scotland. During that summer period, interception (I) losses were relatively high, and higher under forests compared to moorland (46% of gross rainfall (GR) compared with 35%, respectively). Throughfall (TF) volumes exhibited marked spatial variability in forests, depending upon local canopy density, but were more evenly distributed under heather moorland. In the forest stands, stemflow (StF) was a relatively small canopy flow path accounting for only 0.9-1.6% of NP and only substantial in larger events. Overall, the isotopic composition of NP was not markedly affected by canopy interactions; temporal variation of stable water isotopes in TF closely corresponded to that of GR with differences of TF-GR being -0.52 ‰ for δ 2 H and -0.14 ‰ for δ 18 O for forests and 0.29 ‰ for δ 2 H and -0.04 ‰ for δ 18 O for heather moorland. These differences were close to, or within, analytical precision of isotope determination, though the greater differences under forest were statistically significant. Evidence for evaporative fractionation was generally restricted to low rainfall volumes in low intensity events, though at times subtle effects of liquid-vapour moisture exchange and/or selective transmission though canopies were evident. Fractionation and other effects were more evident in StF but only marked in smaller events. The study confirmed earlier work that increased forest cover in the Scottish Highlands will likely cause an increase in interception and green water fluxes at the expenses of blue water fluxes to streams. However, the low energy, humid environment means that isotopic changes during such interactions will only have a minor overall effect on the isotopic composition of NP.

Beschreibung: The accurate measurement ofprecipitation is essential to understanding regional hydrological processes and hydrological cycling.Quantification of precipitation over remote regions such as the Tibetan plateau (TP) is highly unreliable because of thescarcity of rain gauges.The objective of this study is to evaluate the performance of the satellite precipitation product of Tropical Rainfall Measuring Mission (TRMM) 3B42 v7 at daily, weekly, monthly and seasonalscales. Comparison between TRMM grid precipitation and point-based rain gauge precipitation was conducted using nearest neighbor (NN) and bilinear weighted interpolation (BWI) methods. The results showed that the TRMM product could not capture daily precipitation well due to some rainfall events being missed at short time scalesbut provided reasonably good precipitation data at weekly, monthly and seasonal scales. TRMM tended to underestimate the precipitation of small rainfallevents (less than 1 mm/day), while it overestimated the precipitation of large rainfall events (greater than 20 mm/day). Consequently, TRMM showedbetter performance in the summer monsoon season than in the winter season.Through comparison, it was also found that the bilinear weighted interpolation method performs better than the nearest neighbor method in TRMM precipitation extraction.

Beschreibung: Reanalysis of a 10-year record (2004–2013) of seasonal mass balances at Langenferner/Vedretta Lunga, Ortler Alps, Italy Stephan Peter Galos, Christoph Klug, Fabien Maussion, Federico Covi, Lindsey Nicholson, Lorenzo Rieg, Wolfgang Gurgiser, Thomas Mölg, and Georg Kaser The Cryosphere, 11, 1417-1439, https://doi.org/10.5194/tc-11-1417-2017, 2017 Records of glacier mass balance represent important data in climate science and their uncertainties affect calculations of sea level rise and other societally relevant environmental projections. In order to reduce and quantify uncertainties in mass balance series obtained by direct glaciological measurements, we present a detailed reanalysis workflow which was applied to the 10-year record (2004 to 2013) of seasonal mass balance of Langenferner, a small glacier in the European Eastern Alps. The approach involves a methodological homogenization of available point values and the creation of pseudo-observations of point mass balance for years and locations without measurements by the application of a process-based model constrained by snow line observations. We examine the uncertainties related to the extrapolation of point data using a variety of methods and consequently present a more rigorous uncertainty assessment than is usually reported in the literature. Results reveal that the reanalyzed balance record considerably differs from the original one mainly for the first half of the observation period. For annual balances these misfits reach the order of  〉 300 kg m −2 and could primarily be attributed to a lack of measurements in the upper glacier part and to the use of outdated glacier outlines. For winter balances respective differences are smaller (up to 233 kg m −2 ) and they originate primarily from methodological inhomogeneities in the original series. Remaining random uncertainties in the reanalyzed series are mainly determined by the extrapolation of point data to the glacier scale and are on the order of ±79 kg m −2 for annual and ±52 kg m −2 for winter balances with values for single years/seasons reaching ±136 kg m −2 . A comparison of the glaciological results to those obtained by the geodetic method for the period 2005 to 2013 based on airborne laser-scanning data reveals that no significant bias of the reanalyzed record is detectable.

Beschreibung: Using water budget data from published literature, we demonstrate how hydrologic processes govern the function of various stormwater infrastructure technologies. Hydrologic observations are displayed on a Water Budget Triangle, a ternary plot tool developed to visualize simplified water budgets, enabling side-by-side comparison of green and grey approaches to stormwater management. The tool indicates ranges of hydrologic function for green roofs, constructed wetlands, cisterns, bioretention and other stormwater control management structures. Water budgets are plotted for several example systems to provide insight on structural and environmental design factors, and seasonal variation in hydrologic processes of stormwater management systems. Previously published water budgets and models are used to suggest appropriate operational standards for several green and grey stormwater control structures and compare between conventional and low-impact development approaches. We compare models, characterize and quantify water budgets and expected ranges for green and grey infrastructure systems, and demonstrate how the Water Budget Triangle tool may help users to develop a data-driven approach for understanding design and retrofit of green stormwater infrastructure.

Beschreibung: This study investigates 72 catchments across the federal state of Baden-Wuerttemberg, Germany, for changes in water quality during low-flow events. Data from the state's water quality monitoring network provided seven water quality parameters (water temperature, electrical conductivity, concentrations of chloride, sodium, sulfate, nitrate and phosphate), which were statistically related to streamflow variability. Water temperatures increased during low-flow in summer but decreased during low-flow in winter. Nitrate concentrations revealed high spatial heterogeneity with about one third of the stations showing decreasing values during low discharge. For most other parameters concentrations increased during low-flow. Despite consistent trend directions, the magnitudes of changes with streamflow differed markedly across the state. Both multiple linear regression and a multiple analysis of variances were applied to explain these differences with the help of catchment characteristics. Results indicated that for sulfate and conductivity, geology of the catchments was the most important control, whereas for chloride, sodium and nitrate sewage treatment plants had largest influence. For phosphate no clear control could be identified. Independent from the applied method, land use was a less important control on river water quality during low-flow than geology or inflow from sewage treatment plants. These results show that the effects of diffuse and point sources, as well as those of natural and anthropogenic sources differ for different water quality parameters. Overall, a high diversity of potential water quality deterioration signals needs to be considered when the ecological status of rivers is to be protected during low-flow events.

Beschreibung: The deeply buried river-connected Xishan Karst Aquifer (XKA)in western Beijing, China, hasbeen suffering from diminishing recharge for several decades, which in turn leads to the disappearing of spring water outflows and continuously lowering of groundwater level in the area. Thus, it is important to correctly recognize the groundwater recharge and flow paths for the sustainable development of the XKA. To investigate these issues, thehydrochemical and isotopic compositions are analysed for both surface water and groundwater samples collected over an area of about 280 km 2 . Results show that, (1)the river wateris characterized by high Na contents; (2) theδ 2 H and δ 18 O values in the river water are distinctively higher than those of groundwater samples, afterexperiencingthe long-time evaporative enrichment in the upstream reservoir; (3)theSr concentrations and 87 Sr/ 86 Sr ratios of groundwater clearly indicated the interaction between water and carbonate minerals, but excluded the water–silicate interaction; and (4) the groundwater samples in the direct recharge area of the XKA has the lowest Na concentrations as well as the δ 2 H and δ 18 O values. Based on the large differences in the Na contents and 18 O values of groundwater and surface water, a simple two-component mixing model is developed for the study area andthe fractions of the river water are estimated for groundwater samples. We find that the distribution pattern of the river water fractions in the XKA clearly shows a change of directions in the preferential flow path of the groundwaterfrom its source zone to the discharge area.Overall, our results suggest that the recharged surface water can be a useful evidence for delineation the groundwater flow path in river-connected karst aquifer.This studyimprovesour understanding of the heterogeneity in karst groundwater systems.

Beschreibung: Testing hydrological models over different spatio-temporal scales is important both for evaluating diagnostics and aiding process understanding. High-frequency (6hr) stable isotope sampling of rainfall and runoff was undertaken during 3 week periods in summer and winter within 12 months of daily sampling in a 3.2 km 2 catchment in the Scottish Highlands. This was used to calibrate and test a tracer-aided model to assess the: (1) information content of high resolution data; (2) effect of different calibration strategies on simulations and inferred processes; (3) model transferability to 〈1 km 2 sub-catchment. The 6-hourly data were successfully incorporated without loss of model performance, improving the temporal resolution of the modelling, and making it more relevant to the time dynamics of the isotope and hydrometric response. However, this added little new information due to old-water dominance and riparian mixing in this peatland catchment. Time variant results, from differential split sample testing, highlighted the importance of calibrating to a wide range of hydrological conditions. This also provided insights into the non-stationarity of catchment mixing processes, in relation to storage and water ages, which varied markedly depending on the calibration period. Application to the nested sub-catchment produced equivalent parameterisation and performance, highlighting similarity in dominant processes. The study highlighted the utility of high-resolution data in combination with tracer-aided models, applied at multiple spatial scales, as learning tools to enhance process understanding and evaluation of model behaviour across non-stationary conditions. This helps reveal more fully the catchment response in terms of the different mechanistic controls on both wave celerites and particle velocities.

Beschreibung: Rain-on-snow events have generated major floods around the world, particularly in coastal, mountainous regions. Most previous studies focused on a limited number of major rain-on-snow events or were based primarily on model results, largely due to a lack of long-term records from lysimeters or other instrumentation for quantifying event water balances. In this analysis we used records from five Automated Snow Pillow (ASP) sites in south coastal British Columbia, Canada, to reconstruct event water balances for 286 rain-on-snow events over a 10-year period. For large rain-on-snow events (event rainfall 〉 40 mm), snowmelt enhanced the production of water available for runoff (WAR) by approximately 25% over rainfall alone. For smaller events, a range of antecedent and meteorological factors influenced WAR generation, particularly the antecedent liquid water content of the snowpack. Most large events were associated with atmospheric rivers. Rainfall dominated WAR generation during autumn and winter events, while snowmelt dominated during spring and summer events. In the majority of events, the sensible heat of rain contributed less than 10% of the total energy consumed by snowmelt. This analysis illustrated the importance of understanding the amount of rainfall occurring at high elevations during rain-on-snow events in mountainous regions.

Beschreibung: Arctic deltas, such as the Mackenzie Delta, are expected to face major climate change and increased human influence in the near future. Deltas are characterised by highly dynamic fluvial processes and changing climate will cause considerable evolution of the riverine environment. The changes are difficult to predict with existing knowledge and data. This study quantified channel planform change of the Mackenzie Delta (1983-2013), analysing its temporal and spatial patterns. We addressed the main obstacle of research on large remote areas, the lack of data, by developing a unique work flow that utilised Landsat satellite imagery, hydrological time series, remote sensing-based change analysis and automatic vectorisation of channels. Our results indicate that the Mackenzie Delta experienced constant evolution but at a highly varying rate over the 30 years. The study demonstrates that the magnitude and duration of flood peaks and the presence of spring ice breakup floods determine the rate of Arctic delta planform change. Changing winter conditions and spring flood magnitudes may therefore affect the stability of Arctic deltas. However, no clear trends towards decreased recurrence or magnitude of spring floods or increased instability of the delta plain have yet been observed in the Mackenzie Delta. The delta plain was most dynamic at the beginning and at the end of the examined period, corresponding to intense flooding, while the rates of change were subtle during the low-flood period 1994-2007. Largest changes have occurred along the wide Middle Channel and in the outermost delta. Relative to their size however, smaller meandering channels have been highly dynamic. Hotspots of change in the delta plain are located in anastomosing and braiding channel segments and, at the local scale, in point bars and cut-banks along meandering channels. Our study describes how Landsat satellite data can be utilised for advancing fluvial geomorphological research in remote areas. However, cloudiness in the delta restricts production of dense time series with simultaneous coverage of the whole area and requires manual pre-processing.

Beschreibung: Deleterious effects of urban stormwater are widely recognized. In several countries, regulations have been put into place to improve the conditions of receiving water bodies, but planning and engineering of stormwater control is typically carried out at smaller scales. Quantifying cumulative effectiveness of many stormwater control measures on a watershed-scale is critical to understanding how small-scale practices translate to urban river health. We review 100 empirical and modeling studies of stormwater management effectiveness at the watershed-scale in diverse physiographic settings. Effects of networks with stormwater control measures (SCMs) that promote infiltration and harvest have been more intensively studied than have detention-based SCM networks. Studies of peak flows and flow volumes are common, whereas baseflow, groundwater recharge and evapotranspiration have received comparatively little attention. Export of nutrients and suspended sediments have been the primary water quality focus in the United States, while metals, particularly those associated with sediments, have received greater attention in Europe and Australia. Often, quantifying cumulative effects of stormwater management is complicated by needing to separate its signal from the signal of urbanization itself, innate watershed characteristics that lead to a range of hydrologic and water quality responses, and the varying functions of multiple types of SCMs. Biases in geographic distribution of study areas, and size and impervious surface cover of watersheds studied also limit our understanding of responses. We propose hysteretic trajectories for how watershed function responds to increasing imperviousness and stormwater management. Even where impervious area is treated with SCMs, watershed function may not be restored to its pre-development condition because of: the lack of treatment of all stormwater generated from treated impervious surfaces; non-additive effects of individual SCMs; and persistence of urban effects beyond impervious surfaces. In most cases, pollutant load decreases largely result from runoff reductions rather than lowered solute or particulate concentrations. Understanding interactions between natural and built landscapes, including stormwater management strategies, is critical for successfully managing detrimental impacts of stormwater at the watershed scale.

Beschreibung: Multi-scene Landsat 5 TM imagery, Principal Component Analysis (PCA), and the Normalised Difference Vegetation Index (NDVI) were used to produce the first region-scale map of riparian vegetation for the Pilbara (230,000 km2), Western Australia. Riparian vegetation is an environmentally important habitat in the arid and desert climate of the Pilbara. These habitats are supported by infrequent flow events and in some locations by groundwater discharge. Our analysis suggests that riparian vegetation covers less than 4% of the Pilbara region, while almost 10.5% of this area is comprised of Groundwater Dependent Vegetation (GDV). GDV is often associated with open water (river pools), providing refugia for a variety of species. GDV has an extremely high ecological value and are often important Indigenous sites. This paper demonstrates how Landsat data calibrated to Top of Atmosphere (TOA) reflectance can be used to delineate riparian vegetation across 16 Landsat Scenes and two UTM (Universal Transverse Mercator) spatial zones. The proposed method is able to delineate riparian vegetation and GDV, without the need for Bidirectional Reflectance Distribution Function (BRDF) correction. Results were validated using ground-truth data from local and regional scale vegetation surveys.

Beschreibung: A hydraulic invariance (HI)-based methodology was developed as a tool to support implementation of storm flow control measures into land use master-plans (LUMPs) for urban catchments. The methodology is based on the use of simple hydrologic analysis to compare pre- and post-development catchment flow release scenarios. Differently from previous literature examples, for which the parcel scale is usually considered for the analysis, HI was pursued assuming the LUMP areas of transformation as the basic units for assigning storm water control measures in the form of flow release restrictions. The methodology was applied to a case study catchment in the southern part of the City of Catania (Italy), for which the LUMP re-design has been recently proposed. Simulations were run based on the use of the EPA-SWMM model and allowed deriving flow release restrictions in order to achieve HI at the sub-catchment level for design events of different return period.

Beschreibung: Climatic changes have altered surface water regimes worldwide, and climate projections suggest that such alterations will continue. To inform management decisions, climate projections must be paired with hydrologic models to develop quantitative estimates of watershed scale water regime changes. Such modeling approaches often involve downscaling climate model outputs, which are generally presented at coarse spatial scales. In this study, Coupled Model Intercomparison Project Phase 5 (CMIP5) climate model projections were analyzed to determine models representing severe and conservative climate scenarios for the study watershed. Based on temperature and precipitation projections, output from GFDL-ESM2G (RCP2.6) and MIROC-ESM (RCP8.5) were selected to represent conservative (Δ C ) and severe (Δ S ) change scenarios, respectively. Climate data were used as forcing for the Soil and Water Assessment Tool (SWAT) to analyze the potential effects of climate change on hydrologic processes in a mixed-use watershed in central Missouri, USA. Results showed annual streamflow decreases ranging from -5.9% to -26.8% and evapotranspiration (ET) increases ranging from +7.2% to +19.4%. During the mid-21 st century, sizeable decreases to summer streamflow were observed under both scenarios, along with large increases of fall, spring, and summer ET under Δ S . During the late 21 st century period, large decreases of summer streamflow under both scenarios, and large increases to spring (Δ S ), fall (Δ S ) and summer (Δ C ) ET were observed. This study demonstrated the sensitivity of a Midwestern watershed to future climatic changes utilizing projections from CMIP5 models, and presented an approach that used multiple climate model outputs to characterize potential watershed scale climate impacts.

Beschreibung: Models for polythermal ice sheets and glaciers Ian J. Hewitt and Christian Schoof The Cryosphere, 11, 541-551, doi:10.5194/tc-11-541-2017, 2017 Many glaciers contain ice both below and at the melting temperature. Predicting the evolution of temperature and water content in such ice masses is important because they exert a strong control on the flow of the ice. We present two new models to calculate these quantities, demonstrate a number of example numerical calculations, and compare the results with existing methods. The novelty of the new methods is the inclusion of gravity-driven water transport within the ice.

Beschreibung: Experimental observation of transient δ 18 O interaction between snow and advective airflow under various temperature gradient conditions Pirmin P. Ebner, Hans Christian Steen-Larsen, Barbara Stenni, Martin Schneebeli, and Aldo Steinfeld The Cryosphere Discuss., doi:10.5194/tc-2017-16,2017 Manuscript under review for TC (discussion: open, 0 comments) Stable water isotopes (δ 18 O) obtained from snow and ice samples from polar regions are used to reconstruct past climate variability. We present an experimental study on the effect on the snow isotopic composition by airflow through a snowpack in controlled laboratory conditions. The disequilibrium between snow and vapor isotopes changed the isotopic content of the snow. These measurements suggest that the history of metamorphism affects the snow isotopic composition.

Beschreibung: Distinguishing between old and modern permafrost sources 1 with compound-specific δ 2 H analysis Jorien E. Vonk, Tommaso Tesi, Lisa Bröder, Henry Holmstrand, Gustaf Hugelius, August Andersson, Oleg Dudarev, Igor Semiletov, and Örjan Gustafsson The Cryosphere Discuss., doi:10.5194/tc-2017-17,2017 Manuscript under review for TC (discussion: open, 0 comments) Pleistocene ice complex permafrost deposits contain roughly a quarter of the organic carbon (OC) stored in permafrost terrain. When permafrost thaws, its OC is remobilized into the (aquatic) environment where it is available for degradation, transport or burial. Aquatic or coastal environments contain sedimentary reservoirs that can serve as archives of past climatic change. As permafrost thaw is increasing throughout the Arctic, these reservoirs are important locations to assess the fate of remobilized permafrost OC. We here present compound-specific deuterium (δ 2 H) analysis on leaf waxes as a tool to distinguish between OC released from thawing Pleistocene permafrost (Ice Complex Deposits; ICD) and from thawing Holocene permafrost (from near-surface soils). Bulk geochemistry (%OC, δ 13 C, %total nitrogen; TN) was analyzed as well as the concentrations and δ 2 H signatures of long-chain n -alkanes (C 21 to C 33 ) and mid/long-chain n -alkanoic acids (C 16 to C 30 ) extracted from both ICD-PF samples ( n  = 9) and modern vegetation/O-horizon (Topsoil-PF) samples ( n  = 9) from across the northeast Siberian Arctic. Results show that these Topsoil-PF samples have higher %OC, higher OC/TN values, and more depleted δ 13 C-OC values than ICD-PF samples, suggesting that these former samples trace a fresher soil and/or vegetation source. Median concentrations of high-molecular weight n -alkanes (sum of C 25 -C 27 -C 29 -C 31 ) were 210 ± 350 µg/gOC (median ± IQR) for Topsoil-PF and 250 ± 81 µg/gOC for ICD-PF samples. Long-chain n -alkanoic acids (sum of C 22 -C 24 -C 26 -C 28 ) were more abundant than long-chain n -alkanes, both in Topsoil-PF samples (4700 ± 3400 µg/gOC) and in ICD samples (6630 ± 3500 µg/gOC). Whereas the two investigated sources differ on the bulk geochemical level, they are, however, virtually indistinguishable when using leaf wax concentrations and ratios. However, on the molecular-isotope level, leaf wax biomarker δ 2 H values are statistically different between Topsoil-PF and ICD-PF. The mean δ 2 H value of C 29 n -alkane was −246 ± 13 ‰ (mean ± stdev) for Topsoil-PF and −280 ± 12 ‰ for ICD-PF, whereas the C31 n -alkane was −247 ± 23 ‰ for Topsoil-PF and −297 ± 15 ‰ for ICD-PF. The C 28 n -alkanoic acid δ 2 H value was −220 ± 15 ‰ for Topsoil-PF and −267 ± 16 ‰ for ICD-PF. With a dynamic isotopic range (difference between two sources) of 34 to 50 ‰, the isotopic fingerprints of individual, abundant, biomarker molecules from leaf waxes can thus serve as end-members to distinguish between these two sources. We tested this molecular δ 2 H tracer along with another source-distinguishing approach, dual-carbon (δ 13 C-δ 14 C) isotope composition of bulk OC, for a surface sediment transect in the Laptev Sea. Results show that general offshore patterns along the shelf-slope transect are similar, but the source apportionment between the approaches vary, which may highlight the advantages of either. The δ 2 H molecular approach has the advantage that it circumvents uncertainties related to a marine end-member, yet the δ 13 C-δ 14 C approach has the advantage that it represents the bulk OC fraction thereby avoiding issues related to the molecular-bulk upscaling challenge. This study indicates that the application of δ 2 H leaf wax values has potential to serve as a complementary quantitative measure of the source and differential fate of OC thawed out from different permafrost compartments.

Beschreibung: Recent advances in sediment fingerprinting research have seen Bayesian mixing models being increasingly employed as an effective method to coherently translate component uncertainties into source apportionment results. Here, we advance earlier work by presenting an extended Bayesian mixing model capable of providing a full Bayes treatment of geochemical uncertainties. The performance of the extended full Bayes model was assessed against the equivalent empirical Bayes model and traditional frequentist optimisation. The performance of models coded in different Bayesian software (‘JAGS’ and ‘Stan’) was also evaluated, alongside an assessment of model sensitivity to reduced source representativeness and non-conservative fingerprint behaviour. Results revealed comparable accuracy and precision for the full and empirical Bayes models across both synthetic and real sediment geochemistry datasets, demonstrating that the empirical treatment of source data here represents a close approximation of the full Bayes treatment. Contrasts in the performance of models coded in JAGS and Stan revealed that the choice of software employed can impact significantly upon source apportionment results. Bayesian models coded in Stan were the least sensitive to both reduced source representativeness and non-conservative fingerprint behaviour, indicating Stan as the preferred software for future Bayesian sediment fingerprinting studies. Whilst the frequentist optimisation generally yielded comparable accuracy to the Bayesian models, uncertainties around apportionment estimates were substantially greater and the frequentist model was less effective at dealing with non-conservative behaviour. Overall, the effective performance of the extended full Bayes mixing model coded in Stan represents a notable advancement in source apportionment modelling relative to previous approaches. Both the mixing model and the software comparisons presented here should provide useful guidelines for future sediment fingerprinting studies.

Beschreibung: Snowfall in the Alps: Evaluation and projections based on the EURO-CORDEX regional climate models Prisco Frei, Sven Kotlarski, Mark A. Liniger, and Christoph Schär The Cryosphere Discuss., doi:10.5194/tc-2017-7,2017 Manuscript under review for TC (discussion: open, 0 comments) Snowfall is central to Alpine environments, and its future changes will be associated with pronounced impacts. We here assess future snowfall changes in the European Alps based on an ensemble of state-of-the-art regional climate model experiments and on two different greenhouse gas emission scenarios. The results reveal pronounced changes in the Alpine snowfall climate with considerable snowfall reductions at low and mid elevations, but also snowfall increases at high elevations in mid-winter.

Beschreibung: Rainfall interception loss plays an important role in eco-hydrological processes in dryland shrub ecosystems, but its drivers still remain poorly understood. In this study, a statistical model was developed to simulate interception loss based on the mass balance measurements arising from the partitioning of rainfall in two dominant xerophytic shrub ( Hippophae rhamnoides and Spiraea pubescens ) communities in the Loess Plateau. We measured throughfall and stemflow in the field under natural rainfall, calculated the canopy storage capacity in the laboratory, and identified key factors controlling these components for the two shrubs. We quantified and scaled-up the stemflow and the canopy storage capacity measurements from the branches and/or leaves to stand level. The average interception loss, throughfall, and stemflow fluxes account for 24.9%, 72.2%, and 2.9% of the gross rainfall for H. rhamnoides , and 19.2%, 70.7%, and 10.1% for S. pubescens , respectively. Throughfall increased with increasing rainfall for both shrubs, however, it was only correlated with the leaf area index (LAI) for S. pubescens . For stemflow measured from individual branches, we found that the rainfall amount and basal diameter are the best predictors for H. rhamnoides , while rainfall amount and branch biomass appear to be the best predictors for S. pubescens . At the stand level, stemflow production is affected by the rainfall amount for H. rhamnoides , and it is affected by both the rainfall amount and the LAI for S. pubescens . The canopy storage capacity of H. rhamnoides (1.07–1.28 mm) was larger than S. pubescens (0.88–1.07 mm), and it is mainly determined by the branches and stems of H. rhamnoides , and the leaves of S. pubescens . The differences in interception loss between the two shrub stands are mainly attributed to different canopy structures induced differences in stemflow production and canopy storage. We evaluated the effects of canopy structure on rainfall interception loss, and our developed model provides a better understanding of the effects of the canopy structure on the water cycles in dryland shrub ecosystems.

Beschreibung: Wave-ice interactions in the neXtSIM sea-ice model Timothy D. Williams, Pierre Rampal, and Sylvain Bouillon The Cryosphere Discuss., doi:10.5194/tc-2017-24,2017 Manuscript under review for TC (discussion: open, 0 comments) As the Arctic sea ice extent drops, there is more ship traffic seeking to take advantage of this, and with it a need for better wave and sea ice forecasts. One aspect of this is the location of the sea ice edge. The waves here can be quite large, but they die away as they travel into the ice. This causes momentum to be transferred from the waves to the ice, causing ice drift. However, our study found that the effect of the wind drag had more impact on the ice edge position than the waves.

Beschreibung: Evaluating the flow paths that contribute to solute flux in stream networks can lead to greater understanding of the linkages between biogeochemistry and hydrology. We compared the contributions of groundwater in spring brooks and in seepage through the stream bed to nitrate flux in the Emmons Creek network in the Wisconsin sand plains. We predicted that spring brooks would contribute disproportionately to nitrate flux due to the presumed higher advection rates in springs and less opportunity for nitrate removal relative to seeps. Nitrate flux was measured in 15 spring brooks that entered Emmons Creek. Nitrate flux from seepage was measured at the locations of 30 piezometers, based on Darcy's Law, and by a reach-scale injection of Rhodamine WT (RWT). When seepage discharge was estimated from the RWT release groundwater inputs from seepage and springs accounted for the discharge gain in the Emmons Creek channel. Springs brooks and seepage (based on the RWT release) contributed 37% and 63%, respectively, to nitrate flux inputs in the study reach. Contrary to our prediction, seeps contributed disproportionately to nitrate flux relative to their discharge. Relatively high rates of seepage discharge and higher than anticipated nitrate concentrations in the shallow pore water at seepage locations contributed to the unanticipated result.

Beschreibung: Cryostratigraphy, sedimentology, and the late Quaternary evolution of the Zackenberg River delta, northeast Greenland Graham L. Gilbert, Stefanie Cable, Christine Thiel, Hanne H. Christiansen, and Bo Elberling The Cryosphere, 11, 1265-1282, doi:10.5194/tc-11-1265-2017, 2017 We reconstruct the Holocene development of the Zackenberg River delta (northeast Greenland) using a combination of sedimentology, cryostratigraphy, and geochronology. We distinguish four major depositional environments and identify three cryofacies. We apply the principles of cryostratigraphy to infer the aggradational history of permafrost. This paper contains an archive of ground ice in epigenetic permafrost in northeast Greenland.

Beschreibung: Recent dynamic changes on Fleming Glacier after the disintegration of Wordie Ice Shelf, Antarctic Peninsula Peter Friedl, Thorsten C. Seehaus, Anja Wendt, Matthias H. Braun, and Kathrin Höppner The Cryosphere Discuss., doi:10.5194/tc-2017-91,2017 Manuscript under review for TC (discussion: open, 0 comments) Fleming Glacier is the biggest tributary glacier of the former Wordie Ice Shelf (south-western Antarctic Peninsula). Radar satellite data and airborne ice elevation measurements show that the glacier accelerated by ~ 30 % from 2007–2011 and that tinning of the glacier increased by ~ 60–70 %. This was a response to an ungrounding of the glacier tongue from the glacier bed between 2008 and 2011, which was likely crucially triggered by increased basal melt at the grounding line due to ocean warming.

Beschreibung: Evaluation of different methods to model near-surface turbulent fluxes for an alpine glacier in the Cariboo Mountains, BC, Canada Valentina Radić, Brian Menounos, Joseph Shea, Noel Fitzpatrick, Mekdes A. Tessema, and Stephen J. Déry The Cryosphere Discuss., doi:10.5194/tc-2017-80,2017 Manuscript under review for TC (discussion: open, 0 comments) Our overall goal is to improve the numerical modelling of glacier melt in order to better predict the future of glaciers in Western Canada and worldwide. Most commonly used models rely on simplifications of processes that dictate melting at a glacier surface, in particular turbulent processes of heat exchange. We compared modelled against directly measured turbulent heat fluxes at a valley glacier in British Columbia, Canada, and found that more improvements are needed in all the tested models.

Beschreibung: Although fractional integration and differentiation have found many applications in various fields of science, such as physics, finance, bioengineering, continuum mechanics and hydrology, their engineering applications, especially in the field of fluid flow processes, are rather limited. In this study, a finite difference numerical approach is proposed to solve the time-space fractional governing equations of one-dimensional unsteady/non-uniform open channel flow process. By numerical simulations, results of the proposed fractional governing equations of the open channel flow process were compared with those of the standard Saint-Venant equations. Numerical simulations showed that flow discharge and water depth can exhibit heavier tails in downstream locations as space and time fractional derivative powers decrease from 1. The fractional governing equations under consideration are generalizations of the well-known Saint-Venant equations, which are written in the integer differentiation framework. The new governing equations in the fractional order differentiation framework have the capability of modeling nonlocal flow processes both in time and in space by taking the global correlations into consideration. Furthermore, the generalized flow process may possibly shed light on understanding the theory of the anomalous transport processes and observed heavy-tailed distributions of particle displacements in transport processes.

Beschreibung: Calibrated cryo-cell UV-LA-ICPMS elemental concentrations from the NGRIP ice core reveal abrupt, sub-annual variability in dust across the GI-21.2 interstadial period Damiano Della Lunga, Wolfgang Müller, Sune Olander Rasmussen, Anders Svensson, and Paul Vallelonga The Cryosphere, 11, 1297-1309, https://doi.org/10.5194/tc-11-1297-2017, 2017 In our study we combined the wealth of information provided by Greenland ice cores with an ultra-high-resolution technique well known in geoscience (laser ablation). Our set-up was developed and applied to investigate the variability in concentration of ions across a rapid climatic change from the oldest part of the last glaciation, showing that concentrations drop abruptly from cold to warm periods, representing a shift in atmospheric transport that happens even faster than previously thought.

Beschreibung: Evaluation of different methods to model near-surface turbulent fluxes for an alpine glacier in the Cariboo Mountains, BC, Canada Valentina Radić, Brian Menounos, Joseph Shea, Noel Fitzpatrick, Mekdes A. Tessema, and Stephen J. Déry The Cryosphere Discuss., https//doi.org/10.5194/tc-2017-80,2017 Manuscript under review for TC (discussion: open, 0 comments) Our overall goal is to improve the numerical modelling of glacier melt in order to better predict the future of glaciers in Western Canada and worldwide. Most commonly used models rely on simplifications of processes that dictate melting at a glacier surface, in particular turbulent processes of heat exchange. We compared modelled against directly measured turbulent heat fluxes at a valley glacier in British Columbia, Canada, and found that more improvements are needed in all the tested models.

Beschreibung: Recent dynamic changes on Fleming Glacier after the disintegration of Wordie Ice Shelf, Antarctic Peninsula Peter Friedl, Thorsten C. Seehaus, Anja Wendt, Matthias H. Braun, and Kathrin Höppner The Cryosphere Discuss., https//doi.org/10.5194/tc-2017-91,2017 Manuscript under review for TC (discussion: open, 0 comments) Fleming Glacier is the biggest tributary glacier of the former Wordie Ice Shelf (south-western Antarctic Peninsula). Radar satellite data and airborne ice elevation measurements show that the glacier accelerated by ~ 30 % from 2007–2011 and that tinning of the glacier increased by ~ 60–70 %. This was a response to an ungrounding of the glacier tongue from the glacier bed between 2008 and 2011, which was likely crucially triggered by increased basal melt at the grounding line due to ocean warming.

Beschreibung: Cryostratigraphy, sedimentology, and the late Quaternary evolution of the Zackenberg River delta, northeast Greenland Graham L. Gilbert, Stefanie Cable, Christine Thiel, Hanne H. Christiansen, and Bo Elberling The Cryosphere, 11, 1265-1282, https://doi.org/10.5194/tc-11-1265-2017, 2017 We reconstruct the Holocene development of the Zackenberg River delta (northeast Greenland) using a combination of sedimentology, cryostratigraphy, and geochronology. We distinguish four major depositional environments and identify three cryofacies. We apply the principles of cryostratigraphy to infer the aggradational history of permafrost. This paper contains an archive of ground ice in epigenetic permafrost in northeast Greenland.

Beschreibung: Iceberg calving of Thwaites Glacier, West Antarctica: full-Stokes modeling combined with linear elastic fracture mechanics Hongju Yu, Eric Rignot, Mathieu Morlighem, and Helene Seroussi The Cryosphere, 11, 1283-1296, https://doi.org/10.5194/tc-11-1283-2017, 2017 We combine 2-D ice flow model with linear elastic fracture mechanics (LEFM) to model the calving behavior of Thwaites Glacier, West Antarctica. We find the combination of full-Stokes (FS) model and LEFM produces crevasses that are consistent with observations. We also find that calving is enhanced with pre-existing surface crevasses, shorter ice shelves or undercut at the ice shelf front. We conclude that the FS/LEFM combination is capable of constraining crevasse formation and iceberg calving.

Beschreibung: Characterizing permafrost soil active layer dynamics and sensitivity to landscape spatial heterogeneity in Alaska Yonghong Yi, John S. Kimball, Richard Chen, Mahta Moghaddam, Rolf H. Reichle, Umakant Mishra, Donatella Zona, and Walter C. Oechel The Cryosphere Discuss., https//doi.org/10.5194/tc-2017-87,2017 Manuscript under review for TC (discussion: open, 0 comments) An important feature of the Arctic is large spatial heterogeneity in active layer conditions, which is generally poorly represented by global models. In this study, we developed a spatially integrated modelling and analysis framework combining field observations, local scale (~ 50 m) active layer thickness (ALT) and soil moisture maps derived from airborne low frequency (L + P-band) radar measurements, and global satellite environmental observations to investigate the ALT sensitivity to recent climate trends and landscape heterogeneity in Alaska. Model simulated ALT results show good correspondence with in-situ measurements in higher permafrost probability (PP ≥ 70 %) areas (n = 33, R = 0.60, mean bias = 1.58 cm, RMSE = 20.32 cm). The model results also reveal widespread ALT deepening since 2001, with smaller ALT increases in northern Alaska (mean trend = 0.32 ± 1.18 cm yr -1 ) and much larger increases (〉 3 cm yr -1 ) across interior and southern Alaska. The positive ALT trend coincides with regional warming and a longer snow-free season (R = 0.60 ± 0.32). Uncertainty in the spatial and vertical distribution of soil organic carbon (SOC) was found to be the most important factor affecting model ALT accuracy. Potential improvements in characterizing SOC heterogeneity, including better spatial sampling of soil conditions and advances in remote sensing of SOC and soil moisture, will enable more accurate predictions of permafrost active layer conditions.

Beschreibung: Centuries of intense surface melt on Larsen C Ice Shelf Suzanne Bevan, Adrian Luckman, Bryn Hubbard, Bernd Kulessa, David Ashmore, Peter Kuipers Munneke, Martin O'Leary, Adam Booth, Heidi Sevestre, and Daniel McGrath The Cryosphere Discuss., https//doi.org/10.5194/tc-2017-81,2017 Manuscript under review for TC (discussion: open, 0 comments) Five 90 m boreholes drilled into an Antarctic Peninsula ice shelf show units of ice that are denser than expected and must have formed from refrozen surface melt which has been buried and transported downstream. We used surface flow speeds and snow accumulation rates to work out where and when these units formed. Results show that as well as recent surface melt, a period of strong melt occurred during the 18th century. Surface melt is thought to be a factor in causing recent ice shelf break up.

Beschreibung: Modelling debris transport within glaciers by advection in a full-Stokes ice flow model Anna Wirbel, Alexander Helmut Jarosch, and Lindsey Nicholson The Cryosphere Discuss., https//doi.org/10.5194/tc-2017-92,2017 Manuscript under review for TC (discussion: open, 0 comments) As debris cover affects the melt water production and behaviour of glaciers it is important to understand how, and over what timescales, it forms. Here we develop an advanced 3D numerical model that describes transport of sediment through a glacier to the point where it emerges at the surface. The numerical performance of the model is satisfactory and it reproduces debris structures observed within real-world glaciers, thereby offering a useful tool for future studies of debris-covered glaciers.

Beschreibung: Wave-induced stress and breaking of sea ice in a coupled hydrodynamic–discrete-element wave–ice model Agnieszka Herman The Cryosphere Discuss., https//doi.org/10.5194/tc-2017-95,2017 Manuscript under review for TC (discussion: open, 0 comments) It is often assumed that ocean waves break sea ice into floes with sizes depending on wavelength. The results of this modeling study (in agreement with some earlier observations and models) suggest that this is not the case and instead the sizes of ice floes produced by waves depend only on ice thickness and mechanical properties. This may have important consequences for predicting sea ice response to oceanic and atmospheric forcing in regions where sea ice is influenced by waves.

Beschreibung: The modelled liquid water balance of the Greenland Ice Sheet Christian R. Steger, Carleen H. Reijmer, and Michiel R. van den Broeke The Cryosphere Discuss., https//doi.org/10.5194/tc-2017-88,2017 Manuscript under review for TC (discussion: open, 0 comments) Mass loss from the Greenland Ice Sheet, which contributes to sea level rise, is currently dominated by surface melt and runoff. The relation between these two variables is rather uncertain due to the firn layer’s potential to buffer melt in solid (refreezing) or liquid (firn aquifer) form. To address this uncertainty, we analyse output of a numerical firn model run over 1960–2014. Results show a spatially variable response of the ice sheet to increasing melt and an upward migration of aquifers.

Beschreibung: Stable accumulation patterns around Dome C, East Antarctica, over the last glacial cycle Marie G.~P. Cavitte, Frédéric Parrenin, Catherine Ritz, Duncan A. Young, Donald D. Blankenship, Massimo Frezzotti, and Jason L. Roberts The Cryosphere Discuss., https//doi.org/10.5194/tc-2017-71,2017 Manuscript under review for TC (discussion: open, 0 comments) We reconstruct the pattern of surface accumulation in the region around Dome C, East Antarctica, through the last glacial cycle. We use internal isochrones interpreted from ice-penetrating radar surveys and a 1D pseudo-steady ice flow model to invert for both time-averaged accumulation rates and paleoaccumulation rates. We observer that surface accumulation patterns are stable through the last 128 kyrs, this suggests a stable position of the dome throughout the last glacial cycle.

Beschreibung: Glaciological settings and recent mass balance of the Blåskimen Island in Dronning Maud Land, Antarctica Vikram Goel, Joel Brown, and Kenichi Matsuoka The Cryosphere Discuss., https//doi.org/10.5194/tc-2017-61,2017 Manuscript under review for TC (discussion: open, 0 comments) Ice rises are locally-grounded features surrounded by ice shelves. They help stabilize the Antarctic Ice Sheet and in turn are affected by ice-sheet evolution. However, details of these influences depend on the glaciological settings of the ice rises. We report first detailed ground-based investigations from Blåskimen Island ice rise in East Antarctica. We found that the ice rise is at least ~ 600 year old and has been thickening by ~ 0.2 m per year over the past decade.

Beschreibung: Self-affine subglacial roughness: consequences for radar scattering and basal water discrimination in northern Greenland Thomas M. Jordan, Michael A. Cooper, Dustin M. Schroeder, Christopher N. Williams, John D. Paden, Martin J. Siegert, and Jonathan L. Bamber The Cryosphere, 11, 1247-1264, https://doi.org/10.5194/tc-11-1247-2017, 2017 Using radio-echo sounding data from northern Greenland, we demonstrate that subglacial roughness exhibits self-affine (fractal) scaling behaviour. This enables us to assess topographic control upon the bed-echo waveform, and explain the spatial distribution of the degree of scattering (specular and diffuse reflections). Via comparison with a prediction for the basal thermal state (thawed and frozen regions of the bed) we discuss the consequences of our study for basal water discrimination.

Beschreibung: Spatial and temporal variability of water-filled crevasse hydrologic states along the shear margins of Jakobshavn Isbrae, Greenland Casey A. Joseph and Derrick J. Lampkin The Cryosphere Discuss., https//doi.org/10.5194/tc-2017-86,2017 Manuscript under review for TC (discussion: open, 0 comments) This work characterizes the spatial and temporal variability in the hydrologic state (filled or drained) of seven crevasse groups on Jakobshavn Isbræ from 2000–2015 using several optical satellite platforms. Meltwater from these crevasse groups can be transported to the bedrock and accelerate mass loss. The frequency of multi-drainage events were observed to increase over the study period. Multi-drain events may be related to temperature, terminus front location, and strain rate.

Beschreibung: A new approach to estimate ice dynamic rates using satellite observations in East Antarctica Bianca Kallenberg, Paul Tregoning, Janosch Fabian Hoffmann, Rhys Hawkins, Anthony Purcell, and Sébastien Allgeyer The Cryosphere, 11, 1235-1245, https://doi.org/10.5194/tc-11-1235-2017, 2017 Mass balance changes of the Antarctic ice sheet are of significant interest due to its sensitivity to climatic changes and its contribution to changes in global sea level. While regional climate models successfully estimate mass input due to snowfall, it remains difficult to estimate the amount of mass loss due to ice dynamic processes. It has often been assumed that changes in ice dynamic rates only need to be considered when assessing long-term ice sheet mass balance; however, 2 decades of satellite altimetry observations reveal that the Antarctic ice sheet changes unexpectedly and much more dynamically than previously expected. Despite available estimates on ice dynamic rates obtained from radar altimetry, information about ice sheet changes due to changes in the ice dynamics are still limited, especially in East Antarctica. Without understanding ice dynamic rates, it is not possible to properly assess changes in ice sheet mass balance and surface elevation or to develop ice sheet models. In this study we investigate the possibility of estimating ice sheet changes due to ice dynamic rates by removing modelled rates of surface mass balance, firn compaction, and bedrock uplift from satellite altimetry and gravity observations. With similar rates of ice discharge acquired from two different satellite missions we show that it is possible to obtain an approximation of the rate of change due to ice dynamics by combining altimetry and gravity observations. Thus, surface elevation changes due to surface mass balance, firn compaction, and ice dynamic rates can be modelled and correlated with observed elevation changes from satellite altimetry.

Beschreibung: Dark ice dynamics of the south-west Greenland Ice Sheet Andrew J. Tedstone, Jonathan L. Bamber, Joseph M. Cook, Christopher J. Williamson, Xavier Fettweis, Andrew J. Hodson, and Martyn Tranter The Cryosphere Discuss., https//doi.org/10.5194/tc-2017-79,2017 Manuscript under review for TC (discussion: open, 0 comments) The bare-ice albedo of the south-west Greenland ice sheet varies dramatically between melt seasons. Darkening by inorganic particulates, cryoconite hole processes and ice algae can occur, but the reasons for inter-annual albedo variability are unclear. We use satellite imagery to examine dark ice dynamics, and climate model outputs to find likely climatological controls. Melt-out particulates best explain the spatial extent of dark ice, but the darkening itself is likely due to ice algae growth.

Beschreibung: Methanesulfonic acid (MSA) migration in polar ice: Data synthesis and theory Matthew Osman, Sarah B. Das, Olivier Marchal, and Matthew J. Evans The Cryosphere Discuss., https//doi.org/10.5194/tc-2017-84,2017 Manuscript under review for TC (discussion: open, 0 comments) We combine a synthesis of 22 ice core records and a model of soluble impurity transport to investigate the enigmatic, post-depositional migration of methanesulfonic acid (MSA) in polar ice. Our findings suggest that migration may be universal across coastal regions of Greenland and Antarctica, though is mitigated at sites with higher accumulation and (or) lower impurity content. Records exhibiting severe migration may still be useful for inferring decadal and lower-frequency climate variability.

Beschreibung: Optical properties of laboratory grown sea ice doped with light absorbing impurities (black carbon) Amelia A. Marks, Maxim L. Lamare, and Martin D. King The Cryosphere Discuss., https//doi.org/10.5194/tc-2017-76,2017 Manuscript under review for TC (discussion: open, 0 comments) Arctic sea ice extent is declining rapidly. Prediction of sea ice trends rely on sea ice models that need to be evaluated with real data. A realistic sea ice environment is created in a laboratory by the Royal Holloway sea ice simulator and is used to show a sea ice model can replicate measured properties of sea ice e.g. reflectance. Black carbon, a component of soot found in atmospheric pollution, is also experimentally shown to reduce the reflectance of sea ice, which could exacerbate melting.

Beschreibung: Exceptional retreat of Novaya Zemlya's marine-terminating outlet glaciers between 2000 and 2013 J. Rachel Carr, Heather Bell, Rebecca Killick, and Tom Holt The Cryosphere Discuss., https//doi.org/10.5194/tc-2017-32,2017 Manuscript under review for TC (discussion: open, 0 comments) Glaciers on Novaya Zemlya (NVZ) retreated rapidly between 2000 and 2013. This was far faster than the previous 25 years, but retreat then slowed from 2013 onward. This may result from changes in broad-scale climatic patterns. Glaciers ending in lakes retreated at a similar rate to those ending in the ocean and retreat rates were very consistent between glaciers, which contrasts with previous studies.

Beschreibung: Properties of black carbon and other insoluble light-absorbing particles in seasonal snow of northwestern China Wei Pu, Xin Wang, Hailun Wei, Yue Zhou, Jinsen Shi, Zhiyuan Hu, Hongchun Jin, and Quanliang Chen The Cryosphere, 11, 1213-1233, https://doi.org/10.5194/tc-11-1213-2017, 2017 We conducted a large field campaign to collect snow samples in Xinjiang. We measured insoluble light-absorbing particles with estimated black carbon concentrations of 10–150 ng g-1 . We found a probable shift in emission sources with the progression of winter and dominated contributions of BC and OC to light absorption. A PMF model indicated an optimal three-factor/source solution that included industrial pollution, biomass burning, and soil dust.

Beschreibung: Improving gridded snow water equivalent products in British Columbia, Canada: multi-source data fusion by neural network models Andrew Snauffer, William Hsieh, Alex Cannon, and Markus Schnorbus The Cryosphere Discuss., https//doi.org/10.5194/tc-2017-56,2017 Manuscript under review for TC (discussion: open, 0 comments) Estimating winter snowpack throughout British Columbia is challenging due to the complex terrain, thick forests and high snow accumulations present. This paper describes a way to make better snow estimates by combining publicly available data using machine learning, a branch of artificial intelligence research. These improved estimates will help water resources managers better plan for changes in rivers and lakes fed by springtime snowmelt and will aid other research that supports such planning.

Beschreibung: Hypsometric amplification and routing moderation of Greenland ice sheet meltwater release Dirk van As, Andreas Bech Mikkelsen, Morten Holtegaard Nielsen, Jason E. Box, Lillemor Claesson Liljedahl, Katrin Lindbäck, Lincoln Pitcher, and Bent Hasholt The Cryosphere, 11, 1371-1386, https://doi.org/10.5194/tc-11-1371-2017, 2017 The Greenland ice sheet melts faster in a warmer climate. The ice sheet is flatter at high elevation, therefore atmospheric warming increases the melt area exponentially. For current climate conditions, we find that the ice sheet shape amplifies the total meltwater generation by roughly 60 %. Meltwater is not stored underneath the ice sheet, as previously found, but it does take multiple days for it to pass through the seasonally developing subglacial drainage channels, moderating discharge.

Beschreibung: Water flow in the active layer along an arctic slope – An investigation based on a field campaign and model simulations Sebastian F. Zastruzny, Bo Elberling, Lars Nielsen, and Karsten H. Jensen The Cryosphere Discuss., https//doi.org/10.5194/tc-2017-97,2017 Manuscript under review for TC (discussion: open, 0 comments) The hydrological regime in the arctic will change as the climate conditions change and the release and associated transport of nutrients will also be affected. In this study we analyze water flow and tracer transport along a sloping transect in Disko Island in Greenland. The results suggest that the movement of dissolved nitrogen compounds such as nitrate, being released along the slope in consequence of permafrost thawing, can quickly influence nitrogen cycling at the end of the slope.

Beschreibung: Inter-comparison of snow depth retrievals over Arctic sea ice from radar data acquired by Operation IceBridge Ron Kwok, Nathan T. Kurtz, Ludovic Brucker, Alvaro Ivanoff, Thomas Newman, Sinead L. Farrell, Joshua King, Stephen Howell, Melinda A. Webster, John Paden, Carl Leuschen, Joseph A. Macgregor, Jacqueline Richter-Menge, Jeremy Harbeck, and Mark Tschudi The Cryosphere Discuss., https//doi.org/10.5194/tc-2017-103,2017 Manuscript under review for TC (discussion: open, 0 comments) Since 2009, the ultra-wideband snow-radar on Operation IceBridge has acquired data in annual campaigns conducted during the Arctic and Antarctic springs. Existing snow depth retrieval algorithms differ in the way the air-snow and snow-ice interfaces are detected and localized in the radar returns, and in how the system limitations are addressed. Here, we assess five retrieval algorithms by comparisons with field measurements, ground-based campaigns, and analysed fields of snow depth.

Beschreibung: Street and garden trees in urban areas are often exposed to advection of strong vapor pressure deficit ( VPD ) air that can raise the whole-tree transpiration rate ( E T ), known as the oasis effect . However, urban trees tend to have small soil volume compared with natural conditions and so they are believed to strongly regulate stomata. E T characteristics of such urban trees have not been well understood because of a lack of reliable measurement methods. Therefore, we propose a novel weighing lysimeter method and investigate the whole-tree water balance of an isolated container-grown Zelkova serrata to examine (a) which biotic and abiotic factors determine E T , and (b) which spatial and temporal information is needed to predict E T under urban conditions. Whole-tree water balance and environmental conditions were measured from 2010 to 2012. Although leaf area substantially increased in the study period, daily E T did not vary much. E T increased with VPD almost linearly in 2010, but showed saturation in 2011 and 2012. Root water uptake lagged E T by 40 min in 2012. These results suggest that the small planter box interfered with root growth and that hydraulic supply capacities did not increase sufficiently to support leaf area increase. From analysis of water balance, we believe that neglecting soil drought effects on street trees without irrigation in Japan will overestimate E T over 4–5 sunny days at the longest. This is unlike previous studies of forest.

Beschreibung: The saturated hydraulic conductivity, K s , is a soil property that has a key role in the partitioning of rainfall into surface runoff and infiltration. The commonly used instruments and methods for in-situ measurements of K s have frequently provided conflicting results. Comparison of K s estimates obtained by three classical devices – namely the Double Ring Infiltrometer (DRI), the Guelph version of the Constant-Head Well Permeameter (GUELPH-CHP) and the CSIRO version of the Tension Permeameter (CSIRO-TP) is presented. A distinguishing feature in this study is the use of steady deep flow rates, obtained from controlled rainfall-runoff experiments, as benchmark values of K s at local and field-plot scales, thereby enabling an assessment of these methods in reliably reproducing repeatable values and in their capability of determining plot-scale variation of K s . We find that the DRI grossly overestimates K s , the GUELPH-CHP gives conflicting estimates of K s with substantial overestimation in laboratory experiments and underestimation at the plot scale, while the CSIRO-TP yields average K s values with significant errors of 24% in the plot scale experiment and 66% in laboratory experiments. While the DRI would likely yield a better estimate of the nature of variability than the GUELPH-CHP and CSIRO-TP, a separate calibration may be warranted to correct for the overestimation of K s values. The reasons for such discrepancies within and between the measurement methods are not yet fully understood, and serve as motivation for future work to better characterize the uncertainty associated with individual measurements of K s using these methods and the characterization of field scale variability from multiple local measurements.

Beschreibung: This study explores rainfall spatial variability and its influence on runoff modelling. A novel assessment scheme integrated with coefficients of variance (CV) and Moran's I is introduced to describe effective rainfall spatial variability. CV is widely accepted to identify rainfall variability through rainfall intensity, whereas Moran's I reflects rainfall spatial autocorrelation. This new assessment framework combines these two indicators to assess the spatial variability derived from both rainfall intensity and distribution, which are crucial in determining the time and magnitude of runoff generation. Four model structures embedded in the Variable Infiltration Capacity (VIC) model are adopted for hydrological modelling in the Brue catchment of England. The models are assigned with 1, 3, 8 and 27 hydrological response units (HRUs) respectively and diverse rainfall spatial information for 236 events are extracted from 1995. This study investigates the model performance of different partitioning based on rainfall spatial variability through peak volume (Q p ) and time to peak (T p ), along with the rainfall event process. The results show that models associated with dense spatial partitioning are broadly capable of capturing more spatial information with better performance. It is unnecessary to utilize models with high spatial density for simple rainfall events, though they show distinct advantages on complex events. With additional spatial information, Q p experiences a notable improvement over T p . Moreover, seasonal patterns signified by the assessment scheme implies the feasibility of seasonal models.

Beschreibung: Brief communication: The global signature of post-1900 land ice wastage on vertical land motion Riccardo E. M. Riva, Thomas Frederikse, Matt A. King, Ben Marzeion, and Michiel R. van den Broeke The Cryosphere, 11, 1327-1332, https://doi.org/10.5194/tc-11-1327-2017, 2017 The reduction of ice masses stored on land has made an important contribution to sea-level rise over the last century, as well as changed the Earth's shape. We model the solid-earth response to ice mass changes and find significant vertical deformation signals over large continental areas. We show how deformation rates have varied strongly throughout the last century, which affects the interpretation and extrapolation of recent observations of vertical land motion and sea-level change.

Beschreibung: Soil erosion by water in abandoned dry terraces is one of the most important environmental problems in semi-arid areas, enhancing biological degradation and reducing possible resources that can be obtained. However, little is known about the effects of the types of lithology and soil properties on the early stages of soil erosion. Therefore, the main aim of this research was to assess the effect of different lithologies (marls, limestones and metamorphic –phyllites, schists and greywackes- materials) and soil properties on the early stages of soil erosion by water in abandoned dry terraces, compared with similar terraces still in agricultural use. Soil analyses (texture, aggregate stability and bulk density) and 22 rainfall simulations were carried out under dry conditions. During the experiments, local inclination, vegetation and stone cover, total organic matter and antecedent soil moisture were also quantified. The results showed that the highest soil loss (41.41 g m -2 in cultivated plots and 17.05 g m -2 in the abandoned plots) and runoff (3.79 L m -2 in the abandoned plot) occurred on marl substrata. Marls also showed the shallowest infiltration front (9 cm) and lowest infiltration rate (4.3 cm min -1 ). Limestones and, especially, metamorphic areas, showed a lower degree of soil erosion, higher infiltration rates and deeper infiltration fronts.

Beschreibung: Snow farming: Conserving snow over the summer season Thomas Grünewald, Michael Lehning, and Fabian Wolfsperger The Cryosphere Discuss., https//doi.org/10.5194/tc-2017-93,2017 Manuscript under review for TC (discussion: open, 0 comments) Snowfarming is the conservation of snow during summer. Large snow piles are covered with a saw-dust insulation layer, reducing melt and guaranteeing a specific amount of snow available in autumn independent of the weather conditions. Snow volumes changes of two heaps were monitored showing that about 1/3 of the snow was lost. Model simulations confirmed the large effect of the insulation on energy balance and melt. The model can now be used as a tool to examine future snowfarming projects.

Beschreibung: Sonar gas flux estimation by bubble insonification: application to methane bubble flux from seep areas in the outer Laptev Sea Ira Leifer, Denis Chernykh, Natalia Shakhova, and Igor Semiletov The Cryosphere, 11, 1333-1350, https://doi.org/10.5194/tc-11-1333-2017, 2017 Vast Arctic methane deposits may alter global climate and require remote sensing (RS) to map. Sonar has great promise, but quantitative inversion based on theory is challenged by multiple bubble acoustical scattering in plumes. We demonstrate use of a real-world in situ bubble plume calibration using a bubble model to correct for differences in the calibration and seep plumes. Spatial seep sonar maps were then used to improve understanding of subsurface geologic controls.

Beschreibung: Wind-driven snow conditions control the occurrence of contemporary marginal mountain permafrost in the Chic-Choc Mountains, south-eastern Canada: a case study from Mont Jacques-Cartier Gautier Davesne, Daniel Fortier, Florent Domine, and James T. Gray The Cryosphere, 11, 1351-1370, https://doi.org/10.5194/tc-11-1351-2017, 2017 This study presents data from Mont Jacques-Cartier, the highest summit in the Appalachians of south-eastern Canada, to demonstrate that the occurrence of contemporary permafrost body is associated with a very thin and wind-packed winter snow cover which brings local azonal topo-climatic conditions on the dome-shaped summit. This study is an important preliminary step in modelling the regional spatial distribution of permafrost on the highest summits in eastern North America.

Beschreibung: Historically, paired watershed studies have been used to quantify the hydrological effects of land use and management practices by concurrently monitoring two similar watersheds during calibration (pre-treatment) and post-treatment periods. This study characterizes seasonal water table and flow response to rainfall during the calibration period and tests a change detection technique of moving sums of recursive residuals (MOSUM) to select calibration periods for each control-treatment watershed pair when the regression coefficients for daily water table elevation (WTE) were most stable to minimize regression model uncertainty. The control and treatment watersheds were one watershed of 3−4 year-old intensely managed loblolly pine ( Pinus taeda L. ) with natural understory, one watershed of 3−4 year-old loblolly pine intercropped with switchgrass ( Panicum virgatum) , one watershed of 14−15 year-old thinned loblolly pine with natural understory (control), and one watershed of switchgrass only. The study period spanned from 2009 to 2012. Silvicultural operational practices during this period acted as external factors, potentially shifting hydrologic calibration relationships between control and treatment watersheds. MOSUM results indicated significant changes in regression parameters due to silvicultural operations and were used to identify stable relationships for WTE. None of the calibration relationships developed using this method were significantly different from the classical calibration relationship based on published historical data. We attribute that to the similarity of historical and 2010−2012 leaf area index (LAI) on control and treatment watersheds as moderated by the emergent vegetation. While the MOSUM approach does not eliminate the need for true calibration data or replace the classic paired watershed approach, our results show that it may be an effective alternative approach when true data is unavailable, as it minimizes the impacts of external disturbances other than the treatment of interest.

Beschreibung: ABSTRACT The Sierra Gorda aquifer is one of the most extensive of southern Spain. The main groundwater discharge is produced at its northern boundary through several high-flow springs. In this study, stable isotopes of dissolved sulfate (δ 34 S and δ 18 O) and groundwater chemistry were used to determine the origin of the sulfate and to characterize the groundwater flow. We sampled the main springs, as well as other minor outlets related to perched water tables, in order to determine the different sources of SO 4 2- (e.g. dissolution of evaporites, atmospheric deposition, etc.). The substantial difference in the amount of dissolved SO 4 2- between the springs located in its northwestern part (≈25 mg/l) and those elsewhere in the northern part (≈60 mg/l) suggests zones with separate groundwater flow systems. A third group of springs, far from the northeastern boundary of the permeable outcrops, shows higher SO 4 2- content than the rest (≈125 mg/l). The isotopic range of sulfate (-0.3 to 14.82‰ V-CTD) points to several sources, including dissolution of Triassic or Miocene evaporites, atmospheric deposition, and decomposition of organic material in the soil. Among these, the dissolution of Triassic gypsum —which overlies the saturated zone as a consequence of the folds and faults that deform the aquifer— is the main source of SO 4 2- (range from 12.79 to 14.82‰ V-CTD). This range is typical for Triassic gypsum. The higher karstification in the western sector, together with important differences in the saturated thickness between the western and eastern sectors, would also be due to the tectonic structure and could explain the difference in SO 4 2- contents in the water. This singular arrangement may cause a higher residence time of groundwater in the eastern sector; thus, a higher contact time with Triassic evaporitic rocks is inferred. Accordingly, the stable isotopes of SO 4 2- are found to be a valuable tool for identifying areas with different flow systems in the saturated zone of karstic aquifers, as well as for evaluating aspects such as the degree of karstification.

Beschreibung: This study examines the 1914-2015 runoff trends and variability for 136 rivers draining British Columbia's (BC's) Coast and Insular Mountains. Rivers are partitioned into eastward and westward flowing rivers based on flow direction from the Coast Mountains. Thus, eastward and westward runoff trends and influence of topography on runoff are explored. Our findings indicate that rivers flowing eastward to the Nechako and Chilcotin plateaus contribute the lowest annual runoff compared to westward rivers where runoff is high. Low interannual runoff variability is evident in westward rivers and their alpine watersheds, whereas eastward rivers exhibit high interannual runoff variability. On Vancouver Island, some of the rivers with the highest annual runoff exhibit high interannual variability. A significant ( p 〈 0.05) negative correlation exists between mean annual runoff ( R m ) and latitude, gauged area, mean elevation, and its corresponding coefficient of variation (CV). However, a significant positive correlation was found between the glacierized area of mountainous regions and R m . The mean CV in annual runoff is significantly negatively correlated with latitude and glacierized area, but significantly positively correlated with longitude. Annual and seasonal runoff trend analyses of each river were performed for an early (1936-2015), a middle (1966-2015), and a late (1986-2015) period using the Mann-Kendall test. Trend analyses revealed a shift towards more positive detectable (signal-to-noise ratio 〉 1) trends in annual and seasonal runoff from the middle to the late period across the study domain. Most positive detectable seasonal runoff trends in the middle period occur in spring in glacierized westward rivers located 〉1200 m, whereas in the late period they all occur in fall and are regionally coherent around Vancouver Island and south coastal BC. Rivers draining eastward exhibit more positive trends over 1986-2015 compared to westward rivers. This study provides crucial information on the hydrology of mountain watersheds across BC's coast in response to Pacific Decadal Oscillation phase changes, the elevational amplification of regional climate change, and their influences on precipitation and glacier retreat.

Beschreibung: The hydrology and water balance of megadunes and lakes have been investigated in the Badain Jaran Desert of China. Field observations and analyses of sand layer water content, field capacity, secondary salt content and grain size reveal three types of important natural phenomenon: (1) Vegetation bands on the leeward slope of the megadunes reflect the hydrological regime within the sandy vadose zone. (2) Seepage, wet sand deposits and secondary salt deposits indicate the pattern of water movement within the sandy vadose zone. (3) Zones of groundwater seeps and descending springs around the lakes reflect the influence of the local topography on the hydrological regime of the megadunes. The seepage exposed on the sloping surface of the megadunes and gravity water contained within the sand layer confirm the occurrence of preferential flow within the vadose zone of the megadunes. Alternating layers of coarse and fine sand create the conditions for the formation of preferential flows. The preferential flows promote movement of water within the sand layer water that leads to deep penetration of water within the megadunes and ultimately to the recharging of groundwater and lake water. Our results indicate that a positive water balance promotes recharge of the megadunes, which depends on the high permeability of the megadune material, the shallow depth of the surface sand layer affected by evaporation, the occurrence of rainfall events exceeding 15 mm, and the sparse vegetation cover. Water balance estimates indicate that the annual water storage of the megadunes is about 7.5 mm, accounting for only 8% of annual precipitation; however, the shallow groundwater per unit area under the megadunes receives only 3.6% of annual precipitation but it is still able maintain a dynamic balance of the lake water. From a water budget perspective, the annual water storage in the megadunes is sufficient to serve as a recharge source for lake water, thereby enabling the long-term persistence of the lakes. Overall, our findings demonstrate that precipitation is a significant component of the hydrological cycle in arid deserts.

Beschreibung: Measuring snow water equivalent from common offset GPR records through migration velocity analysis James St. Clair and W. Steven Holbrook The Cryosphere Discuss., https//doi.org/10.5194/tc-2017-90,2017 Manuscript under review for TC (discussion: open, 0 comments) We investigate the performance of a semi-automated algorithm for measuring snow water equivalent (SWE) from common-offset ground-penetrating-radar (GPR) data. The algorithm automatically estimates SWE from a selected portion of the data and the user is only required for quality control. GPR derived SWE estimates are similar to manual measurements indicating that the method is reliable. Our results will hopefully make GPR a more attractive tool for monitoring SWE in mountain watersheds.

Beschreibung: Impacts of freshwater changes on Antarctic sea ice in an eddy-permitting sea-ice–ocean model Verena Haid, Doroteaciro Iovino, and Simona Masina The Cryosphere, 11, 1387-1402, https://doi.org/10.5194/tc-11-1387-2017, 2017 Since the Antarctic sea ice extent shows a recent increase, we investigate the sea ice response to changed amount and distribution of surface freshwater addition in the Southern Ocean with the ocean–sea ice model NEMO/LIM2. We find that freshwater addition within the range of current estimates increases the ice extent, but higher amounts could have an opposing effect. The freshwater distribution is of great influence on the ice dynamics and the ice thickness is strongly influenced by it.