ALBERT

Description: Abstract Low‐frequency passive integrated transponders (PIT tags), are commonly used for monitoring pebble mobility in gravel‐bed rivers. Although early studies reported high recovery rates for PIT tags used in small streams, recovery rates in larger systems remain low, substantially limiting the possibilities for their use in such rivers. These low recovery rates are potentially due to missed detections caused by tag signal collision, burial in the sediment layer deeper than the maximum detection range and insufficient (but still exhausting) field effort to cover the concerned areas. A potential solution for addressing these problems is to use active ultra‐high frequency (a‐UHF) transponders as these have a greater detection range and anti‐collision protocols. In order to assess the potential of such transponders for pebble tracking in rivers, we used 433.92 MHz COIN‐ID and COIN‐HC models (ELA Innovation Company, Montpellier, France). We completed several tests to (i) characterize transponder detection ranges in the water and in saturated sediment and (ii) develop field protocols for locating tags by combining global positioning systems (GPS) sites and transponder received signal strength indication (RSSI) levels. The results showed that (i) the maximum detection ranges are about 2.4 m in the water column and more than 2.6 m in a column of saturated gravelly‐sandy sediment, (ii) RSSI spatial interpolation can be used to determine transponder position with good accuracy (〈 1 m), (iii) the desired minimal level of accuracy can be adjusted depending on in‐field effort and signal impulse interval, (iv) the RSSI maximal value observed cannot yet be used to determine transponder burial depth because of the multipath propagation of radio frequencies and the semi‐directional emission of the tag signal. Copyright © 2017 John Wiley & Sons, Ltd.

Description: Abstract Single bed load particle impacts were experimentally investigated in supercritical open channel flow over a fixed planar bed of low relative roughness height simulating high‐gradient non‐alluvial mountain streams as well as hydraulic structures. Particle impact characteristics (impact velocity, impact angle, Stokes number, restitution and dynamic friction coefficients) were determined for a wide range of hydraulic parameters and particle properties. Particle impact velocity scaled with the particle velocity, and the vertical particle impact velocity increased with excess transport stage. Particle impact and rebound angles were low and decreased with transport stage. Analysis of the particle impacts with the bed revealed almost no viscous damping effects with high normal restitution coefficients exceeding unity. The normal and resultant Stokes numbers were high and above critical thresholds for viscous damping. These results are attributed to the coherent turbulent structures near the wall region, i.e. bursting motion with ejection and sweep events responsible for turbulence generation and particle transport. The tangential restitution coefficients were slightly below unity and the dynamic friction coefficients were lower than for alluvial bed data, revealing that only a small amount of horizontal energy was transferred to the bed. The abrasion prediction model formed by Sklar and Dietrich in 2004 was revised based on the new equations on vertical impact velocity and hop length covering various bed configurations. The abrasion coefficient kv was found to be vary around kv ~ 105 for hard materials (tensile strength ft 〉 1 MPa), one order of magnitude lower than the value assumed so far for Sklar and Dietrich's model. Copyright © 2017 John Wiley & Sons, Ltd.

Description: Abstract When fine sediments are present in gravel streambeds (gravel‐framework beds), the gravel can be more easily removed from its original position, compared with gravel in a streambed without fine sediment but otherwise under the same hydraulic conditions. In this study, the effect of the presence of sand on the initiation of gravel motion in gravel riverbeds was investigated using flume experiments. The relationship between the critical Shields stress for gravel motion initiation and the fraction of sand in the bed was determined experimentally. The results can be summarized as follows. (1) When the fraction of sand in the bed is smaller than about 0.4, the critical Shields stress for the initiation of gravel motion decreases with increasing fraction of sand. The critical Shields stress increases, however, with increasing fraction of sand when it is larger than about 0.4. (2) The difference between the value of the critical Shields stress predicted by the Egiazaroff equation and the value obtained from the experimental data becomes maximum at about 0.4 of the fraction of sand. Here an empirical relation between the critical Shields stress and the fraction of sand is proposed so as to consider the effects of the ratio of the characteristic gravel size to the mean size of the bed material on the critical Shields stress. (3) Gravel in armored beds can be more easily mobilized by supplying sand as part of a sediment augmentation scheme. The sand fraction in the subsurface layer of the bed appears to reduce the friction angle of exposed particles. Sediment augmentation using sand has been recently demonstrated to be a viable alternative for mobilizing gravel for the restoration of gravel‐bed rivers downstream of dams. The quantitative evaluation obtained through the experiments reported here may be useful for the design of augmentation schemes. Copyright © 2017 John Wiley & Sons, Ltd.

Description: Abstract The assumption of the equilibrium state of gravel surfaces in flume experiments under feeding or recirculating conditions is generally justified by three equilibrium criteria based on sediment transport, slopes, and bed features. When these parameters become stable, an experiment is expected to reach equilibrium. This equilibrium state, however, is based on a one‐dimensional model, the Exner equation, which may not truly reflect the equilibrium state of the system considering the complex flow and sediment processes. In this paper, the evolutionary process of a gravel surface is investigated based on a large‐scale recirculating flume experiment. The performances of the three equilibrium criteria are evaluated first, and then the evolution of the bed morphology is studied. The key findings include the following: (1) the sediment transport rate, slopes of water and bed surfaces, and one‐dimensional morphological features reach equilibrium roughly simultaneously; (2) two‐dimensional morphology continually evolves after these characteristics reach equilibrium, which is confirmed by the characteristics of the sediment transport process; and (3) the results from a numerical simulation suggest that a much longer time is required to reach an equilibrium state. Our results suggest that sufficient experimental time is required to investigate the equilibrium morphological characteristics of gravel surfaces, which is much longer than the equilibrium time reflected by the one‐dimensional equilibrium criteria. Copyright © 2017 John Wiley & Sons, Ltd.

Description: ABSTRACT The Late Pleistocene Middle Stone Age (MSA) record of Africa provides early examples of standardised stone tool production and complex manufacturing sequences, superficially implying a long-term trend towards greater complexity in MSA technology at a continental scale. However, at this scale, spatial and temporal expressions of technological complexity are uneven. New lithic and chronometric data from the East–Central African record add further regional perspective to these patterns. Stone artefact assemblages from Karonga, northern, Malawi (92–22 ka), persistently lack the complexity demonstrated elsewhere in Africa at the same times, despite similar lithic raw materials. These new data provide an essential avenue for exploring hypotheses about the roles of environmental risk and demography in shaping the expression of MSA technology across the continent, not just at a local scale. When set within this framework, the simplicity of the Karonga MSA is best explained by its position in an environment that was persistently low in relative extrinsic subsistence risk. These results reinforce that motivations to invest in complex tools were variable through space and time, and that this variation, more than factors relating to behavioural capacity, may explain the patchy evidence for lithic complexity in the later MSA.

Description: Abstract In meandering rivers cut into bedrock, erosion across a channel cross‐section can be strongly asymmetric. At a meander apex, deep undercutting of the outer bank can result in the formation of a hanging cliff (which may drive hillslope failure), whereas the inner bank adjoins a slip‐off slope that connects to the hillslope itself. Here we propose a physically‐based model for predicting channel planform migration and incision, point bar and slip‐off slope formation, bedrock abrasion, the spatial distribution of alluvial cover, and adaptation of channel width in a mixed bedrock‐alluvial channel. We simplify the analysis by considering a numerical model of steady, uniform bend flow satisfying cyclic boundary conditions. Thus in our analysis, ‘sediment supply’, i.e. the total volume of alluvium in the system, is conserved. In our numerical simulations, the migration rate of the outer bank is a specified parameter. Our simulations demonstrate the existence of an approximate state of dynamic equilibrium corresponding to a near‐solution of permanent form in which a bend of constant curvature, width, cross‐sectional shape and alluvial cover distribution migrates diagonally downward at constant speed, leaving a bedrock equivalent of a point bar on the inside of the bend. Channel width is set internally by the processes of migration and incision. We find that equilibrium width increases with increasing sediment supply, but is insensitive to outer bank migration rate. The slope of the bedrock point bar varies inversely with both outer bank migration rate and sediment supply. Although the migration rate of the outer bank is externally imposed here, we discuss a model modification that would allow lateral side‐wall abrasion to be treated in a manner similar to the process of bedrock incision. Copyright © 2016 John Wiley & Sons, Ltd.

Description: Abstract Particle dynamics are investigated experimentally in supercritical high‐speed open channel flow over a fixed planar bed of low relative roughness height simulating flows in high‐gradient non‐alluvial mountain streams and hydraulic structures. Non‐dimensional equations were developed for transport mode, particle velocity, hop length and hop height accounting for a wide range of literature data encompassing sub‐ and supercritical flow conditions as well as planar and alluvial bed configurations. Particles were dominantly transported in saltation and particle trajectories on planar beds were rather flat and long compared with alluvial bed data due to (1) increased lift forces by spinning motion, (2) strongly downward directed secondary currents, and (3) a planar flume bed where variation in particle reflection and damping effects were minor. The analysis of particle saltation trajectories revealed that the rising and falling limbs were almost symmetrical contradicting alluvial bed data. Furthermore, no or negligible effect of particle size and shape on particle dynamics were found. Implications of experimental findings for mechanistic saltation‐abrasion models are briefly discussed. Copyright © 2017 John Wiley & Sons, Ltd.

Description: Abstract Large wood along rivers influences entrainment, transport, and storage of mineral sediment and particulate organic matter. We review how wood alters sediment dynamics and explore patterns among volumes of in‐stream wood, sediment storage, and residual pools for dispersed pieces of wood, logjams, and beaver dams. We hypothesized that: volume of sediment per unit area of channel stored in association with wood is inversely proportional to drainage area; the form of sediment storage changes downstream; sediment storage correlates with wood load; the residual volume of pools created in association with wood correlates inversely with drainage area; and volume of sediment stored behind beaver dams correlates with pond area. Lack of data from larger drainage areas limits tests of these hypotheses, but the analyses suggest that sediment volume correlates positively with drainage area and wood volume. The form of sediment storage in relation to wood appears to change downstream, with wedges of sediment upstream from jammed steps most prevalent in small, steep channels and more dispersed sediment storage in lower gradient channels. Pool volume correlates positively with wood volume and negatively with channel gradient. Sediment volume correlates well with beaver pond area. More abundant in‐stream wood and beaver populations present historically equated to greater sediment storage within river corridors and greater residual pool volume. One implication of these changes is that protecting and re‐introducing wood and beavers can be used to restore rivers. This review of the existing literature on wood and sediment dynamics highlights the lack of studies on larger rivers. Copyright © 2016 John Wiley & Sons, Ltd.

Description: Abstract For more than 150 years, humans have tried to limit the geomorphic activity of mountain streams, and the related damage, using torrent control works. Check dams are likely the most emblematic civil engineering structures used in soil conservation programs. Modern mountain societies have inherited thousands of these structures built in upland gullies and streams. To help define their effectiveness and decisions concerning their maintenance or new project designs, a clear understanding of potential effects of check dams on river systems, i.e. their functions, is first needed. The next steps concern quantitative assessments of each function on the flood features and combination of all effects. The present understanding of these sometimes old structures' functions can be complicated because the societal and environmental contexts in which the original structures were built may have changed. To bridge this gap, this paper traces the purposes for which check dams were built, through a detailed analysis of French archives. We first analyze chronologically how each function was theorized and applied in the field. In the nineteenth century, engineers developed a thorough empirical and conceptual knowledge of mountain soil erosion, torrential geomorphology, and sediment transport processes as well as check dam interactions with these natural processes. The second part of this paper synthesizes conceptual descriptions of the check dams' functions, in the light of more than 150 years of experience, with their implication on the features of the structures. The French experience is compared to other countries' pioneering works. Finally, the next steps and remaining research challenges toward a comprehensive analysis of check dams' efficiency in torrent hazard mitigation are presented. This analysis is proposed to remind how, conceptually, check dams may influence geomorphic systems, bearing in mind the knowledge represented in pioneer guidelines and recent works on the subject. Copyright © 2016 John Wiley & Sons, Ltd.

Description: Abstract Structure‐from‐Motion (SfM) photogrammetry is now used widely to study a range of earth surface processes and landforms, and is fast becoming a core tool in fluvial geomorphology. SfM photogrammetry allows extraction of topographic information and orthophotos from aerial imagery. However, one field where it is not yet widely used is that of river restoration. The characterisation of physical habitat conditions pre‐ and post‐restoration is critical for assessing project success, and SfM can be used easily and effectively for this purpose. In this paper we outline a workflow model for the application of SfM photogrammetry to collect topographic data, develop surface models and assess geomorphic change resulting from river restoration actions. We illustrate the application of the model to a river restoration project in the NW of England, to show how SfM techniques have been used to assess whether the project is achieving its geomorphic objectives. We outline the details of each stage of the workflow, which extend from preliminary decision‐making related to the establishment of a ground control network, through fish‐eye lens camera testing and calibration, to final image analysis for the creation of facies maps, the extraction of point clouds, and the development of digital elevation models (DEMs) and channel roughness maps. The workflow enabled us to confidently identify geomorphic changes occurring in the river channel over time, as well as assess spatial variation in erosion and aggradation. Critical to the assessment of change was the high number of ground control points and the application of a minimum level of detection threshold used to assess uncertainties in the topographic models. We suggest that these two things are especially important for river restoration applications. Copyright © 2016 John Wiley & Sons, Ltd.

Description: Abstract Experiments were undertaken to study the nature of granular interaction in running water by examining the influence of fine grain inputs to a coarser sediment bed with a mobile surface. Video recordings of grain sorting by both kinetic sieving and spontaneous percolation are used to diagnose the critical processes controlling the overall bed response. Kinetic sieving takes place in the mobile bed surface, with the finer sediment moving to the bottom of the bedload transport layer at the interface with the underlying quasi‐static coarse bed. We show that the behavior at this interface dictates how a channel responds to a fine sediment input. If, by spontaneous percolation, the fine sediment is able to infiltrate into the underlying quasi‐static bed, the total transport increases and the channel degrades. However, if the fine sediment input rate exceeds the transport capacity or is geometrically unable to infiltrate into the underlying bed, it forms a quasi‐static layer underneath the transport layer that inhibits entrainment from the underlying bed, resulting in aggradation and an increase in bed slope. Copyright © 2016 John Wiley & Sons, Ltd.

Description: Topographic monitoring of a gravel augmentation during a dam‐controlled flood in the Trinity River, CA, indicates that all of the gravel entering the study reach was captured in one of two bed‐material storage reservoirs. Such interactions with storage reservoirs can cause large bed‐material pulses to disperse by fragmenting into multiple smaller pulses. As a refinement to the conceptual model of sediment pulse evolution by dispersion and translation, the concept of pulse fragmentation has practical implications for gravel management. Abstract The geomorphic effect of introducing a gravel augmentation totaling 520 m3 into a gravel‐bed stream during a dam‐controlled flood in May of 2015 was monitored with bedload transport measurements, an array of seismometers, and repeated topographic surveys. Half of the augmented gravel was injected into the flow with front‐end loaders on the rising limb of the flood and the other half was injected on the first day of the peak. Virtually all of the gravel transported past the injection point was deposited within about 7 to 10 channel widths of the injection point. Most of the injected gravel deposited along the left bank of the river whereas the right half of the channel bed was dominated by scour. The downstream third of the depositional area consisted of a small dune field that developed prior to the second gravel injection and subsequently migrated about one channel width downstream. A second depositional front was observed upstream from the gravel injection point, where a delta‐like wedge of bed material developed in the first hours of the flow release and changed little over the remainder of the release. These two depositional areas represent small‐scale bed‐material storage reservoirs with the potential to accumulate and periodically release packets of bed material. Interactions with such storage reservoirs are hypothesized to cause large bed‐material pulses to disperse by fragmenting into multiple smaller pulses. As a refinement to the conceptual model that views sediment pulse evolution in terms of dispersion and translation, the concept of pulse fragmentation has practical implications for gravel management. It implies that gravel augmentations can produce morphologic changes at locations that are separated from the augmentation point by arbitrarily long reaches, and it highlights the dependence of pulse propagation rates on the nature and distribution of the bed‐material storage reservoirs in the channel system. Copyright © 2017 John Wiley & Sons, Ltd.

Description: Abstract The artificial gravel augmentation of river channels is increasingly being used to mitigate the adverse effects of river regulation and sediment starvation. A systematic framework for designing and assessing such gravel augmentations is still lacking, notably on large rivers. Monitoring is required to quantify the movement of augmented gravel, measure bedform changes, assess potential habitat enhancement, and reduce the uncertainty in sediment management. Here we present the results of an experiment conducted in the Rhine River (French and German border). In 2010, 23 000 m3 of sediments (approximately the mean annual bedload transport capacity) were supplied in a by‐passed reach downstream of the Kembs dam to test the feasibility of enhancing sediment transport and bedform changes. A 620‐m‐long and 12‐m‐wide gravel deposit was created 8 km downstream from the dam. Monitoring included topo‐bathymetric surveys, radio‐frequency particle tracking using passive integrated transponder (PIT) tags, bed grain size measurement, and airborne imagery. Six surveys performed since 2009 have been described (before and after gravel augmentation, and after Q2 and Q15 floods). The key findings are that (i) the augmented gravel was partially dispersed by the first flood event of December 2010 (Q1); (ii) PIT tags were found up to 3200 m downstream of the gravel augmentation site after four years, but the effects of gravel augmentation could not be clearly distinguished from the effects of floods and internal remobilization on more than 3500 m downstream; (iii) linear and log‐linear relationships linking bedload transport, particle mobility, and grain size were established; and (iv) combined bathymetry and PIT tag surveys were useful for evaluating potential environmental risks and the first morpho‐ecological responses. This confirmed the complementary nature of such techniques in the monitoring of gravel augmentation in large rivers. Copyright © 2017 John Wiley & Sons, Ltd.

Description: Mountain gravel‐bed rivers are subjected to punctuated floods and sediment delivery. We model this numerically in terms of a cycled hydrograph upstream and a cycled “sedimentograph” midreach. Both the hydrograph and the sedimentograph generate boundary layers, within which the effect of the fluctuations are felt. Outside the boundary layers, steady, uniform conditions representing the overall effects of the hydrograph and sedimentograph are achieved. Our result provides a useful tool for simplifying the modeling of long‐term morphodynamics in mountain rivers. Abstract Sediment often enters rivers in the form of sediment pulses associated with landslides and debris flows. This is particularly so in gravel‐bed rivers in earthquake‐prone mountain regions, such as Southwest China. Under such circumstances, sediment pulses can rapidly change river topography and leave the river in repeated states of gradual recovery. In this paper, we implement a one‐dimensional morphodynamic model of river response to pulsed sediment supply. The model is validated using data from flume experiments, so demonstrating that it can successfully reproduce the overall morphodynamics of experimental pulses. The model is then used to explore the evolution of a gravel‐bed river subject to cycled hydrographs and repeated sediment pulses. These pulses are fed into the channel in a fixed region centered at a point halfway down the calculational domain. The pulsed sediment supply is in addition to a constant sediment supply at the upstream end. Results indicate that the river can reach a mobile‐bed equilibrium in which two regions exist within which bed elevation and surface grain size distribution vary periodically in time. One of these is at the upstream end, where a periodic discharge hydrograph and constant sediment supply are imposed, and the other is in a region about halfway down the channel where periodic sediment pulses are introduced. Outside these two regions, bed elevation and surface grain size distribution reach a mobile‐bed equilibrium that is invariant in time. The zone of fluctuation‐free mobile‐bed equilibrium upstream of the pulse region is not affected by repeated sediment pulses under the scenarios tested, but downstream of the pulse region, the channel reaches different fluctuation‐free mobile‐bed equilibriums under different sediment pulse scenarios. The vertical bed structure predicted by the simulations indicates that the cyclic variation associated with the hydrograph and sediment pulses can affect the substrate stratigraphy to some depth. Copyright © 2017 John Wiley & Sons, Ltd.

Description: Abstract Large wood (LW) is a ubiquitous feature in rivers of forested watersheds worldwide, and its importance for river diversity has been recognized for several decades. Although the role of LW in fluvial dynamics has been extensively documented, there is a need to better quantify the most significant components of LW budgets at the river scale. The purpose of our study was to quantify each component (input, accumulation, and output) of a LW budget at the reach and watershed scales for different time periods (i.e. a 50‐year period, decadal cycle, and interannual cycle). The LW budget was quantified by measuring the volumes of LW inputs, accumulations, and outputs within river sections that were finally evacuated from the watershed. The study site included three unusually large but natural wood rafts in the delta of the Saint‐Jean River (SJR; Québec, Canada) that have accumulated all LW exported from the watershed for the last 50 years. We observed an increase in fluvial dynamics since 2004, which led to larger LW recruitment and a greater LW volume trapped in the river corridor, suggesting that the system is not in equilibrium in terms of the wood budget but is rather recovering from previous human pressures as well as adjusting to hydroclimatic changes. The results reveal the large variability in the LW budget dynamics during the 50‐year period and allow us to examine the eco‐hydromorphological trajectory that highlights key variables (discharge, erosion rates, bar surface area, sinuosity, wood mobility, and wood retention). Knowledge on the dynamics of these variables improves our understanding of the historical and future trajectories of LW dynamics and fluvial dynamics in gravel‐bed rivers. Extreme events (flood and ice‐melt) significantly contribute to LW dynamics in the SJR river system. Copyright © 2017 John Wiley & Sons, Ltd.

Description: Abstract The question: ‘how does a streambed change over a minor flood?’ does not have a clear answer due to lack of measurement methods during high flows. We investigate bedload transport and disentrainment during a 1.5‐year flood by linking field measurements using fiber optic distributed temperature sensing (DTS) cable with sediment transport theory and an existing explicit analytical solution to predict depth of sediment deposition from amplitude and phase changes of the diurnal near‐bed pore‐water temperature. The method facilitates the study of gravel transport by using near‐bed temperature time series to estimate rates of sediment deposition continuously over the duration of a high flow event coinciding with bar formation. The observations indicate that all gravel and cobble particles present were transported along the riffle at a relatively low Shields Number for the median particle size, and were re‐deposited on the lee side of the bar at rates that varied over time during a constant flow. Approximately 1–6% of the bed was predicted to be mobile during the 1.5‐year flood, indicating that large inactive regions of the bed, particularly between riffles, persist between years despite field observations of narrow zones of local transport and bar growth on the order ~3–5 times the median particle size. In contrast, during a seven‐year flood approximately 8–55% of the bed was predicted to become mobile, indicating that the continuous along‐stream mobility required to mobilize coarse gravel through long pools and downstream to the next riffle is infrequent. Copyright © 2017 John Wiley & Sons, Ltd.

Description: Abstract Piping has been recognized as an important geomorphic, soil erosion and hydrologic process. It seems that it is far more widespread than it has often been supposed. However, our knowledge about piping dynamics and its quantification currently relies on a limited number of data for mainly loess‐derived areas and marl badlands. Therefore, this research aimed to recognize piping dynamics in mid‐altitude mountains under a temperate climate, where piping occurs in Cambisols, not previously considered as piping‐prone soils. It has been expressed by the estimation of erosion rates due to piping and elongation of pipes in the Bereźnica Wyżna catchment in the Bieszczady Mountains, eastern Carpathians (305 ha, 188 collapsed pipes). The research was based on the monitoring of selected piping systems (1971–1974, 2013–2016). Changes in soil loss vary significantly between different years (up to 27.36 t ha−1 yr−1), as well as between the mean short‐term erosion rate (up to 13.10 t ha−1 yr−1), and the long‐term (45 years) mean of 1.34 t ha−1 yr−1. The elongation of pipes also differs, from no changes to 36 m during one year. The mean total soil loss is 48.8 t ha−1 in plots, whereas in the whole studied catchment it is 2.0 t ha−1. Hence, piping is both spatially and temporally dependent. The magnitude of piping in the study area is at least three orders of magnitude higher than surface erosion rates (i.e. sheet and rill erosion) under similar land use (grasslands), and it is comparable to the magnitude of surface soil erosion on arable lands. It means that piping constitutes a significant environmental problem and, wherever it occurs, it is an important, or even the main, sediment source. Copyright © 2017 John Wiley & Sons, Ltd.

Description: Abstract This paper reports on a first attempt of using the virtual velocity approach to assess sediment mobility and transport in two wide and complex gravel‐bed rivers of northern Italy. Displacement length and virtual velocity of spray‐painted tracers were measured in the field. Also, the thickness of the sediment active layer during floods was measured using scour chains and post‐flood morphological changes as documented by repeated survey of channel cross‐sections. The effects of eight and seven floods were studied on the Tagliamento and Brenta Rivers, where 259 and 277 spray‐painted areas were surveyed, respectively. In the Tagliamento River 36% of the spray‐painted areas experienced partial transport, whereas in the Brenta River this accounted for 20%. Whereas, full removal/gravel deposition was observed on 37% and 26% of these areas on the Tagliamento and Brenta Rivers, respectively. The mean displacement length of particles, the thickness of the active layer and the extent of partial transport are well correlated with the dimensionless shear stress. The virtual velocity approach allowed calculation of bed material transport over a wide range of flood magnitudes. Annual coarse sediment transport was calculated up to 150 for the Tagliamento, and 30 × 103  m3 yr−1 for the Brenta. The outcomes of this work highlight the relevance of partial transport condition, as it could represent more than 70% of the total bed material transported during low‐magnitude floods, and up to 40% for near‐bankfull events. Results confirm that bed material load tends to be overestimated by traditional formulas. Copyright © 2016 John Wiley & Sons, Ltd.

Description: Abstract During floods, large quantities of wood can be mobilized and transported downstream. At critical sections, such as bridges, the transported wood might be entrapped and a quick succession of backwater effects can occur as a result of the reduction of the cross‐sectional area. The aim of this work is to explore large wood‐related hazards during floods in the gravel‐bed river Czarny Dunajec (Polish Carpathians), where the river flows through the village of Długopole. This work is based on the numerical modelling of large wood transport together with flow dynamics in which inlet and boundary conditions were designed based on field observations. The exploratory approach developed in this study uses multiple scenarios (193) to analyse the factors controlling bridge clogging: wood size, wood supply, flow conditions, morphology and obstacles in the riverbed. Results highlighted the strong control of log length (stronger than that of log diameter) on potential blockage probability; however, according to our results the main factor controlling bridge clogging was the flood discharge. River morphology and wood supply play an important role as well. The river morphology may reduce bridge blockage, as it influences flow velocity and depth, and creates natural retention zones for wood. In addition, the impacts of bridge blockage were analysed in terms of afflux depth and length, and flooded area. Results showed that bridge blockage may result in a significant increase in water depth (up to 0.7 m) and flooded area (up to 33% more), therefore increasing flood risk in the village. Copyright © 2016 John Wiley & Sons, Ltd.

Description: Abstract Regulated rivers generally incise below dams that cut off sediment supply, but how that happens and what the consequences are at different spatial scales is poorly understood. Modern topographic mapping at meter‐scale resolution now enables investigation of the details of spatial processes. In this study, spatial segregation was applied to a meter‐scale raster map of topographic change from 1999 to 2008 on the gravel‐cobble, regulated lower Yuba River in California to answer specific scientific questions about how a decadal hydrograph that included a flood peak of 22 times bankfull discharge affected the river at segment, reach, and morphological unit scales. The results show that the river preferentially eroded sediment from floodplains compared to the channel, and this not only promoted valley‐wide sediment evacuation, but also facilitated the renewal and differentiation of morphological units, especially in the channel. At the reach scale, area of fill and mean net rate of elevational change were directly correlated with better connectivity between the channel and floodplain, while the mean rate of scour in scour areas was influenced by the ratio of slope to bankfull Froude number, a ratio indicative of lateral migration versus vertical downcutting. Hierarchical segregation of topographic change rasters proved useful for understanding multi‐scalar geomorphic dynamics. Copyright © 2016 John Wiley & Sons, Ltd.

Description: The potato cyst nematodes Globodera pallida and G. rostochiensis are economically important plant pathogens causing losses to UK potato harvests estimated at £50m/ year. Implications of climate change on their future pest status have not been fully considered. Here, we report growth of female G. pallida and G. rostochiensis over the range 15 to 25 °C. Females per plant and their fecundity declined progressively with temperatures above 17.5 °C for G. pallida , whilst females per plant were optimal between 17.5 and 22.5 °C for G. rostochiensis . Relative reproductive success with temperature was confirmed on two potato cultivars infected with either species at 15, 22.5 and 25 °C. The reduced reproductive success of G. pallida at 22.5 °C relative to 15 °C was also recorded for a further seven host cultivars studied. The differences in optimal temperatures for reproductive success may relate to known differences in the altitude of their regions of origin in the Andes. Exposure of G. pallida to a diurnal temperature stress for one week during female growth significantly suppressed subsequent growth for one week at 17.5 °C but had no effect on G. rostochiensis . However, after two weeks of recovery female size was not significantly different from that for the control treatment. Future soil temperatures were simulated for medium and high emissions scenarios and combined with nematode growth data to project future implications of climate change for the two species. Increased soil temperatures associated with climate change may reduce the pest status of G. pallida but benefit G. rostochiensis especially in southern UK. We conclude that plant breeders may be able to exploit the thermal limits of G. pallida by developing potato cultivars able to grow under future warm summer conditions. Existing widely deployed resistance to G. rostochiensis is an important characteristic to retain for new potato cultivars. This article is protected by copyright. All rights reserved.

Description: ABSTRACT Hydrology has advanced considerably as a scientific discipline since its recognized inception in the mid-20th century. Modern water resource related questions have forced adaptation from exclusively physical or engineering science viewpoints toward a deliberate interdisciplinary context. Over the past few decades, many of the eventual manifestations of this evolution were foreseen by prominent expert hydrologists. However, their narrative descriptions have lacked substantial quantification. This study addressed that gap by measuring the prevalence of and analyzing the relationships between the terms most frequently used by hydrologists to define and describe their research. We analyzed 16,591 journal article titles from 1965-2015 in Water Resources Research , through which the scientific dialogue and its time-sensitive progression emerged. Our word frequency and term co-occurrence network results revealed the dynamic timing of the lateral movement of hydrology across multiple disciplines as well as the deepening of scientific discourse with respect to traditional hydrologic questions. The conversation among water resource scientists surrounding the hydrologic sub-disciplines of catchment-hydrology, hydro-meteorology, socio-hydrology, hydro-climatology and eco-hydrology all gained statistically significant momentum in the analyzed time period, while hydro-geology and contaminant-hydrology experienced periods of increase followed by significant decline. This study concludes that formerly exotic disciplines can potentially modify hydrology, prompting new insights and inspiring unconventional perspectives on old questions that may have otherwise become obsolete. This article is protected by copyright. All rights reserved.

Description: Threshold estimation in the Peaks Over Threshold (POT) method, and the impact of the estimation method on the calculation of high return period quantiles and their uncertainty (or confidence intervals) are issues that are still unresolved. In the past, methods based on goodness-of-fit tests and EDF-statistics have yielded satisfactory results, but their use has not yet been systematized. This paper proposes a methodology for automatic threshold estimation, based on the Anderson-Darling EDF-statistic and goodness-of-fit test. When combined with bootstrapping techniques, this methodology can be used to quantify both the uncertainty of threshold estimation and its impact on the uncertainty of high return period quantiles. This methodology was applied to several simulated series and to four precipitation/riverflow data series. The results obtained confirmed its robustness. For the measured series, the estimated thresholds corresponded to those obtained by non-automatic methods. Moreover, even though the uncertainty of the threshold estimation was high, this did not have a significant effect on the width of the confidence intervals of high return period quantiles. This article is protected by copyright. All rights reserved.

Description: Multiple domain evaluation of watershed hydrology models Karthik Kumarasamy and Patrick Belmont Hydrol. Earth Syst. Sci. Discuss., doi:10.5194/hess-2017-121,2017 Manuscript under review for HESS (discussion: open, 0 comments) Watershed scale models simulating hydrology and water quality have advanced rapidly in sophistication. Given the importance of these models to support decision-making for a wide range of environmental issues, the hydrology community is compelled to improve the metrics used to evaluate model performance. We introduce a suite of new tools and metrics for model evaluation. We propose general guidelines for selecting parameters that should be included for matching predicted flow with measured flow.

Description: 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.

Description: Moment-based Metrics for Global Sensitivity Analysis of Hydrological Systems Aronne Dell'Oca, Monica Riva, and Alberto Guadagnini Hydrol. Earth Syst. Sci. Discuss., doi:10.5194/hess-2017-90,2017 Manuscript under review for HESS (discussion: open, 0 comments) We propose new metrics to assist global sensitivity analysis of Earth systems. Our approach allows assessing the impact of model parameters on the first four statistical moments of a target model output, allowing to ascertain which parameters can affect some moments of the model output pdf while being uninfluential to others. Our approach is fully compatible with analysis in the context of model complexity reduction, design of experiment, uncertainty quantification and risk assessment.

Description: Risk assessment of liquefaction-induced hazards using Bayesian network based on standard penetration test data Xiao-Wei Tang, Jiang-Nan Qiu, and Ji-Lei Hu Nat. Hazards Earth Syst. Sci. Discuss., doi:10.5194/nhess-2017-80,2017 Manuscript under review for NHESS (discussion: open, 0 comments) Liquefaction-induced hazards are responsible for considerable damages to engineering structures during major earthquakes. Presently, there is not any effective empirical approach that can assess different liquefaction-induced hazards in one model, such as sand boils, ground cracks, settlement, and lateral spreading, due to the uncertainties and complexity of multiple related factors of seismic liquefaction and liquefaction-induced hazards. This study used Bayesian network method to integrate multiple important factors of seismic liquefaction, sand boils, ground cracks, settlement and lateral spreading into a model based on standard penetration test historical data, so that the constructed Bayesian network model can assess the four different liquefaction-induced hazards together for free fields. In the study case, compared with the artificial neural network technology and the Ishihara and Yoshimine simplified method, the Bayesian network method performed a better classification ability, because its prediction probabilities of Accuracy , Brier score , Recall , Precision , and area under the curve of receiver operating characteristic ( AUC of ROC ) are better, which illustrated that the Bayesian network method is a good alternative tool for risk assessment of liquefaction-induced hazards. Furthermore, the performances of the application of the BN model in estimating liquefaction-induced hazards in the Japan's Northeast Pacific Offshore Earthquake also prove the correctness and reliability of it compared with the liquefaction potential index approach. Except for assessing the severity of hazards induced by soil liquefaction, the proposed Bayesian network model can also predict whether the soil is liquefied or not after an earthquake, and it can deduce the process of a chain reaction of the liquefaction-induced hazards and do backward reasoning, the assessment results from the proposed model could provide informative guidelines for decision-makers to detect damage state of a field induced by liquefaction.

Description: Variable displacement vane pumps are used in a variety of applications, most prominently in the context of modern automotive vehicles. Minimal models capturing the main dynamic effects of such pumps have remained scarce. In this contribution, a minimal model taking into account the force effects from line pressure exposure and dead volume compression and expansion is presented. The pump model is autonomous and allows for a simple integration in simulation models for which an example in the form of a non-smooth hydraulic circuit is given. (© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

Description: In this contribution, the LuGre model is extended and the effect of frictional aging is incorporated using the state variable approach. The adapted friction model is used in combination with a single-degree-of-freedom oscillator to investigate the basic effects on the stick-slip amplitude and period. (© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

Description: The response of hillslope processes to changes in precipitation may drive the observed changes in the solute geochemistry of rivers with discharge. This conjecture is most robust when variations in the key environmental factors that affect hillslope processes (e.g., lithology, erosion rate, and climate) are minimal across a river's catchment area. For rivers with heterogenous catchments, temporal variations in the relative contributions of different tributary sub-catchments may modulate variations in solute geochemistry with runoff. In the absence of a dense network of hydrologic gauging stations, alternative approaches are required to distinguish between the different drivers of temporal variability in river solute concentrations. In this contribution, we apportion the water and solute fluxes of a reach of the Madre de Dios River (Peru) between its four major tributary sub-catchments during two sampling campaigns (wet and dry seasons) using spatial variations in conservative tracers. Guided by the results of a mixing model, we identify temporal variations in solute concentrations of the mainstem Madre de Dios that are due to changes in the relative contributions of each tributary. Our results suggest that variations in tributary mixing are, in part, responsible for the observed concentration-discharge (C-Q) relationships. The implications of these results are further explored by re-analyzing previously published C-Q data from this region, developing a theoretical model of tributary mixing, and, in a companion paper, comparing the C-Q behavior of a suite of major and trace elements in the Madre de Dios River system. This article is protected by copyright. All rights reserved.

Description: Solving inverse problems in a complex, geologically realistic, and discrete model space and from a sparse set of observations is a very challenging task. Extensive exploration by Markov chain Monte Carlo (McMC) methods often results in considerable computational efforts. Most optimization methods, on the other hand, are limited to linear (continuous) model spaces and the minimization of an objective function, what often proves to be insufficient. To overcome these problems, we propose a new ensemble based exploration scheme for geostatistical prior models generated by a multiple-point statistics (MPS) tool. The principle of our method is to expand an existing set of models by using posterior facies information for conditioning new MPS realizations. The algorithm is independent of the physical parametrization. It is tested on a simple synthetic inverse problem. When compared to two existing McMC methods (Iterative Spatial Resampling (ISR) and Interrupted Markov chain Monte Carlo (IMcMC)) the required number of forward model runs was divided by a factor of 8-12. This article is protected by copyright. All rights reserved.

Description: Although vegetation is present in many rivers, the bulk of past work concerned with modeling the influence of vegetation on flow has considered vegetation to be morphologically simple, and has generally neglected the complexity of natural plants. Here we report on a combined flume and numerical model experiment which incorporates time-averaged plant posture, collected through Terrestrial Laser Scanning, into a Computational Fluid Dynamics model to predict flow around a submerged riparian plant. For three depth-limited flow conditions (Reynolds number = 65 000 – 110 000), plant dynamics were recorded through high-definition video imagery, and the numerical model was validated against flow velocities collected with an acoustic Doppler velocimeter. The plant morphology shows an 18% reduction in plant height and a 14% increase in plant length, compressing and reducing the volumetric canopy morphology as the Reynolds number increases. Plant shear layer turbulence is dominated by Kelvin–Helmholtz type vortices generated through shear instability, the frequency of which is estimated to be between 0.20 and 0.30 Hz, increasing with Reynolds number. These results demonstrate the significant effect that the complex morphology of natural plants has on in-stream drag, and allows a physically determined, species-dependent drag coefficient to be calculated. Given the importance of vegetation in river corridor management, the approach developed here demonstrates the necessity to account for plant motion when calculating vegetative resistance. This article is protected by copyright. All rights reserved.

Description: The vast majority of continental sediment delivered to the world's oceans moves by suspension in rivers. Depth- or point-integrated bottle sampling are the traditional methods used to determine the mean concentration of suspended sediment in rivers. While there has been some investigation of the error associated with depth-integrated sampling, the representativeness of a point-integrated bottle sample has not been addressed in the literature. Here, we analyze continuous hour-long measurements of suspended sediment and grain size fractions collected using a LISST-SL in the sand-bed portion of the Fraser River, British Columbia to determine an appropriate sampling time. The 2σ uncertainty range of individual 30 s samples varied from ±3% to ±33% about the observed mean, with a systematic increase toward the streambed. Mean concentrations for suspended sediment and grain size fractions were computed over increasing time periods and compared with a long duration mean concentration to determine when a sample becomes representative. A cumulative probability distribution was generated from multiple iterations of this process. All suspended sediment load and grain size fractions bear a low probability of representing the actual mean concentration over standard bottle sample durations. A probability 〉90% of representing the mean concentration and grain-size of various fractions requires ∼570 seconds (9.5 minutes) of sampling. Sampling for a shorter period of 264 seconds (4.4 minutes) can yield a sample with 73% probability of representing the mean concentration. This article is protected by copyright. All rights reserved.

Description: Variations in riverine solute chemistry with changing runoff are used to interrogate catchment hydrology and to investigate chemical reactions in Earth's critical zone. This approach requires some understanding of how spatial and temporal averaging of solute-generating reactions affect the dissolved load of rivers and streams. In this study, we investigate the concentration-runoff (C-Q) dynamics of a suite of major (Na, Mg, Ca, Si, K, and SO 4 ) and trace (Al, Ba, Cd, Co, Cr, Cu, Fe, Ge, Li, Mn, Mo, Nd, Ni, Rb, Sr, U, V, and Zn) elements in nested catchments of variable size, spanning the geomorphic gradient from the Andes mountains to the Amazon foreland-floodplain. The major elements exhibit various degrees of dilution with increasing runoff at all sites, whereas the concentrations of most trace elements either increase or show no relationship with increasing runoff in the three larger catchments (160 to 28 000 km 2 area). We show that the observed mainstem C-Q dynamics are influenced by variable mixing of tributaries with distinct C-Q relationships. Trace element C-Q relationships are more variable among tributaries relative to major elements, which could be the result of variations in geomorphology, lithology, and hydrology of the sub-catchments. Certain trace metals are also lost from solution during in-channel processes (possibly related to colloidal size-partitioning), which may exert an additional control on C-Q dynamics. Overall, we suggest that aggregation effects should be assessed in heterogeneous catchments before C-Q or ratio-Q relationships can be interpreted as reflecting catchment-wide solute generation processes and their relationship to hydrology. This article is protected by copyright. All rights reserved.

Description: 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.

Description: 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.

Description: 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.

Description: 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.

Description: 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.

Description: 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.

Description: No agreement on what constitutes a safe and reproducible anticontamination protocol exists for ancient starch research. Protocols applied to laboratory work may represent ‘symptomatic treatment’ only, as contamination of archaeological materials in the field may be more extensive than realized. This paper is the first systematic study on the impact that modern starches from surface and buried soils, windborne dispersal, human motion, excavation techniques and toolkits, and field attire has on archaeological sample quality. The study area is Olduvai Gorge, Tanzania. We identify seven starch types (discrete granules, n = 788) that embody the starch contamination landscape for the region. This study also demonstrates the various diagenetic changes that buried starch granules undergo in a short time, such as cavitation, fissuring, disruption and gelatinization. There are significant differences in morphotype class representation between the topsoil starches and those collected deeper below ground at excavated sites. Diagenetically transformed granules from underground storage organs dominate in soils, while native starches from cereal endosperm (Panicoideae and Triticeae) abound above ground in airborne samples. Furthermore, we illustrate how lithic samples excavated under standard field conditions can be contaminated, and that when a sample is compromised during excavation, it may be impossible to distinguish between target and introduced starches, especially when granules are identical or morphologically similar. The paper provides field recommendations to control false positives.

Description: A total of three binary tropical cyclone (TC) cases over the west North Pacific are selected to investigate the effects of satellite radiance data assimilation on analyses and forecasts of binary TCs. Two parallel cycling experiments with a 6-h interval are performed for each binary TC case, and the difference between the two experiments is whether satellite radiance observations are assimilated. Satellite radiance observations are assimilated using the Weather Research and Forecasting Data Assimilation (WRFDA)'s three dimensional variational (3D-Var) system, which includes the observation operator, quality control procedures, and bias correction algorithm for radiance observations. On average, radiance assimilation results in slight improvements of environmental fields and track forecasts of binary TC cases, but the detailed effects vary with the case. When there is no direct interaction between binary TCs, radiance assimilation leads to better depictions of environmental fields, and finally it results in improved track forecasts. However, positive effects of radiance assimilation on track forecasts can be reduced when there exists a direct interaction between binary TCs and intensities/structures of binary TCs are not represented well. An initialization method (e.g. dynamic initialization) combined with radiance assimilation and/or more advanced DA techniques (e.g. hybrid method) can be considered to overcome these limitations. This article is protected by copyright. All rights reserved.

Description: The phenology of diameter-growth cessation in trees will likely play a key role in mediating species and ecosystem responses to climate change. A common expectation is that warming will delay cessation, but the environmental and genetic influences on this process are poorly understood. We modeled the effects of temperature, photoperiod and seed-source climate on diameter-growth cessation timing in coast Douglas-fir (an ecologically and economically vital tree) using high-frequency growth measurements across broad environmental gradients for a range of genotypes from different seed sources. Our model suggests that cool temperatures or short photoperiods can induce cessation in autumn. At cool locations (high latitude and elevation), cessation seems to be induced primarily by low temperatures in early autumn (under relatively long photoperiods), so warming will likely delay cessation and extend the growing season. But at warm locations (low latitude or elevation), cessation seems to be induced primarily by short photoperiods later in autumn, so warming will likely lead to only slight extensions of the growing season, reflecting photoperiod limitations on phenological shifts. Trees from seed sources experiencing frequent frosts in autumn or early winter tended to cease growth earlier in the autumn, potentially as an adaptation to avoid frost. Thus, gene flow into populations in warm locations with little frost will likely have limited potential to delay mean cessation dates because these populations already cease growth relatively late. In addition, data from an abnormal heat wave suggested that very high temperatures during long photoperiods in early summer might also induce cessation. Climate change could make these conditions more common in warm locations, leading to much earlier cessation. Thus, photoperiod cues, patterns of genetic variation and summer heat waves could limit the capacity of coast Douglas-fir to extend its growing season in response to climate change in the warm parts of its range. This article is protected by copyright. All rights reserved.

Description: Seasonal forecasting of hydrological drought in the Limpopo Basin: a comparison of statistical methods Mathias Seibert, Bruno Merz, and Heiko Apel Hydrol. Earth Syst. Sci., 21, 1611-1629, doi:10.5194/hess-21-1611-2017, 2017 Seasonal early warning is vital for drought management in arid regions like the Limpopo Basin in southern Africa. This study shows that skilled seasonal forecasts can be achieved with statistical methods built upon driving factors for drought occurrence. These are the hydrological factors for current streamflow and meteorological drivers represented by anomalies in sea surface temperatures of the surrounding oceans, which combine to form unique combinations in the drought forecast models.

Description: A sprinkling experiment to quantify celerity-velocity differences at the hillslope scale Willem J. van Verseveld, Holly R. Barnard, Chris B. Graham, Jeffrey J. McDonnell, J. Renée Brooks, and Markus Weiler Hydrol. Earth Syst. Sci. Discuss., doi:10.5194/hess-2017-125,2017 Manuscript under review for HESS (discussion: open, 0 comments) How stream water responds immediately to a rainfall or snow event while the average time it takes water to travel through the hillslope can be years or decades, is poorly understood. We assessed this difference by combining a 24 day sprinkler experiment (a tracer was applied at the start) with a process based hydrologic model. Immobile soil water, deep groundwater contribution and soil depth variability explained this difference at our hillslope site.

Description: Groundwater impacts on surface water quality and nutrient loads in lowland polder catchments: monitoring the greater Amsterdam area Liang Yu, Joachim Rozemeijer, Boris M. van Breukelen, Maarten Ouboter, Corné van der Vlugt, and Hans Peter Broers Hydrol. Earth Syst. Sci. Discuss., doi:10.5194/hess-2017-99,2017 Manuscript under review for HESS (discussion: open, 0 comments) The study shows the importance of the connection between groundwater and surface water nutrient chemistry in a lowland delta area – the greater Amsterdam area. We expect that taking account of groundwater-surface water interaction is also important in other subsiding and urbanising deltas around the world, where water is managed intensively in order to enable agricultural productivity and achieve water sustainable cities.

Description: Parameter optimisation for a better representation of drought by LSMs: inverse modelling vs. sequential data assimilation Hélène Dewaele, Simon Munier, Clément Albergel, Carole Planque, Nabil Laanaia, Dominique Carrer, and Jean-Christophe Calvet Hydrol. Earth Syst. Sci. Discuss., doi:10.5194/hess-2017-120,2017 Manuscript under review for HESS (discussion: open, 0 comments) Soil Maximum Available Water Content (MaxAWC) is a key parameter in land surface models. Being difficult to measure, this parameter is usually unavailable. A fifteen-year time-series of satellite-derived observations of Leaf Area Index (LAI) is used to retrieve MaxAWC for rainfed croplands over France. LAI is sequentially assimilated into the ISBA LSM. MaxAWC is retrieved minimizing LAI analyses increments. Annual maximum LAI observations correlate with MaxAWC.

Description: 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.

Description: 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.

Description: Because the capability of terrestrial ecosystems to fix carbon is constrained by nutrient availability, understanding how nutrients limit plant growth is a key contemporary question. However, what drives nutrient limitations at global scale remains to be clarified. Using global data on plant growth, plant nutritive status, and soil fertility, we investigated to which extent soil parent materials explain nutrient limitations. We found that N limitation was not linked to soil parent materials, but was best explained by climate: ecosystems under harsh (i.e. cold and or dry) climates were more N-limited than ecosystems under more favourable climates. Contrary to N limitation, P limitation was not driven by climate, but by soil parent materials. The influence of soil parent materials was the result of the tight link between actual P pools of soils and physical-chemical properties (acidity; P richness) of soil parent materials. Some other ground-related factors (i.e. soil weathering stage, landform) had a noticeable influence on P limitation, but their role appeared to be relatively smaller than that of geology. The relative importance of N limitation versus P limitation was explained by a combination of climate and soil parent material: at global scale, N limitation became prominent with increasing climatic constraints, but this global trend was modulated at lower scales by the effect of parent materials on P limitation, particularly under climates favourable to biological activity. As compared with soil parent materials, atmospheric deposition had only a weak influence on the global distribution of actual nutrient limitation. Our work advances our understanding of the distribution of nutrient limitation at global scale. In particular, it stresses the need to take soil parent materials into account when investigating plant growth response to environment changes. This article is protected by copyright. All rights reserved.

Description: Analysis of streamflow response to land use land cover changes using satellite data and hydrological modelling: case study of Dinder and Rahad tributaries of the Blue Nile (Ethiopia/Sudan) Khalid Hassaballah, Yasir Mohamed, Stefan Uhlenbrook, and Khalid Biro Hydrol. Earth Syst. Sci. Discuss., doi:10.5194/hess-2017-128,2017 Manuscript under review for HESS (discussion: open, 0 comments) The Dinder and Rahad experienced significant hydrological changes during recent years. This is claimed to be due to land use land cover changes (LULCC). Specific studies on LULCC in the Dinder and Rahad basins are still missing. This paper aims to understand the LULCC in the Dinder and Rahad and its implications on streamflow using satellite data and hydrological modelling. We expect that this study will be of high importance for decision making related to water resources planning and management.

Description: A conceptual prediction model of seasonal drought processes using atmospheric and oceanic Standardized Anomalies: application in four recent severe drought events in China Zhenchen Liu, Guihua Lu, Hai He, Zhiyong Wu, and Jian He Hydrol. Earth Syst. Sci. Discuss., doi:10.5194/hess-2017-136,2017 Manuscript under review for HESS (discussion: open, 0 comments) Process prediction of seasonal drought is the goal of our study. We developed a drought prediction model based on atmospheric/oceanic anomalies. It is essentially the synchronous statistical relationship between atmospheric/oceanic anomalies and precipitation anomalies, forced by seasonal climate forecast models. It can predict seasonal drought development very well, despite its weakness in drought severity.

Description: 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.

Description: A national-scale seasonal hydrological forecast system: development and evaluation over Britain Victoria A. Bell, Helen N. Davies, Alison L. Kay, Anca Brookshaw, and Adam A. Scaife Hydrol. Earth Syst. Sci. Discuss., doi:10.5194/hess-2017-154,2017 Manuscript under review for HESS (discussion: open, 0 comments) The research presented here provides the first evaluation of the skill of a seasonal hydrological forecast for the UK. The forecast scheme combines rainfall forecasts from the Met Office GloSea5 forecast system with a national-scale hydrological model to provide estimates of river flows 1 to 3 months ahead. The skill in the combined model is assessed for different seasons and regions of Britain, and the analysis indicates that Autumn/Winter flows can be forecast with reasonable confidence.

Description: A national-scale seasonal hydrological forecast system: development and evaluation over Britain Victoria A. Bell, Helen N. Davies, Alison L. Kay, Anca Brookshaw, and Adam A. Scaife Hydrol. Earth Syst. Sci. Discuss., doi:10.5194/hess-2017-154,2017 Manuscript under review for HESS (discussion: open, 0 comments) The research presented here provides the first evaluation of the skill of a seasonal hydrological forecast for the UK. The forecast scheme combines rainfall forecasts from the Met Office GloSea5 forecast system with a national-scale hydrological model to provide estimates of river flows 1 to 3 months ahead. The skill in the combined model is assessed for different seasons and regions of Britain, and the analysis indicates that Autumn/Winter flows can be forecast with reasonable confidence.

Description: High-magnitude flooding across Britain since AD 1750 Neil Macdonald and Heather Sangster Hydrol. Earth Syst. Sci., 21, 1631-1650, doi:10.5194/hess-21-1631-2017, 2017 We use historical records to extend current understanding of flood risk, examining past spatial and temporal variability and ask are the perceived high-magnitude flood events witnessed in recent years really unprecedented? We identify that there are statistically significant relationships between the British flood index and climatic drivers, whereby the largest floods often transcend single catchments affecting regions and that the current flood-rich period is not unprecedented.

Description: A conceptual prediction model of seasonal drought processes using atmospheric and oceanic Standardized Anomalies: application in four recent severe drought events in China Zhenchen Liu, Guihua Lu, Hai He, Zhiyong Wu, and Jian He Hydrol. Earth Syst. Sci. Discuss., doi:10.5194/hess-2017-136,2017 Manuscript under review for HESS (discussion: open, 0 comments) Process prediction of seasonal drought is the goal of our study. We developed a drought prediction model based on atmospheric/oceanic anomalies. It is essentially the synchronous statistical relationship between atmospheric/oceanic anomalies and precipitation anomalies, forced by seasonal climate forecast models. It can predict seasonal drought development very well, despite its weakness in drought severity.

Description: Analysis of streamflow response to land use land cover changes using satellite data and hydrological modelling: case study of Dinder and Rahad tributaries of the Blue Nile (Ethiopia/Sudan) Khalid Hassaballah, Yasir Mohamed, Stefan Uhlenbrook, and Khalid Biro Hydrol. Earth Syst. Sci. Discuss., doi:10.5194/hess-2017-128,2017 Manuscript under review for HESS (discussion: open, 0 comments) The Dinder and Rahad experienced significant hydrological changes during recent years. This is claimed to be due to land use land cover changes (LULCC). Specific studies on LULCC in the Dinder and Rahad basins are still missing. This paper aims to understand the LULCC in the Dinder and Rahad and its implications on streamflow using satellite data and hydrological modelling. We expect that this study will be of high importance for decision making related to water resources planning and management.

Description: High-magnitude flooding across Britain since AD 1750 Neil Macdonald and Heather Sangster Hydrol. Earth Syst. Sci., 21, 1631-1650, doi:10.5194/hess-21-1631-2017, 2017 We use historical records to extend current understanding of flood risk, examining past spatial and temporal variability and ask are the perceived high-magnitude flood events witnessed in recent years really unprecedented? We identify that there are statistically significant relationships between the British flood index and climatic drivers, whereby the largest floods often transcend single catchments affecting regions and that the current flood-rich period is not unprecedented.

Description: 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.

Description: 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.

Description: Community-based early warning systems for flood risk mitigation in Nepal Paul J. Smith, Sarah Brown, and Sumit Dugar Nat. Hazards Earth Syst. Sci., 17, 423-437, doi:10.5194/nhess-17-423-2017, 2017 Risks from flooding are of global importance. Experience gained in Nepal is presented to demonstrate that empowering the communities impacted by flooding to be active participants in risk mitigation can have significant positive impacts. In part this is achieved through community involvement in the provision of warnings based on observations of river flow upstream. The success of simple, robust methodology for the early provision of such warnings based on predicting future river flows is shown.

Description: An operational system for producing a global diurnally varying analysis of skin Sea Surface Temperature (SST) has been developed at the Met Office. Skin SST is formulated as the sum of a foundation temperature, a warm layer temperature difference, and a thermal skin temperature difference. Foundation temperature is taken from the Operational Sea surface Temperature and sea Ice Analysis (OSTIA) system, while numerical models are used for the warm layer and thermal skin layer. Both the thermal skin layer and warm layer models are forced using outputs from the Met Office's numerical weather prediction system. Data assimilation is used to improve estimates of the warm layer, with observations coming from the geostationary SEVIRI and GOES-W instruments, as well as the polar orbiting NOAA-AVHRR sensors. The SST observations of these instruments are converted to observations of the warm layer temperature difference by subtracting an instrument specific foundation SST calculated using just night time data from that sensor. A quality control procedure removes warm layer observations where the satellite specific foundation estimates are less robust due to lack of data. Validation of the analysis system has been performed by comparing the model to the assimilated satellite data, and to independent near-surface observations from Argo floats. The mean state of the system was assessed via a comparison to a climatology generated from drifting buoys. Results from the validation show that the system does a good job of replicating the climatology and that assimilation improves the analysis when assessed against Argo. However, the system has been found to underestimate the diurnal range of skin SST by approximately 0.1-0.3 ° C on average. Data from the system is available free of charge from the Copernicus Marine Environment Monitoring Service.

Description: Ensemble methods are an attractive option for data assimilation (DA) in convection-permitting models, providing flow-dependent covariances which respect the complex balances that apply at these scales. The Met Office deterministic UK forecast currently uses variational assimilation based on predominantly climatological covariances, whilst the MOGREPS-UK ensemble interpolates its initial perturbations from the corresponding global members. An experimental convective-scale ensemble DA system has now been built based on a serial ensemble filter, where observations are assimilated sequentially. This has been tested in a series of one-month trials assimilating sonde, surface and aircraft observations, exploring issues such as cycle length, filter type, localisation and inflation. The tests use 44 perturbed ensemble members, plus an unperturbed control forecast that is updated using the same Kalman gain as the ensemble mean. The best configurations provide control forecasts which are competitive with interpolating global initial states like MOGREPS-UK did at the time, even though the local assimilation has seen fewer observation types than the global DA. An hourly cycle performs much better than a six-hourly one, as suggested by theoretical arguments, even though both see the same boundary conditions and essentially the same total set of observations. The serial filter calculates the difference between each observation and its model equivalent as updated by all previous observations. We call this the Innovation After assimilating Prior Observations (IAPO). The mean square IAPO measures the error of the developing analysis using observations which are statistically independent of it, without the need to involve the forecast model. This diagnostic confirms the beneficial impact of assimilation, can be used to cheaply tune parameters such as localisation radii, and contributes to evaluating the correctness of the ensemble spread.

Description: The ability of a newly developed non-hydrostatic regional climate model (RCM) based on the Unified Model of the UK Met Office (MetUM) at a resolution of 12 km is examined for the simulation of tropical cyclone (TC) activity affecting the South China Sea and compared with the current released RCM version of MetUM at the resolution of 25 km. The results show that both the 25 km and 12 km models can reasonably simulate the TC-associated large-scale environments, while the 12 km model has a better ability to simulate the South Asian monsoon. Compared with the 25 km model, the 12 km model generally improves the simulation of track density and the radial wind structure of TCs. However, the annual cycle of simulated TCs show that both models tend to over-estimate the TC frequency in May and November–January while underestimating the frequency in June-September. Compared with the 25 km model, the 12 km model produces fewer intense TCs with 10 m maximum wind speeds 〉 30 m s −1 . It is also found that both the 12 km and 25 km models reproduce the observed modulation of TC activity associated with different phases of the El Niño/Southern Oscillation (ENSO) such as the reduced track density and accumulated cyclonic energy during El Niño events, while the 12 km model better captures the TC-ENSO response including the track density and the large-scale environments than the 25 km model.

Description: Agricultural land use results in multiple stressors affecting stream ecosystems. Flow reduction due to water abstraction, elevated levels of nutrients and chemical contaminants are common agricultural stressors worldwide. Concurrently, stream ecosystems are also increasingly affected by climate change. Interactions among multiple co-occurring stressors result in biological responses that cannot be predicted from single-stressor effects (i.e. synergisms and antagonisms). At the ecosystem level, multiple-stressor effects can be further modified by biotic interactions (e.g. trophic interactions). We conducted a field experiment using 128 flow-through stream mesocosms to examine the individual and combined effects of water abstraction, nutrient enrichment and elevated levels of the nitrification inhibitor dicyandiamide (DCD) on survival, condition and gut content of juvenile brown trout, and on benthic abundance of their invertebrate prey. Flow velocity reduction decreased fish survival (-12% compared to controls) and condition (-8% compared to initial condition), whereas effects of nutrient and DCD additions and interactions among these stressors were not significant. Negative effects of flow velocity reduction on fish survival and condition were consistent with effects on fish gut content (-25% compared to controls) and abundance of dominant invertebrate prey (-30%), suggesting a negative metabolic balance driving fish mortality and condition decline, which was confirmed by structural equation modelling. Fish mortality under reduced flow velocity increased as maximal daily water temperatures approached the upper limit of their tolerance range, reflecting synergistic interactions between these stressors. Our study highlights the importance of indirect stressor effects such as those transferred through trophic interactions, which need to be considered when assessing and managing fish populations and stream food webs in multiple-stressor situations. However, in real streams compensatory mechanisms, behavioural responses, as well as seasonal and spatial variation may alter the intensity of stressor effects and the sensitivity of trout populations. This article is protected by copyright. All rights reserved.

Description: 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.

Description: Heterogeneity measures in hydrological frequency analysis: review and new developments Ana I. Requena, Fateh Chebana, and Taha B. M. J. Ouarda Hydrol. Earth Syst. Sci., 21, 1651-1668, doi:10.5194/hess-21-1651-2017, 2017 The notion of a measure to quantify the degree of heterogeneity of a region from which information is required to estimate the magnitude of events at ungauged sites is introduced. These heterogeneity measures are needed to compare regions, evaluate the impact of particular sites, and rank the performance of delineating methods. A framework to define and assess their desirable properties is proposed. Several heterogeneity measures are presented and/or developed to be assessed, giving guidelines.

Description: Long-term projections of global water use for electricity generation under the Shared Socioeconomic Pathways and climate mitigation scenarios Nozomi Ando, Sayaka Yoshikawa, Shinichiro Fujimori, and Shinjiro Kanae Hydrol. Earth Syst. Sci. Discuss., doi:10.5194/hess-2017-27,2017 Manuscript under review for HESS (discussion: open, 0 comments) Electricity generation may become a key factor that accelerates water scarcity. In this study, we estimated the future global water use for electricity generation from 2005 to 2100 in 17 global sub-regions. Consequently, We indicated that the socioeconomic changes had a larger impact on water withdrawal and consumption for electricity generation, compared with the climate mitigation changes represented by the climate mitigation scenarios.

Description: Recent changes in terrestrial water storage in the Upper Nile Basin: an evaluation of commonly used gridded GRACE products Mohammad Shamsudduha, Richard G. Taylor, Darren Jones, Laurent Longuevergne, Michael Owor, and Callist Tindimugaya Hydrol. Earth Syst. Sci. Discuss., doi:10.5194/hess-2017-146,2017 Manuscript under review for HESS (discussion: open, 0 comments) This study tests the ability of five commonly used GRACE satellite datasets to measure a large and accurately observed reduction in water storage of 75 km 3 that occurred in the Lake Victoria Basin of East Africa from 2004 to 2006. Substantial differences among the datasets to represent the amplitude of this change in the total terrestrial water storage are revealed. Resolving changes in groundwater storage specifically from GRACE data is hindered by uncertainty in simulated soil moisture data.

Description: Identification of dominant hydrogeochemical processes for groundwaters in the Algerian Sahara supported by inverse modeling of chemical and isotopic data Rabia Slimani, Abdelhamid Guendouz, Fabienne Trolard, Adnane Souffi Moulla, Belhadj Hamdi-Aïssa, and Guilhem Bourrié Hydrol. Earth Syst. Sci., 21, 1669-1691, doi:10.5194/hess-21-1669-2017, 2017 Unpublished chemical and isotopic data taken in November 1992 from the three major Saharan aquifers, namely the Continental Intercalaire (CI), the Complexe Terminal (CT) and the phreatic aquifer (Phr), were integrated with original samples in order to chemically and isotopically characterize the largest Saharan aquifer system and investigate the processes through which groundwaters acquire their mineralization. Instead of classical Debye–Hückel extended law, a specific interaction theory (SIT) model, recently incorporated in PHREEQC 3.0, was used. Inverse modeling of hydrochemical data constrained by isotopic data was used here to quantitatively assess the influence of geochemical processes: at depth, the dissolution of salts from the geological formations during upward leakage without evaporation explains the transitions from CI to CT and to a first end member, a cluster of Phr (cluster I); near the surface, the dissolution of salts from sabkhas by rainwater explains another cluster of Phr (cluster II). In every case, secondary precipitation of calcite occurs during dissolution. All Phr waters result from the mixing of these two clusters together with calcite precipitation and ion exchange processes. These processes are quantitatively assessed by the PHREEQC model. Globally, gypsum dissolution and calcite precipitation were found to act as a carbon sink.

Description: Using street view imagery for 3D survey of rock slope failures Jérémie Voumard, Antonio Abellan, Pierrick Nicolet, Marie-Aurélie Chanut, Marc-Henri Derron, and Michel Jaboyedoff Nat. Hazards Earth Syst. Sci. Discuss., doi:10.5194/nhess-2017-49,2017 Manuscript under review for NHESS (discussion: open, 0 comments) We discuss here the challenges and limitations on surveying rock slope failures using 3D reconstruction from images acquired from Street View Imagery (SVI) and processed with modern photogrammetric workflows. Despite some clear limitations and challenges, this manuscript demonstrates that this original approach might allow obtaining preliminary 3D models of an area without on-field images. Furthermore, the pre-failure topography can be obtained for sites where it would not be available otherwise.

Description: Using street view imagery for 3D survey of rock slope failures Jérémie Voumard, Antonio Abellan, Pierrick Nicolet, Marie-Aurélie Chanut, Marc-Henri Derron, and Michel Jaboyedoff Nat. Hazards Earth Syst. Sci. Discuss., doi:10.5194/nhess-2017-49,2017 Manuscript under review for NHESS (discussion: open, 0 comments) We discuss here the challenges and limitations on surveying rock slope failures using 3D reconstruction from images acquired from Street View Imagery (SVI) and processed with modern photogrammetric workflows. Despite some clear limitations and challenges, this manuscript demonstrates that this original approach might allow obtaining preliminary 3D models of an area without on-field images. Furthermore, the pre-failure topography can be obtained for sites where it would not be available otherwise.

Description: As modeling capabilities at regional and global scales improve, questions remain regarding the appropriate process representation required to accurately simulate multichannel river hydraulics. This study uses the hydrodynamic model LISFLOOD-FP to simulate patterns of water surface elevation (WSE), depth, and inundation extent across a ∼90 km, anabranching reach of the Tanana River, Alaska. To provide boundary conditions, we collected field observations of bathymetry and WSE during a two-week field campaign in summer 2013. For the first time at this scale, we test a simple, raster-based model's capabilities to simulate 2D, in-channel patterns of WSE and inundation extent. Additionally, we compare finer resolution (≤ 25 m) 2D models to four other models of lower dimensionality and coarser resolution (100–500 m) to determine the effects of simplifying process representation. Results indicate that simple, raster-based models can accurately simulate 2D, in-channel hydraulics in the Tanana. Also, the fine-resolution, 2D models produce lower errors in spatiotemporal outputs of WSE and inundation extent compared to coarse-resolution, 1D models: 22.6 cm vs. 56.4 cm RMSE for WSE, and 90% vs. 41% Critical Success Index values for simulating inundation extent. Incorporating the anabranching channel network using subgrid representations for smaller channels is important for simulating accurate hydraulics and lowers RMSE in spatially distributed WSE by at least 16%. As a result, better representation of the converging and diverging multichannel network by using subgrid solvers or downscaling techniques in multichannel rivers is needed to improve errors in regional to global scale models. This article is protected by copyright. All rights reserved.

Description: Attempts to estimate the influence of erosion on the carbon (C) cycle are limited by difficulties in accounting for the fate of mobilized organic material and for the uncertainty associated with land management practices. This study proposes a method to quantify the uncertainty introduced by the influence of land management on soil organic C (SOC) generation and decomposition at eroding soils. The framework is implemented in tRIBS-ECO (Triangulated Irregular Network-based Real-time Integrated Basin Simulator-Erosion and Carbon Oxidation). tRIBS-ECO is a spatially- and depth-explicit model of C dynamics coupled with a process-based hydro-geomorphic model. We assess the impact of soil erosion on the net soil-atmosphere CO 2 exchange at the Calhoun Critical Zone Observatory, one of the most severely agriculturally eroded regions in the U.S. Measurements of SOC storage are used from different catena positions. We demonstrate that the spatio-temporal variations of land management practices introduce significant uncertainty in estimates of the erosion-induced CO 2 exchange with the atmosphere. Observations and simulations suggest that a substantial portion of eroded organic material is buried in alluvial sediments at the study site. According to results, recent reforestation led to a partial decline in soil and SOC erosion rates. It is suggested that the representation of the fine spatio-temporal variability of the dynamics of eroded C is important in the computation of C budgets in regional and global scales. This article is protected by copyright. All rights reserved.

Description: Book review: Wildlife in the Anthropocene – Conservation after Nature Isabelle Arpin Geogr. Helv., 72, 79-80, doi:10.5194/gh-72-79-2017, 2017 No abstract available.

Description: Understanding how historical processes modulate the response of ecosystems to perturbations is becoming increasingly important. In contrast to the growing interest in projecting biodiversity and ecosystem functioning under future climate scenarios, how legacy effects originating from historical conditions drive change in ecosystems remains largely unexplored. Using experiments in combination with Stochastic Antecedent Modelling, we evaluated how extreme warming, sediment deposition and grazing events modulated the ecological memory of rocky intertidal epilithic microphytobenthos (EMPB). We found memory effects in the non-clustered scenario of disturbance (60 days apart), where EMPB biomass fluctuated in time, but not under clustered disturbances (15 days apart), where EMPB biomass was consistently low. A massive grazing event impacted on EMPB biomass in a second run of the experiment, also muting ecological memory. Our results provide empirical support to the theoretical expectation that stochastic fluctuations promote ecological memory, but also show that contingencies may lead to memory loss. This article is protected by copyright. All rights reserved.

Description: The Future of Earth Observation in Hydrology Matthew F. McCabe, Matthew Rodell, Douglas E. Alsdorf, Diego G. Miralles, Remko Uijlenhoet, Wolfgang Wagner, Arko Lucieer, Rasmus Houborg, Niko E. C. Verhoest, Trenton E. Franz, Jiancheng Shi, Huilin Gao, and Eric F. Wood Hydrol. Earth Syst. Sci. Discuss., doi:10.5194/hess-2017-54,2017 Manuscript under review for HESS (discussion: open, 0 comments) We examine the opportunities and challenges that technological advances in Earth observation will present to the hydrological community. From advanced space-based sensors, to unmanned aerial vehicles and ground-based distributed networks, these emergent systems are set to revolutionise our understanding and interpretation of hydrological and related processes.

Description: The Future of Earth Observation in Hydrology Matthew F. McCabe, Matthew Rodell, Douglas E. Alsdorf, Diego G. Miralles, Remko Uijlenhoet, Wolfgang Wagner, Arko Lucieer, Rasmus Houborg, Niko E. C. Verhoest, Trenton E. Franz, Jiancheng Shi, Huilin Gao, and Eric F. Wood Hydrol. Earth Syst. Sci. Discuss., doi:10.5194/hess-2017-54,2017 Manuscript under review for HESS (discussion: open, 0 comments) We examine the opportunities and challenges that technological advances in Earth observation will present to the hydrological community. From advanced space-based sensors, to unmanned aerial vehicles and ground-based distributed networks, these emergent systems are set to revolutionise our understanding and interpretation of hydrological and related processes.

Description: A reconstruction of 1 August 1674 thunderstorms over the Low Countries Gerard van der Schrier and Rob Groenland Nat. Hazards Earth Syst. Sci., 17, 157-170, doi:10.5194/nhess-17-157-2017, 2017 On 1 August 1674, very severe thunderstorms occurred along a squall line from northern France to the northern parts of Holland, where damages were particularly severe. Using reported and pictured observations of damages, a reconstruction of this storm is made and an interpretation using modern meteorological concepts is given. Special attention is given to the city of Utrecht, which was hit hardest and where the impact of this storm is still recognisable in the cityscape.

Description: A 3D refractive-index matching Lagrangian particle tracking (3D-RIM-LPT) system was developed to study the filtration and clogging process inside a homogeneous porous medium. A small subset of particles flowing through the porous medium was dyed and tracked. As this subset was randomly chosen, its dynamics is representative of all the rest. The statistics of particle locations, number, and velocity vectors were obtained as functions of different volumetric concentrations. It is found that, in our system, the clogging time decays with particle concentration following a power law relationship. As the concentration increases, there is a transition from depth filtration to cake filtration. At high concentration, more clogged pores lead to frequent flow redirections and more transverse migrations of particles. In addition, the velocity distribution of the transverse direction is symmetrical around zero, and it is slightly more intermittent than the random Gaussian curve due to particle-particle interactions and particle-grain interactions. In contrast, as clogging develops, the longitudinal velocity of particles along the main flow direction has peak near zero because of those trapped particles. But at the same time, the remaining open pores will experience larger pressure and, as a result, particles through those pores will have a larger longitudinal velocity. This article is protected by copyright. All rights reserved.

Description: Precipitation patterns are changing across the globe causing more severe and frequent drought for many forest ecosystems. Although research has focused on the resistance of tree populations and communities to these novel precipitation regimes, resilience of forests is also contingent on recovery following drought, which remains poorly understood, especially in aseasonal tropical forests. We used rainfall exclusion shelters to manipulate the inter-annual frequency of drought for diverse seedling communities in a tropical forest and assessed resistance, recovery and resilience of seedling growth and mortality relative to everwet conditions. We found seedlings exposed to recurrent periods of drought altered their growth rates throughout the year relative to seedlings in everwet conditions. During drought periods seedlings grew slower than seedlings in everwet conditions (i.e. resistance phase) while compensating with faster growth after drought (i.e. recovery phase). However, the response to frequent drought was species dependent as some species grew significantly slower with frequent drought relative to everwet conditions while others grew faster with frequent drought due to overcompensating growth during the recovery phase. In contrast, mortality was unrelated to rainfall conditions and instead correlated with differences in light. Intra-annual plasticity of growth and increased annual growth of some species led to an overall maintenance of growth rates of tropical seedling communities in response to more frequent drought. These results suggest these communities can potentially adapt to predicted climate change scenarios and that plasticity in the growth of species, and not solely changes in mortality rates among species, may contribute to shifts in community composition under drought. This article is protected by copyright. All rights reserved.

Description: Soil Moisture Estimation Based on Probabilistic Inversion over Heterogeneous Vegetated Fields Using Airborne PLMR Brightness Temperature Chunfeng Ma, Xin Li, and Shuguo Wang Hydrol. Earth Syst. Sci. Discuss., doi:10.5194/hess-2017-34,2017 Manuscript under review for HESS (discussion: open, 0 comments) We present a SM estimation based on the combination of Bayesian probabilistic inversion with airborne L‐band radiometer observations. The work has obtained a desirable SM estimation and uncertainty quantification, which may offer an insight into the future SM inversion based on passive microwave remote sensing.

Description: A GIS-based monitoring and early warning system for cover-collapse sinkholes in karst terrane in Wuhan, China Li Xueping, Xiao Shangde, Tang Huiming, and Peng Jinsheng Nat. Hazards Earth Syst. Sci. Discuss., doi:10.5194/nhess-2017-22,2017 Manuscript under review for NHESS (discussion: open, 0 comments) A GIS-based monitoring and early warning system for cover-collapse sinkholes in karst terrane in Wuhan, China has been established so as to reduce disastrous losses caused by karst collapse. Three types warning criteria for cover-collapse sinkholes has been established in the system. Three levels have been used to classify the warning grade. Level I refers to the stat safe ; level II refers becoming dangerous ; and level III refers dangerous .

Description: Globally, long-term research is critical to monitor the responses of tropical species to climate and land cover change at the range scale. Citizen science surveys can reveal the long-term persistence of poorly known nomadic tropical birds occupying fragmented forest patches. We applied dynamic occupancy models to 13 years (2002-2014) of citizen science driven presence/absence data on Cape parrot ( Poicephalus robustus ), a food nomadic bird endemic to South Africa. We modelled its underlying range dynamics as a function of resource distribution, and change in climate and land cover through the estimation of colonization and extinction patterns. The range occupancy of Cape parrot changed little over time (ψ = 0.75-0.83) because extinction was balanced by recolonization. Yet, there was considerable regional variability in occupancy and detection probability increased over the years. Colonizations increased with warmer temperature and area of orchards, thus explaining their range shifts southeastwards in recent years. Although colonizations were higher in the presence of nests and yellowwood trees ( Afrocarpus and Podocarpus spp .), the extinctions in small forest patches (≤ 227 ha) and during low precipitation (≤ 41 mm) are attributed to resource constraints and unsuitable climatic conditions. Loss of indigenous forest cover, and artificial lake/water bodies increased extinction probabilities of Cape parrot. The land use matrix (fruit farms, gardens and cultivations) surrounding forest patches provides alternative food sources thereby facilitating spatiotemporal colonization and extinction in the human-modified matrix. Our models show that Cape parrots are vulnerable to extreme climatic conditions such as drought which is predicted to increase under climate change. Therefore, management of optimum sized high quality forest patches is essential for long-term survival of Cape parrot populations. Our novel application of dynamic occupancy models to long-term citizen science monitoring data unfolds the complex relationships between the environmental dynamics and range fluctuations of this food nomadic species. This article is protected by copyright. All rights reserved.

Description: A method is presented for estimating the error covariance of the errors in the model equations in observation space. Estimating model errors in this systematic way opens up the possibility to use data assimilation for systematic model improvement at the level of the model equations, which would be a huge step forward. This model error covariance is perhaps the hardest covariance matrix to estimate. It represents how the missing physics and errors in parameterisations manifest themselves at the scales the model can resolve. A new element is that we use an efficient particle filter to avoid the need to estimate the error covariance of the state as well, which most other data-assimilation methods do require. Starting from a reasonable first estimate, the method generates new estimates iteratively during the data assimilation run, and the method is shown to converge to the correct model error matrix. We also investigate the influence of the accuracy of the observation error covariance on the estimation of the model error covariance and show that when the observation errors are known the model error covariance can be estimated well, but, as expected and perhaps unavoidable, the diagonal elements are estimated too low when the observation errors are estimated too high, and vice versa.

Description: ABSTRACT The Met Office developed a prototype high resolution, hourly-cycling NWP forecasting system using four-dimensional variational data assimilation, covering the southern half of England. This system was known as the Met Office Nowcasting Demonstration Project (NDP), and run in real time from June 2012 to March 2013 (covering the period of the London 2012 Olympics and Paralympic Games). It was principally developed to assess the abilities of a frequent update NWP-based nowcasting system to forecast precipitation at short range such as convective storms for flood forecasting. This article provides a comprehensive assessment of the precipitation forecast skill of the NDP and its comparison against the Met-Office operational nowcasting system. It was found that the NWP-based nowcasting system becomes more skillful than an advanced extrapolation-based nowcasting system from T+1.5 to T+2 depending on weather type.

Description: Oceanic dimethyl sulfide (DMS) is of interest due to its critical influence on atmospheric sulfur compounds in the marine atmosphere and its hypothesized significant role in global climate. High resolution shipboard underway measurements of surface seawater DMS and the partial pressure of carbon dioxide ( p CO 2 ) were conducted in the Atlantic Ocean and Indian Ocean sectors of the Southern Ocean (SO), the southeast Indian Ocean and the northwest Pacific Ocean from February – April 2014 during the 30th Chinese Antarctic Research Expedition. The SO, particularly in the region south of 58 °S, had the highest mean surface seawater DMS concentration of 4.1 ± 8.3 nM (ranged from 0.1 to 73.2 nM) and lowest mean seawater p CO 2 level of 337 ± 50 μatm (ranged from 221 to 411 μatm) over the entire cruise. Significant variations of surface seawater DMS and p CO 2 in the seasonal ice zone (SIZ) of SO were observed, which are mainly controlled by biological process and sea ice activity. We found a significant negative relationship between DMS and p CO 2 in the SO SIZ using 0.1 degree resolution, [DMS] seawater = - 0.160 [ p CO 2 ] seawater + 61.8 (r 2 = 0.594, n = 924, p 〈 0.001). We anticipate that the relationship may possibly be utilized to reconstruct the surface seawater DMS climatology in the SO SIZ. Further studies are necessary to improve the universality of this approach.

Description: Recent observations confirm the rising temperatures of Atlantic waters transported into the Arctic Ocean via the West Spitsbergen Current (WSC). We studied the overall abundance and population structure of the North Atlantic keystone zooplankton copepod Calanus finmarchicus , which is the main prey for pelagic fish and some seabirds, in relation to selected environmental variables in this area between 2001 and 2011, when warming in the Arctic and Subarctic was particularly pronounced. Sampling within a three-week time window each summer demonstrated that trends in the overall abundance of C. finmarchicus varied between years, with the highest values in “extreme” years, due to high numbers of nauplii and early copepodite stages in colder years (2001, 2004, 2010), and contrary to that, the fifth copepodite stage (C5) peaking in warm years (2006, 2007, 2009). The most influential environmental variable, driving C. finmarchicus life cycle was temperature, which promoted an increased C5 abundance when the temperature was above 6°C, indicating earlier spawning and/or accelerated development, and possibly leading to their development to adults later in the summer and spawning for the second time, given adequate food supply. Based on the presented high interannual and spatial variability, we hypothesize that under a warmer climate, C. finmarchicus may annually produce two generations in the southern part of the WSC, what in turn could lead to food web reorganization of important top predators, such as little auks, and induce northward migrations of fish, especially the Norwegian herring. This article is protected by copyright. All rights reserved.

Description: Bumblebees in Europe have been in steady decline since the 1900s. This decline is expected to continue with climate change as the main driver. However, at the local scale, land use and land cover (LULC) change strongly affects the occurrence of bumblebees. At present, LULC change is rarely included in models of future distributions of species. This study's objective is to compare the roles of dynamic LULC change and climate change on the projected distribution patterns of 48 European bumblebee species for three change scenarios until 2100 at the scales of Europe, and Belgium, Netherlands and Luxembourg (BENELUX). We compared three types of models: (1) only climate covariates, (2) climate and static LULC covariates and (3) climate and dynamic LULC covariates. The climate and LULC change scenarios used in the models include, extreme growth applied strategy (GRAS), business as might be usual (BAMBU) and sustainable European development goals (SEDG). We analysed model performance, range gain/loss and the shift in range limits for all bumblebees. Overall, model performance improved with the introduction of LULC covariates. Dynamic models projected less range loss and gain than climate-only projections, and greater range loss and gain than static models. Overall, there is considerable variation in species responses and effects were most pronounced at the BENELUX scale. The majority of species were predicted to lose considerable range, particularly under the extreme growth scenario (GRAS; overall mean: 64% ± 34). Model simulations project a number of local extinctions and considerable range loss at the BENELUX scale (overall mean: 56% ± 39). Therefore, we recommend species-specific modelling to understand how LULC and climate interact in future modelling. The efficacy of dynamic LULC change should improve with higher thematic and spatial resolution. Nevertheless, current broad scale representations of change in major land use classes impact modelled future distribution patterns. This article is protected by copyright. All rights reserved.

Description: 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.

Description: No abstract is available for this article.

Description: 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.

Description: Air temperature is correlated with precipitation oxygen isotope (δ 18 O prcp ) variability for much of the eastern and central United States, but the nature of this δ 18 O prcp -temperature relationship is largely based on data coarsely aggregated at a monthly resolution. We constructed a database of 6177 weeks of isotope and precipitation-day air temperature data from 25 sites to determine how more precise data change our understanding of this classic relationship. Because the δ 18 O prcp -temperature relationship is not perfectly linear, trends in the regression residuals suggest the influence of additional environmental factors such as moisture recycling and extratropical cyclone interactions. Additionally, the temporal relationships between δ 18 O prcp and temperature observed in the weekly data at individual sites can explain broader spatial patterns observed across the study region. For 20 of 25 sites, the δ 18 O prcp -temperature relationship slope is higher for colder precipitation than for warmer precipitation. Accordingly, northern and western sites with relatively more cold precipitation events have steeper overall relationships with higher slope values than southeastern sites that have more warm precipitation events. Although the magnitude of δ 18 O prcp variability increases to the north and west, the fraction of δ 18 O prcp variability explained by temperature increases due to wider annual temperature ranges, producing stronger relationships in these regions. When our δ 18 O prcp -temperature data is grouped by month, we observe significant variations in the relationship from month to month. This argues against a principal causative role for temperature and suggests the existence of an alternative environmental control on δ 18 O prcp values that simply co-varies seasonally with temperature.

Description: 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.

Description: 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.

Description: 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.

Description: 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.