ALBERT

Beschreibung: The water retention curve (θ(ψ)), which defines the relationship between soil volumetric water content (θ) and matric potential (ψ), is of paramount importance in characterizing the hydraulic behaviour of soils. However, few methods are so far available for estimating θ(ψ) in undisturbed soil samples. We present a new design of TDR-pressure cell (TDR-Cell) for estimating θ(ψ) in undisturbed soil samples. The TDR-Cell consists of a 50-mm-long and 50-mm internal diameter stainless steel cylinder (which constitutes the outer frame of a coaxial line) attached to a porous ceramic disc and closed at the ends with two aluminium lids. A 49-mm-long and 3-mm-diameter stainless steel rod, which runs longitudinally through the centre of the cylinder, constitutes the inner rod of a coaxial TDR probe. The TDR-Cell was used to determine the θ(ψ) curves of a packed sand and seven undisturbed soil samples from three profiles of agricultural soils. These θ(ψ) curves were subsequently compared to those obtained from the corresponding 2-mm sieved soils using the pressure plate method. Measurements of bulk electrical conductivity, σ a , as a function of the water content, σ a (θ), of the undisturbed soil samples were also performed. An excellent correlation (R 2 = 0.988) was found between the θ values measured by TDR on the different undisturbed soils and the corresponding θ obtained from the soil gravimetric water content. A typical bimodal θ(ψ) function was found for most of the undisturbed soil samples. Comparison between the θ(ψ) curves measured with the TDR-Cell and those obtained from the 2-mm sieved soils showed that the pressure plate method overestimates θ at low ψ values. The σ a (θ) relationship was well described by a simple power expression (R 2 〉 0.95), in which the power factor, defined as tortuosity, ranged between 1.18 and 3.75. Copyright © 2011 John Wiley & Sons, Ltd.

Beschreibung: Snowfall is an important part of the yearly water balance for the Catskill Mountains in New York State, the location of water supply reservoirs for New York City. Recent studies have shown that the effects of climate change on the hydrology of the Catskills will most likely create (1) a decrease in the proportion of precipitation falling as snow, (2) a shift in the timing of snowmelt that will cause snowmelt-supplemented streamflow events to occur earlier in the fall and winter, and (3) a decrease in the magnitude of traditionally high April streamflow. The shift in timing of snowmelt-influenced streamflow events is measured by the winter-early spring centre of volume (WSCV), defined as the Julian Day on which half the total streamflow volume from January to May occurs. Studies of streamflow, precipitation, and temperature trends in the last 50 years have shown that the WSCV is already earlier by about 5–10 days. This study investigates the use of watershed-scale snowpack and snowmelt algorithms that are incorporated in two existing watershed water quality models, Generalized Watershed Loading Functions-Variable Source Area (GWLF-VSA) and Soil and Water Assessment Tool (SWAT), to capture the potential effects of climate change on the timing and magnitude of streamflow during the late fall, winter, and early spring for the Catskill Mountain region. The GWLF-VSA model reasonably simulated the recent shifts in the winter streamflow timing, with simulations over the previous 50-year period yielding shifts in WSCV of 2–15 days. The SWAT model yielded similar results as the GWLF-VSA simulations. Scenarios of potential climate change 100 years in the future showed a similar shift in direction of timing winter streamflow, but at a larger magnitude than observed to date with WSCV occurring 15–20 days earlier. Copyright © 2011 John Wiley & Sons, Ltd.

Beschreibung: In semi-arid areas high-intensity rainfall events are often held responsible for the main part of soil erosion. Long-term landscape evolution models usually use average annual rainfall as input, making the evaluation of single events impossible. Event-based soil erosion models are better suited for this purpose, but cannot be used to simulate longer timescales and are usually applied to plots or small catchments. In this study, the openLISEM event-based erosion model was applied to the medium sized ( 50 km 2 ) Prado catchment in SE Spain. Our aim was to (i) test the model's performance for medium sized catchments; (ii) test the ability to simulate four selected typical Mediterranean rainfall events of different magnitude, and (iii) explore the relative contribution of these different storms to soil erosion using scenarios of future climate variability. Results show that due to large differences in the hydrologic response between storms of different magnitudes, each event needed to be calibrated separately. The relation between rainfall event characteristics and the calibration factors might help in determining optimal calibration values if event characteristics are known. Calibration of the model features some drawbacks for large catchments due to spatial variability in K sat values. Scenario calculations show that, although 50% of soil erosion occurs as a result of high frequency, low intensity rainfall events, large magnitude, low frequency events potentially contribute significantly to total soil erosion. The results illustrate the need to incorporate temporal variability in rainfall magnitude-frequency distributions in landscape evolution models. Copyright © 2011 John Wiley & Sons, Ltd.

Beschreibung: Sustainable water resources management require scientifically sound information on precipitation, as it plays a key role in hydrological responses in a catchment. In recent years, mesoscale weather models in conjunction with hydrological models have gained great attention as they can provide high resolution downscaled weather variables. Many cumulus parameterization schemes (CPSs) have been developed and incorporated into three-dimensional Pennsylvania State University/National Center for Atmospheric Research (PSU/NCAR) mesoscale model 5 (MM5). This study has performed a comprehensive evaluation of four CPSs (the Anthes–Kuo, Grell, Betts–Miller and Kain–Fritsch93 schemes) to identify how their inclusion influences the mesoscale model's precipitation estimation capabilities. The study has also compared these four CPSs in terms of variability in rainfall estimation at various horizontal and vertical levels. For this purpose, the MM5 was nested down to resolution of 81km for domain 1 (domain span 21 x 81 km) and 3km for 4 (domain span 16 x 3km) respectively with vertical resolutions at 23, 40 and 53 vertical levels. The study was carried out at the Brue catchment in Southwest England using both the ERA-40 reanalysis data and the land based observation data. The performances of four CPs were evaluated in terms of their ability to simulate the amount of cumulative rainfall in four months in 1995 representing the four seasonal months viz January (winter), March (spring), July (summer) and October (autumn). It is observed that the Anthes–Kuo scheme has produced inferior precipitation values during spring and autumn seasons while simulations during winter and summer were consistently good. The Betts–Miller scheme has produced some reasonable results, particularly at the small scaled domain (3 km grid size) during winter and summer. The KF2 scheme was the best scheme for the larger scale (81 km grid size) domain during winter season at both 23 and 53 vertical levels. This scheme tended to underestimate rainfall for other seasons including the small scale domain (3 km grid size) in the mesoscale. The Grell scheme was the best scheme in simulating rainfall rates, and was found to be superior to other three schemes with consistently better results in all four seasons and different domain scales. Copyright © 2011 John Wiley & Sons, Ltd.

Beschreibung: Nonlinear dynamics and spatial variability in hydrological systems make difficult the formulation of scaling theories. Therefore, the development of knowledge related to scale effects, scaling techniques, parameterization and linkages of parameters across scales is highly relevant. The main purpose of this work is to analyse the spatial effect of the static storage capacity parameter H u and the saturated hydraulic conductivity parameter k s from microscale (sub-grid level) to mesoscale (grid level) and its implication to the definition of an optimum cell size. These two parameters describe the upper soil water characteristics in the infiltration process conceptualization of the TETIS hydrological model. At microscale, the spatial heterogeneity of H u and k s was obtained generating random parameter fields through probability distribution functions and a spatial dependence model with pre-established correlation lengths. The effective parameters at mesoscale were calculated by solving the inverse problem for each parameter field. Results indicate that the adopted inverse formulation allows transferring the non-linearity of the system from microscale to the mesoscale via non-stationary effective parameters. Their values at each cell and time step are in the range of zero to the mean value of the parameter at microscale. The stochastic simulations showed that the variance of the estimated effective parameters decreases when the ratio between mesoscale cell size and correlation length at microscale increases. For a ratio greater than 1, we found cell sizes having the characteristics of a representative elementary area (REA); in such case, the microscale variability pattern did not affect the system response at mesoscale. Copyright © 2011 John Wiley & Sons, Ltd.

Beschreibung: The scale issue is of central concern in hydrological processes to understand the potential upscaling or downscaling methodologies, and to develop models for scaling the dominant processes at different scales and in different environments. In this study, a typical permafrost watershed in the Qinghai-Tibet Plateau was selected. Its hydrological processes were monitored for four years from 2004 to 2008; measuring the effects of freezing and thawing depth of active soil layers on runoff processes. To identify the nature and cause of variation in the runoff response in different size catchments, catchments ranging from 1.07 km 2 to 112 km 2 were identified in the watershed. The results indicated that the variation of runoff coefficients showed a “V” shape with increasing catchment size during the spring and autumn seasons, when the active soil was subjected to thawing or freezing processes. A two-stage method was proposed to create runoff scaling models to indicate the effects of scale on runoff processes. In summer, the scaling transition model followed an exponential function for mean daily discharge, whereas the scaling model for flood flow exhibited a linear function. In autumn, the runoff process transition across multiple scales followed an exponential function with air temperature as the driving factor. These scaling models demonstrate relatively high simulation efficiency and precision, and provide a practical way for upscaling or downscaling runoff processes in a medium-size permafrost watershed. For permafrost catchments of this scale, the results show that the synergistic effect of scale and vegetation cover is an important driving factor in the runoff response. Copyright © 2011 John Wiley & Sons, Ltd.

Beschreibung: Regression based regional flood frequency analysis (RFFA) methods are widely adopted in hydrology. This paper compares two regression based RFFA methods using a Bayesian Generalized Least Squares (GLS) modelling framework; the two are quantile regression technique (QRT) and parameter regression technique (PRT). In this study, the QRT focuses on the development of prediction equations for a flood quantile in the range of 2 to 100 years average recurrence intervals (ARI), while the PRT develops prediction equations for the first three moments of the log Pearson Type 3 (LP3) distribution, which are the mean, standard deviation and skew of the logarithms of the annual maximum flows; these regional parameters are then used to fit the LP3 distribution to estimate the desired flood quantiles at a given site. It has been shown that using a method similar to stepwise regression and by employing a number of statistics such as the model error variance, average variance of prediction, Bayesian information criterion and Akaike information criterion, the best set of explanatory variables in the GLS regression can be identified. In this study, a range of statistics and diagnostic plots have been adopted to evaluate the regression models. The method has been applied to 53 catchments in Tasmania, Australia. It has been found that catchment area and design rainfall intensity are the most important explanatory variables in predicting flood quantiles using the QRT. For the PRT, a total of four explanatory variables were adopted for predicting the mean, standard deviation and skew. The developed regression models satisfy the underlying model assumptions quite well; of importance, no outlier sites are detected in the plots of the regression diagnostics of the adopted regression equations. Based on ‘one-at-a-time cross validation’ and a number of evaluation statistics, it has been found that for Tasmania the QRT provides more accurate flood quantile estimates for the higher ARIs while the PRT provides relatively better estimates for the smaller ARIs. The RFFA techniques presented here can easily be adapted to other Australian states and countries to derive more accurate regional flood predictions. Copyright © 2011 John Wiley & Sons, Ltd.

Beschreibung: Synthetic data have long been employed in hydrology for model development and testing. The objective of this study was to generate a synthetic dataset of hydrologic response with higher spatial and temporal resolution than could presently be obtained in the field, spanning a longer period than the typical duration of monitoring campaigns in experimental catchments. The synthetic dataset was generated for a rangeland catchment with the Integrated Hydrology Model (InHM), and is presented for future use by the community. The InHM boundary-value problem is based upon the previously reported hypothetical reality of Tarrawarra-like hydrologic response. Whereas the emphasis in developing the hypothetical reality was on parameterizing InHM to reproduce observations from the Tarrawarra catchment, the emphasis in generating the synthetic dataset is on developing an internally valid hydrologic-response dataset that extends well beyond the period of observations at Tarrawarra. The synthetic dataset spans eleven years of continuous forcing and response data (e.g., integrated response, distributed fluxes, state variable dynamics). The dataset should be useful for a wide range of problems including evaluation of simple rainfall runoff modeling techniques, design of measurement networks, development of data-assimilation algorithms, and studies on information theory. The dataset is available at: ftp://pangea.stanford.edu/pub/loague/. Copyright © 2011 John Wiley & Sons, Ltd.

Beschreibung: This work presents a new design of disc infiltrometer, which, associated with a microflowmeter (MF) and a solenoid valve set, makes it possible to automate the infiltration rate ( Q ) measurements at different soil pressure heads (ψ). The MF consists of a 13.8-cm long and 1.5 mm i.d. pipe, with a pressure transducer connecting the two ends of the MF, inserted in a water-flow pipe that connects the Mariotte tube and the water-supply reservoir of the disc infiltrometer. Water flow is calculated from the head losses in the MF. Changes in ψ in the bubble tower, automatically effected when the infiltration rate reaches steady-state, are controlled by a datalogger connected to four solenoid valves. The new design was tested in laboratory and field conditions, and the results showed that the MF allows the soil water infiltration rates to be correctly estimated for different soil characteristics. The solenoid valve set plus datalogger system satisfactorily monitored the changes in ψ and allowed the measurement time to be optimized. Copyright © 2011 John Wiley & Sons, Ltd.

Beschreibung: There are several methods for determining the spatial distribution and magnitude of groundwater inputs to streams. We compared results of conventional methods (dye dilution gauging, acoustic Doppler velocimeter (ADV) differential gauging, and geochemical end-member mixing) to Distributed Temperature Sensing (DTS) using a fiber-optic cable installed along 900 m of Nine Mile Creek in Syracuse, New York, USA during low-flow conditions (discharge = 1.4 m 3 s -1 ). With the exception of differential gauging, all methods identified a focused, contaminated groundwater inflow and produced similar groundwater discharge estimates for that point, with a mean of 66.8 Ls -1 between all methods although the precision of these estimates varied. ADV discharge measurement accuracy was reduced by non-ideal conditions and failed to identify, much less quantify, the modest groundwater input, which was only 5% of total stream flow. These results indicate ambient tracers, such as heat and geochemical mixing, can yield spatially and quantitatively refined estimates of relatively modest groundwater inflow even in large rivers. DTS heat tracing, in particular, provided the finest spatial characterization of groundwater inflow, and may be more universally applicable than geochemical methods, for which a distinct and consistent groundwater end member may be more difficult to identify. Copyright © 2011 John Wiley & Sons, Ltd.

Beschreibung: Remote sensing estimates of snow water equivalent (SWE) in mountainous areas are subject to large uncertainties. As a prerequisite for testing passive microwave algorithm estimations of SWE, this study aims to collect snow depth (SD) data and provide an understanding of its complex spatial structure as part of the Canadian International Polar Year observations theme. Snow accumulation, redistribution and ablation are controlled by processes that depend on a variety of topographic factors as well as land surface characteristics, which leads us to modelling SD as a function of proxy variables derived from digital elevation model and Landsat data. Field measurements were performed at 3924 locations compromising 184 sites in 50 transects over two years. These measurements were used to predict SD over the study area using a spatial linear mixed-effects model, a model type capable of handling the hierarchical structure of the field data. The model, built using stepwise variable selection, uses as predictor variables transformed elevation, slope, the logarithm of slope, potential incoming solar radiation and its transform; the normalized difference vegetation index, and a transformed tasseled cap brightness from Landsat imagery. A second, simpler model links SD with density giving SWE. The cross-validated root mean squared error of the SD distribution model was 14 cm around an overall mean of 80 cm over a domain of 250 x 250 km. This instantaneous end-of-season peak-accumulation snow map will enable the validation of satellite remote sensing over a generally inaccessible area. Copyright © 2011 John Wiley & Sons, Ltd.

Beschreibung: Stream temperature, an important measure of ecosystem health, is expected to be altered by future changes in climate and land use, potentially leading to shifts in habitat distribution for aquatic organisms dependent on particular temperature regimes. To assess the sensitivity of stream temperature to change in a region where such a shift has the potential to occur, we examine the variability of and controls on the direct relationship between air and water temperature across the state of Pennsylvania. We characterized the relationship between air and stream temperature via linear and nonlinear regression for 57 sites across Pennsylvania at daily and weekly timescales. Model fit (r 2 ) improved for 92% (daily) and 65% (weekly) of sites for nonlinear versus linear relationships. Fit for weekly versus daily regression analysis improved by 0.08 for linear and 0.06 for nonlinear regression relationships. To investigate the mechanisms controlling stream temperature sensitivity to environmental change, we define ‘thermal sensitivity’ as the sensitivity of stream temperature of a given site to change in air temperature, quantified as the slope of the regression line between air and stream temperature. Air temperature accounted for 60 to 95% of the daily variation in stream temperature for sites at or above a Strahler stream order of 3, with thermal sensitivities ranging from low (0.02) to high (0.93). The sensitivity of stream temperature to air temperature is primarily controlled by stream size (stream order) and baseflow contribution (BFI). Together, stream order and baseflow index explained 43% of the variance in thermal sensitivity across the state, and 59% within the Susquehanna River Basin. In small streams, baseflow contribution was the major determinant of thermal sensitivity, with increasing baseflow contributions resulting in decreasing sensitivity values. In large streams, thermal sensitivity increased with stream size, as a function of accumulated heat throughout the stream network. Copyright © 2011 John Wiley & Sons, Ltd.

Beschreibung: This paper investigates the quantity of submarine groundwater discharge (SGD) from a coastal multi-layered aquifer system in response to constant rainfall infiltration. The system comprises an unconfined aquifer, a leaky confined aquifer and an aquitard between them and terminates at the coastline. An approximate analytical solution is derived based on the following assumptions: (i) flow is horizontal in the aquifers and vertical in the aquitard, and (ii) flow in the unconfined aquifer is described by nonlinear Boussinesq equation. The analytical solution is compared with numerical solutions of the strictly two-dimensional nonlinear model to validate the model assumptions used for the analytical solution. The SGD from the leaky confined aquifer increases with the inland rainfall infiltration recharge and the specific leakage of aquitard. The maximum SGD ranges from 1.87 m 3 /d to 10.37 m 3 /d per meter of shoreline when rainfall infiltration ranges from 18.2 mm/yr to 182 mm/yr and the specific leakage of aquitard varies from 10 -9 1/d to 10 -1 1/d. Copyright © 2011 John Wiley & Sons, Ltd.

Beschreibung: Predicting the impact of land use changes on the hydrological response is crucial for water resource management. In the particular case of small catchments (1-10 km 2 ), distributed models could provide useful answers regarding the effects of cultivation practices and man-made works on water fluxes. However, the impacts of specific land use spatial arrangements are difficult to predict because of the prohibitive number of possible cases to consider. Focusing on surface runoff, this paper describes a strategy based on a water particle tracking routine to be plugged-in a distributed model that is designed to determine the spatial arrangements of land management practices that have the greatest impact on volume, peak discharge and lag time at the catchment outlet. A case study is described; the hydrological response of the Roujan catchment (Herault, France) is simulated with the MHYDAS model. The Roujan catchment contains a vineyard in a Mediterranean climate in a landscape in which weeding practices highly influence the partition between soil infiltration and runoff. The results showed that the proposed strategy is much more efficient than a random approach to design the spatial arrangements of the vineyard weeding practices with the greatest impact. Therefore, the proposed strategy may lead to innovative policies for the spatial planning of land management practices. Copyright © 2011 John Wiley & Sons, Ltd.

Beschreibung: Slope is a metric essential to describing surface hydrological processes, including overland flow, soil erosion, and sediment transport. Most commercial GIS have built-in functions to calculate slope from Digital Elevation Models (DEMs) using average-neighborhood-methods appropriate for coarse-resolution DEMs. Emergence of high-resolution DEMs from LiDAR data creates a need to re-assess the suitability of existing algorithms in calculating slope for hydrological applications. We investigate the properties of two slope-calculation methods, an average-neighborhood-slope (ANS) and a downhill-slope (DHS) method. Conceptually, the DHS method provides a more intuitive description of surface water-flow characteristics in uneven terrain. Five DEMs were used to evaluate the methods, namely a 1-m and 10-m resolution DEM interpolated from irregular height point-data generated with conventional photogrammetric techniques, and a 1-m, 5-m, and 10-m resolution DEM derived from LiDAR data. Calculated slopes were summarised for the entire DEM, along mapped streams, and within pre-defined “stream buffers”. Slopes generated for the entire DEM with 1-m resolution LiDAR DEM indicated that the ANS method on average produced smaller slopes than the DHS method (0.64 o ). A similar trend was observed in stream buffers, with greatest slope differences (Δ S ) between methods within 20-m buffers when the 1-m LiDAR-based DEM was used (Δ S = 1.12 o ). In contrast to these results, ANS-calculated slopes along mapped streams were generally larger than those calculated with the DHS method for LiDAR-based DEMs (Δ S = 0.81 o ). Results from this study signal the need for caution when estimating slopes along streams from high-accuracy, LiDAR-generated DEMs. Copyright © 2011 John Wiley & Sons, Ltd.

Beschreibung: A simple process-based approach to predict regional-scale loading of nitrate at the water table was implemented in a GIS for Great Britain. This links a nitrate input function, unsaturated zone thickness and lithologically-dependent rate of nitrate unsaturated zone travel to estimate arrival time of nitrate at the water table. The nitrate input function is the loading at the base of the soil and has been validated using unsaturated zone pore-water profiles. The unsaturated zone thickness uses groundwater levels based on regional-scale observations infilled by interpolated river base levels. Estimates of the rate of unsaturated zone travel are attributed from regional-scale hydrogeological mapping. The results indicate that peak nitrate loading may have already arrived at the water table for many aquifers, but that it has not where the unsaturated zone is relatively thick There are contrasting outcomes for the two main aquifers which have similar unsaturated zone velocities, the predominantly low relief Permo-Triassic sandstones and the Chalk, which forms significant topographic features. For about 60% of the Chalk, the peak input has not yet reached the water table and will continue to arrive over the next 60 years. The methodology is readily transferable and provides a robust method for estimating peak arrival time for any diffuse conservative pollutant where an input function can be defined at a regional scale and requires only depth to groundwater and a hydrogeological classification. The methodology is extendable in that if additional information is available this can easily be incorporated into the model scheme. Copyright © 2011 John Wiley & Sons, Ltd.

Beschreibung: Nitrate transport in the unsaturated zone of a riverbank filtration (RBF) system in Karany, Czech Republic, was studied. Previous study of the system (Buzek et al. 2006) estimated RBF recharge as 60% riverbank filtrate and 40% local groundwater contaminated by nitrates. Nitrate concentrations observed in RBF recently cannot be explained by simple groundwater contamination and a new conception of groundwater recharge is suggested. A two-component model based on water 18 O data modelled recharge of local groundwater. One component of groundwater recharge is rainfall and irrigation water moving through the unsaturated zone of the Quaternary sediments in piston flow. The second component is groundwater from the Cretaceous deposits with a free water table. Both the components of groundwater recharge have different nitrate concentrations and resulting contamination of groundwater depends on the participation of water from Quaternary and Cretaceous deposits. Nitrates' origins and their mixing in the subsurface were traced by 15 N data. Nitrate transport from unsaturated zone is important and time variable source of groundwater contamination. Copyright © 2011 John Wiley & Sons, Ltd.

Beschreibung: Increased attention is being paid to the role of reforestation in strategies for sustainable forest management, landscape restoration and carbon sequestration. Reforestation of drainage basins is generally assumed to reduce annual streamflow as well as peak and low flows. However, most studies of reforestation effects on streamflow have been conducted on small experimental basins, and the applicability of their results to larger basins is unclear. This study revisits an earlier examination of streamflow response to headwater reforestation in a 267 km 2 basin (Ganaraska River) in southern Ontario, Canada for 1945 – 2007. Forest cover in the basin headwaters increased from 13 km 2 in 1945 to 31 km 2 by 1990, with most of this change between 1950 and 1965. Streamflow metrics from the reforested basin and two headwater sub-basins were compared to those from a nearby basin and sub-basin of similar size and physiography to the Ganaraska basins but without extensive headwater reforestation. No temporal trends were found for inter-basin differences in annual runoff or runoff ratios for the entire Ganaraska basin or its largest sub-basin; however, reforestation appears to have reduced several metrics of peak streamflow at the basin and sub-basin scale. Relationships between high flows classified according to generating event type and the associated precipitation depth suggest that expansion of forest cover in the Ganaraska River basin and associated changes in microclimatic conditions have reduced the potential for frozen soil to generate surface runoff and high flows in response to rain-on-snow during Spring snowmelt. This was accompanied by increased low flows from the Ganaraska River basin and its sub-basins from 1960 – 2007 relative to the control basin, suggesting that the expanded forest cover has enhanced groundwater recharge by prolonging Spring snowmelt and promoting infiltration of rainfall and snowmelt inputs relative to non-forested areas. Some discrepancies between these results and those of other studies of streamflow response to reforestation may be attributed to the relatively large size of the Ganaraska River basin and the limited extent of reforestation. Nevertheless, the results highlight the importance of considering how reforestation may affect key hydrologic processes in a given landscape when predicting the resulting streamflow response. Copyright © 2011 John Wiley & Sons, Ltd.

Beschreibung: The hyporheic zone (HZ) has the capability to eliminate and attenuate nutrients and contaminants in riverine systems. Biogeochemical reactions and the potential elimination of contaminants is strongly controlled by the flow paths and dynamics in the HZ. Nevertheless, an easily applicable method for the field determination of flow patterns in the HZ is still lacking. Therefore, a heat pulse technique, which traces the movement of a short heat pulse in the upper part of the HZ and other sand beds, was developed. Five rods are vertically driven into the sediment of the streambed; one rod with a heater as point source located in about 10 cm sediment depth and four rods with four temperature sensors in 3 cm distance, arranged concentrically with 7 cm diameter around the heating rod. Subsequently, a heat pulse is applied and the resulting breakthrough curves are indicative of flow velocities and flow directions in the streambed. A rough data analysis procedure is also suggested. In addition, lab experiments were performed to test the heat pulse technique. These experiments were validated based on coupled numerical modelling of flow and heat transport. First field tests of the method prove that the method is easily applicable under field conditions. These first field tests showed highly complex flow patterns with flow velocities from 1.8 to 4.9 cm min -1 and flow directions from parallel to surface flow to opposite to surface flow. This suggests the need for a robust method to quantify hyporheic flow patterns in-situ . Copyright © 2011 John Wiley & Sons, Ltd.

Beschreibung: We propose two techniques for fracture aperture reconstruction. The first one is a correlation technique that estimates the normal aperture or the tangential shift across a discontinuity whose sides present geometrical similarities. The only required material is a pair of appropriately controlled images of each side. Here, the images are maps of the corresponding side topography, obtained from laser profilometry. Assuming a purely normal opening, it is possible, from two corresponding sides of a given discontinuity in a core log, to infer the precise geometry of the in situ aperture. The second technique allows to retrieve the three-dimensional geometry of a sealed discontinuity from non-independent topography measurements of both sides. Both techniques are applied to discontinuities extracted from a core drilled down to 20 m in a fractured marl formation at Draix (French Alps). The probability density functions of the aperture of the sealed and open discontinuities are shown to be Gaussian. At the sample scale, the sealed fracture aperture is self-affine, while the open one shows a cross-over from a self-affine regime at very small scales to an uncorrelated regime at largest scales. After extrapolating those scaling laws at the scale of the whole formation, we discuss when the aperture roughness affects the hydraulic properties of the Draix fractured bedrock. The overall estimated permeability is significant (10 −9 − 10 −8 m 2 ), consistently with some previous indirect inferences. Copyright © 2011 John Wiley & Sons, Ltd.

Beschreibung: The hydrological role of a headwater swamp in a tropical rainforest is studied using chloride mass balance (CMB) and end-member mixing analysis. There are three main contributions to streamflow: (1) the hillside bedrock aquifer, (2) overland flow from the swamp during storm events and (3) groundwater flow from the swamp aquifer. Before rainfall events of the wet season, the pre-event water comprises a mix of 80% of bedrock aquifer and 20% of swamp aquifer. During storms, the relative contribution of overland flow increases according to the rainfall intensity and the initial saturation rate of the pre-event water reservoirs. The yearly contribution of overland flow from the swamp to the stream is about 31%. The relationship between the swamp and the stream fluctuates with space and time. Generally, the swamp is drained by the stream; however, at the end of long dry seasons, after the first rains, indirect recharge occurs from the stream to the swamp with a hydraulic gradient inversion in the swamp aquifer. The net contribution of the swamp aquifer to the stream is only 4%, which is much lower than the hillside aquifer contribution of about 65%. Recharge on the swamp being very low, these results suggest that, except for a few storms at the end of the dry season, the Nsimi swamp does not contribute to flood attenuation. Evapotranspiration is higher on the hillside than in the swamp. Nevertheless, depletion of water stored within the swamp is dominated by evaporation rather than by its contribution to streamflow. The export of solutes through swamp groundwater flow below the weir is low (〈7%). Nevertheless, the swamp is the most active area of weathering in the watershed. Copyright © 2011 John Wiley & Sons, Ltd.

Beschreibung: Compared to downstream fining of a gravel-bedded river, little field evidence exists to support the process of downstream fining in large, fine sand-bedded rivers. In fact, the typically unimodal bed sediments of these rivers are thought to produce equal mobility of coarse and fine grains that may discourage downstream fining. To investigate this topic, we drilled 200 sediment cores in the channel beds of two fine-grained sand-bedded reaches of the Yellow River (a desert reach and a lower reach) and identified a fine surface layer (FSL) developed over a coarse subsurface layer (CSL) in the 3-m thick bed deposits. In both reaches downstream, the thickness of the FSL increased, while that of the CSL decreased. Comparison of the depth-averaged median grain sizes of the CSL and the FSL separately in both reaches reveals a distinct downstream fining dependence to the median grain size, which indicates that at a large scale of 600 ∼ 800 km, the CSL shows a significant downstream fining, but the FSL shows no significant trends in downstream variations in grain size. This result shows that fine sediment supply (〈0.08 mm median grain size) from upstream, combined with lateral fine sediment inputs from tributaries and bank erosion, can cause a rapid fining of the downstream channel bed surface and can develop the FSL layer. However, in the desert reach, lateral coarse sediment supply (〉0.08 mm median grain size) from wind-borne sediments and cross-desert tributaries can interrupt the fine surface layer and coarsen the channel bed surface locally. Copyright © 2011 John Wiley & Sons, Ltd.

Beschreibung: Alpine watersheds are the source region of some of the largest rivers in North America and elsewhere. Understanding of hydrological processes in alpine watersheds is important for understanding the response of river basins to meteorological forcing. Talus units in alpine watersheds have been suggested in the literature as potential reservoirs of groundwater, but relatively little is known about hydrological processes in talus. To develop conceptual understanding of alpine talus and determine its storage capacity and hydraulic properties, we investigated a talus unit in the Lake O'Hara watershed in the Canadian Rockies using ground penetrating radar, electrical resistivity tomography, measurements of talus discharge, tracer tests, and isotopic hydrograph separation. The study talus, consisting mainly of quartzite and carbonate rock fragments, had very high hydraulic conductivity (0.01-0.03 m s -1 ) and fast hydrograph recession (exponential decay coefficient of 1 d -1 ), suggesting that its storage capacity is limited to a time scale of less than a week. Groundwater flow through the talus occurs in a relatively thin (0.01-0.1 m) saturated zone at the base of the talus, which appears to have discrete flow paths rather than a single continuous sheet. A late-lying snowpack, located at the top of the talus and cliff ledges above, sustains baseflow discharging from the talus, which provides moisture to alpine meadows downstream. Although this study indicates limited storage capacity of talus, further research is required to examine the storage and transmission characteristics of talus consisting of different types of geological materials or formed in different environments. Copyright © 2011 John Wiley & Sons, Ltd.

Beschreibung: It has been previously demonstrated theoretically and numerically by the author that square or absolute increments of data sampled from fractional Brownian/Lévy motion (fBm/fLm), or of incremental data sampled from fractional Gaussian/Lévy noise (fGn/fLn), exhibit apparent/spurious multifractality. Here, we generalize these previous development in a way that (a) rigorously subordinates (truncated) fLn to fGn or, in a statistically equivalent manner, (truncated) fLm to fBm; (b) extends the analysis to a wider class of subordinated self-affine processes; (c) provides a simple way to generate such processes and (d) explains why the distribution of corresponding increments tends to evolve from heavy tailed at small lags (separation distances or scales) to Gaussian at larger lags. Copyright © 2011 John Wiley & Sons, Ltd.

Beschreibung: A quantitative description of rock discontinuities present in subsurface cores that were drilled (down to 20 m) in the marls of the Laval and Moulin catchments near Draix (France) is presented. Three kinds of discontinuities are studied: those fully open, those open but filled with clay rich material and those sealed with calcite. With a laser profiler, the topography of facing sides of typical discontinuities was measured with a normal resolution of 1 µm. The probability distribution of the elevation of each surface are obtained and shown to be normal. Possible self-affine scaling invariance of the topography were explored. The mineralogical content of an interface between the marl bulk and the embedded calcite vein is also investigated using X-ray computed tomography. Implication of this study for water transport in such discontinuities is addressed in a companion paper in the same issue. Copyright © 2011 John Wiley & Sons, Ltd.

Beschreibung: To examine the feasibility of using ecophysiological data from excised leaves for a meteorological simulation model of gas exchange, we compared the obtained gas exchange rates and the modeled ones using excised leaves and those using intact leaves. Instantaneous gas exchange rates of excised leaves and stomatal control in response to environmental conditions were not significantly different from those of attached leaves. Modeled gas exchange rates based on excised leaf data showed a good fit to the diurnal patterns of in situ measurements. This suggests that use of excised leaf data to predict gas exchange of intact leaves is permissible as long as the effects of excision is prescreened as described in this paper. Copyright © 2011 John Wiley & Sons, Ltd.

Beschreibung: High resolution, spatially-extensive climate grids can be useful in regional hydrologic applications. However, in regions where precipitation is dominated by snow, snowmelt models are often used to account for timing and magnitude of water delivery. We developed an empirical, nonlinear model to estimate 30-year means of monthly snowpack and snowmelt throughout Oregon. Precipitation and temperature for the period 1971-2000, derived from 400 m resolution PRISM data, and potential evapotranspiration (estimated from temperature and day length) drive the model. The model was calibrated using mean monthly data from 45 SNOTEL sites and accurately estimated snowpack at 25 validation sites: R 2 = 0.76, Nash-Sutcliffe Efficiency (NSE) = 0.80. Calibrating it with data from all 70 SNOTEL sites gave somewhat better results ( R 2 = 0.84, NSE = 0.85). We separately applied the model to SNOTEL stations located 〈 200 and ≥ 200 km from the Oregon coast, since they have different climatic conditions. The model performed equally well for both areas. We used the model to modify moisture surplus (precipitation minus potential evapotranspiration) to account for snowpack accumulation and snowmelt. The resulting values accurately reflect the shape and magnitude of runoff at a snow-dominated basin, with low winter values and a June peak. Our findings suggest that the model is robust with respect to different climatic conditions, and that it can be used to estimate potential runoff in snow-dominated basins. The model may allow high resolution, regional hydrologic comparisons to be made across basins that are differentially affected by snowpack, and may prove useful for investigating regional hydrologic response to climate change. Copyright © 2011 John Wiley & Sons, Ltd.

Beschreibung: Stochastic simulation of multivariate hydrologic variables has a key role in evaluating alternative designs and operation rules of hydrologic facilities. The recently developed decomposition analysis, Independent Component Analysis (ICA), allows us to apply the simple univariate time series model to each extracted component by: (1) decomposing multivariate time series into independent components with ICA; (2) modeling and generating each component independently; and (3) mixing the generated components to come back to observational domain. However, we illustrate in the current study that fitting a univariate time series model to each extracted component might end up with the underestimation of the serial dependence that the observation data might contain. A alternative for parameter estimation is suggested to preserve the serial dependence of the observation variable using the relationship between the observation variable and the decomposed variable. The case study of the Upper Colorado River basin shows that some improvement is made through the suggested alternative. Copyright © 2011 John Wiley & Sons, Ltd.

Beschreibung: The annual peak-flow series of the Polish rivers are mixtures of summer and winter flows. In this part I of a sequence of two papers, theoretical aspects of applicability of seasonal approach to flood frequency analysis (FFA) in Poland are discussed. A testing procedure is introduced for the seasonal model and the data overall fitness. Conditions for objective comparative assessment of accuracy of AM (annual maxima) and SM (seasonal maxima) approaches to FFA are formulated and finally Gumbel (EV1) distribution is chosen as seasonal distribution for detailed investigation. Sampling properties of AM quantile x ( F ) estimates are analyzed and compared for the SM and AM models for equal seasonal variances. For this purpose 4 estimation methods were used, employing both asymptotic approach and sampling experiments. Superiority of the SM over AM approach is stated evident in the upper quantile range, particularly for the case of no seasonal variation in the parameters of Gumbel distribution. In order to learn whether the standard two- and three-parameter flood frequency distributions can be used to model the samples generated from the Two-Component EV1 distribution, the shape of TCEV1 pdf has been tested in terms of bimodality. Then the use of upper quantile estimate got from the dominant season of extreme floods (DEFS) as AM upper quantile estimate is studied and respective systematic error is assessed. The second part of the paper deals with advantages and disadvantages of SM and AM approach when applied to real flow data of Polish rivers. Copyright © 2011 John Wiley & Sons, Ltd.

Beschreibung: Ground subsidence of detrital deposits in the Almería Basin (SE Spain) was studied using the remote sensing technique of Differential Interferometry SAR (DInSAR). This basin is one of the most arid in Europe, receiving an average rainfall of 250 mm per year. Over the last sixty years the region has experienced an enormous agricultural and urban expansion, whose water demand has been largely supplied from groundwater, leading to the current situation of overexploitation of water resources. This paper outlines the likely relationship between groundwater abstraction and subsidence. To this end, thirty-four ERS and Envisat images, taken between 2003 and 2009, were analysed to estimate ground surface deformations and hence compared with water table variations measured in a number of piezometers in the basin. The analysis shows a clear parallelism between the variations in piezometric level and deformation of the ground surface. In addition, the zones of greatest subsidence coincide with those areas where groundwater abstractions are concentrated. Subsidence over the examined period varies from 10 to 30 mm, with extreme values as high as 50 mm, which translates to a rate of between 1.7 and 5 mm/year, reaching maximum rates of 8 mm/year at some points. Given such subsidence rates, damage to urban infrastructures are, for the moment, incipient. Copyright © 2011 John Wiley & Sons, Ltd.

Beschreibung: Evaporation and heat transfer mechanisms differ for different types of soils. In this study, Evapotranspiration (ET) models for the bare soil, vegetation land and the mixed regions were developed based on the Land Surface Energy Balance Theory. Surface energy fluxes and daily ET of the Heihe River Basin were estimated using Moderate Resolution Imaging Spectroradiometer (MODIS) satellite data and meteorological observation data, including the daily duration time of the sun, air temperature, etc. based on the revised three-temperature model (3T model), and then the distribution map of ET were retrieved. Thereafter, Evaporator pan (E-601) measurements obtained from meteorological observation stations in the study area were chosen to validate the accuracy of the calculated ET. Results showed that the maximum absolute error was 1.70mm/d whereas the minimum was 0.05mm/d, which indicated that the revised 3T model was of adequate accuracy in estimating ET in the study area and could be extended to the regional scale. Also, the spatial distribution of surface ET was different in the upper, middle and lower reaches in the study area and fit with vegetation conditions. On the whole, the ET increased from desert of northeast to mountain of southwest. The results showed that the ET in the study area ranged from 0.06 to 7.00mm/d, with an average value of 2.43mm/d, on 2 August 2008. The highest ET values was from the forest or alpine meadow areas in the upper reaches, with more than 4mm/d, the lowest values was from the Gobi desert in the lower reaches, with below 2mm/d, and ET of oasis in the middle reaches was not only changed with the crop growth stage and vegetation conditions, but also controlled greatly by human activities, with more than 3.5mm/d. Copyright © 2011 John Wiley & Sons, Ltd.

Beschreibung: The annual peak-flow series of Polish rivers are mixtures of summer and winter flows. As part II of a sequence of two papers, practical aspects of applicability of seasonal approach to flood frequency analysis (FFA) of Polish rivers are discussed. Taking Two-Component Extreme Value ( TCEV 1) model as an example it was shown in the first part that regardless of estimation method, the seasonal approach can give profit in terms of upper quantile estimation accuracy that rises with the return period of the quantile and is the greatest for no seasonal variation. In this part, an assessment of AM (annual maxima) versus SM (seasonal maxima) approach to FFA was carried out with respect to seasonal and annual peak-flow series of 38 Polish gauging stations. First, the assumption of mutual independence of the seasonal maxima has been tested. The smoothness of SM and AM empirical probability distribution functions was analysed and compared. The TCEV 1 model with seasonally estimated parameters was found to be not appropriate for most Polish data as it considerably underrates the skewness of AM distributions and upper quantile values as well. Consequently, the discrepancies between the SM and AM estimates of TCEV 1 are observed. Taking SM and TCEV 1 distribution, the dominating season in AM series was confronted with predominant season for extreme floods. The key argument for presumptive superiority of SM approach that SM samples are more statistically homogeneous than AM samples has not been confirmed by the data. An analysis of fitness to SM and AM of Polish data sets made for seven distributions pointed to Pearson (3) distribution as the best for AM and Summer Maxima, whereas it was impossible to select a single best model for winter samples. In the multi-model approach to FFA, the tree functions, i.e., Pe(3), CD3 and LN3, should be involved for both SM and AM. As the case study, Warsaw gauge on the Vistula River was selected. While most of AM elements are here from winter season, the prevailing majority of extreme annual floods are the summer maxima. The upper quantile estimates got by means of classical annual and two-season methods happen to be fairly close; what's more they are nearly equal to the quantiles calculated just for the season of dominating extreme floods. Copyright © 2011 John Wiley & Sons, Ltd.

Beschreibung: The Dakar region is a mega city with multiple contaminant sources from urban expansion as well as industrial and agricultural activities. The major part of the region is underlain by unconfined sandy aquifer, which is vulnerable to contaminants derived from human land use. At present, the contaminated groundwater which extends over a large area in the suburban zone of Thiaroye poses a threat in the future of this valuable resource and more specifically a health threat. This study focuses on nitrate pollution occurrences and associated processes using nitrate isotope data ( 15 N NO3 , 18 O NO3 ) combined with environmental isotopic tracers ( 18 O, 2 H and 3 H). Samples from 36 wells were collected to determine the level, distribution and sources of contamination in relation to land use. Results indicate that shallow groundwater in the urbanized area of Thiaroye shows distinct evidence of surface contamination with nitrate as much as 300 mg/l NO 3 - . In rural area not serviced by water supply distribution network, much higher NO 3 - contents were found in few wells due to household and livestock feedlots. In most groundwater samples δ 15 N values ranged from + 10 to + 22‰, indicative of predominantly human and animal wastes. This was confirmed by environmental isotope data which suggest a mixture of polluted recharge waters. By using the dual δ 15 N vs. δ 18 O as well as δ 15 N vs. NO 3 - approach, denitrification may occur to some extent but it is blurred by mixing with new infiltrated nitrates and cycling derived from continuous leaky septic system. Results suggest that nitrate contamination of the aquifer is a consequence of unregulated urbanization (home-made latrines), continuing contaminant transfer in shallow water depth where aerobic conditions prevail. Copyright © 2011 John Wiley & Sons, Ltd.

Beschreibung: The Mekong Delta is one of the largest and most intensively used estuaries in the world. Each year it witnesses widespread flooding which is both the basis of the livelihood for more than 17 Million people but also the major hazard. Therefore, a thorough understanding of the hydrologic and hydraulic features is urgently required for various planning purposes. While the general causes and characteristics of the annual floods are understood, the inundation dynamics in the floodplains in Vietnam which are highly controlled by dikes and other control structures have not been investigated in depth. Especially quantitative analyses are lacking, mainly due to scarce data about the inundation processes in the floodplains. Therefore, a comprehensive monitoring scheme for channel and floodplain inundation was established in a study area in the Plain of Reeds in the North-Eastern part of the Vietnamese Delta. This in-situ data collection was complemented by a series of high resolution inundation maps derived from the TerraSAR-X satellite for the flood seasons 2008 and 2009. Hence, the inundation dynamics in the channels and floodplains and the interaction between channels and floodplains could be quantified for the first time. The study identifies the strong human interference which is governed by flood protection levels, cropping patterns and communal water management. In addition, we examine the tidal influence on the inundation in various parts of the Delta, since it is expected that climate change induced sea level rise will increase the tidal contribution to floodplain inundation. Copyright © 2011 John Wiley & Sons, Ltd.

Beschreibung: Influences of climatic change on the components of global hydrological cycle, including runoff and evapotranspiration are significant in the mid and high latitude basins. In this paper, the effect of climatic change on annual runoff is evaluated in a large basin- Songhua River Basin which is located at the Northeast of China. A method based on Budyko - type equation is applied to separate the contributions of climatic factors to changes in annual runoff from 1960 to 2008, which are computed by multiplying their partial derivatives by the slopes of trends in climate factors. Furthermore, annual runoff changes are predicted under IPCC SRES A2 and B2 scenarios with projections from five GCMs. The results showed that contribution of annual precipitation to annual runoff change was more significant than that of annual potential evapotranspiration in the Songhua River Basin; and the factors contributing to annual potential evapotranspiration change were ranked as temperature, wind speed, vapor pressure and sunshine duration. In the 2020s, 2050s and 2080s, changes in annual runoff estimated with the GCM projections exhibited noticeable difference and ranged from -8.4 to -16.8 mm a -1 (-5.77% to -11.53% of mean annual runoff) Copyright © 2011 John Wiley & Sons, Ltd.

Beschreibung: Using the defined sensitivity index, the sensitivity of streamflow, evapotranspiration, and soil moisture to climate change was investigated in four catchments in the Haihe River basin (HRB). Climate change contained three parts: annual precipitation and temperature change, and the change of the percentage of precipitation in the flood season ( P f ). With satisfying monthly streamflow simulation using the Variable Infiltration Capacity model, the sensitivity was estimated by the change of simulated hydrological variables with hypothetical climatic scenarios and observed climatic data. The results indicated that: (1) the sensitivity of streamflow would increase as precipitation or P f increased, but would decrease as temperature increased; (2) the sensitivity of evapotranspiration and soil moisture would decrease as precipitation or temperature increased, but it to P f varied in different catchments; (3) hydrological variables were more sensitive to precipitation, followed by P f , and then temperature. The non-linear response of streamflow, evapotranspiration, and soil moisture to climate change could provide a reference for water resources planning and management under future climate change scenarios in the HRB. Copyright © 2011 John Wiley & Sons, Ltd.

Beschreibung: A comparison between half-hourly and daily measured and computed evapotranspiration (ET) using three models of different complexity, namely the Priestley-Taylor (P-T), reference Penman-Monteith (P-M), and Common Land Model (CLM) was conducted using three AmeriFlux sites under different land cover and climate conditions (i.e., arid grassland, temperate forest, and sub-humid cropland). Using the reference P-M model with a semi-empirical soil moisture function to adjust for water-limiting conditions yielded ET estimates in reasonable agreement with the observations (root-mean-square errors (RMSE) of 64–87 W m -2 for half-hourly and RMSE of 0.5-1.9 mm day -1 for daily) and similar to the complex CLM (RMSE of 60–94 W m -2 for half-hourly and RMSE of 0.4-2.1 mm day -1 for daily) at the grassland and cropland sites. However, the semi-empirical soil moisture function was not applicable for the P-T model at the forest site suggesting that more physically-based approaches are required. On the other hand, under certain land cover/environmental conditions, use of microwave-derived soil moisture information was found to be a reliable metric of regional moisture conditions to adjust simple ET models for water-limited cases. Further studies are needed to evaluate the utility of the simplified methods for different landscapes. Copyright © 2011 John Wiley & Sons, Ltd.

Beschreibung: In accounting for uncertainties in future simulations of hydrological response of a catchment, two approaches have come to the fore; deterministic scenario based approaches and stochastic probabilistic approaches. As scenario based approaches result in a wide range of outcomes, role of probabilistic based estimates of climate change impacts for policy formulation has been increasingly advocated by researchers and policy makers. This study evaluates the impact of climate change on seasonal river flows by propagating daily climate time series, derived from probabilistic based climate scenarios using a weather generator (WGEN), through a set of conceptual hydrological models. Probabilistic scenarios are generated employing two different techniques. The first technique employed probabilistic climate scenarios developed from statistically downscaled scenarios for Ireland, hereafter referred to as SDprob . The second technique employed output from 17 global climate models (GCMs), all of which participated in CMIP3, to generate change factors (hereafter referred to as CF ). Outputs from both the SDprob and CF approach where then employed in combination with WGEN to generate daily climate scenarios for use in the hydrological models. The range of simulated flow derived with the CF method are in general larger than those estimated with the SDprob method in winter and vice versa due to the strong seasonality in the precipitation signal for the 17GCMs. In spite of this, the simulated PDF of seasonal mean streamflow estimated with both methods are similar. This indicates the usefulness of the SDprob or probabilistic approach derived from regional scenarios compared to the change factor method that relies on sampling a diversity of response from the global climate models. Irrespective of technique employed, the PDFs of seasonal mean flow produced for four selected basins is wide indicating considerable modelling uncertainties. Such a finding has important implications for developing adaptation strategies at the catchment level in Ireland. Copyright © 2011 John Wiley & Sons, Ltd.

Beschreibung: Stream surface albedo was measured at a location downstream of Place Glacier, Canada, in a steep bouldery channel. Portions of the water surface were visibly aerated as a result of the cascading flow even at lower discharges; at high flows, the stream was near-continuous whitewater. Albedo generally increased with discharge, from around 0.1 at the lower flows to 0.4 at the highest flows. This increase is consistent with the known effect of aeration on the reflectance of water. This discharge-dependence of albedo needs to be accounted for in physically based models for predicting stream temperature to avoid biased predictions of net radiation. For steep proglacial streams that experience decreasing late-summer flows as a result of ongoing and future glacier recession, the associated decrease in albedo could promote higher stream temperatures, in addition to the effects of reduced flow depth and velocity. Copyright © 2011 John Wiley & Sons, Ltd.

Beschreibung: Two-dimensional flood inundation models are widely used tools for flood hazard mapping and an essential component of statutory flood risk management guidelines in many countries. Yet we still don't know how much physically complexity a flood inundation model needs for a given problem. Here, three two-dimensional explicit hydraulic models, that can be broadly defined as simulating diffusive, inertial or shallow water waves, have been benchmarked using test cases from a recent Environment Agency for England and Wales (EA) study, where results from industry models are also available. To ensure consistency the three models were written in the same code and share subroutines for all but the momentum (flow) and time stepping calculations. The diffusive type model required much longer simulation times that the other models, whilst the inertia model was the quickest. For flows that vary gradually in time, differences in simulated velocities and depths due to physical complexity were within 10% of the simulations from a range of industry models. Therefore, for flows that vary gradually in time it appears unnecessary to solve the full two-dimensional shallow water equations. As expected however, the simpler models were unable to simulate supercritical flows accurately. Finally, implications of the results for future model benchmarking studies are discussed in light of a number of subtle factors that were found to cause significant differences in simulations relative to the choice of model. Copyright © 2011 John Wiley & Sons, Ltd.

Beschreibung: Potential changes in glacier area, mass balance and runoff in the Yarkant River Basin (YRB) and Beida River Basin (BRB) are projected for the period from 2011 to 2050 employing the modified monthly degree-day model forced by climate change projection. Future monthly air temperature and precipitation were derived from the simple average of 17, 16 and 17 GCM projections following the A1B, A2 and B1 scenarios, respectively. These data were downscaled to each station employing the Delta method, which computes differences between current and future GCM simulations and adds these changes to observed time-series. Model parameters calibrated with observations or results published in the literature between 1961 and 2006 were kept unchanged. Annual glacier runoff in YRB is projected to increase until 2050, and the total runoff over glacier area in 1970 is projected to increase by about 13–35% during 2011–2050 relative to the average during 1961–2006. Annual glacier runoff and the total runoff over glacier area in 1970 in BRB is projected to increase initially and then to reach a tipping point during 2011–2030. There are prominent increases in summer, but only small increase in May and October of glacier runoff in YRB, and significantly increases during late spring and early summer and significant decreases in July and late summer of glacier runoff in BRB. This study highlights the great differences among basins in their response to future climate warming. The specific runoff from areas exposed after glacier retreat relative to 1970 is projected to general increasing, which must be considered when evaluating the potential change of glacier runoff. Copyright © 2011 John Wiley & Sons, Ltd.

Beschreibung: Fluid flow in single fractures with non-uniform apertures is an important research subject in many disciplines. The abruptly changing aperture is a special case of such non-uniformity. This paper simulates water flow in a single fracture with abruptly changing aperture (SF-ACA) using the Lattice Boltzmann Method (LBM) and the Finite Volume Method (FVM). The flow occurs with the Reynolds number ( Re ) ranging from 5 to 900 and the ratio of aperture change ( E ) of 3 ( E= D/d , where D and d are the larger and smaller apertures, respectively). For Re value between 5 and 100, both LBM and FVM can successfully simulate the eddy development in the expansion regime of a SF-ACA. Flow with high Re values (up to 900) is simulated by FVM which appears to be numerically more stable than LBM for high- Re flow problems studied here. The flow symmetry in the expansion regime breaks at the Re value between 400 and 500, which is larger than those reported by Fearn et al . (1990), Battaglia et al . (1997), and Durst et al . (1974). Our simulation result shows a linear relationship between l 1 / d and Re at low Re (5-100) or higher Re (110-900) values where l 1 is defined as the length from the location of abrupt expansion to the right edge of the first eddy (the one on the far right in Figure 4) along the flow direction. If considering the simulation results for the entire simulated range of Re (5-900), the l 1 / d-Re relationship is better described by a nonlinear logarithmical function. The l 1 / d approaches an asymptotic constant at large Re . Copyright © 2011 John Wiley & Sons, Ltd.

Beschreibung: The Gurbantonggut Desert, China, is an ideal site for study of sublimation from the snowpack because there are sparse vegetation and simple topography, and the wind speed is not large enough to blow snow into the atmosphere from the snowpack. Daily sublimation was measured by manual snow lysimeters at 8:00, and an automatic weather station was deployed at the top of a stout longitudinal dune chain at the southeastern edge of the desert. It is shown that on a daily scale, there was an extremely significant no-intercept linear relationship between the measured sublimation and that calculated by the bulk aerodynamic method, although the former was only 83.8% of the latter. It is also demonstrated that −10°C and 2 m/s were the thresholds where the sublimation varied with the air temperature and the wind speed. When these two thresholds were exceeded, the sublimation accelerated. However, the air temperature and the wind speed at 2 m above the ground averaged −17.2°C and 1.3 m/s, respectively, and the percentages of the time when the air temperature was below −10 °C and the wind speed was below 2 m/s were 76.9% and 85.1%, respectively. As a result, the rate of sublimation was quite low most of the time, and the thin snowpack remained in a quasi-static state until the melt stage started. Copyright © 2002 John Wiley & Sons, Ltd.

Beschreibung: Digital elevation models often contain depressions that result in areas described as having no drainage, referred to as sinks or pits. These depressions disrupt the drainage surface, which disrupt routing of flow over the surface. Most of the attributes that can be extracted from a digital elevation model rely on flow-routing algorithms to calculate the upslope contributing area. There is few information on the influence of the various algorithms on the position and on the connectivity of the extracted networks. The aim of this study is to assess the effects of pit removal methods, data sources and flow routing algorithms on the position of river networks. The results show that all factors and methods have an impact on the position of the extracted networks. The pit removal method combining filling and carving extracted river networks closer to the reference, as well the elevation models with higher resolution. Single flow direction methods provided more accurate positioning of river network, in this test area where the drainage is generally well defined. Copyright © 2011 John Wiley & Sons, Ltd.

Beschreibung: The use of data-driven modelling techniques to deliver improved suspended sediment rating curves has received considerable interest in recent years. Studies indicate an increased level of performance over traditional approaches when such techniques are adopted. However, closer scrutiny reveals that, unlike their traditional counterparts, data-driven solutions commonly include lagged sediment data as model inputs and this seriously limits their operational application. In this paper we argue the need for a greater degree of operational reasoning underpinning data-driven rating curve solutions and demonstrate how incorrect conclusions about the performance of a data-driven modelling technique can be reached when the model solution is based upon operationally-invalid input combinations. We exemplify the problem through the re-analysis and augmentation of a recent and typical published study which uses gene expression programming to model the rating curve. We compare and contrast the previously-published, solutions, whose inputs negate their operational application, with a range of newly developed and directly comparable traditional and data-driven solutions which do have operational value. Results clearly demonstrate that the performance benefits of the published gene expression programming solutions are dependent on the inclusion of operationally-limiting, lagged data inputs. Indeed, when operationally-inapplicable input combinations are discounted from the models, and the analysis is repeated, gene expression programming fails to perform as well as many simpler, more standard multiple linear regression, piecewise linear regression and neural network counterparts. The potential for overstatement of the benefits of the data-driven paradigm in rating curve studies is thus highlighted. Copyright © 2011 John Wiley & Sons, Ltd.

Beschreibung: Reducing or stabilizing the stream temperature of ChiChiaWan Creek is a crucial work for Formosan Landlocked Salmon because ChiChiaWan Creek is the only one habitat for this endangered species. Planting trees in the riparian zone would be one of the alternatives. The purpose of this study was to evaluate the effects of several planting strategies on daily maximum stream temperature along the river. The results showed the effective vegetative shading angles should be more than 50° along ChiChiaWan Creek to reduce the direct solar radiation heating effectively. Upstream planting with 70° vegetative shading angle could be the most effective way among all the scenarios. However, this planting strategy could not improve the worst situations in summer because of the large solar elevation angles. The upstream planting in ChiChiaWan Creek was strongly recommended because the canopies could be easier to extend to totally cover the narrow width of river producing the most effective shades. Practicing the upstream planting with 90° vegetative shading angle can increase more than 1 km-long suitable habitats for the endangered Salmon in summer. Alternatively the west-side planting scenario was the second effective way for temperature reduction. Our result provided a useful suggestion for the authorities in charge of saving the Formosan Landlocked Salmon, particularly under the stress of global warming. Copyright © 2011 John Wiley & Sons, Ltd.

Beschreibung: In many agricultural areas, hedgerows give rise to strong expectations of reducing the inputs of excess nitrate to the groundwater and rivers. This study aims to analyse the spatial and seasonal influence of a hedgerow on nitrate dynamics in the soil and groundwater. Nitrate (NO 3 - ) and chloride (Cl - ) concentrations were measured with spatially dense sampling in the unsaturated soil and in the groundwater along a transect intersecting a bottomland oak ( Quercus rubor ) hedgerow after the growing season and during the dormant season. We explain NO 3 - dynamics by using Cl - as an index of tree root extension and water transfer. At the end of the growing season, NO 3 - is entirely absorbed by the trees over a large and deep volume corresponding to the rooting zone, where, in contrast Cl - is highly concentrated due to root exclusion. But these observed patterns in the soil have no influence on the deep groundwater composition at this season. During the dormant season, water transfer processes feeding the shallow groundwater layer are different upslope and downslope from the hedgerow in relation to the thickness of the unsaturated zone. Upslope, the shallow groundwater is fed by rainwater infiltration through the soil which favours Cl - dilution. Right under the hedge and downslope, the rapid ascent of the groundwater near the ground surface prevents rainwater input and Cl - dilution. Under the hedgerow the highest concentrations of Cl - coincide with the absence of NO 3 - in the shallow groundwater layer and with high concentrations of dissolved organic carbon (DOC). The absence of NO 3 - during the dormant season seems to be due to denitrification in the hedgerow rooting zone when it is rapidly saturated by groundwater. Copyright © 2011 John Wiley & Sons, Ltd.

Beschreibung: River restoration projects have installed j-hook deflectors along the outer bank of meander bends to reduce hydraulic erosion, and in this study we use a computational fluid dynamics (CFD) model to document how these deflectors initiate changes in meander hydrodynamics. We validated the CFD with streamwise and cross-channel bankfull velocities from a 193° meander bend flume (inlet at 0°) with a fixed point bar and pool equilibrium bed but no j-hooks, and then used the CFD to simulate changes to flow initiated by bank-attached boulder j-hooks (1 st attached at 70°, then a 2 nd at 160°). At bankfull and half bankfull flow the j-hooks flattened transverse water surface slopes, formed backwater pools upstream of the boulders, and steepened longitudinal water slopes across the boulders and in the conveyance region off the mid-channel boulder tip. Streamwise velocity and mass transport jets upstream of the j-hooks were stilled, mid-channel jets were initiated in the conveyance region, eddies with a cross-channel axis formed below boulders, and eddies with a vertical axis were shed into wake zones downstream of the point bar and outer bank boulders. At half bankfull depth conveyance region flow cut toward the outer bank downstream of the j-hook boulders and the secondary circulation cells were reshaped. At bankfull depth the j-hook at 160° was needed to redirect bank-impinging flow sent by the upstream j-hook. The hooked boulder tip of both j-hooks funneled surface flow into mid-channel plunging jets, which reversed the secondary circulation cells and initiated 1 to 3 counter rotating cells through the entire meander. The main outer bank collision zone centered at 50° without the j-hook was moved by the j-hook to within and just beyond the 70° j-hook boulder region, which displaced other mass transport zones downstream. J-hooks re-organized water surface slopes, streamwise and cross-channel velocities, and mass transport patterns, to move shear stress from the outer bank and into the conveyance and mid-channel zones at bankfull flow. At half bankfull flows a patch of high shear re-attached to the outer bank below the downstream j-hook. J-hook geometry and placement within natural meanders can be analyzed with CFD models to help restoration teams reach design goals and understand hydraulic impacts. Copyright © 2011 John Wiley & Sons, Ltd.

Beschreibung: This paper presents the development of a probabilistic multi-model ensemble (PME) of statistically downscaled future projections of precipitation of a watershed in New Zealand. Climate change research based on the point estimates of a single model is considered less reliable for decision making and multiple realizations of a single model or outputs from multiple models are often preferred for such purposes. Similarly a probabilistic approach is preferable over deterministic point estimates. In the area of statistical downscaling, no single technique is considered a universal solution. This is due to the fact that each of these techniques has some weaknesses, owing to its basic working principles. Moreover, watershed scale precipitation downscaling is quite challenging and is more prone to uncertainty issues than downscaling of other climatological variables. So multi-model statistical downscaling studies based on a probabilistic approach are required. In the current paper, results from the three well reputed statistical downscaling methods are used to develop a Bayesian weighted multi-model ensemble. The three members of the downscaling ensemble of this study belong to the following three broad categories of statistical downscaling methods ;(1) multiple linear regression; (2) multiple non-linear regression; and (3) stochastic weather generator. The results obtained in this study show that the new strategy adopted here is promising because of many advantages it offers e.g. it combines the outputs of multiple statistical downscaling methods, provides probabilistic downscaled climate change projections and enables the quantification of uncertainty in these projections. This will encourage any future attempts for combining the results of multiple statistical downscaling methods. Copyright © 2011 John Wiley & Sons, Ltd.

Beschreibung: Calculation of actual crop evapotranspiration under soil water stress conditions is crucial for hydrological modeling and irrigation water management. Results of actual evapotranspiration depend on the estimation of water stress coefficient from soil water storage in the root zone, which varies with numerical methods and time step used. During soil water depletion periods without irrigation or precipitation, the actual crop evapotranspiration can be calculated by an analytical method and various numerical methods. We compared the results from several commonly used numerical methods, including the explicit, implicit and modified Euler methods, the midpoint method, and the Heun's third order method, with results of the analytical method as the bench mark. Results indicate that relative errors of actual crop evapotranspiration calculated with numerical methods in one time step are independent of the initial soil water storage in the range of soil water stress. Absolute values of relative error decrease with the order of numerical methods. They also decrease with the number of time step, which can ensure the numerical stability of successive simulation of soil water balance. Considering the calculation complexity and calculation errors caused by numerical approximation for different time step and maximum crop evapotranspiration, the explicit Euler method is recommended for the time step of 1 day (d) or 2 d for maximum crop evapotranspiration less than 5 mm/d, the midpoint method or the modified Euler method for the time step of up to one week or 10 d for maximum crop evapotranspiration less than 5 mm/d, and the Heun's third order method for the time step of up to 15 d. Copyright © 2011 John Wiley & Sons, Ltd.

Beschreibung: This paper explores the relations between network properties and the effect from moving rainstorms in terms of the peak response and time to centroid of hydrographs. A simple conceptual rectangular catchment is introduced with different configurations of drainage network simulated by Gibbs' stochastic model. The efficiency of the urban pipe networks vary widely compared with natural river networks, hence, Gibbs' model can be an appropriate approach to represent the network properties in urban drainage system. Simple cases of rainstorms moving with upstream and downstream directions and different speeds are considered in order to investigate the effect of rainstorm movement on urban drainage network runoff hydrographs. The results indicate that the effect of the direction and speed of the rainstorm movement varies significantly depending on the network properties. The relation between storm speed and direction and the change in the peak runoff is dependent on the network configuration and network efficiency. In contrast to previous studies, this study indicates that the speed and direction of the rainfall movement that produces the maximum peak discharge changes depending on the network configuration. Copyright © 2011 John Wiley & Sons, Ltd.

Beschreibung: Better parameterization of hydrological model can lead to improved streamflow prediction. This is particularly important for seasonal streamflow forecasting using hydrological modeling. Considering the possible effects of hydrologic non-stationarity, this paper examined 10 parameterization schemes at twelve catchments, located in three different climatic zones in east Australia. These schemes are grouped into four categories based on the period where the data are used for model calibration, i.e., calibration using: 1) data from a fixed period in the historical records, 2) different lengths of historical records prior to prediction year, 3) data from different climatic analogue years in the past, 4) data from individual month. Parameterization schemes were evaluated according to model efficiency in both calibration and verification period. The results show that the calibration skill changes with different historic periods where data are used at all catchments. Comparison of model performance between calibration schemes indicates that it is worth calibrating the model using data from each individual month for purpose of seasonal streamflow forecasting. For the catchments in winter-dominant rainfall region of southeast Australia, more significant shift in rainfall-runoff relationships in different periods was found. For those catchments, model calibration using 20 years of data prior to the prediction year leads to more consistent performance. Copyright © 2011 John Wiley & Sons, Ltd.

Beschreibung: Evaporation of soil moisture is one of the most important processes affecting water availability in semiarid ecosystems. Biological soil crusts, which are a widely distributed ground cover in these ecosystems, play a recognized role on water processes. Where they roughen surfaces, water residence time and thus infiltration can be greatly enhanced, whereas their ability to clog soil pores or cap the soil surface when wetted can greatly decrease infiltration rate, thus affecting evaporative losses. In this work, we compared evaporation in soils covered by physical crusts, biological crusts in different developmental stages, and in the soils underlying the different biological crust types. Our results show that during the time of the highest evaporation (Day 1), there was no difference among any of the crust types or the soils underlying them. On Day 2, when soil moisture was moderately low (11%), evaporation was slightly higher in well-developed biological soil crusts than in physical or poorly-developed biological soil crusts. However, crust removal did not cause significant changes in evaporation compared to the respective soil crust type. These results suggest that the small differences we observed in evaporation among crust types could be caused by differences in the properties of the soil underneath the biological crusts. At low soil moisture (〈6%), there was no difference in evaporation among crust types or the underlying soils. Water loss for the complete evaporative cycle (from saturation to dry soil) was similar in both crusted and scraped soils. Therefore, we conclude that for the specific crust and soil types tested, the presence or the type of biological soil crust did not greatly modify evaporation with respect to physical crusts or scraped soils. Copyright © 2011 John Wiley & Sons, Ltd.

Beschreibung: Time-lapse photography provides an attractive source of information about snow cover characteristics, especially at the small catchment scale. The objective of this study was to design and test a monitoring system, which allows multi-resolution observations of snow cover characteristics. The main aim was to simultaneously investigate the spatio-temporal patterns of snow cover, snow depth and snowfall interception in the area very close to the camera, and the spatio-temporal patterns of snow cover in the far range. The multi-resolution design was tested at three sites in the eastern part of the Austrian Alps (Hochschwab-Rax region). Digital photographs were taken at hourly time steps between 6:00 and 18:00 in the period November, 2004 to December, 2006. The results showed that the time-lapse photography allows effective mapping of the snow depths at high temporal resolution in the region close to the digital camera at many snow stake locations. It is possible to process a large number of photos by using an automatic procedure for accurate snow depth readings. The digital photographs can also be used to infer the settling characteristics of the snow pack and snow interception during the day. Although it is not possible to directly estimate the snow interception mass, the photos may indeed give very useful information on the snow processes on and beneath the forest canopy. The main advantage of using time-lapse photography in the far range of the digital camera is to observe the spatio-temporal patterns of snow cover over different landscape configurations. The results illustrate that digital photographs can be very useful for parameterising processes such as sloughing on steep slopes, snow deposition in gullies and snow erosion on mountain ridges in a distributed snow model. Copyright © 2002 John Wiley & Sons, Ltd.

Beschreibung: The fill-spill of surface depressions (wetlands) results in intermittent surface water connectivity between wetlands in the prairie wetland region of North America. Dynamic connectivity between wetlands results in dynamic contributing areas for runoff. However, the impact of fill-spill and the resultant variable or dynamic basin contributing area has largely been ignored in the hydrological community.Long-term field observations recorded at the St. Denis National Wildlife Area, Saskatchewan, allow fill-spill in the basin to be identified and quantified. Along with historical water level observations dating back to 1968, recent data collected for the basin include snow surveys, a surface water survey and production of a Light Detection and Ranging (LiDAR)-derived digital elevation model (DEM). Data collection for the basin includes both wet and dry antecedent basin conditions during spring runoff events.A surface water survey at St. Denis in 2006 reveals a disconnected channel network during the spring freshet runoff event. Rather than 100% of the basin contributing runoff to the outlet, which most hydrological models assume, only approximately 39% of the basin contributes to the outlet. Anthropogenic features, such as culverts and roads were found to influence the extent and spatial distribution of contributing areas in the basin. Historical pond depth records illustrate the impact of antecedent basin conditions on fill-spill and basin contributing area. A large pond at the outlet of the St. Denis basin, that only receives local runoff during dry years when upstream surface storage has not been satisfied, has pond runoff volumes that increase by a factor of 20 or more during wet years when upstream antecedent basin surface storage is satisfied and basin-wide runoff contributes to the pond. Copyright © 2002 John Wiley & Sons, Ltd.

Beschreibung: The effect of preferential flow in soil pipes on nitrate retention in riparian zones is poorly understood. The characteristics of soil pipes and their influence on patterns of groundwater transport and nitrate dynamics were studied along four transects in a 1 to 〉3 m deep layer of peat and marl overlying an oxic sand aquifer in a riparian zone in southern Ontario, Canada. The peat-marl deposit which consisted of several horizontal layers with large differences in bulk density contained soil pipes that were generally 0.1-0.2 m in diameter and often extended vertically for 1 to 〉 2 m. Springs that produced overland flow across the riparian area occurred at some sites where pipes extended to the peat surface. Concentrations of NO 3 - -N (20–30 mg L -1 ) and DO (4–6 mg L -1 ) observed in peat pipe systems and surface springs were similar to values in the underlying sand aquifer indicating that preferential flow transported groundwater with limited nitrate depletion. Low NO 3 - -N concentrations of 〈 5 mg L -1 and enriched δ 15 N values indicated that denitrification was restricted to small areas of the peat where pipes were absent. Groundwater DO concentrations declined rapidly to 〈 2 mg L -1 in the peat matrix adjacent to pipes, whereas high NO 3 - -N concentrations of 〉 15 mg L -1 extended over a larger zone. Low DOC values at these locations suggest that supplies of organic carbon were not sufficient to support high rates of denitrification, despite low DO conditions. These data indicate that it is important to develop a greater understanding of pipes in peat deposits which function as sites where the transport of large fluxes of water with low biogeochemical reaction rates can limit the nitrate removal capacity of riparian zones. Copyright © 2002 John Wiley & Sons, Ltd.

Beschreibung: Using the multi-scale entropy analysis (MSE), we study the effects of water reservoirs on the river flow records based on long streamflow series covering January 1, 1954 and December 31, 2009 at four representative hydrological stations, i.e. the Longchuan, the Heyuan, the Lingxia and the Boluo stations. Hydrological effects of two major water reservoirs, the Xinfengjiang and the Fengshuba water reservoirs, are evaluated. The results indicate that: (1) before the construction of the water reservoirs, the complexity of the streamflow series comes to be decreasing from the upper to the lower East River and which should be attributed to the topographical properties and buffering effects of the river channel; (2) construction of water reservoirs greatly increases the complexity degree of the hydrological processes and this influence is subjected to a damping process with the increase of distance between the water reservoirs and the hydrological stations; (3) power generation is the major function of the water reservoirs in the East River basin. The results of this study should be of theoretical and scientific merits in terms of conservation of the ecological environment and also water resources management under the influences of climate changes and intensifying human activities. Copyright © 2011 John Wiley & Sons, Ltd.

Beschreibung: Heavy rainfall events during the fall season are causing extended damages in Southern France catchments. A peaks-over-threshold model is developed for the extreme daily areal rainfall occurrence and magnitude in the fall over six Mediterranean catchments in Southern France. The main driver of the heavy rainfall events observed in this region is the humidity flux from the Mediterranean Sea. Reanalysis data are used to compute the daily humidity flux (FHUM) during the period 1958–2008, to be included as a covariate in the model parameters. Results indicate that the introduction of FHUM as a covariate in the model parameters can improve the modelling of extreme areal precipitation. The seasonal average of FHUM can improve the modelling of the seasonal occurrences of heavy rainfall events, while the daily FHUM values can improve the modelling of the events magnitudes. In addition, an ensemble of simulations produced by five different general circulation models are used to compute FHUM in future climate and hence to evaluate the impact of climate change on the heavy rainfall distribution in the selected catchments. This ensemble of climate models allows the evaluation of the uncertainties of climate projections. By comparison to the reference period 1960–1990, all models projects an amplification of mean seasonal FHUM from the Mediterranean Sea during the projection period 2070–2099, on average by +22%. This increase in the humidity flux leads to an increase in the number of heavy rainfall events, from an ensemble average of 2.55 events during the fall season in present climate to 3.57 events projected for the period 2070–2099. However, the projected changes have limited impacts on the magnitude of extreme events, with a 5% increase in the median of 100-year quantiles. Copyright © 2011 John Wiley & Sons, Ltd.

Beschreibung: The snowfall in the Baltimore/Washington metropolitan area during the winter of 2009/2010 was unprecedented and caused serious snow-related disruptions. In February 2010, snowfall totals approached 2 m, and because maximum temperatures were consistently below normal, snow remained on the ground the entire month. One of the biggest contributing factors to the unusually severe winter weather in 2009/10, throughout much of the mid latitudes, was the Arctic Oscillation. Unusually high pressure at high latitudes and low pressure at mid-latitudes, forced a persistent exchange of mass from north to south. In this investigation, a concerted effort was made to link remotely sensed falling snow observations to remotely sensed snow cover and snowpack observations in the Baltimore/Washington area. Specifically, the Advanced Microwave Scanning Radiometer (AMSR-E) onboard the Aqua satellite was used to assess snow water equivalent (SWE), and the Advanced Microwave Sounding Unit-B (AMSU-B) and Microwave Humidity Sounder (MHS) were employed to detect falling snow. AMSR-E passive microwave signatures in this study are both related to snow on the ground and to surface ice layers. In regards to falling snow, signatures indicative of snowfall can be observed in high frequency brightness temperatures of AMSU-B/MHS. Indeed, retrievals show an increase in SWE after the detection of falling snow. Yet this work also shows that falling snow intensity and or the presence of liquid water clouds impacts the ability to reliably detect SWE. Moreover, changes in the condition of the snowpack, especially in the surface features, negatively affect retrieval performance. Copyright © 2011 John Wiley & Sons, Ltd.

Beschreibung: Short-term Quantitative Precipitation Forecasts (QPFs) can be achieved fromNumericalWeather Prediction (NWP) models or radar nowcasting, that is the extrapolation of the precipitation at a future time from consecutive radar scans. Hybrid forecasts obtained by merging rainfall forecasts from radar nowcasting and NWP models are potentially more skilful than either radar nowcasts or NWP rainfall forecasts alone. This paper provides an assessment of deterministic and probabilistic high-resolution QPFs achieved by implementing the Short-term Ensemble Prediction System (STEPS) developed by the UK Met Office. Both radar nowcasts and hybrid forecasts have been performed. The results show that the performance of both deterministic nowcasts and deterministic hybrid forecasts decreases with increasing rainfall intensity and spatial resolution. The results also show that the blending with the NWP forecasts improves the performance of the forecasting system. Probabilistic hybrid forecasts have been obtained through the modelling of a stochastic noise component to produce a number of equally likely ensemble members, and the comparative assessment of deterministic and probabilistic hybrid forecasts shows that the probabilistic forecasting system is characterized by a higher discrimination accuracy than the deterministic one. Copyright © 2011 John Wiley & Sons, Ltd.

Beschreibung: Dominant flow pathways (DFPs) in mesoscale watersheds are poorly characterized and understood. Here we make use of a conservative tracer (Gran alkalinity) and detailed information about climatic conditions and physical properties to examine how temporally and spatially variable factors interact to determine DFPs in 12 catchments draining areas from 3.4 to 1829.5 km² (Cairngorms, Scotland). After end-member mixing was applied to discriminate between near surface and deep groundwater flow pathways, variation partitioning, canonical redundancy analyses and regression models were used to resolve: (i) What is the temporal variability of DFPs in each catchment?; (ii) How do DFPs change across spatial scales and what factors control the differences in hydrological responses?; and (iii) Can a conceptual model be developed to explain the spatiotemporal variability of DFPs as a function of climatic, topographic and soil characteristics? Overall, catchment characteristics were only useful to explain the temporal variability of DFPs but not their spatial variation across scale. The temporal variability of DFPs was influenced most by prevailing hydroclimatic conditions and secondarily soil drainability. The predictability of active DFPs was better in catchments with soils supporting fast runoff generation on the basis of factors such as the cumulative precipitation from the seven previous days, mean daily air temperature and the fractional area covered by Rankers. The best regression model R 2 was 0.54, thus suggesting that the catchments' internal complexity was not fully captured by the factors included in the analysis. Nevertheless, this study highlights the utility of combining tracer studies with digital landscape analysis and multivariate statistical techniques to gain insights into the temporal (climatic) and spatial (topographic and pedologic) controls on DFPs. Copyright © 2011 John Wiley & Sons, Ltd.

Beschreibung: A nonlinear function approach for the normalized complementary relationship evaporation model that is different from the methodology maintaining the symmetric complementary relationship with appropriate definitions of potential and wet environment evaporation is proposed and verified. This approach employs the definitions used in the advection-aridity model, wherein the potential is estimated using the Penman equation. Normalized by Penman potential evaporation, the complementary relationship model is expressed as a function describing the relationship between the evaporation ratio (the ratio of the actual to the Penman potential evaporation) and the proportion of the radiation term in Penman potential evaporation. The new nonlinear function proposed in the current study is approximately equivalent to the advection-aridity and the modified Granger models under conditions that are neither too wet nor too dry, but is more reasonable under arid and wet conditions. The new nonlinear function model performs well in estimating actual evaporation, as verified by the observed data from four sites under different land covers. Copyright © 2011 John Wiley & Sons, Ltd.

Beschreibung: In this paper, the possibility of sharing rain barrels and the potential benefit of reducing storage size through physical and non-physical connections of rain barrels in a community are investigated. Using the concepts of homogeneous/heterogeneous users in rainwater harvesting systems (RWHS), two simple cases of a community composed of four prospective users are examined. The first is performed with the users who have the same mean and variance in water demands (homogeneous users) and the second is with the users with different means and variances (heterogeneous users). In order to take account for the rainfall characteristics in different places, historical records from six cities in the United States are used for storage-reliability-yield (SRY) analysis. The result indicates that required total storage can be reduced by connecting multiple rain barrels. In addition, a significant difference is found between homogeneous and heterogeneous user groups. Homogeneous users do not achieve a substantial benefit from connecting their rain barrels; these users may even be disadvantaged by sharing. In contrast, heterogeneous users receive benefit by reducing the total required storage. Most benefit is expected between users with maximum difference in mean water demands. The reduction in storage size was as considerable as 37% in this study. The quantity of storage reduction depends on locations and target reliabilities. Knowledge of the benefits and limitations of rain barrel connections can improve RWHS performance through ability to customize a network plan for individual users. Copyright © 2011 John Wiley & Sons, Ltd.

Beschreibung: This study examines the variability of in-pool temperatures in Imnavait Creek, a beaded arctic stream consisting of small pools connected by shallow chutes, for the purpose of predicting potential impacts of climate variations on the system. To better understand heat fate and transport through this system, the dominant heat sources and sinks creating and influencing thermal stratification within even the smallest and shallowest pools must be quantified. To do this, temperature data were collected vertically within the pool water column and surrounding bed sediments during stratified conditions. These temperature and other supporting data (e.g., instream flow, weather data, and bathymetry) were used to formulate and develop an instream temperature model that captures the site specific processes occurring within the pools during summer low flow conditions. The model includes advective, air-water interface, and bed conduction fluxes, simplified vertical exchange between stratified pool layers, and attenuation of shortwave radiation within the water column. We present the model formulation, data collection methods used in support of model development and population, and the resulting model calibration and validation for one of the study pools. We also provide information regarding dominant heat sources and sinks and residence times of different layers within the stratified pool. We found the dominant heat sources vary between stratified layers and that increases in thaw depths surrounding these pools due to possible climate changes can shift stratification, mixing, and instream storage dynamics thereby influencing the fate and transport of heat and other constituents of interest (e.g., nutrients). Copyright © 2011 John Wiley & Sons, Ltd.

Beschreibung: Advancements in both land surface models (LSM) and land surface data assimilation, especially over the last decade, have substantially advanced the ability of land data assimilation systems (LDAS) to estimate evapotranspiration (ET). This article provides a historical perspective on international LSM intercomparison efforts and the development of LDAS systems, both of which have improved LSM ET skill. In addition, an assessment of ET estimates for current LDAS systems is provided along with current research that demonstrates improvement in LSM ET estimates due to assimilating satellite-based soil moisture products. Using the Ensemble Kalman Filter in the Land Information System, we assimilate both NASA and Land Parameter Retrieval Model (LPRM) soil moisture products into the Noah LSM Version 3.2 with the North American LDAS phase 2 (NLDAS-2) forcing to mimic the NLDAS-2 configuration. Through comparisons with two global reference ET products, one based on interpolated flux tower data and one from a new satellite ET algorithm, over the NLDAS2 domain, we demonstrate improvement in ET estimates only when assimilating the LPRM soil moisture product. Copyright © 2011 John Wiley & Sons, Ltd.

Beschreibung: This study aims to investigate the changing properties of drought events in Weihe River basin, China, by modeling the multivariate joint distribution of drought duration, severity and peak using trivariate Gaussian and Student t copulas. Monthly precipitations of Xi'an gauge are used to illustrate the meta-elliptical copula-based methodology for a single-station application. Gaussian and Student t copulas are found to produce a better fit comparing with other six symmetrical and asymmetrical Archimedean copulas, and, checked by the goodness-of-fit tests based on a modified bootstrap version of Rosenblatt's transformation, both of them are acceptable to model the multivariate joint distribution of drought variables. Gaussian copula, the best-fitting, is employed to construct the dependence structures of positively associated drought variables so as to obtain the multivariate joint and conditional probabilities of droughts. A Kendall's return period (KDP) introduced by Salvadori and De Michele (2010) is then adopted to assess the multivariate recurrent properties of drought events, and its spatial distributions indicate that prolonged droughts are likely to break out with rather short recurrence intervals in the whole region while drought status in the southeast seems to be severer than the northwest. The study is of some merits in terms of multivariate drought modeling using a preferable copula-based method, the results of which could serve as a reference for regional drought defense and water resources management. Copyright © 2011 John Wiley & Sons, Ltd.

Beschreibung: Seasonal streamflow forecasts based on climate information can guide water managers toward superior reservoir operations, leading to improved water resources management efficiency. Uncertainty, however, is always present in seasonal streamflow forecasts, affecting the forecast value. Thus, a forecast should not be considered complete without a description of its uncertainty, which is critical for climate risk and water resources management. This study investigates the uncertainties of a seasonal streamflow forecast system for Northeastern Brazil based on climate precipitation forecasts and hydrologic modeling. These two sources of uncertainty are treated independently and then compared in order to guide future investments in the forecast system. Sea surface temperature is considered to be the primary source of uncertainty for the seasonal precipitation forecasts, based upon a 10-member climate model ensemble. Parameter uncertainty is considered to be the only source of uncertainty for the hydrologic model. Estimation of parameter uncertainty is estimated by the Shuffled Complex Evolution Metropolis (SCEM-UA) algorithm, which employs a Markov Chain Monte Carlo scheme to provide the posterior distribution of the parameters and form uncertainty bounds on streamflow forecasts. Results indicate that uncertainties associated with the climate forecast are much larger than those from parameter estimation in the hydrologic model. Although model structure has not been considered in the evaluation of hydrologic uncertainties, this study indicates that future efforts to address the predominant source of uncertainty should focus on the climate prediction models. Copyright © 2011 John Wiley & Sons, Ltd.

Beschreibung: In order to better understand storage-runoff dynamics, transient groundwater responses were examined in one of the steep watersheds in British Columbia's coastal mountains. Streamflow and piezometric data were collected for one year to determine the spatial and temporal relations between transient water levels and discharge. Correlations between piezometer responses and lag-time analysis were used to identify and better understand runoff generation mechanisms in this watershed. Results showed a large spatial and temporal variation in transient water table dynamics and indicated that two distinct zones existed; a lower hillslope zone and an upslope zone. Each zone was characterized by very different water table responses. The upper hillslope was disconnected from the stream for the majority of time, suggesting that during most events it does not directly contribute to streamflow. Piezometers in the lower hillslope zone showed hydrologically limited responses, suggesting rapid subsurface flow, likely through the many macropores and soil pipes. The lag time between peak streamflow and peak groundwater level decreased with increasing antecedent moisture conditions and was more variable for piezometers further away from the stream than for piezometers close to the stream. The study results indicate that a single storage-runoff model is not appropriate for this steep watershed and that a two or three compartment model would be more suitable. Copyright © 2011 John Wiley & Sons, Ltd.

Beschreibung: Grout curtains are vertical grout walls installed in the ground. In karst terrains their construction is primarily connected with dams and reservoirs. Their main role is to increase watertightness and prevent progressive erosion, blocking possible seepage paths along karst fissures and conduits. In this paper changes in the behaviour of the groundwater level (GWL) and the water temperature in nine deep piezometers, which were caused by the construction of a grout curtain at the Đale Reservoir on the Cetina River (Croatia) were analysed. The total length of the grout curtain is 3,966 m. It spreads 120 m below the dam. The most of analysed data is from the period after the dam had been built. Only few data and figures concern the comparison between pre and post dam periods. The hourly data of the GWL and the water temperature were analysed for the period between 1 Sep. 2008 at 02 h to 31 Dec. 2009 at 23 h (11,687 hours total) in six deep piezometers (marked in the text and figures as 1, 2, 3, 4, 5 and 6). For three piezometers (marked in the text and figures as A, B and C) some discontinuous measurements of the GWL and the water temperature were available for analysis. The construction of the grout curtain made strong, sudden and possibly dangerous changes to the characteristics of the aquifer and the circulation of groundwater in the local area. Special attention is paid to analyses of the behaviour of the hourly GWL data measured in the piezometers pairs (two neighbouring piezometers, one inside and the other outside of the grout curtain). During more than 80% of the analysed period the GWL was higher in the piezometer inside the grout curtain than the one outside of it. The intensity and range of the dynamics of GWL was higher in piezometer outside the grout curtain than the inside ones. After the construction of the grout curtain, the maximum measured hydrostatic pressure on some parts of the grout curtain was about 40 m. It changes quickly in both time and direction. The water temperature was found to be similar in all of the measured piezometers and it varies between 10.2 and 15.7 °C with an average value of 12.7 °C. Copyright © 2011 John Wiley & Sons, Ltd.

Beschreibung: Hydrological connectivity between floodplain wetlands and rivers is one of the principal driving mechanisms for the diversity, productivity and interactions of the major biota in river-floodplain systems. This paper describes a method of quantifying flood-induced overbank connectivity using a hydrodynamic model (MIKE 21) to calculate the timing, duration and spatial extent of the connections between a number of floodplain wetlands and rivers in the Tully-Murray catchment, north Queensland, Australia. Areal photogrammetry and field surveyed stream-cross data were used to reproduce floodplain topography and rivers in the model. Laser altimetry (LiDAR) derived fine resolution elevation data, for the central floodplain, were added to the topography model to improve the resolution of key features including wetlands, flow pathways and natural and artificial flow barriers. The hydrodynamic model was calibrated using a combination of in-stream and floodplain gauge records. A range of off-stream wetlands including natural and artificial, small and large were investigated for their connectivity with two main rivers (Tully and Murray) flowing over the floodplain for flood events of 1, 20 and 50 year recurrence intervals. The duration of connection of individual wetlands varied from 1 to 12 days, depending on flood magnitude and location in the floodplain, with some wetlands only connected during large floods. All of the wetlands studied were connected to the Tully River for shorter periods than they were to the Murray River, due to the higher bank heights and levees on the Tully River and wetland proximity to the Murray River. Other than hydrology, land relief, river bank elevation and levee banks along the river were found key factors controlling the degree of connectivity. These variations in wetland connectivity could have important implications for aquatic biota that move between rivers and off-stream habitats during floods. Copyright © 2011 John Wiley & Sons, Ltd.

Beschreibung: Soil moisture influences many hydrologic applications including agriculture, land management, and flood prediction. Most remote-sensing methods that estimate soil moisture produce coarse-resolution patterns, so methods are required to downscale such patterns to the resolutions required by these applications (e.g., 10–30 m grid cells). At such resolutions, topography is known to impact soil moisture patterns. Although methods have been proposed to downscale soil moisture based on topography, they usually require the availability of past high-resolution soil moisture patterns from the application region. The objective of this paper is to determine whether a single topographic-based downscaling method can be used at multiple locations without relying on detailed local observations. The evaluated downscaling method is developed based on empirical orthogonal function (EOF) analysis of space-time soil moisture data at a reference catchment. The most important EOFs are then estimated from topographic attributes and the associated expansion coefficients (ECs) are estimated based on the spatial-average soil moisture. To test the portability of this EOF-based method, it is developed separately using four datasets (Tarrawarra, Tarrawarra2, Cache la Poudre, and Satellite Station), and the relationships that are derived from these datasets to estimate the EOFs and ECs are compared. In addition, each of these downscaling methods is applied not only for the catchment where it was developed but also to the other three catchments. The results suggest that the EOF downscaling method performs well for the location where it is developed, but its performance degrades when applied to other catchments. Copyright © 2011 John Wiley & Sons, Ltd.

Beschreibung: A statistically-based runoff-yield model is proposed in this paper. The model considers spatial heterogeneities of rainfall, soil infiltration capacity and soil water storage capacity that are main factors controlling runoff-yield process. It assumes that the spatial variation of rainfall intensity at each time step can be characterized by a probability density function (PDF) which is estimated by matching the hyetograph through goodness-of-fit measure, while the spatial heterogeneities of soil infiltration capacity and soil water storage capacity are described by parabola-type functions. Surface runoff is calculated according to infiltration excess mechanism, the statistical distribution of surface runoff rate can be deduced with the joint distribution of rainfall intensity and soil infiltration rate, thus obtaining a quasi-analytical solution for surface runoff. Based on saturation excess mechanism, the groundwater flow (flows below ground are collectively referred to as groundwater flow ) is calculated by infiltration and the probability distribution of soil water storage capacity. Consequently, the total runoff is composed of infiltration excess and saturation excess runoff components. As an example, this model is applied to flood event simulation in Dongwan catchment, a semi-humid region and a tributary of Yellow River in China. It indicates that the proposed runoff-yield model could achieve acceptable accuracy. Copyright © 2011 John Wiley & Sons, Ltd.

Beschreibung: Little attention has been given to the role of groundwater in the hydrologic cycle of lowland watersheds. Our objective in this study was to estimate total recharge to groundwater by analyzing water table response to storm events, and the rate at which water was transferred into the shallow aquifer. This was conducted at three sites in a rural watershed in the lower Atlantic coastal plain near Charleston, South Carolina USA. A novel version of the water table fluctuation method was used to estimate total recharge to the shallow aquifer by comparing hourly data of water table position following storm events and measuring water table recession behavior, rather than subjective graphical analysis methods. Also, shallow aquifer recharge rates (vertical fluxes) were estimated using Darcy's Law by comparing static water levels in a water table well and in a shallow piezometer during dry periods. The total annual recharge estimated ranged from 107 ± 39 mm yr -1 (5 - 10% of annual precipitation) at a poorly-drained topographic low area to 1140 ± 230 mm yr -1 (62 - 94% of annual precipitation) for a moderately well-drained upland site. The average aquifer recharge rate was 114 ± 60 mm yr -1 , which is similar to previous estimations of base flow for the ephemeral third order streams in this watershed. The difference in the two methods may have been due to processes not accounted for in the Darcy flux method, soil moisture deficits, as well as and evapotranspiration demand, which is about 1000 mm yr -1 for this region. While other factors can also affect partitioning of recharge, an integrated approach to inspecting easily-gathered groundwater data can provide information on an often-neglected aspect of water budget estimation. We also discuss the effects of land use change on recharge reduction given a typical development scenario for the region. Copyright © 2011 John Wiley & Sons, Ltd.

Beschreibung: This paper explores the flow paths and turnover times within a catchment characterized by the transmissivity feedback mechanism where there is a strong increase in the saturated hydraulic conductivity towards the soil surface and precipitation inputs saturate progressively more superficial layers of the soil profile. The analysis is facilitated by the correlation between catchment water storage and groundwater levels which made it possible to model the daily spatial distribution of water storage, both vertically in different soil horizons and horizontally across a 6,300 m 2 till catchment. Soil properties and episodic precipitation input dynamics, combined with the influence of topographic features, concentrate flow in the horizontal, vertical and temporal dimensions. Within the soil profile, there was a vertical concentration of lateral flow to superficial soil horizons (upper 30 cm of the soil), where much of the annual flow occurred during runoff episodes. Overland flow from a limited portion of the catchment can contribute to peak flows, but is not a necessary condition for runoff episodes. The spatial concentration of flow, and the episodic nature of runoff events, resulted in a strong and spatially structured differentiation of local flow velocities within the catchment. There were large differences in the time spent by the laterally flowing water at different depths, with turnover times of lateral flow across a one m wide soil pedon ranging from under one hour at 10-20 cm depth to a month at 70-80 cm depth. In many regards, the hydrology of this catchment appears typical of the hydrology in till soils which are widespread in Fenno-Scandia. Copyright © 2011 John Wiley & Sons, Ltd.

Beschreibung: The statistical properties of annual runoff in major rivers of China are studied based on the theory of stochastic process and technology of time series analysis. These properties include the characteristics of intra-annual and inter-annual variations of runoff, trends, abrupt changes and periodicities. The new findings from the intensive calculations and appropriate analysis of data in longer period are: 1) compared with the nonuniformity of intra-annual runoff before 1980, the nonuniformity of intra-annual runoff in China generally decreased after 1980, except for Huaihe River and Songhua River; 2) compared with the annual runoff before 1980, the annual runoff in China generally decreased after 1980 except for WangJiaba station in Huaihe River and Ha-Erbin station in Songhua River; The frequency of continuous low flow and continuous high flow in Haihe River and the downstream of Yellow River is higher than those in other rivers in China; 3) annual runoff shows a downward trend in major rivers of China especially in Haihe River, Liao River and the midstream and downstream of Yellow River; 4) there exist certain abrupt changes of annual runoff in major rivers of China. The abrupt change-points are different among different river basins; and 5) almost periodicities of annual runoff sequences in major rivers of China are generally 20 years below, that is, 3 ~ 7 yr, and 12 ~ 20-yr. The reasons for these changes are mainly caused by climate change and human activities. Copyright © 2011 John Wiley & Sons, Ltd.

Beschreibung: This paper proposes a method to spatially lump a distributed rainfall-sediment-runoff model at the catchment scale. Based on a kinematic wave rainfall-sediment-runoff model, the proposed method spatially integrates (1) a rainfall-runoff model that simulates unsaturated, saturated subsurface and surface runoff processes and (2) a rainfall-sediment-runoff model that simulates soil erosion and transport processes induced by raindrops and surface flow detachment, respectively. The method deductively derives a set of lumped equations that relates the streamflow discharge and the catchment storage of water and sediment, which are then used together with continuity equations to predict the sediment runoff fluxes from the catchment outlet. The main advantage of the method is that the derived lumped model parameters are reflected by the spatially distributed topographical and soil property information, and yet the model can be implemented with a much less computational load compared to the original distributed model. Thus, the model gives a possibility of its numerous applications − such as the application to real-time flood forecasting, sediment yield-flood prediction for hydraulical structure designing, and for a climate change impact analysis on hydrological responses − coupled with the risk and uncertainty analyses which require a number of simulations. The developed lumped model successfully simulated the original distributed model outputs, as well as the observed streamflow and sediment at the Lesti River Catchment (381 km 2 ), a tributary of the Brantas River Basin in Indonesia. After validating the proposed lumped model, the most effective lumping scale was then investigated by conducting multiple simulations, the results of which suggested that approximately 200 km 2 is the ideal lumping scale for this model. Copyright © 2011 John Wiley & Sons, Ltd.

Beschreibung: Improved estimates of evapotranspiration (ET) are needed for water resource management and irrigation scheduling. We review the use of imaging spectroscopy to capture estimates of water vapor flux and biophysical components of ET. Remote sensing has long attempted to quantify and predict ET, with most applications relying only on green vegetation indexes from multispectral imagers combined with thermal radiance and weather data. In contrast, imaging spectrometry is an advanced remote sensing technology that measures hundreds of spectral bands in the solar spectrum. Plant pigments, water, and dry matter have unique spectral signatures that can advance estimates of ET and detection of drought stress. This allows analyses based on the physics of spectroscopy and avoids a requirement for continual empirical calibration. These spectral components provide unprecedented information about plant physiological processes, which improve understanding of the regulation of water fluxes and the energy budget. Laboratory, field, and airborne studies of spectral properties in the near- and shortwave-infrared show strong relationships with plant water relations like water content, relative water content, and water potential. Because water absorption features are spectrally independent of pigment absorptions in the visible, they provide a new source of information about environmental conditions. These new observations from imaging spectroscopy will lead to better understanding of ecological and hydrological processes. Copyright © 2011 John Wiley & Sons, Ltd.

Beschreibung: Hydrological and carbon cycles are inherently coupled and play a pivotal role in the earth system. Water stress is one of the most limiting factors constraining vegetation productivity in both direct and indirect ways (mainly through nutrition cycling). In this article, we first reviewed the concepts of hydrological and carbon cycles and their interactions, and then summarized recent advances in our understanding of how global climate change affects water stress, ecosystem carbon cycling, disturbances, and water use efficiency. A warming climate may continue to benefit plant growth in energy limited areas such as high latitudes and altitudes. However, over many water-limited regions of the world, a warming climate has led to a drying trend, posing negative effects on land carbon sink capability, as shown by reductions in vegetation growth and increases in ecosystem disturbances (wildfires, insect outbreaks and tree mortality). Carbon cycle and water use efficiency have responded to climate change in different ways in different areas. Further integrating information from climate records, flux measurements at eddy flux towers, and observations from satellites will greatly advance our understanding of the hydrological and carbon cycles and their evolution. Advancement in our understanding of the evolution of hydrological and carbon cycles under the changing climate will help us to adapt and mitigate the adverse effects of climate change. Copyright © 2011 John Wiley & Sons, Ltd.

Beschreibung: Snowmelt is an important component of the river discharge in mountain environments. In the past fourty years, the snowmelt dynamics has been mostly evaluated using degree-day based models like the Snowmelt Runoff Model (SRM). This model has no control on the volume of the melting snow, even if SRM includes as data input the snow covered area. This lack explains why the application of SRM may lead to inaccurate snowmelt volume estimations, even if the discharge volumes are accurately reproduced. Here we introduce in SRM the control on the melted snow volume, and consider it in the determination of SRM parameters. The total snow volume, accumulated at the end of winter season, is evaluated by a snow water equivalent statistically-based model, SWE-SEM, and used as an estimate of the melting snow during the summer season. The benefit deriving by the introduction of the control on the melting snow volume is investigated in Mallero basin (northern Italy), for 2003 and 2004 snow melting seasons. The analysis compares the model's results adopting different parameters’ sets, both considering and ignoring the control on the melting snow volume. Copyright © 2011 John Wiley & Sons, Ltd.

Beschreibung: Natural floodplains are spatially heterogeneous and dynamic ecosystems, but at the same time, a highly endangered landscape feature due to climate change and human impacts such as water storage, flood control and hydropower production. Flow is considered a master variable that shapes channel morphology, and the heterogeneity, distribution, and turnover of floodplain habitats. Despite their highly dynamic nature, the relative abundance of different habitat elements (islands, gravel bars) in natural floodplains seems to remain relatively constant over ecological time periods, and is referred to as the “shifting mosaic steady state” concept. In this conceptual context, we analysed spatio-temporal changes in relative habitat abundance and channel complexity of an alpine floodplain from its near natural state in 1940 before water abstraction and levee construction till 2007 using historical aerial images. Within the first decades of impairment, the relative abundance of floodplain habitats that depend on flood and flow pulses such as parafluvial channels and islands shifted towards a greater abundance of terrestrial forest and grassland habitats. After 1986, the duration and frequencies of high precipitation events (〉60 mm 24 h -1 ) triggering major, channel-reworking floods increased substantially and caused a restructuring of the floodplain and decrease in the abundance of more terrestrial habitat types. These results are contrary to expectations of the “shifting mosaic steady state” concept, yet suggest its potential application as an indicator of landscape transformation and human impacts on floodplain ecosystems. Lastly, the results raise the applied question as to whether an increased frequency of high flow events induced by climate change can contribute to floodplain restoration. Copyright © 2011 John Wiley & Sons, Ltd.

Beschreibung: Sublimation is a critical component of the snow cover mass balance. While sublimation can be directly measured using eddy covariance (EC), such measurements are relatively uncommon in complex mountainous environments. EC measurements of surface snowpack sublimation from three consecutive winter seasons (2004, 2005 and 2006) at a wind-exposed and wind-sheltered site were analyzed to characterize sublimation in mountainous terrain. During the 2006 snow season, snow surface and near-surface air temperature, humidity and wind were also measured, permitting the calculation of sublimation rates and a comparison with EC measurements. This comparison showed that measured and simulated sublimation was very similar at the exposed site, but less so at the sheltered site. Wind speeds at the exposed site were nearly four times that at the sheltered site, and the exposed site yielded measured sublimation that was two times the magnitude of that at the sheltered site. Time variation of measured sublimation showed diurnal increases in the early afternoon and increased rates overall as the snow season progressed. Measured mean daily sublimation rates were 0.39 mm day -1 and 0.15 mm day -1 at the exposed and sheltered sites, respectively. At the exposed site, measured sublimation accounted for 16% and 41% of the maximum snow accumulation in 2006 and 2005, respectively. At the sheltered site, measured seasonal sublimation was approximately 4% in 2004 and 2006 and 8% in 2005 of the maximum snow water equivalent. Simulated sublimation was only available for 2006 and suggested smaller but comparable percentages to the sublimation estimated from observations. At the exposed site, a total of 42 mm sublimated for the snow season, which constituted 12% of the maximum accumulation. At the sheltered site, 17 mm (2.2% of maximum accumulation) was sublimated over the snow season. Copyright © 2011 John Wiley & Sons, Ltd.

Beschreibung: An efficient management of our precious water resources is not possible without acquiring a comprehensive and detailed understanding on water fluxes at irrigated areas. In the past few decades, agricultural water balance analyses have been carried out at a wide variety of temporal (from hourly to annual) and spatial (from plant root zone to basin) scales. Scheme-wide water balance analyses, in particular, provide information on the amount of water supplied to irrigation schemes and its fate. This paper attempts to summarize the results of previous studies in quantifying water balance components of irrigation schemes, as well as to present challenges and opportunities of conducting such research projects. With recent improvements in air- and space-borne imaging of land surfaces, remote sensing techniques nowadays can serve as a powerful tool in monitoring/modeling water movements, at or near real time. Remote sensing contribution to water balance studies could be as simple as developing crop classification maps, or as complicated as estimating the spatially-distributed evapotranspiration, which is perhaps the most critical water flux in irrigated areas. Therefore, this paper also aims to review the few studies that have incorporated satellite-derived products in their water budget analysis. Finally, the results of a case study from the southern California are presented to better demonstrate the potential of remotely sensed data. Copyright © 2011 John Wiley & Sons, Ltd.

Beschreibung: The goal of the presented research is the derivation of flood hazard maps, using Monte Carlo simulation of flood propagation at an urban site in the UK, specifically an urban area of the city of Glasgow. A hydrodynamic model describing the propagation of flood waves, based on the De Saint Venant equations in two dimensional form capable of accounting for the topographic complexity of the area (preferential outflow paths, buildings, manholes, etc.) and for the characteristics of prevailing imperviousness typical of the urban areas has been used to derive the hydrodynamic characteristics of flood events (i.e, water depths and flow velocities). The knowledge of the water depth distribution and of the current velocities derived from the propagation model along with the knowledge of the topographic characteristics of the urban area from digital map data allowed for the production of hazard maps based on properly defined hazard indexes. These indexes are evaluated in a probabilistic framework to overcome the classical problem of single deterministic prediction of flood extent for the design event and to introduce the concept of the likelihood of flooding at a given point as the sum of data uncertainty, model structural error and parameterization uncertainty. Copyright © 2011 John Wiley & Sons, Ltd.

Beschreibung: A conceptual instantaneous unit hydrograph (IUH) based on geomorphological association of linear reservoirs developed by López et al . (2005), (GR) has been compared with other IUH models: a distributed GR variation (GR(v)); the Nash IUH (Nash); the Chutha and Dooge IUH (CD); and the Troutman and Karlinger IUH (TK) for the analysis of direct runoff hydrographs recorded in three experimental watersheds of the north of Spain. The comparison was made through a calibration-validation process in which the leave-one-out cross-validation method of Zhao et al . (1995) was applied. The results indicate the satisfactory performance of all the models, with the advantage for the GR(u) model of the dependence on only one parameter, which can be identified from the watershed and event characteristics. This property makes its use easier than that of other models. Copyright © 2011 John Wiley & Sons, Ltd.

Beschreibung: The understanding of nutrient uptake in streams is impeded by limited understanding of how geomorphic setting and flow regime interact with biogeochemical processing. This study investigates these interactions as they relate to transient storage and nitrate uptake in small agricultural and urban streams. Sites were selected across a gradient of channel conditions and management modifications and included three 180-m long geomorphically distinct reaches on each of two streams in north-central Colorado. The agricultural stream has been subject to historically variable cattle-grazing practices and the urban stream exhibits various levels of stabilization and planform alteration. Reach-scale geomorphic complexity was characterized using highly detailed surveys of channel morphology, substrate, hydraulics, and habitat units. Breakthrough-curve modeling of conservative bromide (Br - ) and non-conservative nitrate (NO 3 - ) tracer injections characterized transient storage and nitrate uptake along each reach. Longitudinal roughness and flow depth were positively associated with transient storage, which was related to nitrate uptake, thus underscoring the importance of geomorphic influences on stream biogeochemical processes. Additionally, changes in geomorphic characteristics due to temporal discharge variation led to complex responses in nitrate uptake. Copyright © 2011 John Wiley & Sons, Ltd.

Beschreibung: Grassland degradation resulting from global climate change, overgrazing, and rodent damage is expected to influence the magnitude of canopy hydrological fluxes because of reduced vegetation biomass and changed species composition. The objectives of this study were to: estimate herbaceous canopy rainfall storage capacity (S) along three different stages of sub-alpine grassland degradation (non-degraded, lightly degraded and moderately degraded) in the Qinghai-Tibetan Plateau, China, and relate changes in S to canopy properties. An artificial wetting method and the water budget balance method, using rain simulations, were used for estimating S. Grassland degradation significantly reduced S. In non-degraded, lightly degraded and moderately degraded grasslands, S estimated using the artificial wetting method were 0.612 ± 0.08 mm, 0.289 ± 0.04 mm, 0.217 ± 0.01 mm, respectively; S estimated using the water budget balance method were 0.979 ± 0.32 mm, 0.493 ± 0.13 mm, 0.419 ± 0.09 mm, respectively. These changes could be explained by accompanying changes in above-ground biomass and leaf area index, as well as changes in species composition. Species-specific rainfall storage capacity varied by a factor of 2.7 among the investigated species, with graminoids having the lowest values. Leaf area index was more correlated to S than was canopy coverage. Converting fresh weight of non-leaf tissues into effective leaf area of corresponding species and then introducing a coefficient of leaf area according to the specific storage capacity of leaves improved the linear relationship between S and leaf area index. Copyright © 2011 John Wiley & Sons, Ltd.

Beschreibung: Evapotranspiration (ET) is an important hydrologic process that can be studied and estimated at multiple spatial scales ranging from a leaf to a river basin. We present a review of methods in estimating basin scale ET and its applications in understanding basin water balance dynamics. The review focuses on two aspects of ET: 1) how the basin scale water balance approach is used to estimate ET and 2) how “direct” measurement and modeling approaches are used to estimate basin scale ET. Obviously, the basin water-balance-based ET requires the availability of good precipitation and discharge data to calculate ET as a residual on longer time scales (annual) where net storage changes are assumed to be negligible. ET estimated from such a basin water balance principle is generally used for validating the performance of ET models. On the other hand, many of the direct estimation methods involve the use of remotely sensed data to estimate spatially explicit ET and use basin-wide averaging to estimate basin scale ET. The direct methods can be grouped into soil moisture balance modeling, satellite-based vegetation index methods, and methods based on satellite land surface temperature measurements that convert potential ET into actual ET using a proportionality relationship. The review also includes the use of complementary ET estimation principles for large area applications. The review identifies the need to compare and evaluate the different ET approaches using standard data sets in basins covering different hydro-climatic regions of the world. Copyright © 2011 John Wiley & Sons, Ltd.

Beschreibung: In this paper a mathematical model is presented for the dispersion problem in finite porous media in which the flow is two-dimensional, the seepage flow velocity is periodic and dispersion parameter is proportional to the flow velocity. In addition to these, first order decay and zero order production parameters have also been considered directly proportional to the velocity. Retardation factor is taken into account in the present problem. First-type boundary condition of periodic nature is considered at the extreme end of the boundary. Mixed-type boundary condition is assumed at the originof the domain. A classical mathematical substitution transforms the original advection–dispersion equation into diffusion equation in terms of another dependent and independent variables, with constant coefficients. Laplace transform technique (LTT) is used to obtain the analytical solution. Copyright © 2002 John Wiley & Sons, Ltd.

Beschreibung: The vertical and lateral profiles of temporal variations in soil moisture are important for understanding the hydrological process along hillside transects. In this study, relationships among measured soil moistures were explored in order to configure the hydrologic contributions of different flowpaths. All the measured soil moistures included a common stochastic structure because rainfall, the hydrometeological driver, is the main factor that determines the soil moisture response feature, and the infiltration process through the topsoil at a shallow depth is also common in all measured soil moisture histories. Therefore, the relationships between the measured series are also affected by both rainfall and topsoil infiltration. The common stochastic structure of the soil moisture series was removed via a pre-whitening procedure. A systematic analysis procedure is presented to delineate the exclusive causal relationships among multiple soil moisture measurements. A monitoring system based on multiplexed time domain reflectometry (TDR) was used to obtain soil moisture time series along two transects on a steep hillslope during the rainy season. The application of the proposed method for monitoring points in two adjacent locations provided 8, 12, 14, and 13, 16, 22 causal relationships for vertical, lateral in parallel, and diagonal directions, respectively, along the two transects. The point-based contributions of the internal flowpath can be evaluated as the correlation is normalized in the context of inflow and outflow. The hydrological processes in the soil layer, vertical flow, lateral flow, downslope recharge, and return flow were quantified, and the relative importance of each hydrological component was determined to improve our understanding of the hydrological processes along the two transects of the study area. Copyright © 2002 John Wiley & Sons, Ltd.

Beschreibung: Application of models for estimating rainfall partitioning in decidous forests may be considered time-consuming and laborious given the need for two different parameter sets to describe leafed and leafless periods. This paper reports how rainfall partitioning modelling was done for a downy oak forest plot (Eastern Pyrenees Mountains, NE Spain) using sparse Rutter and Gash interception loss models and their suitability for such studies. Moreover, variability in model sensitivity is evaluated and an attempt to simplify their application is also presented. The estimation error for interception loss in the leafed period was −26.3% and −4.2% with the Rutter model and the Gash model applied with Penman-Monteith-based evaporation rate, respectively. The estimate for the leafless period was less accurate in both models, suggesting that modelling in the leafless period is more susceptible to error. Nevertheless, with the Gash model, the result was well below the expected measurement error. Models proved to be highly sensitive to change in canopy cover in all periods tested. The Rutter model was especially sensitive to zero plane d23 isplacement changes in the leafed period, while the Gash model showed high linear sensitivity to evaporation rate. In addition, a decrease in rainfall rate affects the estimation of interception loss more than an increase in it. Regardless of its high sensitivity to these parameters, the Gash model yielded a good estimate of rainfall partitioning for the total period, when only one set of parameters was used, although event-based error compensation occurred and some periods were over or underestimated. Copyright © 2002 John Wiley & Sons, Ltd.

Beschreibung: A spatially autocorrelated effect exists in precipitation of a mountainous basin. This study examines the relationship between maximum annual rainfall and elevation in the Kaoping River Basin of southern Taiwan using spatial regression models (i.e., geographically weighted regression (GWR), simultaneous autoregression (SAR), and conditional autoregression (CAR)). Results show that the GWR, SAR, and CAR models can improve spatial data fitting and provide an enhanced estimation for the rainfall-elevation relationship than the ordinary least squares (OLS) approach. In particular, GWR achieves the most accurate estimation and SAR and CAR achieves similar performance in terms of the Akaike information criterion (AIC). The relationship between extreme rainfall and elevation for longer duration is more concise than that for short durations. Results show that the spatial distribution of precipitation depends on elevation, and that rainfall patterns in study area are heterogeneous between the southwestern plain and the eastern mountain area. Copyright © 2002 John Wiley & Sons, Ltd.

Beschreibung: Biofiltration systems represent an effective technology for the management of urban stormwater runoff volumes and quality. The performance of these systems, although largely dependent on their physical characteristics, is also strongly affected by the natural variability of runoff occurrence and volumes. This paper presents a model that describes the statistical behaviour of the main variables involved in the water balance of a biofiltration system, given its main physical properties (filter media and vegetation types) and accounting for the natural inflow variability in terms of occurrence and water volumes. The model permits the analytical derivation of the long-term ( e.g ., annual) probability density function of the soil water content in the filter media and the estimation of the main statistics of water fluxes, i.e ., outflow, evapotranspiration, and overflow. By relating the soil water content in the filter media before inflow events to the outflow total nitrogen concentrations, the model also gives estimates of the statistics of nitrogen removal performance as a function of inflow variability. The model was tested against field data collected at a stormwater biofiltration system in Melbourne, Australia. The model could be used to rapidly assess the hydrologic and nitrogen treatment performance of alternative applications of biofiltration for stormwater management across a range of climates. Copyright © 2002 John Wiley & Sons, Ltd.

Beschreibung: Recognizing the spatial heterogeneity of hydraulic parameters, many researchers have studied the solute transport by both groundwater and channel flow in a stochastic framework. One of the methodologies used to up-scale the stochastic solute transport equation, from a point-location scale to a grid scale, is the cumulant expansion method combined with the calculus for the time-ordered exponential and the calculus for the Lie operator. When the point-location scale transport equation is scaled up to the grid scale, using the cumulant expansion method, a new dispersion coefficient emerges in the dispersive term of the solute transport equation in addition to the molecular dispersion coefficient. This velocity driven dispersion is called “macrodispersion”. The macrodispersion coefficient is the integral function of the time ordered covariance of the random velocity field. The integral is calculated over a Lagrangian trajectory of the flow. The Lagrangian trajectory depends on: (1) the spatial origin of the particle, (2) the time when the macrodispersion is calculated, and (3) the mean velocity field along the trajectory itself. The Lagrangian trajectory is a recursive function of time; since, the location of the particle along the trajectory at a particular time depends on the location of the particle at the previous time. This recursive functional form of the Lagrangian trajectory makes the calculation of the macrodispersion coefficient difficult. Especially for the unsteady, spatially non-stationary, non-uniform flow field, the macrodispersion coefficient is a highly complex expression and so far calculated using numerical methods in the discrete domains. Here, an analytical method was introduced to calculate the macrodispersion coefficient in the discrete domain for the unsteady and steady, spatially non-stationary flow cases accurately and efficient. This study can fill the gap between the theory of the ensemble averaged solute transport model and its numerical implementations. Copyright © 2011 John Wiley & Sons, Ltd.

Beschreibung: The rise in stream stage during high flow events (floods) can induce losing stream conditions even along stream reaches that are gaining during baseflow conditions. The aquifer response to flood events can impact the geochemical composition of both near-stream groundwater and post-event streamflow, but the amount and persistence of recharged floodwater may differ as a function of local hydrogeologic forcings. As a result, this study focuses on how vertical flood recharge varies under different hydrogeologic forcings and the significance that recharge processes can have on groundwater and streamflow composition after floods. River and shallow groundwater samples were collected along three reaches of the Upper San Pedro River (Arizona, USA) before, during and after the 2009 and 2010 summer monsoon seasons. Tracer data from these samples indicates that subsurface floodwater propagation and residence times are strongly controlled by the direction and magnitude of the dominant stream-aquifer gradient. A reach that is typically strongly gaining shows minimal floodwater retention shortly after large events, whereas the moderately gaining and losing reaches can retain recharged floodwater from smaller events for longer time periods. The moderately gaining reach likely returned flood recharge to the river as flow declined. These results indicate that reach-scale differences in hydrogeologic forcing can control (1) the amount of local flood recharge during events, and (2) the duration of it's subsurface retention and possible return to the stream during low-flow periods. Our observations also suggest that the presence of floodwater in year-round baseflow is not due to long-term storage beneath the streambed along predominantly gaining reaches, so three alternate mechanisms are suggested: (1) repeated flooding that drives lateral redistribution of previously recharged floodwater, (2) vertical recharge on the floodplain during overbank flow events, and (3) temporal variability in the stream-aquifer gradient due to seasonally varying water demands of riparian vegetation. Copyright © 2011 John Wiley & Sons, Ltd.