ALBERT

Description: Soil and vadose zone profiles are used as an archive of changes in groundwater recharge and water quality following changes in land use in an area of the Loess Plateau of China. A typical rain-fed loess-terrace agriculture region in Hequan, Guyuan is taken as an example and multiple tracers (chloride mass balance, stable isotopes, tritium, and water chemistry) are used to examine groundwater recharge mechanisms and to evaluate soil water chloride as an archive for recharge rate and water quality. Results show that groundwater recharge beneath natural uncultivated grassland, used as a baseline, is about 94–100 mm yr -1 and the time it takes for annual precipitation to reach water table through the thick unsaturated zone is from decades to hundreds of years (tritium free). This recharge rate is 2–3 orders of magnitude more than in the other semiarid areas with similar annual rainfall and with deep rooted vegetation and relatively high temperature. Most of the water that eventually becomes recharge originally infiltrated in the summer months. The conversion from native grassland to winter wheat has reduced groundwater recharge by 42–50% (50–55 mm yr -1 for recharge), and from winter wheat to alfalfa resulted in a significant chloride accumulation in the upper soil zone which terminated deep drainage. The paper also evaluates the time lag between potential recharge and actual recharge to aquifer and between increase in solute concentration in soil moisture and that in the aquifer following land-use change due to the deep unsaturated zone. Copyright © 2012 John Wiley & Sons, Ltd.

Description: Shallow upland drains, grips, have been hypothesized as responsible for increased downstream flow magnitudes. Observations provide counterfactual evidence, often relating to the difficulty of inferring conclusions from statistical correlation and paired catchment comparisons; and the complexity of designing field experiments to test grip impacts at the catchment-scale. Drainage should provide drier antecedent moisture conditions, providing more storage at the start of an event; but, grips have higher flow velocities than overland flow so potentially delivering flow more rapidly to the drainage network. We develop and apply a model for assessing the impacts of grips upon flow hydrographs. The model was calibrated on the gripped case; then the gripped case was compared with the intact case by removing all grips. This comparison showed that even given parameter uncertainty, the intact case had significantly higher flood peaks and lower baseflows, mirroring field observations of the hydrological response of intact peat. The simulations suggest that this is because delivery effects may not to translate into catchment-scale impacts for three reasons. First, in our case, the proportions of flow path lengths that were hillslope were not changed significantly by gripping. Second, the structure of the grip network as compared with the structure of the drainage basin mitigated against grip-related increases in the concentration of runoff in the drainage network, although it did marginally reduce the mean timing of that concentration at the catchment outlet. Third, the effect of the latter upon downstream flow magnitudes can only be assessed by reference to the peak timing of other tributary basins, emphasizing that drain effects are both relative and scale dependent. However, given the importance of hillslope flow paths, we show that if upland drainage causes significant changes in surface roughness on hillslopes, then critical and important feedbacks may impact upon the speed of hydrological response. Copyright © 2012 John Wiley & Sons, Ltd.

Description: Natural soil pipes are found in peatlands but little is known about their hydrological role. This paper presents the most complete set of pipe discharge data to date from a deep blanket peatland in northern England. In a 17.4-ha catchment, we identified 24 perennially-flowing and 60 ephemerally-flowing pipe outlets. Eight pipe outlets along with the catchment outlet were continuously gauged over an 18-month period. The pipes in the catchment were estimated to produce around 13.7 % of annual streamflow with individual pipes often producing large peak flows (maximum peak of 3.8 L s -1 ). Almost all pipes, whether ephemeral, perennially-flowing, shallow or deep (outlets 〉 1 m below the peat surface), showed increased discharge within a mean of 3 hours after rainfall commencement and were dominated by stormflow, indicating good connectivity between the peatland surface and the pipes. However, almost all pipes had a longer time period between hydrograph peak and return to baseflow compared to the stream (mean of 23.9 hours for pipes, 19.7 hours for stream). As a result, the proportion of streamflow produced by the pipes at any given time increased at low flows and formed the most important component of stream discharge for the lowest 10 % of flows. Thus, a small number of perennially-flowing pipes became more important to the stream system under low flow conditions and probably received water via matrix flow during periods between storms. Given the importance of pipes to streamflow in blanket peatlands, further research is required into their wider role in influencing stream-water chemistry, water temperature and fluvial carbon fluxes, as well as their role in altering local hydrochemical cycling within the peat mass itself. Enhanced piping within peatlands caused by environmental change may lead to changes in streamflow regime with larger low flows and more prolonged drainage of the peat. Copyright © 2012 John Wiley & Sons, Ltd.

Description: The hydrology of Quebec (Canada) boreal fens is poorly documented. Many peatlands are located in watersheds with impounded rivers. In such cases, their presence influences reservoir inflows. In recent years, some fens have been subjected to an increase of their wet area, a sign that they may be evolving towards an aquatic ecosystem. This dynamic process is referred to as aqualysis. This paper presents the seasonal and monthly hydrological budgets of a small watershed including a highly aqualysed fen (James Bay region). Monitoring of precipitation ( P ), runoff ( Q ) and groundwater levels ( WL ) was conducted during the ice-free season. Three semi-empirical equations (Thornthwaite, Priestley-Taylor and Penman-Monteith) were used and compared to calculate potential evapotranspiration ( PET ). The first two equations, having fewer parameters, estimate higher PET values than the third equation. The use of pressure level gauges installed in wells, for the calculation of peatland water storage, is inconclusive. Swelling of peat, peat decomposition and plant composition could be responsible for non-negligible amounts of absorbed water, which are not entirely accounted for by well levels. The estimation of peat matrix water storage is potentially the largest source of error and the limiting factor to calculate water balances in this environment. The results show that the groundwater level and the water storage vary depending on the season and especially after a heavy rainfall. Finally, the results illustrate the complexity of water routing through the site and, thus, raise several questions to be resolved in the future. Copyright © 2012 John Wiley & Sons, Ltd.

Description: Meander bends in alluvial rivers morphologically evolve toward meander cutoff with narrowing intra-meander necks, and this should steepen hydraulic gradients and intensify intra-meander hyporheic flux. This research used dye tracking and head loss measurements in a 1:500 planimetrically scaled laboratory river table to quantify the spatial and temporal intensification of intra-meander flux rates at two evolution ages. The younger meander bend, M1, had a sinuosity of 2.3, a river neck width of 0.39 cm, and 0.6% river slope, and the older meander bend, M3, had a sinuosity of 5.2, a river neck width of 0.12 cm, and 0.5% river slope. Flux into and out of the meander bend was estimated along the normalized curvilinear distance s *, with the meander neck at s * = 0.1 and s * = 0.9, the meander centroid at s * = 0.37 and s * = 0.63, and the apex at s * = 0.5. Between the meander centroid and neck we documented a 60% spatial intensification for M1 and a 90% spatial intensification for M3. Between M1 and M3 we documented a 135% temporal intensification at the neck and a 100% intensification at the centroid. Our empirical spatial and temporal intensification rates involving the M1 and the M3 scenario were 1 to 3 times lower than theoretical rates derived from a river evolution model with equivalent M1 and M3 planimetry. Over estimation by the theoretical model was attributed to exaggerated head loss caused by the model neglecting groundwater contributions to river stage. Hyporheic exchange provides critical ecosystem services and its spatial and temporal variation with meander evolution should be considered in river management. Copyright © 2012 John Wiley & Sons, Ltd.

Description: Watershed models which combine hydrology and water quality are being widely utilized in integrated watershed management for the determination of best water management practices. In this study, the hydrology of the Lower Porsuk Stream Watershed in Turkey has been modeled with SWAT to determine optimal water management strategies. The calibration and validation process have been accomplished using data from two monitoring stations. The model has been run for the 1978–2009 period and while the 1998–2004 period has been used for calibration, the validation has spanned the whole period. The SWATCup calibration and uncertainity program has been utilized for this purpose. No significant differences have been detected among different iteration numbers in the calibration period. The monthly Nash-Sutcliffe and R 2 performance indicatiors for the upstream Esenkara station have been 0.74 and 0.88, respectively for the calibration period, and 0.87 and 0.87, respectively for the validation period. The Kıranharmanı station which is located close to the watershed outlet has shown values of 0.59 and 0.72, respectively for the calibration period, and 0.44 and 0.56, respectively for the validation period. There are uncertanities in the abstracted irrigation and groundwater quantities which have reflected in the results in the Kıranharmanı station which is more affected as it lies downstream of the irrigation areas. The effects of different irrigation practices on the flow regime have been also investigated. A scenario has been implemented in which drip irrigation wholly replaces conventional furrow and sprinkler irrigation. The scenario has shown increases in stream flows by 87 % for the whole year. The adoption of more efficient irrigation practices thus results in reducing the water stress induced by irrigation demands. With this study a modeling framework has been founded to aid water management applications in the Lower Porsuk Stream Watershed by generating scenarios for best management practices. Copyright © 2012 John Wiley & Sons, Ltd.

Description: In recent decades, copula functions have been applied in bivariate drought duration and severity frequency analysis. Among a number of potential copulas, Clayton has been mostly employed in drought analysis. In this research, we study the influence of the tail shape of various copula functions (i.e. Gumbel, Frank, Clayton, and Gaussian) on drought bivariate frequency analysis. The appropriateness of Clayton copula for the characterization of drought characteristics is also investigated. Drought data are extracted from standardized precipitation index (SPI) time series for four stations in Canada (La Tuque and Grande Prairie) and Iran (Anzali and Zahedan). Both duration and severity datasets are positively skewed. Different marginal distributions were first fitted to drought duration and severity data. The gamma and exponential distributions were respectively selected for drought duration and severity according to the positive skewness and Kolmogorov- Smirnov test. The results of copula modeling show that the Clayton copula function is not an appropriate choice for the employed datasets in the current study, and does not give more drought risk information than an independent model for which the duration and severity dependence is not significant. The reason is that the dependence of two variables in the upper tail of Clayton copula is very weak and similar to the independent case, while the observed data in the transformed domain of cumulative density function shows high association in the upper tail. Instead, the Frank and Gumbel copula functions show better performance than Clayton function for drought bivariate frequency analysis. Copyright © 2012 John Wiley & Sons, Ltd.

Description: Wetlands are valuable ecosystems that provide many valuable services, yet many of these important ecosystems are at risk because of current trends in climate change. The Prairie Pothole Region (PPR) in the upper-midwest of the U.S. and south-central Canada, characterized by glacially-sculpted landscapes and abundant wetlands, is one such vulnerable region. According to regional/global climate model predictions, drought occurrence will increase in the PPR region through the 21st century and thus will probably cause the amount of water in wetlands to decline. Water surface area (WSA) of Kidder County, ND from 1984-2011 was measured by classifying TM/ETM+ images through the Modified Normalized Difference Water Index (MNDWI).We then developed a linear model based on the water surface area (WSA) of these wetlands and historical climate data, and used this to determine the wetland sensitivity to climate change and predict future wetlands WSA in the PPR. Our model based on Palmer Drought Severity Index (PDSI) of the current year (PDSI t-0 ) and two years previous (PDSI t-2 ) can explain 79% of the annual wetland WSA variance, suggesting a high sensitivity of wetlands to drought/climate change. We also predicted the PPR wetlands WSA in the 21st century under A1B scenario (a mid-carbon emission scenario) using simulated PDSI based on IPCC AR4 22-model ensemble climate. According to our prediction, the WSA of the PPR wetlands will decrease to less than half of the baseline WSA (defined as the mean wetlands WSA of the 2000s) by the mid of the 21st century, and to less than one-third by the 2080s, and will then slightly increase in the 2090s. This considerable future wetland loss caused only by climate change provides important implication to future wetland management and climate adaptation policy. Copyright © 2012 John Wiley & Sons, Ltd.

Description: In hydrology, the storage-discharge relationship is a fundamental catchment property. Understanding what controls this relationship is at the core of catchment science. To date, there are no direct methods to measure water storage at catchment scales (10 1 -10 3  km 2 ). In this study, we use direct measurements of terrestrial water storage dynamics by means of superconducting gravimetry in a small headwater catchment of the Regen River, Germany, to derive empirical storage-discharge relationships in nested catchments of increasing scale. Our results show that the local storage measurements are strongly related to streamflow dynamics at larger scales (〉 100 km 2 ; correlation coefficient = 0.78-0.81), but at small scale no such relationship exists (~ 1 km 2 ; correlation coefficients = -0.11). The geologic setting in the region can explain both the disconnection between local water storage and headwater runoff, and the connectivity between headwater storage and streams draining larger catchment areas. More research is required to understand what controls the form of the observed storage-discharge relationships at the catchment scale. This study demonstrates that high-precision gravimetry can provide new insights into the complex relationship between state and response of hydrological systems. Copyright © 2012 John Wiley & Sons, Ltd.

Description: Water resources availability in the semi-arid regions of Iran has experienced severe reduction due to increasing water use and lengthening of dry periods. To better manage this resource we investigated the impact of climate change on water resources and wheat yield in the Karkheh River Basin (KRB) in the semi-arid region of Iran. Future climate scenarios for 2020-2040 were generated from the Canadian Global Coupled Model for scenarios A1B, B1 and A2. We constructed a hydrological model of KRB using SWAT to project water resources availability. Blue and green water components were modeled with uncertainty ranges for both historic and future data. SUFI2 was used with parallel processing option to calibrate the model based on river discharge and wheat yield. Furthermore, a newly developed program “critical continuous day calculator” (CCDC) was used to determine the frequency and length of critical periods for precipitation, maximum temperature and soil moisture. We found that in the northern part of KRB freshwater availability will increases from 1716 to 2670 m 3 /capita/year despite an increase of 28% in the population in 2025 in B1 scenario. In the southern part, where much of the agricultural lands are located, the freshwater availability will on the average decrease by 44%. The long term average irrigated wheat yield, however will increase in the south by 1.2% to 21% in different subbasins; but for rainfed wheat, this variation is from -4% to 38%. The results of CCDC showed an increase of up to 25% in both frequency and length of dry periods in south Karkheh, while increasing flood events could be expected in the northern and western parts of the region. In general, there is variability in the impact of climate change in the region where some areas will experience net negative, while other areas experience a net positive impact. Copyright © 2013 John Wiley & Sons, Ltd.

Description: Numerical models are frequently used for the regional quantification of groundwater recharge. However there is a wide-range of potential models available that represent the land surface with varying degrees of complexity, but which are rarely tested against observations at the field-scale. We compared four models that simulate potential recharge at four intensively monitored sites with different vegetation and soil types in two adjacent catchments. These models were: Penman-Grindley (PG), UN Food and Agricultural Organisation (FAO), SPAtial Distributed Evaporation (SPADE) and Joint UK Land Environment Simulator (JULES). Standardised, unoptimised land surface datasets and pertinent literature were used for parameterisation to reflect practice in regional water resource management and planning in the UK. The models were validated against soil moisture observations at all sites, as well as observed transpiration and interception and calculated total evaporation over a year at a woodland site. Soil moisture observations were generally reproduced well but there were significant differences in how the models apportioned precipitation through the hydrological cycle. This demonstrates that soil moisture data alone are not a good diagnostic for groundwater recharge models. Significant differences in potential recharge were produced by models at both grassland sites, although simulated average annual potential recharge varied by only 15% at the grassland site on permeable soil. At the woodland sites, soil moisture contents were reproduced least accurately and there were large differences in potential recharge at both woodland sites. This predominantly resulted from varied and inaccurate simulation of evaporation, particularly in the form of interception losses where this was explicitly represented in models. Differences in model structure, such as runoff representation, and parameter selection also influenced all results. Copyright © 2013 John Wiley & Sons, Ltd.

Description: In many mountain basins river discharge measurements are located far away from runoff source areas. This study tests whether a basic snowmelt runoff conceptual model can be used to estimate relative contributions of different elevation zones to basin-scale discharge in the Cache la Poudre, a snowmelt-dominated Rocky Mountain river. Model tests evaluate scenarios that vary model configuration, input variables, and parameter values to determine how these factors affect discharge simulation and the distribution of runoff generation with elevation. Results show that the model simulates basin discharge well (NSCE and R 〉0.90) when input precipitation and temperature are distributed with different lapse rates, with a rain-snow threshold parameter between 0-3.3 °C, and with a melt rate parameter between 2-4 mm °C -1 d -1 because these variables and parameters can have compensating interactions with each other and with the runoff coefficient parameter. Only the hydrograph recession parameter can be uniquely defined with this model structure. These non-unique model scenarios with different configurations, input variables, and parameter values all indicate that the majority of basin discharge comes from elevations above 2900 m, or less than 25% of the basin total area, with a steep increase in runoff generation above 2600 m. However, the simulations produce unrealistically low runoff ratios for elevations above 3000 m, highlighting the need for additional measurements of snow and discharge at under-sampled elevations to evaluate the accuracy of simulated snow and runoff patterns. Copyright © 2013 John Wiley & Sons, Ltd.

Description: Predicting long-term consequences of climate change on hydrologic processes has been limited due to the needs to accommodate the uncertainties in hydrological measurements for calibration, and to account for the uncertainties in the models that would ingest those calibrations and uncertainties in climate predictions as basis for hydrological predictions. We implemented a hierarchical Bayesian (HB) analysis to coherently admit multiple data sources and uncertainties including data inputs, parameters, and model structures to identify the potential consequences of climate change on soil moisture and streamflow at the head watersheds ranging from low to high elevations in the southern Appalachian region of the United States. We have considered climate change scenarios based on three greenhouse gas emission scenarios of the Interovernmental Panel on Climate Change: A2, A1B and B1 emission scenarios. Full predictive distributions based on hierarchical Bayesian models are capable of providing rich information and facilitating the summarization of prediction uncertainties. With predictive uncertainties taken into account, the most pronounced change in soil moisture and streamflow would occur under the A2 scenario at both low and high elevations, followed by the A1B scenario and then by the B1 scenario. Uncertainty in the change of soil moisture is less than that of streamflow for each season, especially at high elevations. A reduction of soil moisture in summer and fall, a reduction or slight increase of streamflow in summer, and an increase of streamflow in winter are predicted for all three scenarios at both low and high elevations. The hydrological predictions with quantified uncertainties from a HB model could aid more-informed water resource management in developing mitigation plans, and dealing with water security under climate change. Copyright © 2012 John Wiley & Sons, Ltd.

Description: This research proposes a combination of SWAT and MODFLOW, MD-SWAT-MODFLOW, to address the multi-aquifers condition in Choushui River alluvial fan, Taiwan. The natural recharge and unidentified pumping/recharge are separately estimated. The model identifies the monthly pumping/recharge rates in multi-aquifers so that the daily streamflow can be simulated correctly. A multi-aquifers condition means a subsurface formation composed of at least the unconfined aquifer, the confined aquifer, and an in-between aquitard. In such a case, the variation of groundwater level is related to pumping/recharge activities in vertically adjacent aquifer and the river-aquifer interaction. Both factors in turn affect the streamflow performance. Results show that MD-SWAT-MODFLOW performs better than SWAT alone in terms of simulated streamflow, especially during low flow period, when pumping/recharge rates are properly estimated. A sensitivity analysis of individual parameter suggests that the vertical leakance may be the most sensitive among all investigated MODFLOW parameters in terms of the estimated pumping/recharge among aquifers, and the LH-OAT sensitivity analysis indicates that the hydraulic conductivity of channel is the most sensitive to the model performance. It also points out the necessity to simultaneously estimate pumping/recharge rates in multi-aquifers. The estimated net pumping rate can be treated as a lower bound of the actual local pumping rate. As a whole, the model provides the spatio-temporal groundwater use, which gives the authorities insights to manage groundwater resources. Copyright © 2012 John Wiley & Sons, Ltd.

Description: We report on the calibration of the one-dimensional hydrodynamic lake model DYRESM to simulate the water temperature conditions of the pre-alpine Lake Ammersee (South-east Germany) which is representative of deep and large lakes in this region. Special focus is given to the calibration in order to reproduce the correct thermal distribution and stratification including the time of onset and duration of summer stratification. To ensure the application of the model to investigate the impact of climate change on lakes, an analysis of the model sensitivity under stepwise modification of meteorological input parameters (air temperature, wind speed, precipitation, global radiation, cloud cover, vapor pressure, and tributary water temperature) was conducted. The total mean error of the calibration results is –0.23 °C, the root mean square error amounts to 1.012 °C. All characteristics of the annual stratification cycle were reproduced accurately by the model. Additionally, the simulated deviations for all applied modifications of the input parameters for the sensitivity analysis can be differentiated in the high temporal resolution of monthly values for each specific depth. The smallest applied alteration to each modified input parameter caused a maximum deviation in the simulation results of at least 0.26 °C. The most sensitive reactions of the model can be observed through modifications of the input parameters air temperature and wind speed. Hence the results show that further investigations at Lake Ammersee, such as coupling the hydrodynamic model with chemo-dynamic models to assess the impact of changing climate on biochemical conditions within lakes, can be carried out using DYRESM. Copyright © 2012 John Wiley & Sons, Ltd.

Description: In semi-arid and arid river basins, understanding the connectivity between rivers and alluvial aquifers is one of the key challenges for the management of groundwater resources. The type of connection present (gaining, losing-connected, transitional and losing-disconnected) was assessed at 12 sites along six Murray-Darling Basin river reaches. The assessments were made by measuring the hydraulic head in the riparian zone near the rivers to evaluate if the water tables intersected the riverbeds and by measuring fluid pressure (ψ) in the riverbeds. The rationale for the latter was that ψ will always be greater than or equal to zero under connected conditions (either losing or gaining) and always lesser than or equal to zero under losing-disconnected conditions. A mixture of losing-disconnected, losing-connected and gaining conditions was found among the 12 sites. The losing-disconnected sites all had a riverbed with a lower hydraulic conductivity than the underlying aquifer, usually in the form of a silty clay or clay unit 0.5 – 2 m in thickness. The riparian water tables were 6 to 25 m below riverbed level at the losing-disconnected sites but never lower than 1 m below riverbed level at the losing-connected ones. The contrast in water table depth between connected and disconnected sites was attributed to the conditions at the time of the study, when a severe regional drought had generated a widespread decline in regional water tables. This decline was apparently compensated near losing-connected rivers by increased infiltration rates, while the decline could not be compensated at the losing-disconnected rivers because the infiltration rates were already maximal there. Copyright © 2012 John Wiley & Sons, Ltd.

Description: Abstact The distribution of groundwater inflows in a stream reach plays a major role in controlling the stream temperature, a vital component shaping the riverine ecosystem. In this study, the DTS system was installed in a small Danish lowland stream, Elverdamsåen, to assess the seasonal dynamics of groundwater inflow zones using high spatial (1 m) and temporal (3 minutes) resolution of water temperature measurements. Four simple criteria consisting of 30 min average temperature at 16:00, mean and standard deviation of diurnal temperatures, and the day-night temperature difference were applied to three DTS datasets representing stream temperature responses to the variable meteorological and hydrological conditions prevailing in summer, winter and spring. The standard deviation criterion was useful to identify groundwater discharge zones in summer and spring conditions, while the mean temperature criterion was better for the winter conditions. In total, 20 interactions were identified from the DTS datasets representing summer, 16 in winter and 19 in spring, albeit with only two interactions contributing in all three seasons. Higher baseflow to streamflow ratio, antecedent precipitation and presence of fractured clayey till in the stream reach were deemed as the vital factors causing apparent seasonal variation in the locations of upwelling zones, prompting use of DTS not only in preconceived scenarios of large diurnal temperature change but rather a long term deployment covering variable meteorological and hydrological scenarios. Copyright © 2012 John Wiley & Sons, Ltd.

Description: Non-point source pollution is a key issue in integrated river basin management around the world, and has resulted in water contamination, aquatic ecology deterioration and eutrophication. Xin'anjiang Catchment is the key drinking water source area for Hangzhou City, China. A promising model (Soil and Water Assessment Tool: SWAT) was applied to assess the non-point source pollution and its effect on drinking water. Sensitivity analysis of model parameters was carried out using the SUFI-2 sensitivity technique. Water discharge, sediment, total nitrogen and total phosphorus loads processes from 2000 to 2010 were simulated and the spatial distributions of non-point source pollutants were evaluated at the catchment and administrative country levels. The results show that the hydrological parameters of SWAT were dominantly sensitive for non-point source pollution simulation, including CN2, RCHRG_DP, ALPHA_BF, SOL_AWC, ESCO and SOL_K, and the characteristic parameters of sub-basins (viz. HRU_SLP, SLSUBBSN). Also, water quality parameters (viz. CH_EROD, NPERCO, RSDCO and PPERCO, PHOSKD, etc.) have a significant effect on nutrients. The model performance was very satisfactory, especially for runoff, sediment, and TP simulation. The non-point source pollutant load increased from 2001 to 2010 in the whole catchment. Total nitrogen (TN) load increased from 3,428 tons (0.59 ton/km 2 ) to 7,315 tons (1.25 ton/km 2 ) and total phosphorus (TP) load increased from 299 tons (0.05 ton/km 2 ) to 867 tons (0.15 ton/km 2 ). The contribution of rice land was the largest, accounting for nearly 95%, followed by tea garden (3.56%), winter wheat (1.37%), forest (0.07%) and grassland (0.02%). Moreover, She County and Xiuning County contributed more than half of the non-point source pollutants. This study was expected to provide a method and reference for non-point source pollution quantification, and to support water quality management implementation in China. Copyright © 2012 John Wiley & Sons, Ltd.

Description: Cosmogenic 7 Be is a natural tracer of short-term hydrological processes, but its distribution in upland fluvial environments over different temporal and spatial scales has not been well described. We measured 7 Be in 450 sediment samples collected from perennial channels draining the middle of the Connecticut River Basin, an environment that is predominantly well-sorted sand. By sampling tributaries that have natural and managed fluctuations in discharge, we find that the 7 Be activity in thalweg sediments is not necessarily limited by the supply of new or fine-grained sediment, but is controlled seasonally by atmospheric flux variations and the magnitude and frequency of bed mobilizing events. In late winter, 7 Be concentrations in transitional bedload are lowest, typically 1 to 3 Bq kg -1 as 7 Be is lost from watersheds via radioactive decay in the snowpack. In mid-summer, however, 7 Be concentrations are at least twice as high because of increased convective storm activity which delivers high 7 Be fluxes directly to the fluvial system. A mixed layer of sediment at least 8 cm thick is maintained for months in channels during persistent low rainfall and flow conditions, indicating that stationary sediments can be recharged with 7 Be. However, bed mobilizing rain on snowmelt events in late Spring can “reset” 7 Be amounts and concentrations in the channel as previously buried “old” sediment with low 7 Be is mixed into the thalweg. We conclude that given proper temporal and spatial sampling, 7 Be is a valuable tracer of seasonal-timescale mass transport and exchange in coarse-grained fluvial systems. Copyright © 2013 John Wiley & Sons, Ltd.

Description: A statistical framework based on nonlinear dynamics theory and recurrence quantification analysis (RQA) of dynamical systems is proposed to quantitatively identify the temporal characteristics of extreme (maximum) daily precipitation series. The methodology focuses on both observed and general circulation model (GCM) generated climates for present (1961-2000) and future (2061-2100) periods which correspond to 1xCO 2 and 2xCO 2 simulations. The daily precipitation has been modeled as a stochastic process coupled with atmospheric circulation. An automated and objective classification of daily circulation patterns (CPs) based on optimized fuzzy rules was used to classify both observed CPs and ECHAM4 GCM-generated CPs for 1xCO 2 and 2xCO 2 climate simulations (scenarios). The coupled model “CP-precipitation” was suitable for precipitation downscaling. The overall methodology was applied to the medium-sized mountainous Mesochora catchment in Central-Western Greece. Results reveal substantial differences between the observed maximum daily precipitation statistical patterns and those produced by the two climate scenarios. A variable nonlinear deterministic behavior characterizes all climate scenarios examined. Transitions' patterns differ in terms of duration and intensity. The 2xCO 2 scenario contains the strongest transitions highlighting an unusual shift between floods and droughts. The implications of the results to the predictability of the phenomenon are also discussed. Copyright © 2013 John Wiley & Sons, Ltd.

Description: Accurate knowledge of hydrogeological parameters is essential for groundwater modeling, protection and remediation. Three methods (type curve fitting method (TCFM), inflection point method (IPM) and global curve-fitting method (GCFM)) which are frequently applied in the estimation of leaky aquifer parameters were compared using synthetic pumping tests. The results revealed GCFM could provide best parameter estimation among the three methods with fewer uncertainties associated with the processes of parameter estimation. GCFM was also found to be both time-saving and low cost, and is thus more preferable for hydrogeological parameter estimation than the other two methods. Copyright © 2013 John Wiley & Sons, Ltd.

Description: The effects of climate change have a substantial influence on the extremely vulnerable hydrologic environment of the Tibetan Plateau (TP). The estimation of alpine inland lake water storage variations is essential to modeling the alpine hydrologic process and evaluating water resources. Due to a lack of historical hydrologic observations in this remote and inaccessible region, such estimations also fill a gap in studies on the continuous inter-annual and seasonal changes in the inland lake water budget. Using Lake Siling Co as a case study, we derived a time-series of lake surface extents from MODIS imagery, and scarce lake water level data from the satellite altimetry of two sensors (GLAS/ICESat and RA-2/ENVISAT) between 2001 and 2011. Then, based on the fact that the rise in lake water levels is tightly dependent on the expansion of the lake extent, we established an empirical model to simulate a continuous lake water level dataset corresponding to the lake area data during the lake's unfreezing period. Consequently, from three dimensions, the lake surface area, water level, and water storage variations consistently revealed that Lake Siling Co exhibited a dramatic trend to expand, particularly from 2001 ~ 2006. Based on the statistical model and lake area measurements from Landsat images since 1972, the extrapolated lake water level and water storage indicate that the lake has maintained a continual expansion process, and that the cumulative water storage variations during 1999 ~ 2011 account for 66.84% of the total lake water budget (26.87 km 3 ) from 1972 to 2011. Copyright © 2013 John Wiley & Sons, Ltd.

Description: Precipitation phase is fundamental to a catchment's hydrological response to precipitation events. Phase is particularly variable over time and space in the Canadian Rockies where snowfall or rainfall can occur any month of the year. Phase is controlled by the microphysics of the falling hydrometeor, but microphysical calculations require detailed atmospheric information that is often lacking for hydrological analyses. In hydrology, there have been many methods developed to estimate phase, but most are regionally calibrated and many depend on air temperature ( T a ) and use daily time steps. Phase is not only related to T a , but to other meteorological variables, and precipitation events are temporally dynamic, adding uncertainty to the use of daily indices to estimate phase. To better predict precipitation phase, the psychrometric energy balance of a falling hydrometeor was calculated and used to develop a method to estimate precipitation phase. High quality precipitation phase and meteorological data were observed at multiple elevations in a small Canadian Rockies catchment, Marmot Creek Research Basin, at 15-minute intervals over several years to develop and test the method. The results of the psychrometric energy balance method were compared to phase observations, to other methods over varying time scales and seasons and at varying elevations and topographic exposures. The results indicate that the psychrometric energy balance method performs much better than T a index methods and that this improvement, and the accuracy of the psychrometric energy balance method, increases as the time step of calculation decreases. Copyright © 2013 John Wiley & Sons, Ltd.

Description: Thanks to its simple division into agricultural and forestry land use, the Corbeira catchment (Galicia, Spain) is used as a case study to build a predictive model using hydrogeochemical signatures. Stream data acquired under recessional flow conditions over a one year period were obtained from a sampling station near the downstream end of the catchment, and using principal component analysis it is shown hat some of the analytical parameters are covariant and some are negatively correlated. These findings support inferences about the pathways of rainfall in the catchment. Specific signatures may be associated with the dominant hydrological source, either surface runoff or subsurface waters: additionally, the dominant land use in that part of the catchment, where the flow originated can also be predicted. The dominant runoff shows a strong covariance between suspended solids (SS) and particulate phosphorus (PP), with a clear negative correlation with pH. Dissolved organic carbon (DOC) data are associated with this covariant set when these compounds are available in the soils in question. Dissolved phosphorus, total organic nitrogen and dissolved nitrates are also associated with the same covariant set when the runoff flows through areas of extensive agricultural use. The SS − PP covariance is less significant at lower flows. Typical base flow regimes show a significant covariance between salinity and pH, with a marked negative correlation with SS − PP set, confirming the dominance of subsurface waters in the baseflow, as expected. Seasonally divergent DOC − SS behavior proves to be a useful tracer for rainfall regimes. The DOC trend shows a sinusoidal annual variation in amplitude, determined by the rainfall regime. As a result, flow from the catchment is dominated by surface water whenever there is synchronicity between the peaks of DOC and SS. Copyright © 2013 John Wiley & Sons, Ltd.

Description: Haihe plain is an important food production area in China, facing an increasing water shortage. The water used for agriculture accounts for about 70% of total water resources. Thus, it is critical to optimize the irrigation scheduling for saving water and increasing crop water productivity (CWP). This study firstly simulated crop yield and CWP for winter wheat and summer maize in historical scenario during 1961–2005 for Haihe plain using previously well-established SWAT model. Then scenarios under historical irrigation (scenario 1) and sufficient irrigation (scenario 2) were respectively simulated both with sufficient fertilizer. The crop yield in scenario 2 was considered as the potential crop yield. The optimal irrigation scheduling with sufficient fertilizer (scenario 3) was explored by iteratively adjusting irrigation scheduling based on the scenario 1 and previous studies related to water stress on crop growth. Results showed that net irrigation amount was respectively reduced 23.1% and 18.8% in scenario 3 for winter wheat and summer maize when compared with scenario 1. The CWP was 12.1% and 8.2% higher with very slight change of crop yield. Using optimal irrigation scheduling could save 8.8 × 10 8  m 3 irrigation water and reduce about 16.3% groundwater over-exploitation in winter wheat growth period. The corresponding yield was 18.5% and 12.9% less than potential yield for winter wheat and summer maize but using less irrigation water. Therefore, it could be considered that the optimal irrigation was reasonable, which provided beneficial suggestions for increasing efficiency of agricultural water use with sustainable crop yield in Haihe plain. Copyright © 2013 John Wiley & Sons, Ltd.

Description: Recently, a USDA Curve Number based method for obtaining estimates of event runoff has been developed for use in enhancing the capacity of RUSLE2 to deal with runoff-driven phenomena. However, RUSLE2 still uses the EI 30 index as the basis for determining the erosivity of the rainfall for sets of runoff producing storms at a location even though the product of the runoff ratio ( Q R ) and EI 30 index is better at prediction event erosion when runoff is known or predicted well. This paper reports the results of applying the Q R EI 30 index using data available from tables within RUSLE2 to predict storm event soil losses from bare fallow areas and areas with continuous corn at Holly Springs, MI, and Morris, MN. In RUSLE2, all rainfall during a calendar year is considered to detach soil material that is flushed from the area if and when runoff occurs. However, the Q R EI 30 index is calculated using the EI 30 value for the amount of rain in the storm that produces runoff. Consequently, changes were made to the timing of events during the calendar year in order to meet the criteria for using the Q R EI 30 index. As a general rule, the peak event soil loss produced using the Q R EI 30 index were higher than produced by RUSLE2 and the peak event soil loss for the bare fallow occurred later than for the continuous corn. The results of the work reported here show that the Q R EI 30 index may be used to model event erosion produced by a set of storms within RUSLE2 provided that the appropriate mathematical rules upon which the USLE was developed are adhered to. Copyright © 2013 John Wiley & Sons, Ltd.

Description: Human-induced disturbances and climate-driven warming have resulted in unprecedented permafrost thaw in the zone of discontinuous permafrost. In a peatland environment south of Fort Simpson, NWT, we study the contribution of increases in incoming radiation to the ground surface, caused by removal of the tree canopy along linear disturbances, to changes in the ground thermal regime. A physically-based understanding of thaw processes along linear disturbances is required in order to better understand the slow recovery of lines in this environment and to be able to efficiently reduce this impact during future resource exploration. The impact of increases in incoming radiation are examined through the development of a model (SIRM) to quantify these inputs, which are then used to drive the one-dimensional coupled atmospheric-surface-subsurface model COUP. Results of this study show that incoming radiation (shortwave + longwave) is increased by up to 11% in a typical cutline compared to an undisturbed canopy. Relative to potential changes in near-surface soil moisture, these increases in radiation do not appear to be an important control of permafrost thaw along linear disturbances. Field observations confirm that increased permafrost thaw on disturbances often occur irrespective of variations in incoming radiation. Copyright © 2013 John Wiley & Sons, Ltd.

Description: Coastal groundwater discharge (CGD) plays an important role in coastal hydrogeological systems as they are a water resource that needs to be managed, particularly in wetland areas. Despite its importance, identifying and monitoring CGD often presents physical and logistical constraints, restraining the application of more traditional submarine groundwater discharge (SGD) surveying techniques. Here we investigate the capability of electrical resistivity imaging (ERI) in the Peníscola wetland (Mediterranean coast, Spain). ERI surveying made it possible to identify and delineate an ascending regional groundwater flow of thermal and Ra-enriched groundwater converging with local flows and seawater intrusion. The continuous inputs of Ra-rich groundwater have induced high activities of Ra isotopes and 222 Rn into the marsh area, becoming among the highest previously reported in wetlands and coastal lagoons. Geoelectrical imaging enabled inferring focused upward discharging areas, leaking from the aquifer roof through a confining unit and culminating as spring pools nourishing the wetland system. Forward modeling over idealized subsurface configurations, borehole datasets, potentiometric records from standpipe piezometers, petrophysical analysis, and four natural and independent tracers ( 224 Ra, 222 Rn, temperature and salinity) permitted assessing the geoelectrical model and a derived hydrogeological pattern. The research highlights the potential of ERI to improve hydrogeological characterization of subsurface processes in complex contexts, with different converging flows. Additionally, a hydrogeological conceptual model for a groundwater-fed coastal wetland was proposed, based on the integration of surveying datasets. Copyright © 2013 John Wiley & Sons, Ltd.

Description: The Powder River Basin (PRB) of Wyoming and Montana contains significant coal and coal bed natural gas (CBNG) resources. Coal bed natural gas extraction requires the production of large volumes of water, much of which is discharged into existing drainages. Compared to surface waters, the CBNG produced water is high in sodium relative to calcium and magnesium, elevating the sodium adsorption ratio (SAR). To mitigate the possible impact this produced water may have on the quality of surface water used for irrigation, the State of Montana passed water anti-degradation legislation, which could affect CBNG production in Wyoming. In this study, we sought to determine the proportion of CBNG produced water discharged to tributaries that reaches the Powder River by implementing a four end-member mixing model within a Bayesian statistical framework. The model accounts for the 87 Sr/ 86 Sr, δ 13 C DIC , [Sr] and [DIC] of CBNG produced water and surface water interacting with the three primary lithologies exposed in the PRB. The model estimates the relative contribution of the end-members to the river water, while incorporating uncertainty associated with measurement and process error. Model results confirm that both of the tributaries associated with high CBNG activity are mostly composed of CBNG produced water (70-100%). The model indicates that up to 50% of the Powder River is composed of CBNG produced water downstream from the CBNG tributaries, decreasing with distance by dilution from non-CBNG impacted tributaries from the point sources to ~10-20% at the Montana border. This amount of CBNG produced water does not significantly affect the SAR or electrical conductivity (EC) of the Powder River in Montana. Copyright © 2013 John Wiley & Sons, Ltd.

Description: Eighteen groundwater well sites located in Kafr Al-Zayat (Egypt) were sampled monthly from January 2009 to November 2011 for microbial content, Mn +2 , Fe +2 , total dissolved solids (TDS), total hardness, NO 3 - , and turbidity. The data were analyzed combining the integrated use of factor and cluster analyses as well as the geostatistical semi-variogram modeling. The prime objectives were to assess the groundwater suitability for drinking, to document the factors governing the spatio-tempral variability, and to recognize distinctive groundwater quality patterns to help enable effective sustainability and proactive management of the limited resource. The groundwater microbial, Mn +2 , Fe +2 , TDS, and total hardness contents violated the drinking water local standards while the turbidity and the nitrate content complied with them. Factor analysis indicated that the microbial content is the most influential factor raising the variability potential followed, in decreasing order, by Mn 2+ , Fe 2+ , TDS, NO 3 - , turbidity, and finally the total hardness. Turbidity resulting from urban and agricultural run-off was strongly associated with most of the quality parameters. Quality parameters fluctuate sporadically without concrete pattern in space and time while their variability scores peak in November every year. Three spatially distinctive quality patterns were recognized that were consistent with and affected by the cumulative effects of the local topography, depth to water table, thickness of the silty clay (cap layer), surface water and groundwater flow direction and hence the recharge from contaminated surface canals and agricultural drains. Copyright © 2013 John Wiley & Sons, Ltd.

Description: Karst terrain (carbonate rocks) covers a vast land of 0.446 million km 2 in southwest China. Water yield and carbonate rocks weathering in this region have been receiving increased attention due to a large-scale forest recovery. Using both hydrological measurements and forest inventories from 1986 to 2007 in the Houzhai karst basin (HKB), we analyzed the responses of water yield and dissolved inorganic carbon (DIC) export to forest recovery in southwest China. With implementation of both the Natural Forest Conservation Program (NFCP) and the Conversion of Farmland to Forests Program (CFFP), the fraction of forest area in HKB was increased from near zero to 18.9% during the study period, but the ratio of total water yield (surface and underground) to precipitation varied very little over the annual period, neither in wet season nor in dry season. By contrast, the concentration of DIC in water, especially in the surface water had a pronounced increase during the study period, with an increase of 0.53 and 0.25 g C m -3  yr -1 for surface water and underground water, respectively. As a result, total annual DIC export at mean annual rainfall significantly increased from the low to high forest area stage. This increase was largely driven by surface water during the wet season, presumably being related to biological activity. It was concluded that forest recovery in HKB had no significant effect on water yield, but resulted in more carbon dioxide (CO 2 ) dissolved in karst water accompanying with carbon uptake by forests. Our results suggested that implementations of both NFCP and CFFP had no shifted water yield regimes in southwest China, instead, they might have alleviated global climate change by increasing carbon uptake through combined biological processes and carbonate rocks weathering. Copyright © 2013 John Wiley & Sons, Ltd.

Description: The Mekong is one of the world's great rivers. It has the greatest mean annual flow in the world for a river basin of comparable size. The flow regime, with very distinct wet and dry seasons, supports a rich biodiversity and the world's largest freshwater fishery. Given that at the present time the hydrological regime of the Mekong remains in its natural state, the accelerating pace of water resources development will induce hydrological change. The natural productivity of the system is therefore potentially jeopardized. This paper reports the findings of simulation studies of the potential hydrological impacts of water resource development scenarios over future planning horizons. In the Definite Future scenario (next 5 years), the seasonal redistribution of water by on-going hydropower development will increase the dry season flow by 40-60% in the upper portion of the basin and by 20-30% in the Mekong Delta. The Foreseeable Future scenario (next 20 years) and Long-Term Future scenario (next 50 years) will result in relatively small changes to the flow regime as further increases in dry season reservoir releases will be offset by planned increases in irrigation and other consumptive water demands. All scenarios were predicted to reduce the average wet season flows by 4-14%, flow reversal to the Tonle Sap Lake by 7-16%, flooded areas by 5-8% and salinity intrusion areas in the Viet Nam Delta by 15-17%. Predicted changes in Definite Future scenario will be irreversible, necessitating improved coordination the between LMB countries and cooperation with China in order to manage the risks and maximize the regional benefits. The scenario assessments highlighted the areas where research is necessary to mitigate and manage impacts in order to ensure the reasonable and equitable use of the Mekong basin's water resources. Copyright © 2013 John Wiley & Sons, Ltd.

Description: The hydrological response characteristics for the catchments in the Republic of Korea are related to a strong seasonality in the rainfall and streamflow distributions with distinct wet and dry seasons. This study aims to improve a model's ability to predict streamflows by minimising information loss from the available data during the calibration processes. This study assesses calibration techniques incorporating a multi-objective approach and seasonal calibration. The lumped conceptual rainfall-runoff model IHACRES was applied to selected catchments in Korea. The model was calibrated based on three different methods: the classical approach using a single performance statistic (the single-objective method), the multi-objective approach (the multi-objective method (I)) and the combined approach incorporating multi-objective and seasonal calibrations (the multi-objective method (II)). In the multi-objective approach, the ‘best fit’ models in the calibration period were selected by considering the trade-offs among multiple statistics. During seasonal calibration, the calibration period was divided into four seasons to investigate whether these calibrated models can improve the model performance with regards to seasonal climate, rainfall and streamflow distributions. The adequacy of the three different calibration methods was assessed through comparison of the variability of model performance in high and low flows and water balance for the entire period and for each seasonal period. The multi-objective methods yielded more accurate and consistent predictions for high and low flows and water balance simultaneously, compared to the single-objective method. In particular, the multi-objective method (II) produces the best modelling capacity to capture the non-stationary nature of the hydrological response under different climate conditions. The pattern of improvement with the multi-objective method (II) was generally consistent through the seasons, with the exception of the winter period in the regions partially affected by snow. This exception is due to a potential limitation of the IHACRES model in reflecting the impact of snow on the catchment hydrology. Copyright © 2013 John Wiley & Sons, Ltd.

Description: The connectivity and upscaling of overland runoff and sediment transport are important issues in hillslope hydrology to identify water flux and sediment transport within landscape. These processes are highly variable in time and space with regard to their interactions with vegetation and soil surface conditions. The generation of overland runoff and its spatial connectivity were examined along a slope to determine the variations in the transport mechanism of runoff and soil particles by rain splash and overland runoff. Field experiments were conducted by erosion plots on a steep hillslope at lengths of 5, 10, and 15 meters. The overland runoff connectivity and flow transport distance decreased with the slope length, while spatial variability of infiltration increased significantly with the slope length. Observation of subsurface flow revealed that surface soil and litter layer could have important role in water transport. However, the surface soil water content and water flux transport along the slope was highly variable for different storm events; the variability was related to the complexity of the system, mainly by way of the initial wetness conditions and infiltration characteristics. Only net rain-splashed soil was measurable, but examination of the water flux, overland runoff and sediment transport connectivity, characteristics of sheetwash, and the variability in spatial infiltration indicated an increase in the contribution of the rain splash transport mechanism along the slope. Copyright © 2013 John Wiley & Sons, Ltd.

Description: Stemflow of xerophytic shrubs was monitored on event-basis within a revegetated sand dune. Quantity of stemflow showed a clear species-specific dependence in combination with the rainfall characteristics. Results obtained revealed that for ovate-leaved C. korshinskii with an inverted cone-shaped canopy and smooth bark, the quantity of stemflow in depth accounted for 7.2% of the individual gross rainfall, while it was 2.0% for needle-leaved A. ordosica with a cone-shaped canopy and coarse bark. There were significant positive linear relationships between stemflow and individual gross rainfall and rainfall intensity for the two shrubs. An individual gross rainfall of 1.4 and 1.8 mm was necessary for stemflow generation for C. korshinskii and A. ordosica , respectively. Multiple regression analysis showed that the abiotic and biotic variables including the individual gross rainfall, mean windspeed, canopy height, branch length, and canopy volume have significant influence on stemflow for C. korshinskii , whereas for A. ordosica , the notable influencing variables were individual gross rainfall, stem diameter, and leaf area index. Generally, windspeed has less effect on stemflow than that of rainfall for A. ordosica . The correlation relationship between individual gross rainfall and funneling ratio showed that the funneling ratio attains its peak when the gross rainfall is 13 and 16 mm for C. korshinskii and A. ordosica , respectively, implying that the canopy morphology emerged as determining factors on funneling ratio decrease when the individual gross rainfall exceeds these values. In comparison, higher windspeed increased the funneling ratio remarkably for C. korshinskii than A. ordosica due partly to the greater branch length and canopy projection area in C. korshinskii . Funneling ratio can be used as an integrated variable for the effects of canopy morphology and rainfall characteristics on stemflow. The implication of stemflow on water balance and its contribution to sustain the shrubs and the revegetation efforts was discussed. Copyright © 2013 John Wiley & Sons, Ltd.

Description: Despite human is an increasingly significant component of the hydrologic cycle in many river basins, most hydrologic models are still developed to accurately reproduce the natural processes and ignore the effect of human activities on the watershed response. This results in non-stationary model forecast errors and poor predicting performance every time these models are used in non-pristine watersheds. In the last decade, the representation of human activities in hydrological models has been extensively studied. However, mathematical models integrating the human and the natural dimension are not very common in hydrological applications and nearly unknown in the day-to-day practice. In this paper we propose a new simple data-driven flow forecast correction method that can be used to simultaneously tackle forecast errors from structural, parameter and input uncertainty, and errors that arise from neglecting human-induced alterations in conceptual rainfall-runoff models. The correction system is composed of two layers: (i) a classification system that, based on the current flow condition, detects whether the source of error is natural or human-induced; and (ii) a set of error correction models that are alternatively activated, each tailored to the specific source of errors. As a case study we consider the highly anthropized Aniene river basin in Italy, where a flow forecasting system is being established to support the operation of a hydropower dam. Results show that, even by using very basic methods, namely if-then classification rules and linear correction models, the proposed methodology considerably improves the forecasting capability of the original hydrological model. Copyright © 2013 John Wiley & Sons, Ltd.

Description: Proglacial icings are one of the most common forms of extrusive ice found in the Canadian Arctic. However, the icing adjacent to Fountain Glacier, Bylot Island, is unique due to its annual cycle of growth and decay, and perennial existence without involving freezing point depression of water due to chemical characteristics. Its regeneration depends on the availability of subglacial water and on the balance between ice accretion and hydro-thermal erosion. The storage and conduction of the glacial meltwater involved in the accretion of the icing was analyzed by conducting topographic and ground penetrating radar surveys in addition to the modelling of the subglacial drainage network and the thermal characteristics of the glacier base. The reflection power analysis of the geophysical data shows that some areas of the lower ablation zone have a high accumulation of liquid water, particularly beneath the centre part of the glacier along the main supraglacial stream. A dielectric permittivity model of the glacier – sediment interface suggests that a considerable portion of the glacier is warm based; allowing water to flow through unfrozen subglacial sediments towards the proglacial outwash plain. All these glacier related characteristics contribute to the annual regeneration of the proglacial icing and allows for portions of the icing to be perennial. Copyright © 2013 John Wiley & Sons, Ltd.

Description: The importance of satellite datasets as alternative sources of precipitation information has been argued in numerous studies. Future developments in satellite precipitation algorithms as well as utilization of satellite data in operational applications rely on a more in-depth understanding of satellite errors and biases across different spatial and temporal scales. This paper investigates the capability of satellite precipitation data sets with respect to detecting heavy precipitation rates over different temporal accumulations. In this study, the performance of TRMM-RT, PERSIANN and CMORPH is compared against radar-based gauge-adjusted Stage IV data. The results show that none of the high temporal resolution (3-hr) datasets are ideal for detecting heavy precipitation rates. In fact, the detection skill of all products drops as the precipitation thresholds (i.e., 75 and 90 percentiles) increase. At higher temporal accumulations (6-, 12-, and 24-hr), the detection skill improves for all precipitation products, with CMORPH showing a better detection skill compared to all other products. On the other hand, all precipitation products exhibit high false alarm ratios above the heavy precipitation thresholds, although TRMM-RT lead to a relatively smaller level of false alarms. These results indicate that further efforts are necessary to improve the precipitation algorithms so that they can capture heavy precipitation rates more reliably. Copyright © 2013 John Wiley & Sons, Ltd.

Description: The flood seasonality of catchments in Switzerland is likely to change under climate change due to anticipated alterations of precipitation as well as snow accumulation and melt. Information on this change is crucial for flood protection policies, for example, or regional flood frequency analysis. We analysed projected changes in mean annual and maximum floods of a 22 yr period for 189 catchments in Switzerland and two scenario periods in the 21st century based on an ensemble of climate scenarios. The flood seasonality was analysed with directional statistics that allow assessing both changes in the mean date a flood occurs as well as changes in the strength of the seasonality. We found that the simulated change in flood seasonality is a function of the change in flow regime type. If snow accumulation and melt is important in a catchment during the control period, then the anticipated change in flood seasonality is most pronounced. Decreasing summer precipitation in the scenarios additionally affects the flood seasonality (mean date of flood occurrence) and leads to a decreasing strength of seasonality, i.e. a higher temporal variability in most cases. The magnitudes of mean annual floods and more clearly of maximum floods (in a 22 yr period) are expected to increase in the future, due to changes in flood generating processes and scaled extreme precipitation. Southern alpine catchments show a different signal, though: The simulated mean annual floods decrease in the far future, i.e. at the end of the 21st century. Copyright © 2013 John Wiley & Sons, Ltd.

Description: The increased socio-economic relevance of flood risk assessment has led to the development of innovative methodologies for the hydraulic simulation of river and floodplain systems, and has promoted the development of new techniques for flood hazard and inundation mapping (e.g. Di Baldassarre et al., 2010; Vorogushyn et al., 2010). In particular, one-dimensional (1D) and two-dimensional (2D) hydraulic models have been used more and more as numerical tools (e.g. Aronica et al., 2002; Hesselink et al., 2003; Horritt et al., 2007; Pappenberger et al., 2005) as these models have proven to be able to effectively simulate river hydraulics and floodplain inundation at different levels of detail (e.g. Horritt & Bates, 2001, 2002). Flood inundation models appear also to be useful tools for the reconstruction and analysis of historical events (e.g. Di Baldassarre et al., 2009; Horritt et al., 2010), which can be very important to provide a comprehensive assessment of exposure to floods and to develop flood risk management plans as required by the recent Floods Directive 2007/60/EC (European Commission, 2007). Copyright © 2012 John Wiley & Sons, Ltd.

Description: During the Asian monsoon period, intense and precipitation commonly occurs for an extended period in accompaniment with a reduction in solar radiation. This suggests that wet surface evapotranspiration is important contributor to the total evapotranspiration. Therefore, investigating evapotranspiration over a wet canopy surface is critical to achieve a better understanding of water and energy cycles in Asia. In this study, we estimated surface resistances under wet conditions in a mixed forest influenced by the East Asian monsoon system. We showed that the surface resistance had a non-negligible magnitude of about 30  sm −1 even under wet conditions. We also found that the ratio between the actual and potential evapotranspiration depended on the friction velocity regardless of the time of day. Our analyses suggest that this dependency is tightly related to the underestimation of turbulent fluxes by the eddy-covariance system under wet surface conditions. Together, our findings suggest that the wet surface resistance, although small, should be considered in simulating evapotranspiration because the forest ecosystem is strongly coupled to the overlying atmosphere. This could significantly improve the shortcomings of evapotranspiration measurement in Asian forest canopies influenced by the monsoon system. Copyright © 2012 John Wiley & Sons, Ltd.

Description: Forecast ensembles of hydrological and hydrometeorologial variables are prone to various uncertainties arising from climatology, model structure and parameters, and initial conditions at the forecast date. Postprocessing methods are usually applied to adjust the mean and variance of the ensemble without any knowledge about the uncertainty sources. This study initially addresses the drawbacks of a commonly used statistical technique, Quantile Mapping (QM), in bias correction of hydrologic forecasts. Then, an auxiliary variable, the failure index (γ) is proposed to estimate the ineffectiveness of the postprocessing method based on the agreement of adjusted forecasts with corresponding observations during an analysis period prior to the forecast date. An alternative postprocessor based on copula functions is then introduced such that marginal distributions of observations and model simulations are combined to create a multivariate joint distribution. A set of 2500 hypothetical forecast ensembles with parametric marginal distributions of simulated and observed variables are postprocessed with both QM and the proposed multivariate postprocessor. Deterministic forecast skills show that the proposed copula-based postprocessing is more effective than the QM method in improving the forecasts. It is found that the performance of QM is highly correlated with the failure index, unlike the multivariate postprocessor. In probabilistic metrics, the proposed multivariate postprocessor generally outperforms QM. Further evaluation of techniques is conducted for river flow forecast of Sprague River Basin in southern Oregon. Results show that the multivariate postprocessor performs better than the QM technique; it reduces the ensemble spread and is a more reliable approach for improving the forecast. Copyright © 2012 John Wiley & Sons, Ltd.

Description: We propose a new runoff model including an outflow process that was applied to two adjacent basins (CL, TL) located in Lambir Hills National Park in north-central Sarawak, Malaysia. Rainfall, runoff, topography, and soil layer thickness were observed. About 19 % of annual runoff was observed in the CL basin (21.97 ha), whereas about 46 % was observed in the TL basin (23.25 ha). It was inferred that the CL basin has an outflow because of low base flow, small runoff peak, and excessive water loss. By incorporating the outflow process into the HYdrological CYcle MODEL (HYCYMODEL), good agreement between the data generated by the model and that observed was shown, with the exception of the data from the rainless period. Then, the fitting parameters for each basin were exchanged, except for the outflow parameter, and the characteristics of each basin were compared by calculating virtual runoff. As a result, the low base flow of the CL basin was estimated by the movement of the rainwater that escaped from the basin as deep percolation or lateral flow (11 % of rainfall). The potential of the CL basin for mitigating flood and drought appeared to be higher than that of the TL basin. This is consistent with the topographic characteristics of the CL basin, which has a gentler slope than the TL basin. Copyright © 2012 John Wiley & Sons, Ltd.

Description: For many basins, identifying changes to water quality over time and understanding current hydrologic processes are hindered by fragmented and discontinuous water-quality and hydrology data. In the coal mined region of the New River basin and Indian Fork sub-basin, muted and pronounced changes, respectively, to concentration-discharge relationships were identified using linear regression on log-transformed historical (1970s-1980s) and recent (2000s) water-quality and streamflow data. Changes to concentration-discharge relationships were related to coal mining histories and shifts in land use. Hysteresis plots of individual storms from 2007 (New River) and the fall of 2009 (Indian Fork) were used to understand current hydrologic processes in the basins. In the New River, storm magnitude was found to be closely related to the reversal of loop rotation in hysteresis plots; a peak-flow threshold of 25 cubic meters per second (m 3 /s) segregates hysteresis patterns into clockwise and counterclockwise rotational groups. Small storms with peak flow less than 25 m 3 /s often resulted in dilution of constituent concentrations in headwater tributaries like Indian Fork and concentration of constituents downstream in the mainstem of the New River. Conceptual two or three component mixing models for the basins were used to infer the influence of water derived from spoil material on water quality. Copyright © 2012 John Wiley & Sons, Ltd.

Description: Thus far, measurements and estimations of actual evapotranspiration (ET) from high-altitude grassland ecosystems in remote areas like the Qinghai-Tibetan plateau are still insufficient. To address these issues, a comparison between the results of the eddy covariance (EC) measurements and the estimates, considering the Katerji and Perrier (KP), the Todorovic (TD) and the Priestley-Taylor (PT) models, was carried out over an alpine grassland (38 o 03’1.7'' N, 100 o 27’ 26'' E; 3032 m a.s.l.) during the growing seasons in 2008 and 2009. The results indicated that the KP model after a particularly simple calibration gave the most effective ET values in different time scales, the PT model slightly underestimate ET at night, and the TD model significantly overestimated ET at noon. In addition, the canopy resistance calculated by the TD model was completely different from that calculated using the inverted EC-measured data and the KP model, which may be due to some unrealistic assumptions made by the TD model. The KP parameters were a  = 0.17 and b  = 1.50 for the alpine grassland, and appeared to be interannually stable. However, the PT parameter showed some interannual variations ( α  = 0.83 and 0.74 for 2008 and 2009, respectively). Therefore, the KP model was preferred to estimate the actual ET at both hourly and daily time scales. The PT model, being the simplest approach and field condition dependent, was recommended when available weather data were rare. On the contrary, the TD model always overestimated the actual ET and should be avoided in case of the alpine grassland ecosystems. Copyright © 2012 John Wiley & Sons, Ltd.

Description: Stochastic weather generators have evolved as tools for creating long time-series of synthetic meteorological data at a site for risk assessments in hydrologic and agricultural applications. Recently, their use has been extended as downscaling tools for climate change impact assessments. Non-parametric weather generators, which typically use a K-Nearest Neighbour (K-NN) resampling approach, require no statistical assumptions about probability distributions of variables and can be easily applied for multisite use. Two characteristics of traditional K-NN models result from resampling daily values: (a) temporal correlation structure of daily temperatures may be lost, and (b) no values lying below or exceeding historical observations can be simulated. Temporal correlation in simulated temperature data is important for hydrologic applications. Temperature is a major driver of many processes within the hydrologic cycle (for example, evaporation, snow melt, etc) that may affect flood levels. As such, a new methodology for simulation of climate data using the K-NN approach is presented (named KnnCAD Version 4). A block resampling scheme is introduced along with perturbation for the reshuffled daily temperature data to create 675 years of synthetic historical daily temperatures for the Upper Thames River basin in Ontario, Canada. The updated KnnCAD model is shown to adequately reproduce observed monthly temperature characteristics, temporal and spatial correlations while simulating reasonable values outside the range of observations. Copyright © 2012 John Wiley & Sons, Ltd.

Description: Global change is predicted to increase temperature substantially in the North as well as altering run-off regimes with less synchronicity as the importance of snow melt declines. River biota and ecosystem processes will be influenced across all levels of organization, both in concert and individually. It is of vital importance that the impacts, and their likely magnitude, can be identified in order to deploy suitable adaptation strategies at the catchment scale. In this paper, we re-analyse 4 data sets from studies conducted in Greenland (66-69 o N), Iceland (64 o N), Sweden (60 o N) and Denmark (55-57 o N) to try and tease out the likely impacts of water temperature and hydrology in shaping the stream communities and ecosystem processes in high-latitude catchments. Water temperature was the environmental variable that best explained macroinvertebrate community composition across latitudes. In contrast, no significant relationship between macroinvertebrate community composition and measures of hydraulic stability (or nutrients) was found. We found a strong linear relationship between decay rate of leaf litter and water temperature (r 2  = 0.68; p 〈 0.0001) independent of latitudes. Our study suggests that temperature could be the primary driver of ecosystem change in future with northern catchments likely to be especially vulnerable. Copyright © 2012 John Wiley & Sons, Ltd.

Description: The velocity field in a river flow cross-sectional area can be determined by applying entropy as done by Chiu (1987), who developed a two-dimensional model of flow velocity based on the knowledge of maximum velocity, u max , and the dimensionless entropic parameter, characteristic of the river site. This is appealing in the context of discharge monitoring, particularly for high floods, considering that u max occurs in the upper portion of flow area and can be easily sampled, unlike velocity in the lower portion of flow area. The simplified form of Chiu's entropy-based velocity model, proposed by Moramarco et al. (2004), has been found to be reasonably accurate for determining mean flow velocity along each vertical sampled in the flow area, but no uncertainty analysis has been reported for this simplified entropy-based velocity model. This study, therefore, performed uncertainty analysis of the simplified model following a procedure proposed by Misirli et al. (2003). The flow velocity measurements at the Rosciano River section along the Chiascio River, central Italy, carried out for a period spanning 20 years were used for this purpose. Results showed that the simplified entropy velocity model was able to provide satisfactory estimates of velocity profiles in the whole flow area and the 95% confidence bands for the computed estimated mean vertical velocity were quite representative of observed values. In addition, using these 95% confidence bands, it was possible to have an indication of the uncertainty in the determination of mean cross-sectional flow velocity as well. Copyright © 2012 John Wiley & Sons, Ltd.

Description: Total evaporation ( ET ) is one of the major components of the water budget of a wetland. Very little research has been conducted on the loss of water to the atmosphere from different wetland vegetation types occurring in southern Africa. This study on the ET of taro (locally known as madumbe) and sedge within the Mbongolwane wetland was conducted to assess the potential impact of madumbe cultivation on the hydrology of the wetland. Sugarcane planted on the contributing catchment outside the wetland was the other crop examined. Two field campaigns were conducted in November 2009 and January 2010 during the growing season of the madumbe crop to quantify ET rates in the Mbongolwane wetland and from sugar cane in the surrounding catchment. Total evaporation was measured over two vegetation types in the wetland, namely: madumbe ( Colocasia esculenta ); sedge ( Cyperus latifolius ) with some reeds ( Phragmites australis ); and sugarcane in adjacent terrestrial areas. Total evaporation from the madumbes ranged from 1.0 to 6.0 mm day -1 . The daily average ET rates in November 2009 were 3.5 and 4.9 mm for the madumbe and sedge sites respectively and 4.0 mm for sugarcane grown in the catchment. The daily average ET rates in January 2010 were 3.3 and 3.7 mm for the madumbes and sedge sites, respectively and 2.4 mm for the sugarcane site. The daily ET was therefore lower at the madumbe site in November 2009 and in January 2010 compared to the sedge site. An average crop factor ( Kc ) of 0.6 was obtained from this study during the growth stage of the madumbes. Copyright © 2012 John Wiley & Sons, Ltd.

Description: Much of what is known about groundwater circulation and geochemical evolution in carbonate platforms is based on platforms that are fully confined or unconfined. Much less is known about groundwater flow paths and geochemical evolution in partially confined platforms, particularly those supporting surface water. In north-central Florida, sea level rise and a transition to a wetter climate during the Holocene formed rivers in unconfined portions of the Florida carbonate platform. Focusing on data from the Santa Fe River basin, we show river formation has led to important differences in the hydrological and geochemical evolution of the Santa Fe River basin relative to fully confined or unconfined platforms. Runoff from the siliciclastic confining layer drove river incision and created topographic relief, reorienting the termination of local and regional groundwater flow paths from the coast to the rivers in unconfined portions of the platform. The most chemically evolved groundwater occurs at the end of the longest and deepest flow paths, which discharge near the center of the platform because of incision of the Santa Fe River at the edge of the confining unit. This pattern of discharge of mineralized water differs from fully confined or unconfined platforms where discharge of the most mineralized water occurs at the coast. Mineralized water flowing into the Santa Fe River is diluted by less evolved water derived from shorter, shallower flow paths that discharge to the river downstream. Formation of rivers shortens flow path lengths, thereby decreasing groundwater residence times and allowing freshwater to discharge more quickly to the oceans in the newly formed rivers than in platforms that lack rivers. Similar dynamic changes to groundwater systems should be expected to occur in the future as climate change and sea level rise develop surface water on other carbonate platforms and low lying coastal aquifer systems. Copyright © 2012 John Wiley & Sons, Ltd.

Description: Sea ice dynamic and thermodynamic processes are important and highly variable elements of the marginal ice zone (MIZ). This study examines the detection and classification of statistically separable sea ice classes in the MIZ through a range of temporal and spatial scales. A helicopter-based laser system was used to obtain large-scale and a ship-based laser profiler to identify small-scale roughness types respectively. The analysis of variance (ANOVA) of surface height data from helicopter- and ship-based laser systems, active microwave (AMW) C-band backscattering data and passive microwave (PMW) (37 and 89 GHz) brightness temperature data reveal different classes that statistically differ from one another. We found significant statistical difference in variances in AMW data with six classes that differ in VV polarization, three classes in VH polarization and five classes in HH polarization in the MIZ (e.g. snow-covered first-year ice, ice rubble, pancake ice, frost flowers, melt pond, flooded ice, and ice edge) of southeastern Beaufort Sea. The PMW emission was not as effective at discrimination, yielding only one statistically separable class. The results can potentially be extended to satellite-based investigations of the MIZ at regional scales. Copyright © 2012 John Wiley & Sons, Ltd.

Description: The USLE/RUSLE model was designed to predict long term (~20 years) average annual soil loss by accounting for the effects of climate, soil, topography and crops. The USLE/RUSLE model operates mathematically in two steps. The first step involves the prediction of soil loss from the “unit” plot, a bare fallow area 22.1 m long on a 9 % slope gradient with cultivation up and down the slope. Appropriate values of the factors accounting for slope length, gradient, crops and crop management and soil conservation practice are then used to adjust that soil loss to predict soil loss from areas that have conditions that are different from the unit plot. Replacing EI 30 , the USLE/RUSLE event erosivity index, by the product of the runoff ratio ( Q R ) and EI 30 can enhance the capacity of the model to predict short term soil loss from the unit plot if appropriate data on runoff is available. Replacing the EI 30 index by another index has consequences on other factors in the model. The USLE/RUSLE soil erodibility factor cannot be used when the erosivity factor is based on Q R EI 30 . Also, the USLE/RUSLE factors for slope length, slope gradient crops and crop management, and soil conservation practice cannot be used when runoff from other than the unit plot is used to calculate Q R . Here equations are provided to convert the USLE/RUSLE factors to values suitable for use when the erosivity factor is based on the Q R EI 30 index under these circumstances. At some geographic locations, non linear relationships exist between soil loss from bare fallow areas and the Q R EI 30 index. The effect of this on the slope length factor associated with the Q R EI 30 index is demonstrated using data from runoff and soil loss plots located at the Sparacia site, Sicily. Copyright © 2012 John Wiley & Sons, Ltd.

Description: A raster based glacier sub-model was successfully introduced in the distributed hydrological model FEST-WB to simulate the water balance and surface runoff of large Alpine catchments. The glacier model is based on temperature-index approach for melt, on linear reservoir for melt water propagation into the ice and on mass balance for accumulation; the initialization of the volume of ice on the basin was based on a formulation depending on surface topography. The model was first tested on a sub-basin of the Rhone basin (Switzerland), which is for 62% glaciated; the calibration and validation were based on comparison between simulated and observed discharge from 1999 to 2008. The model proved to be suitable to simulate the typical discharge seasonality of a heavily glaciated basin. The performance of the model was also tested by simulating discharge in the whole Swiss Rhone basin, in which glaciers contribution is not negligible, in fact in summer about the 40% of the discharge is due to glacier melt. The model allowed to take into account the volume of water coming from glaciers melt and its simple structure is suitable for analysis of the effects of climate change on hydrological regime of high mountain basins, with available meteorological forcing from current RCM. Copyright © 2012 John Wiley & Sons, Ltd.

Description: As part of this special issue on Hydrological Ensemble Prediction Systems (HEPS), this paper reports on the intercomparison experiment for post-processing techniques that has been initiated in 2011 by the international community on Hydrologic Ensemble Predictions (HEPEX). The design of this inter-comparison experiment and the data sets available are presented. The post-processing methods that have been applied to date are listed and example results are shown. It is expected that through the exchange and joint verification and analysis of the post-processing results, the inter-comparison experiment will contribute to a fast improvement and applicability of post-processing techniques. Readers are invited to join the inter-comparison experiment. Copyright © 2012 John Wiley & Sons, Ltd.

Description: Biocrusts abound in southern Israel, covering the Hallamish dune field near Nizzana (NIZ) in the Negev (mean annual precipitation of 95 mm) and the coast of Nizzanim (NIM) near Ashdod (mean annual precipitation of 500 mm). While the hydrological response of the NIZ crust to natural rain events was thoroughly investigated, no data is available on the hydrological response of the NIM crust. Runoff was monitored in runoff plots during the years 2005-2008 and in addition, sprinkling experiments were carried out on NIM and NIZ crusts. For the evaluation of the possible factors that may control runoff initiation, fine content of the parent material, crust thickness, compressional strength, hydrophobicity, surface microrelief, organic matter, biomass (chlorophyll a and total carbohydrates) and the crust's species composition of NIM were studied and compared to that of NIZ. The data showed that in comparison to the NIZ crust that readily generated runoff, no runoff was produced by the NIM crust. This was so despite the fact that (a) Microculeus vaginatus predominated in both crusts, (b) the substantially higher rain intensities in NIM (c) the greater thickness and higher chlorophyll content and (d) the lower microrelief at NIM in comparison to NIZ. The lack of runoff in NIM was explained by its low amounts of exopolysaccharides that did not suffice to affectively clog the surface and in turn to facilitate runoff initiation. The absence of runoff and its consequences on the NIM ecosystem are discussed. Copyright © 2012 John Wiley & Sons, Ltd.

Description: The Soil Conservation Service (SCS) curve number estimates of direct runoff from rainfall for semiarid catchments can be inaccurate. Investigation of the Walnut Gulch Experimental Watershed (Southeastern Arizona) and its 10 nested catchments determined that the inaccuracy is due to the original SCS ratio ( λ ) of 0.2 between initial abstraction and maximum potential retention. Sensitivity analyses indicate that runoff estimation can be very sensitive to the initial abstraction ratio, especially for relatively low rainfall amount and for watersheds covered by deep, coarse, and porous soil, conditions that dominate many semiarid watersheds worldwide. Changing the ratio of initial abstraction to the maximum potential retention to optimal values ranging from 0.01 to 0.53 for different Walnut Gulch catchments improved runoff estimates. The greater the channel area and the finer the soil, the smaller the initial abstraction ratio is. The variation of the initial abstraction ratio for the Walnut Gulch Experimental Watershed is due to the variation of maximum potential retention and initial abstraction, which are channel area and soil dependent parameters. The greater the channel area, the higher the maximum potential retention S is; and the coarser the soil, the larger the initial abstraction I a is. In addition, the effect of initial abstraction ratio on runoff estimation increases with decreasing curve number. Thus, impacts of initial abstraction ratio on runoff estimation should be considered, especially for semiarid watersheds where the curve number is usually low. Copyright © 2012 John Wiley & Sons, Ltd.

Description: The Future Midwestern Landscapes (FML) project is part of the U.S. Environmental Protection Agency's undertaken Ecosystem Services Research Program. The goal of the FML project is to quantify changes in ecosystem services across the region as a result of the growing demand for biofuels. Watershed models are an efficient way to quantify ecosystem services of water quality and quantity. By calibrating models we can better capture watershed characteristics before they are applied to make predictions. The Kaskaskia River watershed in Illinois was selected to investigate the effectiveness of different calibration strategies (single-site and multi-site calibrations) for streamflow, total suspended sediment (TSS) and total nitrogen (TN) loadings using the Soil and Water Assessment Tool (SWAT). Four USGS gauges were evaluated in this study. Single-site calibration was performed from downstream site to upstream site, and multi-site calibration was performed and fine-tuned based on the single-site calibration results. Generally, simulated streamflow and TSS were not much affected by different calibration strategies. However, when single-site calibration was performed at the most downstream site, the Nash-Sutcliffe Efficiency (NSE) values for TN ranged between -0.09 and 0.53 at the other sites; and when single-site calibration was performed at the most upstream site, the NSE values ranged between -8.38 and -0.07 for the other sites. The NSE values for TN were improved to 0.5 – 0.59 for all four sites when multi-site calibration was performed. The results of multi-site calibration and validation showed an improvement on model performance on TN and highlighted that multi-site calibrations are needed to assess the hydrological and water quality processes at various spatial scales. Copyright © 2012 John Wiley & Sons, Ltd.

Description: Recently evapotranspiration has been hypothesized to promote the secondary formation of calcium carbonate year-round on tree islands in the Everglades by influencing groundwater ions concentrations. However, the role of recharge and evapotranspiration as drivers of shallow groundwater ion accumulation has not been investigated. The goal of this study is to develop a hydrologic model that predicts the chloride concentrations of shallow tree island groundwater and to determine the influence of overlying biomass and underlying geologic material on these concentrations. Groundwater and surface water levels and chloride concentrations were monitored on eight constructed tree islands at the Loxahatchee Impoundment Landscape Assessment (LILA) from 2007–2010. The tree islands at LILA were constructed predominately of peat, or of peat and limestone, and were planted with saplings of native tree species in 2006 and 2007. The model predicted low shallow groundwater chloride concentrations when inputs of regional groundwater and evapotranspiration-to-recharge rates were elevated, while low evapotranspiration-to-recharge rates resulted in a substantial increase the chloride concentrations of the shallow groundwater. Modeling results indicated that evapotranspiration typically exceeded recharge on the older tree islands and those with a limestone lithology, which resulted in greater inputs of regional groundwater. A sensitivity analysis indicated the shallow groundwater chloride concentrations were most sensitive to alterations in specific yield during the wet season and hydraulic conductivity in the dry season. In conclusion the inputs of rainfall, underlying hydrologic properties of tree islands sediments and forest structure may explain the variation in ion concentration seen across Everglades tree islands. Copyright © 2012 John Wiley & Sons, Ltd.

Description: Drought is a slow-onset, creeping natural hazard which is an inevitable part of normal climate fluctuation especially in arid and semiarid regions and its variability can be explained in terms of large-scale atmospheric circulation patterns. Standardized streamflow index (SSFI) was utilized to characterize hydrological drought in the west of Iran for the hydrological years of 1969–1970 to 2008–2009. The linkage of atmospheric circulation patterns (ENSO, NAO) to hydrological drought was also used to reveal relations of climate variability affecting hydrological drought. River discharges exhibited negative anomalies during the warm phase of ENSO (El Niño) which caused the extreme and sever droughts in the study area, being strongest during the hydrological years of 2007–2008 and 2008–2009. The analysis also indicated the teleconnection impact of ENSO on the hydrological drought severity in the first half of the hydrological year especially between November and March. Moreover, the concurrent and lag correlations revealed a weak relationship between the SSFI drought severity and the NAO index. Copyright © 2012 John Wiley & Sons, Ltd.

Description: Interception losses in stands of non-native trees in Hawaiian forests and their potential negative impacts on fresh water availability are poorly understood. In this study, a canopy water balance analysis was conducted to estimate interception losses using measurements of rainfall (RF), throughfall (TF), and stemflow (SF) at three locations, each dominated by one or more of the following non-native tree species: Psidium cattleianum Sabine (Strawberry guava), Schinus terebinthifolius Raddi (Christmas berry), Syzygium cumini (L.) Skeels (Java plum), and Coffea arabica L . (Coffee). Mean TF expressed as percentage of total RF was the lowest (43.3%) under a monotypic stand of P. cattleianum and the highest (56.5%) under mixture of S. terebinthifolius , P. cattleianum , and S. cumini . Observed SF was highest (33.9%) under P. cattleianum and lowest (3.6%) under a mixture of S. terebinthifolius , P. cattleianum , and S. cumini . The relatively high SF under P. cattleianum can be attributed to its smooth bark, stem density and steep branching. The mean observed canopy interception varied between 23% under P. cattleianum and 45% at the site dominated by C. arabica . Mean direct TF coefficients from individual events at each location ranged from a low of 0.36 under the canopy dominated by C. arabica to a high of 0.51 under the canopy dominated by S. terebinthifolius , P. cattleianum , and S. cumini . In contrast, the mean SF partitioning coefficients from individual storm events at each location ranged from a low of 0.05 under the canopy dominated by S. terebinthifolius , P. cattleianum , and S. cumini to a high of 0.37 under P. cattleianum . Mean canopy storage capacity was highest (1.90) at the site dominated by S. terebinthifolius , P. cattleianum , and S. cumini whereas trunk storage capacity was highest (0.54) under the P. cattleianum . Copyright © 2012 John Wiley & Sons, Ltd.

Description: Multi-step ahead inflow forecasting has a critical role to play in reservoir operation and management in Taiwan during typhoons as statutory legislation requires a minimum of 3-hours warning to be issued before any reservoir releases are made. However, the complex spatial and temporal heterogeneity of typhoon rainfall, coupled with a remote and mountainous physiographic context makes the development of real-time rainfall-runoff models that can accurately predict reservoir inflow several hours ahead of time challenging. Consequently, there is an urgent, operational requirement for models that can enhance reservoir inflow prediction at forecast horizons of more than 3-hours. In this paper we develop a novel semi-distributed, data-driven, rainfall-runoff model for the Shihmen catchment, north Taiwan. A suite of Adaptive Network-based Fuzzy Inference System solutions is created using various combinations of auto-regressive, spatially-lumped radar and point-based rain gauge predictors. Different levels of spatially-aggregated radar-derived rainfall data are used to generate 4, 8 and 12 sub-catchment input drivers. In general, the semi-distributed radar rainfall models outperform their less complex counterparts in predictions of reservoir inflow at lead-times greater than 3-hours. Performance is found to be optimal when spatial aggregation is restricted to 4 sub-catchments, with up to 30% improvements in the performance over lumped and point-based models being evident at 5-hour lead times. The potential benefits of applying semi-distributed, data-driven models in reservoir inflow modelling specifically, and hydrological modelling more generally, is thus demonstrated. Copyright © 2012 John Wiley & Sons, Ltd.

Description: There has been a long term interest in understanding the incubation environment within salmonid spawning gravels. This focus has been motivated primarily by concerns over the impact of increased fine sediment loadings released from a range of catchment sources including, amongst others, forestry or agricultural activity (Ringer & Hall 1987; Collins et al., 2011). Greig et al.,(2005a;2007a) and Sear et al., (2008a) have shown how the accumulation of fine sediment (〈1 mm) influences the supply of oxygen to incubating salmonid eggs via three main processes; 1) physical occlusion of the micropores on the surface of the egg resulting in reduced oxygen diffusion through the egg wall (Greig et al., 2005b); 2) physical occlusion of the pore spaces between gravel particles in the bed, resulting in reduced interstitial flow velocity and longer flow paths and 3) increased oxygen demand arising from active elements within the infiltrated sediments resulting in a reduction in oxygen concentration; termed Sediment Oxygen Demand (SOD). Copyright © 2012 John Wiley & Sons, Ltd.

Description: Hydrological processes change from the impacts of climate variability and human activities. Runoff in the upper reaches of the Hun-Taizi River basin, which is mainly covered by forests in northeast China, decreased from 1960 to 2006. The data used in this study were based on runoff records from six hydrological stations in the upper reaches of the Hun-Taizi River basin. Nonparametric Mann-Kendall statistic was used to identify change trends and abrupt change points, and consequently analyze the change characteristics in hydrological processes. The abrupt change in the annual runoff in most subcatchments appeared after 1975. Finally, the effects of climate change and land-cover change on water resources were identified using regression analysis and a hydrology model. Results of the regression analysis suggest that the correlation coefficients between precipitation and runoff prior to the abrupt change were higher compared with those after the abrupt change. Moreover, using hydrology model analysis, the water yield was found to increase because of the decrease in forest land. Copyright © 2012 John Wiley & Sons, Ltd.

Description: In this article, we investigated the variability of precipitation conditions in the Haihe River basin (HRB) during 1961–2010 by analyzing four daily precipitation scenarios. These scenarios were set with the values of, equal to 0 mm/day, 10–20 mm/day, 20–50 mm/day, and greater than 50 mm/day, which were denoted as P0, P10, P20, and P50, respectively. Results indicate that the mean values of daily precipitation decline and its fluctuation becomes weak with years in HRB. The contour of daily precipitation with the mean value of 1.4 mm/day moves more than 100 km toward southeast in the basin from 1960s to 2000s. The variations of four precipitation scenarios show difference. The Tianjin and Langfang cities were the P0 drought center in HRB after 1980s, and the days and regions without precipitation increase with years. The magnitude of P10 extrema shows no significant changes over the last fifty years, but the rainfall centers vary with areas in HRB. The magnitude of P20 extrema shows no obvious changes in 1961–2000 but increases in 2000s. The magnitude of P50 extrema obviously declines in the last fifty years, with the rainfall center moving from northeast to south of HRB. Urbanization impacts are reflected in some cities in 1980s and 1990s, but after 2000 the urbanization impacts were not clearly detected due to the significant precipitation decreases in HRB. In summary, precipitation decrease is caused by the decreases of P50 extrema rather than P10 and P20 extrema in HRB, which would be favorable for the flood resources utilization through ample-low flow operations over space. Copyright © 2012 John Wiley & Sons, Ltd.

Description: Protection of groundwater-dependent ecosystems (GDEs) is an important criterion in sustainable groundwater management, particularly when human water consumption is in competition with environmental water demands; however, the delineation of GDEs is commonly a challenging task. The Groundwater-dependent Ecosystem Mapping (GEM) method proposed here is based on interpretation of the land surface response to the drying process derived from combined changes in two multispectral indices, the Normalised Difference Vegetation Index (NDVI) and the Normalised Difference Wetness Index (NDWI), both derived from Landsat imagery. The GEM method predicts three land cover classes used for delineation of potential GDEs: vegetation with permanent access to groundwater; vegetation with diminishing access to groundwater; and water bodies that can persist through a prolonged dry period. The method was applied to a study site in the Ellen Brook region of Western Australia, where a number of GDEs associated with localised groundwater, diffuse discharge zones and riparian vegetation were known. The estimated accuracy of the method indicated a good agreement between the predicted and known GDEs; Producer's accuracy was calculated as up to 91% for some areas. The method is most applicable for mapping GDEs in regions with a distinct drying period. Copyright © 2012 John Wiley & Sons, Ltd.

Description: The use of precipitation estimates from weather radar reflectivity has become widespread in hydrologic predictions. However, uncertainty remains in the use of the non-linear reflectivity-rainfall ( Z-R ) relation, in particular for mountainous regions where ground validation stations are often lacking, land surface datasets are inaccurate and the spatial variability in many features is high. In this study, we assess the propagation of rainfall errors introduced by different Z-R relations on distributed hydrologic model performance for four mountain basins in the Colorado Front Range. To do so, we compare spatially-integrated and distributed rainfall and runoff metrics at seasonal and event time scales during the warm season when convective storms dominate. Results reveal that the basin simulations are quite sensitive to the uncertainties introduced by the Z-R relation in terms of streamflow, runoff mechanisms and the water balance components. The propagation of rainfall errors into basin responses follow power law relationships that link streamflow uncertainty to the precipitation errors and streamflow magnitude. Overall, different Z-R relations preserve the spatial distribution of rainfall relative to a reference case, but not the precipitation magnitude, thus leading to large changes in streamflow amounts and runoff spatial patterns at seasonal and event scales. Furthermore, streamflow errors from the Z-R relation follow a typical pattern that varies with catchment scale where higher uncertainties exist for intermediate-sized basins. The relatively high error values introduced by two operational Z-R relations (WSR-57 and NEXRAD) in terms of the streamflow response indicate that site-specific Z-R relations are desirable in the complex terrain region, particularly in light of other uncertainties in the modeling process, such as model parameter values and initial conditions. Copyright © 2012 John Wiley & Sons, Ltd.

Description: Historically, observing snow depth over large areas has been difficult. When snow depth observations are sparse, regression models can be used to infer the snow depth over a given area. Data sparsity has also left many important questions about such inference unexamined. Improved inference, or estimation, of snow depth and its spatial distribution from a given set of observations can benefit a wide range of applications from water resource management, to ecological studies, to validation of satellite estimates of snow pack. The development of LiDAR technology has provided non-sparse snow depth measurements which we use in this study to address fundamental questions about snow depth inference using both sparse and non-sparse observations. For example, when are more data needed and when are data redundant? Results apply to both traditional, manual snow depth measurements and to LiDAR observations. Through sampling experiments on high-resolution LiDAR snow depth observations at six separate 1.17  km 2 sites in the Colorado Rocky Mountains, we provide novel perspectives on a variety of issues affecting the regression estimation of snow depth from sparse observations. We measure the effects of observation count, random selection of observations, quality of predictor variables, and cross-validation procedures using three skill metrics: percent error in total snow volume, root mean squared error, and R 2 . Extremes of predictor quality are used to understand the range of its effect; how do predictors downloaded from internet perform against more accurate predictors measured by LiDAR? While cross validation remains the only option for validating inference from sparse observations, in our experiments the full set of LiDAR-measured snow depths can be considered the “true” spatial distribution and used to understand cross-validation bias at the spatial scale of inference. We model at the 30 m resolution of readily-available predictors which is a popular spatial resolution in the literature. Three regression models are also compared and we briefly examine how sampling design affects model skill. Results quantify the primary dependence of each skill metric on observation count which ranges over 3 orders of magnitude, doubling at each step from 25 up to 3200. While uncertainty (resulting from random selection of observations) in percent error of true total snow volume is typically well constrained by 100-200 observations, there is considerable uncertainty in the true spatial distribution ( R 2 ) even at medium observation counts (200-800).Weshowthatpercenterrorintotalsnowvolumeisnotsensitivetopredictor quality, though RMSE and R 2 (measures of spatial distribution) often depend critically on it. In accuracies of downloaded predictors (most often the vegetation predictors) caneasily require a quadrupling of observation count to match RMSE and R 2 scores obtained by LiDAR-measured predictors. Under cross validation, the RMSE and R 2 skill measures are consistently biased towards poorer results than the true validation. This is primarily a result of greater variance at the spatial scales of point observations used for cross validation than at the 30  m resolution of the model. The magnitude of this bias depends on individual site characteristics, observation count (for our experimental design), and on sampling design. Sampling designs which maximize independent information maximize cross-validation bias but also maximize true R 2 . The bagging tree model is found to generally out-perform the other regression models in the study on several criteria. Finally, we discuss and recommend use of LiDAR in conjunction with regression modeling to advance understanding of snow depth spatial distribution at spatial scales of thousands of square kilometers. Copyright © 2012 John Wiley & Sons, Ltd.

Description: Processes controlling streamflow generation were determined using geochemical tracers for water years 2004–2007 at eight headwater catchments at the Kings River Experimental Watersheds (KREW) in the Southern Sierra Nevada. Four catchments are snow dominated and four receive a mix of rain and snow. Results of diagnostic tools of mixing models indicate that Ca 2+ , Mg 2+ , K + and Cl - behaved conservatively in streamflow at all catchments, reflecting mixing of three endmembers. Using endmember mixing analysis, the endmembers were determined to be snowmelt runoff (including rain on snow), subsurface flow, and fall storm runoff. In seven of the eight catchments, streamflow was dominated by subsurface flow, with an average relative contribution (% of streamflow discharge) greater than 60%. Snowmelt runoff contributed less than 40% and fall storm runoff less than 6% on average. Streamflow peaked 2–4 weeks earlier at mixed rain-snow than snow-dominated catchments, but relative endmember contributions were not significantly different between the two groups of catchments. Both soil water in the unsaturated zone and regional groundwater were not significant contributors to streamflow. The contributions of snowmelt runoff and subsurface flow, when expressed as discharge, were linearly correlated with streamflow discharge (R 2 of 0.85-0.99). These results suggest that subsurface flow is generated from the soil-bedrock interface through preferential pathways and is not very sensitive to snow-rain proportions. Thus a declining of the snow-rain ratio under a warming climate should not systematically affect the processes controlling the streamflow generation at these catchments. Copyright © 2012 John Wiley & Sons, Ltd.

Description: High latitude drainage basins are experiencing increases in temperature higher than the global average with snowmelt dominated basins most sensitive to effects in winter due to snowpack's integration of these changes over the season. This may influence the timing of snowmelt onset, the melt-refreeze period, and snowpack accumulation resulting in changes in spring runoff, associated flooding, and drought conditions later in the year, possibly enhancing forest fire potential. Large burned areas cleared of vegetation change discharge dynamics and may affect snowmelt characteristics and discharge in subsequent seasons. Correlations are tested by comparing forest fire occurrence with spring melt onset, the end of melt-refreeze period (after which snow rapidly depletes) and early snowmelt events. Snow characteristics are derived from brightness temperature (T b ) data from the Advanced Microwave Scanning Radiometer for EOS (AMSR-E) for 2003–2010. Dates of melt onset, end of melt-refreeze, and early melt events are defined with T b and diurnal amplitude variation thresholds. Areas and intensities of forest fires are from MODIS thermal anomaly data (MOD14) and all data are mapped to an EASE-grid to assess spatial correlations. Earlier melt onset and end of melt-refreeze are found in years and areas of high forest fire occurrence by comparing high (2004–2005) and low (2006–2007) fire years in the Porcupine sub-basin of the Yukon River in northeastern Alaska and the Yukon Territory. The burned areas also correlate with relatively later melt onset and later end of melt-refreeze in subsequent low fire years. Copyright © 2012 John Wiley & Sons, Ltd.

Description: Temporal stability of soil water content is an often-observed phenomenon, which characterization finds multiple applications. Climate and variability in soil properties are usually mentioned as factors of temporal stability of soil water content, but their effects are far from clear. The objective of this work was to use soil water content modeling to evaluate the effects of climate and soil hydraulic properties on the temporal stability of soil water at different measurement schedules. We selected four representative climates found in USA and simulated the multiyear soil water content dynamics for sandy loam, loam, and silty clay loam soils, all having the lognormal spatial distribution of the saturated hydraulic conductivity. The CLIMGEN and the HYDRUS6 codes were used to generate weather patterns and to simulate soil water content respectively. Four different methods were applied to select the representative location. The low probability of having the same variability of mean relative differences of soil water under different climates was found in most of the cases. The probability that the variance of mean relative differences depended on sampling frequency was generally higher than 91% for the three soils. The inter-annual difference in mean relative differences variation from short and intensive summer campaigns was highly probable for all climates and soils. The representative locations changed as climate and measurement scheduling changed, and they were less pronounced for coarse textured soils. The Representative location selection methods based solely on bias provided more consistency as compared with other methods. The temporal stability appears to be the result of the interplay between climate, soil properties, and survey protocols. One implication of this factor interaction effect on temporal stability soil water content is that a simulation study can be useful to decide on the feasibility of including a search for temporal stability-based representative locations for a specific site. Copyright © 2013 John Wiley & Sons, Ltd.

Description: Field measurements and morphodynamic simulations were carried out along a 5 km reach of the sandy, braided, lower Tana River in order to detect temporal and spatial variations in river bed modifications and to determine the relative importance of different magnitude discharges on river bed and braid channel evolution during a time span of one year (2008–2009). Fulfilling these aims required testing the morphodynamic model's capability to simulate changes in the braided reach. We performed the simulations using a 2-D morphodynamic model and different transport equations (Meyer-Peter and Müller [1948] and van Rijn [1989]). The survey showed that more deposition than erosion occurred during 2008–2009. Continuous bed-load transport and bed elevation changes of ±1 m and a 70–188 m downstream migration of the thalweg occurred. Simulation results indicated that, during low water periods, modifications occurred in both the main channel and in other braid channels. Thus, unlike some gravel-bed rivers, the sandy lower Tana River does not behave like a single thread channel at low discharge. But at higher discharge, i.e. exceeding 497 m 3 /s, the river channel resembled a single-thread channel when channel banks confined the flow. Although the spring discharge peaks caused more rapid modifications than slower flows, the cumulative volumetric changes of the low water period were greater. The importance of low water period flows for channel modifications is emphasised. Although the 2-D model requires further improvements, the results were nevertheless promising for the future use of this approach in braided rivers. Copyright © 2013 John Wiley & Sons, Ltd.

Description: This study compared summer stream temperature between two years in the Star Creek catchment, Alberta, a headwater basin on the eastern slopes of the Canadian Rocky Mountains. Star Creek is a subsurface water dominated stream, which represents important habitat for native salmonid species. Hydro-meteorological data from May-September of 2010 and 2011 accompanied by stream energy budget calculations were used to describe the drivers of stream temperature in this small forested stream. Mean, maximum and minimum weekly stream temperatures were lower from May to August and higher in September 2011 compared to 2010. Weekly range in stream temperature was also different between years with a higher range in 2010. Inter-annual stream temperature variation was attributed discharge differences between years, shown to be primarily governed by catchment-scale moisture conditions. This study demonstrates that both meteorological and hydrological processes must be considered in order to understand stream temperature response to changing environmental conditions in mountainous regions. Copyright © 2013 John Wiley & Sons, Ltd.

Description: The long term “Millennium Drought” has put significant pressure on water resources across Australia. In south eastern Australia and in particular the Murray-Darling Basin, removal of the exotic, high water use Salix may provide a means to return water to the environment. This paper describes a simple model to estimate evapotranspiration of two introduced Salix species under non-water-limited conditions across 7 biogeoclimatic zones in Australia. In this study, Salix evapotranspiration was calculated using the Penman-Monteith model. Field measurements of leaf area index and stomatal conductance for Salix babylonica and Salix fragilis were used to parameterise the models. Each model was validated using extensive field estimates of evapotranspiration from a semi-arid ( S . babylonica , r 2  = 0.88) and cool temperate ( S . fragilis , r 2  = 0.99) region. Modelled mean annual evapotranspiration showed strong agreement with field measurements, being within 32 and 2 mm year -1 for S . babylonica and S . fragilis , respectively. Monthly pan coefficients (the ratio of mean evapotranspiration to mean pan evaporation) were developed from 30 years of meteorological data, for 30 key reference sites across Australia for both species using the validated Penman-Monteith models. Open water evaporation was estimated from field measurements and was used to develop a simple linear regression model for open water evaporation across the 30 reference sites. Differences between modelled evapotranspiration and open water evaporation at each site provide an indication of the amount of water which might be returned to the environment from removal of in-stream Salix species. The monthly pan coefficient method reported has application across riparian environments worldwide where measured ET is available for model validation. Copyright © 2013 John Wiley & Sons, Ltd.

Description: We hypothesized that the transport of E. coli strains harvested from springs could be characterized by a similar set of cell characteristics and transport parameters. The hypothesis was tested by sampling springs throughout the Lubigi catchment in Kampala, Uganda. Chemo-physical parameters in addition to total coliform (TC) concentrations were determined. Furthermore, E. coli strains were harvested, and cell properties determined. Column experiments in saturated quartz columns of 7 cm height were conducted to determine transport parameters of selected E. coli strains. Using a two-site non-equilibrium sorption model, transport was modeled by fitting breakthrough data in HYDRUS 1-D. Results indicated fecal contamination of the springs with high concentrations of total coliforms (TC), chloride and nitrate. Furthermore, the maximum relative E. coli concentrations (C/C 0 ) max in the column experiments were high. Compared to our previous work on E. coli strains, collected from a pasture and from zoo animals, attachment was low. Modeling revealed that both equilibrium and kinetic sorption were not important under conditions employed in the experiments. These observations are explained by the way in which the strains were harvested: from termination points of flowlines (springs). Such strains may possess characteristics that might have influenced their transport in the subsurface leading to their low attachment efficiency and possibly contributing to the lack of influence of equilibrium and kinetic sorption characteristics. There was no significant correlation between cell properties and transport parameters. Furthermore, 58% of the tested strains were of the O21:H7 serotype and all definable serotypes identified were associated with diseases. We speculate that this serotype may possess characteristics that allow preferential transport through the aquifers of the area. We demonstrated that bacteria harvested from termination points of flow lines compared to those obtained from pollution sources, which have not undergone transport yet, present a good option for the assessment of bacteria transport characteristics in aquifers. Copyright © 2013 John Wiley & Sons, Ltd.

Description: In climate-change studies, a macroscale hydrologic model (MHM) operating over large scales can be an important tool in developing consistent hydrological variability estimates over large basins. MHMs, which can operate at coarse grid resolutions of about one degree latitude by longitude, have been used previously to study climate change impacts on the hydrology of continental scale or global river basins. They can provide a connection between global atmospheric models and water resource systems on large spatial scales and long timescales. In this study, the Variable Infiltration Capacity (VIC) macroscale hydrologic model is used to study large scale hydrologic impacts of climate change for Indian river basins. Large-scale changes in runoff, evapotranspiration and soil moisture for India, as well as station-scale changes in discharges for three major river basins with distinct climatic and geographic characteristics are examined in this study. Climate model projections for meteorological variables (precipitation, temperature and windspeed) from three General Circulation Models (GCMs) and three emissions scenarios are used to drive the VIC MHM. GCM projections are first interpolated to a one degree by one degree hydrologic model grid and then bias-corrected using a quantile-quantile mapping. The VIC model is able to reproduce observed statistics for discharges in the Ganga, Narmada and Krishna basins reasonably well, even at the coarse grid resolution employed using a calibration period for years 1965–1970 and testing period from 1971-73/74. An increasing trend is projected for summer monsoon surface runoff, evapotranspiration and soil moisture in most central Indian river basins, while a decrease in runoff and soil moisture is projected for some regions in southern India, with important differences arising from GCM and scenario variability. Discharge statistics show increases in mid- and low flows at Farakka station on Ganga river, increased high flows at Jamtara station upstream of Narmada, and increased high, mid- and low flows for Vijayawada station on Krishna river in the future. Copyright © 2013 John Wiley & Sons, Ltd.

Description: As a critical water discharge term in basin-scale water balance, accurate estimation of evapotranspiration (ET) is therefore important for sustainable water resources management. The understanding of the relationship between ET and groundwater storage change can improve our knowledge on the hydrological cycle in such regions with intensive agricultural land usage. Since the 1960s the North China Plain (NCP) has experienced groundwater depletion because of overexploitation of groundwater for agriculture and urban development. Using meteorological data from 23 stations, the Complementary Relationship Areal Evapotranspiration (CRAE) model is evaluated against of estimates of evapotranspiration derived from regional water balance in the NCP during the period 1993–2008. The discrepancies between calculated ET and that derived by basin water balance indicate seasonal and interannual variations in model parameters. The monthly actual evapotranspiration variations during the period from 1960 to 2008 are investigated by the calibrated model, and then are used to derive groundwater storage change. The estimated actual evapotranspiration is positively correlated with precipitation, and the general higher ET than precipitation indicates the contributions of groundwater irrigation to the total water supply. The long term decreasing trend in the actual evapotranspiration can be explained by declining in precipitation, sunshine duration and wind speed. Over the past ~50 years, the calculated average annual water storage change, represented by the difference between actual evapotranspiration and precipitation, was approximately 36 mm, or 4.8 km 3 ; and the cumulative groundwater storage depletion was approximately 1,700 mm, or 220 km 3 in the NCP. The significantly groundwater storage depletion conversely affects the seasonal and interannual variations of evapotranspiration. Irrigation especially during spring cause an marked increase in seasonal ET, while the rapid increasing of agricultural coverage over the NCP reduces the annual ET and is the primary control factor of the strong linear relationship between actual and potential ET. Copyright © 2013 John Wiley & Sons, Ltd.

Description: Skillful and reliable precipitation data is essential for seasonal hydrologic forecasting, and generation of hydrological data. Though output from dynamic downscaling methods is used for hydrological application, the existence of systematic errors in dynamically downscaled data adversely affects the skill of hydrologic forecasting. This study evaluates the precipitation data derived by dynamically downscaling the global atmospheric reanalysis data by propagating them through three hydrological models. Hydrological models are calibrated for 28 watersheds located across the southeastern United States (U.S.) that is minimally affected by human intervention. Calibrated hydrological models are forced with five different types of datasets: global atmospheric reanalysis (NCEP R2 and ERA40) at their native resolution; dynamically downscaled global atmospheric reanalysis at 10 km grid resolution; stochastically generated data from weather generator; bias-corrected dynamically downscaled and bias-corrected global reanalysis. The reanalysis products are considered as surrogates for large-scale observations. Our study indicates that over the 28 watersheds in the southeastern U.S., the simulated hydrological response to the bias-corrected dynamically downscaled data is superior to the other four meteorological datasets. In comparison to synthetically generated meteorological forcing (from weather generator), the dynamically downscaled data from global atmospheric reanalysis result in more realistic hydrological simulations. Therefore, we conclude that dynamical downscaling of global reanalysis, which offers data for sufficient number of years (in this case 22 years), although resource intensive is relatively more useful than other sources of meteorological data with comparable time period in simulating realistic hydrological response at watershed scales. Copyright © 2013 John Wiley & Sons, Ltd.

Description: Assessments of water resources using macro-scale models tend to be conducted at the continental or large-catchment scale. However, security of freshwater supplies is a local issue, and thus necessitates study at such a scale. This research aims to evaluate the suitability of the Land Processes and eXchanges Dynamic Global Vegetation Model (LPX-DGVM) for simulating runoff for small catchments in the UK. Simulated annual and monthly runoff is compared against National River Flow Archive streamflow observations from twelve catchments of varying size (500-10,000 km 2 ) and climate regimes. Results show that LPX reproduces observed inter- and intra-annual runoff variability successfully in terms of both flow timings and magnitudes. Interannual variability in flow timings is simulated particularly well (as indicated by Willmott Index of Agreement values of ≥0.7 for the majority of catchments), whereas runoff magnitudes are generally slightly overestimated. In the densely populated Thames catchment, these overestimations are partly accounted for by water consumption. Seasonal variability in runoff is also modelled well, as shown by Willmott Index of Agreement values of ≥0.9 for all but one catchment. Absence of river routing and storage from the model, in addition to precipitation uncertainties, are also suggested as contributing to simulated runoff discrepancies. Overall, the results show that the LPX DGVM can successfully simulate runoff processes for small catchments in the UK. This study offers promising insights into the use of global scale models and datasets for local scale studies of water resources, with the eventual aim of providing local-scale projections of future water distributions. Copyright © 2013 John Wiley & Sons, Ltd.

Description: A procedure combining the Soil Conservation Service - Curve Number (SCS-CN) method and the Green-Ampt (GA) infiltration equation was recently developed to overcome some of the drawbacks of the classic SCS-CN approach when estimating the volume of surface runoff at a sub-daily time resolution. The rationale of this mixed procedure, named CN4GA (Curve Number for Green Ampt), is to use the GA infiltration model to distribute the total volume of the net hyetograph (rainfall excess) provided by the SCS-CN method over time. The initial abstraction and the total volume of rainfall given by the SCS-CN method are used to identify the ponding time and to quantify the hydraulic conductivity parameter of the GA equation. In this paper, a sensitivity analysis of the mixed CN4GA parameters is presented with the aim to identify conditions where the mixed procedure can be effectively used within the Prediction in Ungauged Basin (PUB) perspective. The effects exerted by changes in selected input parameters on the outputs is evaluated using rectangular and triangular synthetic hyetographs as well as 100 maximum annual storms selected from synthetic rainfall time series. When applied to extreme precipitation events, which are characterized by predominant peaks of rainfall, the CN4GA appears to be rather insensitive to the input hydraulic parameters of the soil, which is an interesting feature of the CN4GA approach and makes it an ideal candidate for the rainfall excess estimation at sub-daily temporal resolution at ungauged sites. Copyright © 2013 John Wiley & Sons, Ltd.

Description: Despite significant recent advancements in global hydrological modeling, current modeling frameworks and their input databases have limited capabilities in supporting many spatially detailed research questions and integrated assessments, such as required in freshwater ecology or applied water resources management. In order to address these challenges, the scientific community needs to create improved large scale datasets and more flexible data structures that enable the integration of information across and within spatial scales; develop new and advanced models that support the assessment of longitudinal and lateral hydrological connectivity; and provide an accessible modeling environment for researchers, decision makers, and practitioners. As a contribution, we here present a new modeling framework that integrates hydrographic baseline data at a global scale (enhanced HydroSHEDS layers and coupled datasets) with new modeling tools, specifically a river network routing model (HydroROUT) that is currently under development. The resulting ‘hydro-spatial fabric’ is designed to provide an avenue for advanced hydro-ecological applications at large scales in a consistent and highly versatile way. Preliminary results from case studies to assess human impacts on water quality and the effects of dams on river fragmentation and downstream flow regulation illustrate the potential of this combined data-and-modeling framework to conduct novel research in the fields of aquatic ecology, biogeochemistry, geo-statistical modeling, or pollution and health risk assessments. The global scale outcomes are at a previously unachieved spatial resolution of 500 meters and can thus support local planning and decision making in many of the world's large river basins. Copyright © 2013 John Wiley & Sons, Ltd.

Description: The flow of precipitation from the surface through to groundwater in karst systems is a complex process involving storage in the unsaturated zone and diffuse and preferential recharge pathways. The processes associated with this behaviour are not well understood, despite karst aquifers being used as freshwater supplies. As a result, uncertainty regarding the ecohydrological processes in this geological setting remains large. In response to the need to better understand the impact of woody vegetation on groundwater recharge, annual evapotranspiration rates and tree water sources were measured for two years above a shallow, fresh karst aquifer. Water use strategies of the co-occurring Eucalyptus diversifolia subsp. diversifolia Bonpl. and Allocasuarina verticillata (Lam.) L. Johnson were investigated using a monthly water balance approach, in conjunction with measurement of the stable isotopes of water, leaf water potentials and soil matric potentials. The results suggest that it is unlikely groundwater resources are required to sustain tree transpiration, despite its shallow proximity to the soil surface, and that similarities exist between evapotranspiration losses and the estimated long term average rainfall for this area. Irrespective of stand and morphological differences, E . diversifolia and A . verticillata evapotranspiration rates showed remarkable convergence, demonstrating the ability of these co-occurring species to maximise their use of the available precipitation, and avoids the requirement to differentiate between these species when estimating ET at a landscape scale. We conclude that the water holding capacity of porous geological substrates, such as those associated with karst systems, will play an important role in equilibrating annual rainfall variability and should be considered when assessing ecohydrological links associated with karst systems. Copyright © 2013 John Wiley & Sons, Ltd.

Description: Watershed subdivision is a useful discretization method for distributed hydrological models at large river basins. A subwatershed codification method which is able to identify the subwatershed uniquely and reflect the topological relationship is desired. According to the previous literatures, there are two types of coding methods suitable for the subwatershed codification: the Pfafstetter-group rules and the modified binary tree codification method. But, both of them have some shortcomings in theory and application. A new coding method named stem-branch-topological codification (SBTC) is developed to overcome these shortcomings, which is based on the stem-branch topological structure of the drainage networks and capable of reflecting the river hierarchy. The basic coding elements of the method are river reaches in the drainage networks, which are not only generated by the tributary junctions, but also by the splitting points of hydrological factors (e.g. hydrological gauge stations, reservoirs). Also, the method could handle complex confluences (e.g. river reaches with more than two upstream inflows) which are rare under natural conditions, but more frequent in the DEM extracted or artificial drainage networks (e.g. sewage systems or irrigation drainage networks). With the SBTC codes, it is easy to identify the upstream (or downstream) relationship between any two subwatersheds and to calculate the directly connected subwatershed codes. Also, if some changes have occured in the drainage network, there is no need to recode the whole watershed, but by modifying the existed codes to form the new ones. Copyright © 2013 John Wiley & Sons, Ltd.

Description: Rivers in watersheds dominated by agriculture throughout the US are impaired by excess sediment, a significant portion of which comes from non-field, near-channel sources. Both land-use and climate have been implicated in altering river flows and thereby increasing stream-channel erosion and sediment loading. In the wetland-rich landscapes of the upper Mississippi basin, twentieth century crop conversions have lead to an intensification of artificial drainage, which is now a critical component of modern agriculture. At the same time, much of the region has experienced increased annual rainfall. Uncertainty in separating these drivers of streamflow fuels debate between agricultural and environmental interests on responsibility and solutions for excess riverine sediment. To disentangle the effects of climate and land-use we compared changes in precipitation, crop conversions, and extent of drained depressional area in 21 Minnesota watersheds over the past 70 years. Watersheds with large land-use changes had increases in seasonal and annual water yields of 〉50% since 1940. On average, changes in precipitation and crop evapotranspiration explained less than one-half of the increase, with the remainder highly correlated with artificial drainage and loss of depressional areas. Rivers with increased flow have experienced channel widening of 10-40% highlighting a source of sediment seldom addressed by agricultural best management practices. Copyright © 2013 John Wiley & Sons, Ltd.

Description: This study presents a new method to measure stream cross section without having contact with water. Compared with conventional measurement methods which apply instruments such as sounding weight, ground penetration radar (GPR), used in this study, is a non-contact measurement method. This non-contact measurement method can reduce the risk to hydrologists when they are conducting measurements, particularly in high flow period. However, the original signals obtained by using GPR are very complex. Different from studies in the past where the measured data were mostly interpreted by experts with special skill or knowledge of GPR so that the results obtained were less objective. This study employs Hilbert Huang Transform (HHT) to process GPR signals which are difficult to interpret by hydrologists. HHT is a newly developed signal processing method that can not only process the nonlinear and non-stationary complex signals, but also maintain the physical significance of the signal itself. Using GPR with HHT, this study establishes a non-contact stream cross section measurement method with the ability to measure stream cross-sectional areas precisely and quickly. Also, in comparison with the conventional method, no significant difference in results is found to exist between the two methods, but the new method can considerably reduce risk, measurement time, and manpower. It is proven that the non-contact method combining GPR with HHT is applicable to quickly and accurately measure stream cross section. Copyright © 2013 John Wiley & Sons, Ltd.

Description: This study sought to test a widely used hypothesis in water transport from soil to root: the soil textural effect on soil–root interfacial conductance can be quantified by the degree of soil water saturation. This hypothesis is inferred from basic soil physics and is commonly used in modeling root water uptake. However, it has never been subjected to rigorous experimental test. In the current study, the soil-texture effect on the interfacial hydraulic conductance was evaluated on well-watered pot-grown cotton plants, with soil particle-size ranges of 0–0.05, 0.05–0.1, 0.1–0.2, 0.2–0.3, 0.3–0.45, 0.45–0.6 and 0.6–1 mm in seven treatments, in addition to hydroponics. However, our experimental results showed that the volumetric soil water content, not degree of saturation, is the best explanatory variable for quantifying the interfacial effect on hydraulic conductance. Further analysis indicated that if temporal change of this interfacial effect on hydraulic conductance is the subject of concern, degree of saturation may still be a valid option. If soil textural or spatial variation in root water uptake is the subject of concern, volumetric soil water content is best suited to quantifying the interfacial effect on hydraulic conductance. Copyright © 2013 John Wiley & Sons, Ltd.

Description: We measured stream temperature continuously during the 2011 summer runoff season (May through October) in nine watersheds of southeast Alaska that provide spawning habitat for Pacific salmon. The nine watersheds have glacier coverage ranging from 0 to 63%. Our goal was to determine how air temperature and watershed land cover, particularly glacier coverage, influence stream temperature across the seasonal glacial meltwater hydrograph. Multiple linear regression models identified mean watershed elevation (related to glacier extent) and watershed lake coverage (%) as the strongest landscape controls on mean monthly stream temperature, with the weakest (May) and strongest (July) models explaining 86% and 97% of the temperature variability, respectively. Mean weekly stream temperature was significantly correlated with mean weekly air temperature in seven streams; however, the relationships were weak to non-significant in the streams influenced by glacial runoff. Streams with 〉30% glacier coverage showed decreasing stream temperatures with rising summer air temperatures, while those with 〈30% glacier coverage exhibited summertime warming. Glaciers also had a cooling effect on monthly mean stream temperature during the summer (July through September) equivalent to a decrease of 1.1 °C for each 10% increase in glacier coverage. The maximum weekly average temperature (MWAT, an index of thermal suitability for salmon) in the six glacial streams was substantially below the lower threshold for optimum salmon growth. This finding suggests that while glaciers are important for moderating summer stream temperatures, future reductions in glacier runoff may actually improve the thermal suitability of some glacially dominated streams in southeast Alaska for salmon. Copyright © 2013 John Wiley & Sons, Ltd.

Description: High resolution topography, e.g. 1-meter Digital Elevation Model (DEM) from LiDAR (Light Detection and Ranging), offers opportunity for accurate identification of topographic features of relevance for hydrologic and geomorphologic modeling. Yet, the computation of some derived topographic properties, such as the Topographic Index (TI), is characterized by daunting challenges, which hamper the full exploration of topography-based models. Particular problems, for example, arise when a distributed (or semi-distributed) rainfall-runoff model is applied to high-resolution DEMs. Indeed, the characteristic dependency between landscape resolution and the computed TI distribution results in the formation of un-physical, unconnected saturated zones, which in turn cause unrealistic representation of rainfall-runoff dynamics. In this study we present a methodology based on a multi-resolution wavelet transformation which, by means of a soft-thresholding scheme on the wavelet coefficients, filters the noise of high resolution topography to construct regularized sets of locally smoother topography on which the TI is computed. While the methodology needs a somewhat arbitrary definition of the wavelet coefficients threshold, our study shows that when the information content (entropy) of the TI distribution is used as filtering efficiency metric, a critical threshold automatically emerges in the landscape reconstruction. The methodology is demonstrated using 1- m LiDAR data for the Elder Creek River basin in California. While the proposed case study uses a TOPMODEL approach, the methodology can be extended to different topography-based models and is not limited to hydrological applications. Copyright © 2012 John Wiley & Sons, Ltd.

Description: Uncertainty communication is an important topic within hydrological forecasting. Hydrological ensemble prediction systems are established tools for the generation of forecasts including uncertainty information. The interpretation of such forecasts requires new visualization and verification tools to help forecasters and end-users in their decision making. While the visualization of hydrographs is important for estimating flood volumes, little support is provided for the interpretation of peak-flow forecasts. We introduce the “Peak-Box”, a novel visual support that envelops all ensemble peak-timings and peak-discharge, from which specific verification metrics are defined. A user-defined metric quantifies the sharpness concerning peak-timing and peak-discharge and allows communicating a-priori, if the spread of peak-forecasts is acceptable. 18 months of ensemble predictions for four basins have been evaluated. A probabilistic verification which relies on the relationships between the spread and the ROC area indicates the quality of the ensemble predictions in all basins. A sub-sample of 485 events was used for exploring the value of the “Peak-Box”. The combined spread of forecast peak-time and peak-discharge is higher than a tailored reference sharpness for most of the considered events. We show that, depending on the lead-time of the forecasts, 30% to 55% of the observed peaks are found outside the predicted range. Most correct forecasts (hits) were obtained for forecasts having a lead-time of 2 or more days. Further analyses indicate that the median of the ensemble-peak forecast provides reliable estimates on either peak-timing or peak-discharge in more than 80% of the events evaluated. Finally, a score system was defined in order to combine different verification measures and obtain an overall assessment on the quality of both the peak-discharge and peak-timing of the ensemble forecasts. We demonstrate that the “Peak-Box” can be adopted in different ways in order to obtain quantitative and qualitative insights on the quality of peak-forecasts. Copyright © 2012 John Wiley & Sons, Ltd.

Description: Fish mortality in the middle reaches of the Pilcomayo River (Bolivia), locally called ‘borrachera’, can be observed almost every year at the onset of the rainy season. In order to study the potential causes of the ‘borrachera’, suspended sediment (SS) and selected water quality parameters have been monitored from mid-September until mid-December 2010. Gill samples were taken and analysed, before and during the ‘borrachera’ event on December 7th 2010. Data on river discharge were obtained from a database. During the sampling period the river hydrology changed dramatically. At the day of the ‘borrachera’ heavy rains in upstream reaches of the river catchment changed the river from a quiet stream into a turbulent river with extremely high concentrations of suspended sediment (SS) (〉 100 g l -1 ). This may be caused by the inundation of the entire riverbed, which causes easily erodible material, left on the riverbanks at the end of the former rainy season, to be transported by the river during the first peak discharges. As concentrations of heavy metals in filtered water samples did not show higher values during the ‘borrachera’ it is concluded that the ‘borrachera’ is unlikely to be caused by heavy metal toxicity. Results showed a strong association between the SS concentration and the ‘borrachera’. Gills of fish collected during the ‘borrachera’ were clogged with sediment to such an extent that oxygen uptake became virtually impossible. High SS concentrations are therefore considered to be the cause of this typical fish mortality phenomenon. Copyright © 2012 John Wiley & Sons, Ltd.

Description: Improvements in our ability to model runoff from glaciers remain an important scientific goal. This paper describes a new temperature-radiation-index glacier melt model specifically enhanced for use in High-Arctic environments, utilising high temporal and spatial resolution datasets while retaining relatively modest data requirements. The model employs several physically constrained parameters and was tuned using a lidar-derived surface elevation model of Midtre Lovénbreen, meteorological data from sites spanning ~70% of the glacier's area-altitude distribution, and periodic ablation surveys during the 2005 melt season. The model explained 80% of the variance in observed ablation across the glacier, an improvement of ~40% on a simplified energy balance model (EBM), yet equivalent to the performance of a full EBM employed at the same location. Model performance was assessed further by comparing potential and measured runoff from the catchment, and through application to an earlier (2004) melt season. The additive model form and consideration of a priori parameters for the Arctic locality were shown to be beneficial, with a planimetry correction eliminating systematic errors in potential runoff. Further parameterisations defining modelled incident radiation failed to yield significant improvements to model output. Our results suggest that such enhanced melt models may perform well for singular melt seasons, yet are highly sensitive to the choice of lapse rates and their transferability to different locations and seasons may be limited. While modelling ablation requires detailed consideration of the transition between snow- and ice-melt, our study suggests that description of the ratio between radiative and turbulent heat fluxes may provide a useful step towards dynamic parameterisation of melt factors in temperature-index models. Copyright © 2012 John Wiley & Sons, Ltd.

Description: Hemispherical photographs of forest canopies can be used to develop sophisticated models that predict incident below canopy shortwave radiation on the surface of interest (i.e. soil, water). Hemispherical photographs were collected on eight dates over the course of a growing season to estimate leaf area index (LAI) and to quantify solar radiation incident on the surface of two stream reaches based on output from Gap Light Analyzer and Hemisfer software. Stream reaches were shaded by a mixed-deciduous Ozark border forested riparian canopy. Hemispherical photo model results were compared to observed solar radiation sensed at climate stations adjacent to each stream reach for the entire 2010 water year. Modeled stream-incident shortwave radiation was validated with above-stream pyranometers for the month of September. On average, the best hemispherical photo models underestimated daily averages of solar radiation by approximately 14 % and 12 % for E-W and N-S flowing stream reaches, respectively (44.7 W/m 2 measured vs. 38.4 W/m 2 modeled E-W, 46.8 W/m 2 vs. 41.1 W/m 2  N-S). The best hemispherical photo models overestimated solar radiation relative to in-stream pyranometers placed in the center of each stream reach by approximately 7% and 17% for E-W and N-S stream reaches respectively (31.3 W/m 2 measured vs. 33.5 W/m 2 modeled E-W, 31.5 W/m 2 vs. 37.1 W/m 2  N-S). The model provides a geographically transferable means for quantifying changes in the solar radiation regime at a stream surface due to changes in canopy density through a growing season, thus providing a relatively simple method for estimating surface and water heating in canopy altered environments (e.g. forest harvest). Copyright © 2012 John Wiley & Sons, Ltd.

Description: An ensemble Kalman Filter (EnKF) is developed to identify a hydraulic conductivity distribution in a heterogeneous medium by assimilating solute concentration measurements of solute transport in the field with a steady state flow. A synthetic case with the mixed Neumann/ Dirichlet boundary conditions is designed to investigate the capacity of the data assimilation methods to identify a conductivity distribution. The developed method is demonstrated in 2-D transient solute transport with two different initial instant solute injection areas. The influences of the observation error and model error on the updated results are considered in this study. The study results indicate that the EnKF method will significantly improve the estimation of the hydraulic conductivity field by assimilating solute concentration measurements. The larger area of the initial distribution and the more observed data obtained, the better the calculation results. When the standard deviation of the observation error varies from 1% to 30% of the solute concentration measurements, the simulated results by the data assimilation method do not change much, which indicates that assimilation results are not very sensitive to the standard deviation of the observation error in this study. When the inflation factor is more than 1.0 to enlarge the model error by increasing the forecast error covariance matrix, the updated results of the hydraulic conductivity by the data assimilation method are not good at all. Copyright © 2012 John Wiley & Sons, Ltd.

Description: Reference evapotranspiration ( ET 0 ) is an important element in the water cycle that integrates atmospheric demands and surface conditions, and analysis of changes in ET 0 is of great significance for understanding climate change and its impacts on hydrology. As ET 0 is an integrated effect of climate variables, increases in air temperature should lead to increases in ET 0 . However, this effect could be offset by decreases in vapor pressure deficit, wind speed and solar radiation which lead to the decrease in ET 0 . In this study, trends in the Penman–Monteith ET 0 at 80 meteorological stations during 1960–2010 in the driest region of China (Northwest China) were examined. The results show that there was a change point for ET 0 series around the year 1993 based on the Pettitt's test. For the region average, ET 0 decreased from 1960 to 1993 by −2.34 mm yr -2 , while ET 0 began to increase since 1994 by 4.80 mm yr -2 . A differential equation method based on FAO Penman–Monteith formula was used to attribute the change in ET 0 . The attribution results show that the significant decrease in wind speed dominated the change in ET 0 , which offset the effect of increasing air temperature and led to the decrease in ET 0 from 1960 to 1993. However, wind speed began to increase and the amplitude of increase in air temperature also rose significantly since the mid-1990s. Increases in air temperature and wind speed together reversed the trend in ET 0 and led to the increase in ET 0 since 1994. Copyright © 2012 John Wiley & Sons, Ltd.

Description: Wildfire can cause substantial changes to runoff, erosion and downstream sediment delivery processes. In response to these disturbance effects, the main sources of sediment transported within burned catchments may also change. Sediment tracing offers an approach to determine the proportional contributions of fine sediment (typically 〈63 µm) from burned catchment sources. In this paper, we review the application of various sediment tracers to discriminate fine sediment sources following wildfire. Fallout radionuclides provide the most effective tracers for discriminating hillslope surface and sub-surface (usually channel bank) sources. Previous tracer studies quantifying contributions from these sources after wildfire are based exclusively on radionuclides. The potential for fallout radionuclides to discriminate spatial sources defined according to burned and unburned areas depends on burn-related changes in surface soil concentrations. Tracing of burned and unburned source areas will be problematic where most radionuclides in surface material are bound to ash rather than soil. Geochemical properties of surface soils are probably too susceptible to natural and burn-related variability to consistently discriminate burn-defined spatial sources. Mineral magnetic properties have shown potential for discriminating soil burned at different severities as well as unburned areas. More research is needed to assess the use of soil organic compounds as tracers of burned source areas. Linking fallout radionuclide-based hillslope and channel source discrimination with process measurements and monitoring after fire can provide enhanced insight into fine sediment transfer and related water quality impacts. Adopting such integrated and multi-scale approaches would contribute to improved understanding of hydrological and geomorphological responses to wildfire. Copyright © 2012 John Wiley & Sons, Ltd.

Description: Suspended matter is an important indicator of water quality in freshwater systems. The flood-induced turbidity current plays a dominant role in the seasonal dynamic of suspended matter in Liuxihe reservoir (23°45′50″N; 113°46′52″E), a large, stratified reservoir at the Tropic of Cancer in southern China. Field measurements show that loading and distribution of suspended matter in the reservoir differ in typical wet, dry and medium years, as a result of different discharge volumes and water level variation patterns. Using historical data and the practical demand for water supply and flood control, we generalized two feasible reservoir operational modes: flood impounding mode (drawing down the reservoir to a low level before flood events to impound inflow during the flooding season) and moderate level change mode (drawing down the reservoir to a moderate level before flood events, then keeping the level within the flood control level during runoff events). To examine the effects of different operational modes and outlet depths on the reservoir's flood-induced turbidity current, a numerical simulation model was applied in three types of hydrological conditions. The results show that the mode with moderate drawdown and recharge processes can decrease loading of suspended matter in spring and promote turbidity current release during flood events, and upper withdrawal can improve the effects of turbid water release. We suggest that more attention should be focused on water quality management in the reservoir operation stage, severe artificial water level fluctuation being avoided and selective withdrawal becoming an optional management measure. Copyright © 2012 John Wiley & Sons, Ltd.

Description: In recent years, the Xitiaoxi river basin in China has experienced intensified human activity, including city expansion and increased water demand. Climate change also has influenced streamflow. Assessing the impact of climate variability and human activity on hydrological processes is important for water resources planning and, management, and for the sustainable development of eco-environmental systems. The non-parametric Mann-Kendall test was employed to detect the trends of climatic and hydrological variables. The Mann-Kendall-Sneyers test and the moving t-test were used to locate any abrupt change of annual streamflow. A runoff model, driven by precipitation and potential evapotranspiration, was employed to assess the impact of climate change on streamflow. A significant downward trend was detected for annual streamflow from 1975 to 2009, and an abrupt change occurred in 1999, which was consistent with the change detected by the double mass curve test between streamflow and precipitation. The annual precipitation decreased slightly, but upward trends of annual mean temperature and potential evapotranspiration were significant. The annual streamflow during the period 1999-2009 reduced 26.19% compared with the reference stage, 1975-1998. Climate change was estimated to be responsible for 42.8% of the total reduction in annual streamflow, and human activity accounted for 57.2%. Copyright © 2012 John Wiley & Sons, Ltd.

Description: This study is aimed at quantifying the difference in aquifer's response to recharge between some different locations in a fan aquifer and a delta aquifer for a preliminary study of revealing mechanisms of water transport in alluvial aquifer. The aquifer's response to recharge is statistically quantified with the two viewpoints: (1) timing and volume of recharge and (2) time length of aquifer's holdig water. For the first point, a statistical model that links precipitation and groundwater level is introduced, and its parameters are identified using correlation analysis. Our results show that the recharge rate at the toe is higher than both that at the apex and that at the delta. For the second point, the concept of “memory effect” of aquifer is adopted and quantified using the autocorrelation and spectral analyses. Our results show that the memory effect is longer at the toe of fan than at the apex, and thus a temporary increase of water level has about five-times as long-term influence on subsequent water levels at the toe of the fan as at the apex. This study demonstrates that the statistical analyses and modeling of hydrological data are useful for characterizing aquifer's hydrodynamics. Copyright © 2012 John Wiley & Sons, Ltd.