ALBERT

Description: Few studies exist on infiltration processes in badlands, although infiltration and subsurface lateral flows are known to contribute to soil erosion and to control slope instability. Our investigation was carried out in a 100 m² plot located in a 0.5 ha landslide in black marls (South-East France). An artificial sprinkling was performed with an intensity of 10 mm.h -1 during 66.4 h interrupted with 8.4 h. breaks. KBr and KCl were used as tracers. A pseudo-steady state was reached after 25-35 hours and 250-350 mm of rainfall. The runoff coefficient was 40% (ratio total runoff volume/total sprinkling water amount). Pre-event water (PE) contributed to the groundwater recharge at the very beginning of the experiment but PE contribution dropped steadily while the soil was saturating. After around 200 mm cumulative rainfall, PE contribution started to rise steeply before reaching a nearly constant value. This original mechanism implies an efficient transfer process of PE. It was assumed from the description of the material structure and from hydrological evidences that PE was mainly drained from a structure porosity made of the marl's flaked nature. Total pre-event water contributions ranged from 25 to 79 % (PE contribution was over 50 % in 2/3 of the observations wells). Over the recession phase, release of pre-event water occurred from the drainage of a texture porosity. The study showed that at the plot scale, infiltration processes proved well organised despite the high heterogeneity and anisotropy of the material. It was possible to propose a general conceptual model explaining the hydrological processes over time and area. The peculiar structure of regolith originating from black marl is preserved over a large part of the weathering time, so that the material structure (type, orientation of grains, small/large pores) remains a first order control of water flow generation in Black marl soils. Copyright © 2012 John Wiley & Sons, Ltd.

Description: In this work, the multifractal properties of hourly rainfall data recorded at a location in Southern Spain have been related to the scale properties of the corresponding Intensity-Duration-Frequency (IDF) curves. Four parametric models for the IDF curves have been fitted to the quantiles of rainfall obtained by using the Generalized Pareto frequency distribution function with the extreme data series obtained for the same place. The scaling of the rainfall intensity moments has been analysed and the empirical moments scaling exponent function has been obtained. The corresponding values of q 1 and γ 1 have been empirical and theoretically calculated and compared to some characteristics of the different IDF models. Thus, the scaling behaviour of IDF curves has been analysed and the best model has been selected. Copyright © 2012 John Wiley & Sons, Ltd.

Description: Major-ion compositions of groundwater are employed in this study of the water-rock interactions and hydrogeochemical evolution within a carbonate aquifer system. The groundwater samples were collected from boreholes or underground tunnels in the Ordovician limestone of Yanzhou Coalfield where catastrophic groundwater inflows can be hazardous to mining and impact use of the groundwater as a water supply. The concentration of TDS ranged from 961 to 3,555 mg/l and indicates moderately to highly mineralized water. The main water-type of the middle Ordovician limestone groundwater is Ca-Mg-SO 4 , with SO 4 2- ranging from 537 mg/l to 2,297 mg/l, and average values of Ca 2+ and Mg 2+ of 455.7 mg/l and 116.6 mg/l, respectively. The water samples were supersaturated with respect to calcite and dolomite and undersaturated or saturated with respect to gypsum. Along the general flow direction, deduced from increases of TDS and Cl - , the main water-rock interactions that caused hydrogeochemical evolution of the groundwater within the aquifer were the dissolution of gypsum, the precipitation of calcite, the dissolution or precipitation of dolomite, and ion exchange. Ion exchange is the major cause for the lower mole concentration of Ca 2+ than that of SO 4 2- . The groundwater level of Ordovician aquifer is much higher than that of C-P coal-bearing aquifers, so the potential flow direction is upward and the pyrite in coal is not a possible source of sulfate, additional data on the stable sulfur and oxygen isotopic composition of the sulfate may be helpful to identify its origin. Although ion exchange probably accounts for the higher mole concentration of Na + than that of Cl - , the dissolution of aluminosilicate can not be ruled out. The data evaluation methods and results of this study could be useful in other areas to understand flow paths in aquifers and to provide information needed to identify the origin of groundwater. Copyright © 2012 John Wiley & Sons, Ltd.

Description: Quantitative evaluation of the effect of climate variability and human activities on runoff is of great importance for water resources planning and management in term of maintaining the ecosystem integrity and sustaining the society development. In this paper, hydro-climatic data from 4 catchments (i.e., Luanhe River Catchment, Chaohe River Catchment, Hutuo River Catchment and Zhanghe River Catchment) in the Haihe River Basin from 1957–2000 were used to quantitatively attribute the hydrological response (i.e., runoff) to climate change and human activities separately. To separate the attributes, the temporal trends of annual precipitation, potential evapotranspiration (PET) and runoff during 1957–2000 were first explored by the Man-Kendall test. Despite that only Hutuo River Catchment was dominated by significant negative trend in annual precipitation, all four catchments presented significant negative trend in annual runoff varying from −0.859 mm a -1 (Chaohe River) to −1.996 mm a -1 (Zhanghe River). Change points in 1977 and 1979 are detected by precipitation-runoff double cumulative curves method and Pettitt's test for Zhanghe River and other three rivers, respectively, and are adopted to divide data set into two study periods as the pre-change period and post-change period. Three methods including hydrological model method, hydrological sensitivity analysis method and climate elasticity method were calibrated with the hydro-climatic data during the pre-change period. And then, hydrological runoff response to climate variability and human activities were quantitatively evaluated with the help of the three methods and based on the assumption that climate and human activities are the only drivers for streamflow and are independent to each other. Similar estimates of anthropogenic and climatic effects on runoff for catchments considered can be obtained from the three methods. We found that human activities were the main driving factors for the decline in annual runoff in Luanhe River Catchment, Chaohe River Catchment and Zhanghe River Catchment, accounting for over 50% of runoff reduction. However, Climate variability should be responsible for the decrease in annual runoff in the Hutuo River Catchment. Copyright © 2012 John Wiley & Sons, Ltd.

Description: Measurements of river water quality at Haridwar, India, taken during 2005 – 2006 show that the river water does not meet the WHO and Bureau of Indian Standards criteria of drinking water quality, especially with respect to total coliform and fecal-coliform. This study investigates the removal of pathogens at a river bank filtration (RBF) site in Haridwar. Using the quality of river water and the quality of abstracted water from a nearby production well, semi-empirical models based on the concept of filtration coefficient are developed and tested for their effectiveness in removing pathogens under varying bacteriological quality of source water. A two-tier model which includes the effect of clogged layer is developed to obtain an equivalent filtration coefficient. This coefficient is found to be linearly related with natural logarithm of the concentration of pathogens in the source water. Copyright © 2012 John Wiley & Sons, Ltd.

Description: Nonpoint source pollution and hydromodification are the leading causes of impairment to our nation's rivers and streams. Roadside ditch networks, ubiquitous in both rural and urban landscapes, intercept and shunt substantial quantities of overland runoff and shallow groundwater to stream systems. By altering natural flowpaths, road ditches contribute not only to hydromodification but also potentially to nonpoint-source (NPS) pollution by acting as hydrologic links between agricultural fields and natural streams. Unfortunately, the impacts of these alterations on watershed hydrology and water quality are not well understood. Through a series of field measurements, including field surveys and discharge monitoring, this study examined the effect of road ditch networks on basin morphometry, field- and watershed-scale hydrology, and pollutant transport in a 38 km 2 agricultural watershed in south-central NY. Salient findings include: (i) 94% of road ditches discharged directly to natural streams, effectively doubling the drainage density, (ii) on average, road ditches increased peak and total event flows in their receiving streams by 78% and 57%, respectively, but displayed significant variation across ditches, (iii) ditches intercepted large quantities of surface and subsurface runoff from agricultural fields and therefore represent efficient conduits for the transport of agricultural NPS pollutants to sensitive receiving waterbodies. Our results provide useful information for hydrologists who wish to further understand how artificial drainage may be affecting watershed hydrology and for managers and engineers tasked with designing appropriate flood and NPS pollution control measures. Copyright © 2012 John Wiley & Sons, Ltd.

Description: We coupled the process-based NIES Integrated Catchment-based Eco-hydrology (NICE) model to an urban canopy model (UCM) and the Regional Atmospheric Modeling System (RAMS) in order to simulate the effect of urban geometry and anthropogenic exhaustion on the hydrothermal changes in the atmospheric/land and the interfacial areas of the Japanese megalopolis. The simulation was conducted with multi-scale in horizontally regional–urban–point levels, and in vertically atmosphere–surface–unsaturated–saturated layers. The model reproduced reasonably the observed hydrothermal values by using ground-truth data in various types of natural/artificial land covers. The simulated results also suggested that the latent heat flux in new water-holding pavement (consisting of porous asphalt and water-holding filler made of steel by-products based on silica compound) has a strong impact on hydrologic cycle and cooling temperature in comparison with the observed heat budget by newly incorporating the effect of water amount on the heat conductivity in the pavement. Furthermore, the model predicted the hydrothermal changes under two types of land cover scenarios to promote evaporation and to reduce air temperature against heat island phenomenon. Finally, we evaluated the relationship between the effect of groundwater use to ameliorate the heat island and the effect of infiltration on the water cycle in the catchment. These procedures to integrate the multi-scaled model simulation with political scenario based on the effective management of water resources as heat sink/source would be very powerful approaches to recovering a sound hydrologic cycle and create thermally-pleasing environments in the megalopolis. Copyright © 2012 John Wiley & Sons, Ltd.

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: 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: 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: 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.

Description: Climate change due to global warming is a public concern in Central Asia. Due to specific orography and climate conditions, the republic of Tajikistan is considered as the main glacial center of Central Asia. In this study regional climate change impacts in the two large basins of Tajikistan, Pyanj and Vaksh River basins located in the upstream sector of the Amu Darya River basin are analyzed. A statistical regression method with Model Output Statistics corrections using the ground observation data, Willmott archived dataset and GSMaP satellite driven dataset, was developed and applied to the basins in order to downscale the Global Climate Model Projections at a 0.1 degree grid and to assess the regional climate change impacts at subbasin scale. It was found that snow and glacier melting are of fundamental importance for the state of the future water resources and flooding at the target basins since the air temperature had a clearly increasing trend toward the future. It was also found that the snowfall will decrease but the rainfall will increase due to the gradual increase in the air temperature. Such changes may result in an increase in flash floods during the winter and the early spring, and in significant changes in the hydrologic regime during a year in the future. Furthermore, the risks of floods in the target basins may be slightly increasing due to the increase in the frequencies and magnitudes of high daily precipitation and the increase in the rapid snowmelt with high air temperatures toward the future. Copyright © 2012 John Wiley & Sons, Ltd.

Description: For many practical reasons, the empirical black-box models have become an increasingly popular modeling tool for river-flow forecasting, especially in mountainous areas where have a very few meteorological observatories. In this paper, precipitation data is employed as the only input to estimate river flow. Using five empirical black-box models—the simple linear model (SLM), the linear perturbation model (LPM), the linearly varying gain factor model (LVGFM), the constrained non-linear system model (CNLSM) and the nonlinear perturbation model ( NLPM-API)—modeling results are compared to actual results in three catchments within the Heihe River Basin. The linearly varying gain factor model and the nonlinear perturbation model yielded excellent predictions. For better simulation accuracy, a commonly used multi-layer feed-forward neural network model (NNM) was applied to incorporate the outputs of the individual models. Comparing the performance of these models, it was found that the best results were obtained from the NNM model. The results also suggest that more reliable and precise predictions of river flow can be obtained by using the NNM model while also incorporating the combined outputs of different empirical black-box models. Copyright © 2012 John Wiley & Sons, Ltd.

Description: Mathematical relationships have been developed for reaeration rate coefficient ( K a ) by various researchers. These relationships have a number of variables such as depth, velocity, width, slope, Froud number, molecular diffusion coefficient, kinematic viscosity and the gas transfer Reynolds number. From these variables, 29 relations have been developed and divided into four groups. To evaluate their predictive capability for highly variable flow rivers receiving high pollution loads form large cities, these relationships have been used to model dissolved oxygen (DO) in the River Ravi. Such rivers are either saturated with DO during high flows or anaerobic during critical low flow conditions. The evaluation is based on the agreement between model DO values calculated using K a obtained from the available equations and the measured DO concentrations in the river samples in terms of sum of square of residuals (SSR) and coefficient of determination (R 2 ). It has been found that in general, the group of equations containing depth and velocity as the only two variables affecting K a performed better than the equations in other groups as reflected by lower SSR and higher R 2 values. The study results also reveal that the turbulence based reaeration rate coefficient equation containing additional variables also resulted in close agreement between DO model results and the measured values. The study results identify, the most important parameters affecting the reaeration rate coefficient, and the suitability of various K a relationships as well for rivers with highly variable flows. Copyright © 2012 John Wiley & Sons, Ltd.

Description: Year-to-year dynamics in weather affect both the timing of application and potential hydrologic transport of pesticides. Further, most commonly used pesticides dissipate in the environment during the growing season. Interactions among these factors – hydrology, timing of application, and dissipation kinetics – hinder the detection of temporal trends in transport. It is increasingly important to be able to discern such trends, to judge effectiveness of management practices or to determine whether observed changes were caused by management or weather. In previous work, a cumulative vulnerability index (CVI) was developed to account for these three factors. It explained 63% of annual variation in atrazine load in the Goodwater Creek Experimental Watershed (GCEW). The objectives of the current work were to 1) generalize the CVI to explicitly account for variation in watershed size, area treated with atrazine, and average application rate; 2) test the overall performance on watersheds showing such variation, and 3) test whether the generalized index properly accounted for the additional input parameters. The generalized index was tested using data from GCEW (73.7 km 2 ) and 7 additional watersheds in the northeast Missouri claypan region that varied in size from 212 to 1180 km 2 and from 4% to 23% of watershed area planted to corn or sorghum. Across 32 site-years, the generalized index explained 84% of variation in annual atrazine load. Further, tests of residuals showed no dependence on either watershed area or fraction of area planted to corn and sorghum, indicating that these parameters were properly integrated into the index. The performance of the index supports the conclusion that data obtained from GCEW is representative of the Mark Twain Lake Basin and likely the entire Central Claypan Major Land Resource Area. Copyright © 2012 John Wiley & Sons, Ltd.

Description: Since the Three Gorges Reservoir (TGR) was put into operation in June 2003, the impacts of the TGR on downstream hydrology and water resources have become the focus of public attention. This paper examines the impacts of the TGR on the hydrological droughts at the downstream Yichang hydrological station during the period of 2003-2011. The two-parameter monthly water balance (TPMWB) model was employed to generate the monthly discharges at Yichang station for the period of 2003-2011 to represent the unregulated flow regime, and thus to provide a comparison benchmark for the observed flow series at Yichang station after the operation of the TGR. To provide a reference series for the observed monthly discharge series of the entire study period of 1951-2011, the naturalized monthly discharge series at Yichang station was constructed by joining the observed monthly discharge at Yichang station for the period of 1951-2002 and the TPMWB simulated monthly runoff at Yichang station for the period of 2003-2011. For both the observed and naturalized monthly discharge series of 1951-2011, the hydrological drought index series were calculated using the standardized streamflow index ( SSI ) method. By comparing the drought indices of these two monthly discharge series, we investigated the impacts of the TGR on the hydrological droughts at the downstream Yichang station during the period of 2003-2011. The results show that the hydrological droughts at the downstream Yichang station are slightly aggravated by the TGR's initial operation from 2003 to 2011. The river flow reduction at Yichang station after impoundment of the TGR might account for the downstream drought aggravation. Copyright © 2012 John Wiley & Sons, Ltd.

Description: This paper explores the relationship between temperature, evaporation and soil moisture using a planetary boundary layer (PBL) model. It focuses on illustrating and quantifying the effect of soil moisture on the evolution of daytime temperatures. A simple convective PBL model coupled with the Penman-Monteith equation is used to estimate evapotranspiration. Following calibration and sensitivity analysis, the model was used to simulate the relative impact of dry and wet soil moisture conditions on daytime temperatures by changing the surface resistance parameter in the Penman-Monteith equation. It was found that the maximum temperature that can be reached during a day is constrained by the amount of soil moisture and the available net radiation, confirming previously published results. Higher temperatures can be reached with greater net radiation and dry soil moisture conditions. Copyright © 2012 John Wiley & Sons, Ltd.

Description: Stream temperature will be subject to changes due to atmospheric warming in the future. We investigated the effects of the diurnal timing of air temperature changes – daytime warming vs. nighttime warming – on stream temperature. Using the physically-based model, Heat Source, we performed a sensitivity analysis of summer stream temperatures to 3 diurnal air temperature distributions of +4 °C mean air temperature: 1) uniform increase over the whole day; 2) warmer daytime; and 3) warmer nighttime. The stream temperature model was applied to a 37-km section of the Middle Fork John Day River in northeastern Oregon, USA. The 3 diurnal air temperature distributions generated 7-day average daily maximum (7dADM) stream temperatures increases of approximately +1.8 ±0.1 °C at the downstream end of the study section. The 3 air temperature distributions, with the same daily mean, generated different ranges of stream temperatures, different 7dADM temperatures, different durations of stream temperature changes, and different average daily temperatures in most parts of the reach. The stream temperature changes were out of phase with air temperature changes and, therefore in many places, the greatest daytime increase in stream temperature was caused by nighttime warming of air temperatures. Stream temperature changes tended to be more extreme and of longer duration when driven by air temperatures concentrated in either daytime or nighttime instead of uniformly distributed across the diurnal cycle. Copyright © 2012 John Wiley & Sons, Ltd.

Description: Infiltration along ephemeral channels plays an important role in groundwater recharge in arid regions. A model is presented for estimating spatial variability of seepage due to streambed heterogeneity along channels based on measurements of streamflow-front velocities in initially dry channels. The diffusion-wave approximation to the Saint-Venant equations, coupled with Philip's equation for infiltration, is connected to the groundwater model MODFLOW, and is calibrated by adjusting the saturated hydraulic conductivity of the channel bed. The model is applied to portions of two large water delivery canals, which serve as proxies for natural ephemeral streams. Estimated seepage rates compare well with previously published values. Possible sources of error stem from uncertainty in Manning's roughness coefficients, soil hydraulic properties, and channel geometry. Model performance would be most improved through more frequent longitudinal estimates of channel geometry and thalweg elevation, and with measurements of stream stage over time to constrain wave timing and shape. This model is a potentially valuable tool for estimating spatial variability in longitudinal seepage along intermittent and ephemeral channels over a wide range of bedslopes, and the influence of seepage rates on groundwater levels. Copyright © 2012 John Wiley & Sons, Ltd.

Description: The overexploitation and impairment of our freshwater resources require land management strategies that support the preservation of green and blue water flow and various ecosystem services. Historical landscape analysis and the influential driving factors of landscape development provide an essential basis for tackling current environmental questions in land and water management. Hence, this paper investigates the influence of historical land use pattern on the hydrological processes and provision of blue and green water flow and storage for man and ecosystems under current climate conditions. Moreover, we discuss in how far these findings could be used to predict or optimise future land management options or as a reference for future land and water management. We used digitalized historical land use maps from 1787, 1827, 1940, 1984 and a digital land use map of present situation from 2009 for our study areas, which are two small scale Slovenian catchments (Reka and Dragonja). The integrated river basin model Soil and Water Assessment Tool (SWAT) was used to simulate the land use change impacts on blue and green water flow. The results showed for both catchments that the influence of land use change on total and green water quantity would be statistically insignificant, but would have considerable impacts on the seasonal flows. In the Reka catchment, historical situations indicate impacts on spring and summer blue and green water flow due to decreased percentage of forest and increased percentage of grassland and vineyards in the past. Results for the Dragonja catchment indicate past shift from arable land use to forest as decrease in summer green water flow and increase in blue water flow. Possible effects are also increased levels of blue water flow and decreased levels of green water flow during the growing period of the year. Copyright © 2012 John Wiley & Sons, Ltd.

Description: The increasing complexity of hydrological models results in a large number of parameters to be estimated. In order to better understand how these complex models work, efficient screening methods are required in order to identify the most important parameters. This is of particular importance for models which are used within an operational real-time forecasting chain such as HQsim. The objectives of this investigation are to i) identify the most sensitive parameters of the complex HQsim model applied in the Alpine Lech catchment and ii) compare model parameter sensitivity rankings attained from three global sensitivity analysis techniques. The techniques presented are the i) Regional Sensitivity Analysis (RSA), ii) Morris analysis and iii) State Dependent Parameter (SDP) modelling. The results indicate that parameters affecting snow melt as well as processes in the unsaturated soil zone reveal high significance in the analysed catchment. The snow melt parameters show clear temporal patterns in the sensitivity while most of the parameters affecting processes in the unsaturated soil zone do not vary in importance across the year. Overall, the maximum degree day factor ( meltfunc_max ) has been identified to play a key role within the HQsim model. Although the parameter sensitivity rankings are equivalent between methods for a number of parameters, for several key parameters differing results were obtained. An uncertainty analysis demonstrates that a parameter ranking attained from only one method is subjected to large uncertainty. Copyright © 2012 John Wiley & Sons, Ltd.

Description: The dissolution-induced finger pattern in geological medium plays an important role in both geological processes and engineering practices. Numerical models have been developed to investigate the evolution of the chemical dissolution front within a fluid-saturated porous medium. In these models, several permeability-porosity relationships have been proposed and incorporated into the numerical model for describing simultaneous changes in permeability and porosity induced by mineral dissolution, but limited experimental data are available to justify one form superior to the other. This study investigates the effects of the permeability-porosity relationships on the morphological evolution of the chemical dissolution front. Three porosity-permeability relationships, namely modified Fair-Hatch, Kozeny-Carman and Verma-Pruess models are incorporated into the numerical model. A series of numerical simulation are performed to evaluate the morphological evolution of reaction front and the corresponding behavior diagrams are constructed. Results shows that the morphological development are similar each other for modified Fair-Fatch and Kozeny-Carman model. The Verma-Pruess model yields a relative low primary and secondary critical upstream pressure gradient value owing to the flow-focusing effect enhanced by the stronger dependence of permeability on porosity. A comparison of behavior diagrams of front morphology among three relationships show that the double-fingering front occurs under condition of lower upstream pressure gradient and smaller non-uniformity spacing for Verma-Pruess model. Our simulations demonstrate that the choice of the permeability-porosity function plays important roles on the evolution patterns of dissolution front. Therefore, an adequate description of the permeability-porosity relationship may lead to a more realistic simulation of field problems. Copyright © 2012 John Wiley & Sons, Ltd.

Description: The groundwater of the Korba plain represents major water resources in Tunisia. The Plio-Quaternary unconfined aquifer of the Cap-Bon (north-east Tunisia) is subject to the intensive agricultural activities and high groundwater pumping rates due to the increasing of the groundwater extraction. The degradation of the groundwater quality is characterized by the salinization phenomena. Groundwater were sampled and analysed for physic-chemical parameters: Ca 2+ , Mg 2+ , Na + , K + , Cl - , SO 4 2- , HCO 3 - , NO 3 - , pH, electrical conductivity (EC), and the temperature (T°). The hydrochemical analysis is coupled with the calculation of the saturation Indexes (SI Gypsum, SI Halite, SI Calcite and SI Dolomite), ionic derivation and with the ion correlations compared to chloride concentrations: Na + / Cl - , Ca 2+ / Cl - and Mg 2+ / Cl - ratios. Seawater fractions in the groundwater were calculated using the chloride concentration. Those processes can be used as indicators of seawater intrusion progression. Electrical conductivity methods was also conducted to obtain new informations on the spatial scales and dynamics of the fresh water-seawater interface of coastal groundwater exchange. The mixing zone between freshwater and saltwater was clearly observed from the EC profile in the investigated area where a strong increase in electrical conductivity with depth was observed, corresponding to the freshwater and saltwater interface. Results of hydrochemical study revealed the presence of direct cation exchange linked to seawater intrusion and dissolution processes associated with cations exchange. These results, together with EC investigation, indicated that the groundwater is affected by seawater intrusion and is still major actor as a source of salinization of the groundwater in Korba coastal plain. Further isotopic and hydrological investigations will be necessary to identify and more understood the underlying mechanisms. Copyright © 2012 John Wiley & Sons, Ltd.

Description: The quality of hydrological discharge simulations depends to a great extent on the uncertainties in the meteorological input and the model parameterization. To quantify these uncertainties, we adopt ensemble techniques in a four-year nowcast experiment for two nested flash-flood-prone basins in the southern Swiss Alps. The spatiotemporal uncertainties in the weather radar quantitative precipitation estimates (QPE) were accounted for by applying an ensemble of 25 radar fields. To account for uncertainties in model parameterization a Monte Carlo experiment was run to find 26 equifinal model realizations. The resulting parameter ensemble, consisting of 26 members, was run with precipitation input obtained from interpolated pluviometer data and with the deterministic operational weather radar QPE. To produce the discharge nowcast a semi-distributed rainfall-runoff model (PREVAH) was used. PREVAH was calibrated for the main catchment Verzasca. The results for the sub-catchment Pincascia are an independent internal verification of the nowcasting system. The three ensemble nowcasts and the two deterministic nowcasts are evaluated for a four-year time series and for two events included in that period. The event analysis shows no clear superiority for either pluviometer-based or radar-based nowcasts. The performance for single events depends heavily on the storm characteristics. However, the evaluation of the four-year nowcast shows that pluviometer-based nowcasts outperform radar-based nowcasts in the gauged and calibrated catchment and that there is added value in the application of parameter ensembles. For the small, ungauged catchment the results achieved by the radar-based nowcasts are superior to the pluviometer-based nowcasts. Especially the radar ensemble proves to be of significant advantage for flash flood nowcasts in such catchments. Copyright © 2012 John Wiley & Sons, Ltd.

Description: This special issue of Hydrological Processes is drawn from selected papers presented in sessions organized by the Eastern Snow Conference (ESC) at its 2011 annual meetings at McGill University in Montreal, Quebec. The cross-disciplinary nature of these sessions is reflected in the papers included in this special issue. The ESC is a joint American, Canadian and international forum for discussing recent work on operational, applied, and scientific issues related to snow and ice Copyright © 2012 John Wiley & Sons, Ltd.

Description: Five years of hydrogeological monitoring and field activities performed in the complex hydrogeological system of the Acque Albule basin were conducted to define the hydrogeological setting, the relationship between deep and shallow aquifers and a conceptual groundwater flow model of this exploited area using conventional quantitative techniques. The basin, which is located close to Rome (Italy) on the west side of the Apennine chain and just north of the Colli Albani volcano, subsided after development of a north–south fault system (about 115,000 y bp). The Acque Albule basin experiences intense hydrothermal activity, which has produced a large travertine deposit (80   m thick). The travertine deposit constitutes a fractured aquifer that is the final destination of more than 5   m 3   s -1 of water and is strongly dewatered by quarry activities. The complex hydrogeology of this basin was investigated, revealing two main hydraulically connected aquifers, one thermalised and partly confined into the limestone bedrock and one unconfined in the travertine. The two aquifers are separated by a non-continuous clayey aquiclude. The hydrogeological survey and geological characterisation contributed to the development of the groundwater flow conceptual model. Analysis and comparison of the monitored levels highlighted the pattern of flow between the deep and shallow parts of the flow system. Copyright © 2012 John Wiley & Sons, Ltd.

Description: The mesoscale Numerical Weather Prediction (NWP) model is gaining popularity among the hydrometeorological community in providing high-resolution rainfall forecasts at the catchment scale. Although the performance of the model has been verified in capturing the physical processes of severe storm events, the modelling accuracy is negatively affected by significant errors in the initial conditions used to drive the model. Several meteorological investigations have shown that the assimilation of real-time observations, especially the radar data can help improve the accuracy of the rainfall predictions given by mesoscale NWP models. The aim of this study is to investigate the effect of data assimilation for hydrological applications at the catchment scale. Radar reflectivity together with surface and upper-air meteorological observations is assimilated into the Weather Research and Forecasting (WRF) model using the three-dimensional variational (3DVar) data assimilation technique. Improvement of the rainfall accumulation and its temporal variation after data assimilation is examined for four storm events in the Brue catchment (135.2 km 2 ) located in southwest England. The storm events are selected with different rainfall distributions in space and time. It is found that the rainfall improvement is most obvious for the events with one-dimensional evenness in either space or time. The effect of data assimilation is even more significant in the innermost domain which has the finest spatial resolution. However, for the events with two-dimensional unevenness of rainfall, i.e., the rainfall is concentrated in a small area and in a short time period, the effect of data assimilation is not ideal. WRF fails in capturing the whole process of the highly convective storm with densely concentrated rainfall in a small area and a short time period. A shortened assimilation time interval together with more efficient utilisation of the weather radar data might help improve the effectiveness of data assimilation in such cases. Copyright © 2012 John Wiley & Sons, Ltd.

Description: Environmental tracer methods have been used to quantify groundwater discharge to rivers for the past few decades. A number of different tracers have been used in these studies, including individual ion concentrations, electrical conductivity, stable isotopes 2  H and 18 O, and the dissolved gases helium, chlorofluorocarbons and radon. This paper discusses the assumptions of the method, as well as its resolution and accuracy. The method will be most accurate when the tracer concentration in groundwater is very distinct from that in the river. Based on typical parameters, groundwater inflow rates as low as 5 mm/day can usually be estimated with electrical conductivity and ion tracers. A lower limit of resolution of approximately 2 mm/day is usually possible with radon, principally because the ratio of the river concentration to the groundwater concentration will be higher. However, hyporheic exchange can also contribute radon to the river. Where this process is significant, it is more difficult to estimate groundwater inflow from radon activities in the river, thus reducing the accuracy of the method. For CFCs, the lower limit of resolution is approximately 30 mm/day. Helium has not been widely used, but can potentially be very accurate if the groundwater is old. The method assumes steady state conditions, and so can only be applied when river flows are stable. Sampling resolution is also particularly important for dissolved gases, and uncertainty in where groundwater inflow occurs between sampling points can cause large uncertainty in inflow rates if the distance between sample locations is large. Poor mixing of solutes within the river can limit the method if the river is wide and shallow. When correctly applied, however, the environmental tracer method is able to provide robust estimates of groundwater discharge at a scale and accuracy that is not possible with most other methods. Copyright © 2012 John Wiley & Sons, Ltd.

Description: In this study, we examined the role of bedrock groundwater discharge and recharge on the water balance and runoff characteristics in forested headwater catchments. Using rigorous observations of catchment precipitation, discharge and streamwater chemistry, we quantified net bedrock flow rates and contributions to streamwater runoff and the water balance in three forested catchments (second- to third-order catchments) underlain by uniform bedrock in Japan. We found that annual rainfall in 2010 was 3130 mm. In the same period, annual discharge in the three catchments varied from 1800 to 3900 mm/year. Annual net bedrock flow rates estimated by the chloride mass balance method at each catchment ranged from −1600 to 700 mm/year. The net bedrock flow rates were substantially different in the second- and third-order catchments. During baseflow, discharge from the three catchments was significantly different; conversely, peak flows during large storm events and direct runoff ratios were not significantly different. These results suggest that differences in baseflow discharge rates, which are affected by bedrock flow and inter-catchment groundwater transfer, result in the differences in water balance among the catchments. This study also suggests that in these second- to third-order catchments the drainage area during baseflow varies because of differences between the bedrock drainage area and surface drainage area, but that the effective drainage area during storm flow approaches the surface drainage area. Copyright © 2012 John Wiley & Sons, Ltd.

Description: Experimental work has clearly shown that the effective hydraulic conductivity ( K e ) or effective infiltration rate ( f e ) on the local scale of a plot cannot be considered as constant but are dependent on water depth and rainfall intensity because non-random microtopography-related variations in hydraulic conductivity occur. Rainfall-runoff models generally do not account for this: models assume that excess water is uniformly spread over the soil surface and within-plot variations are neglected. In the present study we propose a model that is based on the concepts of microtopography-related water depth-dependent infiltration and partial contributing area. Expressions for the plot-scale K e and f e were developed that depend on rainfall intensity and runon from upslope (and thus on water depth). In order to calibrate and validate the model, steady state infiltration experiments were conducted on maize fields on silt loam soils in Belgium, with different stages and combinations of rainfall intensity and inflow, simulating rainfall and runon. Water depth-discharge and depth-inundation relationships were established and used to estimate the effect of inundation on K e . While inflow-only experiments were found to be unsuitable for calibration, the model was successfully calibrated and validated with the rainfall simulation data and combined rainfall – runon data ( R ²: 0.43 – 0.91). Calibrated and validated with steady state infiltration experiments, the model was combined with the Green-Ampt infiltration equation and can be applied within a 2D distributed rainfall – runoff model. The effect of water depth-dependency and rainfall intensity on infiltration was illustrated for a hillslope. Copyright © 2012 John Wiley & Sons, Ltd.

Description: Karstic watersheds are highly complex hydrogeological systems that are characterized by a multi-scale behavior corresponding to the different pathways of water in these systems. The main issue of karstic spring discharge fluctuations consists in the presence and the identification of characteristic time-scales in the discharge time series. In order to identify and characterize these dynamics, we acquired, for many years at the outlet of two karstic watershed in South of France, discharge data at 3-mn, 30-mn and daily sampling rate. These hydrological records constitute to our knowledge the longest uninterrupted discharge time series available at these sampling rates. The analysis of the hydrological records at different levels of detail leads to a natural scale analysis of these time series in a multifractal framework. From a universal class of multifractal models based on cascade multiplicative processes, the time series first highlights two cut-off scales around 1-h and 16-h that correspond to distinct responses of the aquifer drainage system. Then we provide estimates of the multifractal parameters α and C 1 and the moment of divergence q D corresponding to the behavior of karstic systems. These results constitute the first estimates of the multifractal characteristics of karstic spingflows based on 10 years of high resolution discharge time series and should lead to several improvements in rainfall-karstic springflow simulation models. Copyright © 2012 John Wiley & Sons, Ltd.

Description: This paper analyses the performance of an integrated Hydrological Ensemble Prediction System (HEPS) adapted to small to mid-sized catchments (100 up to 600 km 2 ) situated in the Cévennes-Vivarais region (Southern France) and characterized by short lag-times (3 to 12 hours). In this framework, flood forecasts need hourly Probabilistic Quantitative Precipitation Forecasts (PQPF) so as to provide early warning with 24 to 72 hours of anticipation. Here, two sources of PQPF at daily and sub-daily (6 hours) meteorological time-steps are considered: EPS from ECMWF and analogy-based PQPF provided in real-time at LTHE (Laboratoire d'étude des Transferts en Hydrologie et Environnement). The two PQPF are firstly disaggregated in order to respect the required hydrological hourly time-step, through either the use of a stochastic rainfall generator or the application of a multi-model approach. Then, disaggregated PQPF are used as input to the hydrological model TOPSIMPL in order to provide hourly ensemble discharge forecasts up to 48 hours ahead. Illustration and evaluation of ensemble discharge forecasts issued in near real-time conditions are given for some recently observed flash flood events. It is shown that hourly discharge forecasts are first-order conditioned by the accuracy of PQPF at daily or sub-daily time-step. 6-hour EPS correctly reproduce the rainfall temporal dynamics, while daily analogy-based PQPF are less underdispersive in terms of rainfall amounts. As a result, the merging of the two sources of PQPF substantially increases the performance of discharge forecasts, the contribution of a more sophisticated hourly rainfall generator becoming marginal. Copyright © 2012 John Wiley & Sons, Ltd.

Description: ABSTRACT This study investigates the potential of the low resolution images (150 m) derived by the Advanced Synthetic Aperture Radar (ASAR) onboard the ENVISAT satellite to calibrate a hydraulic model coupled with a semi-distributed hydrologic model applied to a sub-catchment of the Upper-Middle Tiber River, Genna basin (〈100 km 2 ), in central Italy, wherein a flood event occurred on 28 th November, 2010 causing high damages. Specifically for this flood event, an ASAR image is available for the peak region of the discharge hydrograph. Different image processing techniques are employed for the assessment of the flooded areas by using both a single image and a change detection image based on an additional (dry) reference image. The satellite-derived flooded areas are adopted for the calibration of the channel and floodplain Manning's roughness coefficients of a “quasi two-dimensional” hydraulic model applied to the study basin which allows to distinguish the main channel from the floodplain. The inflows for the hydraulic model corresponding to each tributary of the main channel are determined by a semi-distributed hydrologic model calibrated by using a set of historical flood events. The hydraulic model calibration is also carried out by using the same set of historical flood events. For the event of November 2010, the modelled discharge and water level hydrographs obtained with the two sets of Manning roughness (via satellite and historical calibration) are compared with in situ observations at the outlet of the basin. This application on a small sized catchment contributes to strengthen the value of remote sensing data confirming the potential of SAR imagery to reduce uncertainties in hydraulic modeling calibration. Copyright © 2012 John Wiley & Sons, Ltd.

Description: Reliable and prompt information on river ice condition and extent is needed to make accurate hydrological forecasts, to predict ice jams breakups and issue timely flood warnings. This study presents a technique to detect and monitor river ice using observations from the MODIS instrument onboard the Terra satellite. The technique incorporates a threshold-based decision tree image classification algorithm to process MODIS data and to determine the extent of ice. To differentiate between ice-covered and ice-free pixels within the riverbed the algorithm combines observations in the visible and near infrared spectral bands. The developed technique presents the core of the MODIS-based river ice mapping system which has been developed to support NOAA NWS's operations. The system has been tested over the Susquehanna River in northeastern U.S. where ice jam events leading to spring floods are a frequent occurrence. The automated algorithm generates three products: daily ice maps, weekly composite ice maps and running cloud-free composite ice maps. The performance of the system was evaluated over 9 winter seasons. The analysis of the derived products has revealed their good agreement with the aerial photography and with in situ observations-based ice charts. The probability of ice detection determined from the comparison of the product with the high resolution Landsat imagery was equal to 91 %. A consistent inverse relationship was found between the river discharge and the ice extent. The correlation between the discharge and the ice extent as determined from the weekly composite product reached 0.75. The developed CREST River Ice Observation System (CRIOS) has been implemented at NOAA-Cooperative Remote Sensing Science and Technology Center (CREST) as an operational web tool allowing end-users and forecasters to assess ice conditions on the river. Copyright © 2012 John Wiley & Sons, Ltd.

Description: The pore water pressure head that builds in the soil during storms is a critical factor for the prediction of potential slope instability. We report findings from a 3-year study of pressure head in 83 piezometers distributed within a 13-ha forested catchment on the northern coast of California. The study's primary objective was to observe the seasonal and storm-based dynamics of pressure head at a catchment scale in relation to observed rainfall characteristics and in situ topography to better understand landscape patterns of pressure head. An additional goal was to determine the influence of the interaction between rainfall and forest canopy in altering delivery of water and pressure head during the large storms necessary to induce landsliding. We found that pressure head was highly variable in space and time at the catchment scale. Pore pressures peaked close to maximum rainfall intensity during the largest storms measured. The difference between rainfall and throughfall delivered through the canopy was negligible during the critical landslide producing peak rainfall periods. Pore pressure was spatially variable within the catchment and did not strongly correlate with surficial topographic features. Only 23% of the piezometers located in a variety of slope positions were found to be highly responsive to rainfall. Topographic index statistically explained peak pressure head at responsive locations during common storms, but not during the larger storms with potential to produce landslides. Drainage efficiency throughout the catchment increased significantly in storms exceeding 2 to 7 months peak pressure head return period indicated by slowing or cessation of the rate of increase of pressure head with increasing storm magnitude. This asymptotic piezometric pattern persisted through the largest storm measured during the study. Faster soil drainage suppressed pressure head response in larger storms with important process implications for pore pressure development and landslide hazard modeling. Copyright © 2012 John Wiley & Sons, Ltd.

Description: Establishment and “crediting” for total maximum daily loads (TMDL) of sediment require development of stream monitoring programs capable of detecting changes in land-use and erosion “connectivity” conditions across the watershed. As a “proof of concept” directed at developing such an effective stream monitoring program considering only the effects of soils disturbances or restoration in the Lake Tahoe Basin, variability in daily stream sediment load predictions from a local-scale, field-data based distributed runoff and erosion model developed previously is analyzed for the west-shore watersheds of Homewood (HMR) and Madden Creeks. The areal extent effects of forest fuels reductions (slight soil disturbances in Madden) and soil restoration efforts (e.g. dirt road removal, skirun rehabilitation in HMR) on watershed daily sediment loads for the 1994–2005 period are considered. Based on model predictions, forest fuels management in the Madden Creek watershed must occur across more than 30% of the basin area to result in a detectable increase in daily sediment loads at the 〉95% confidence level. Similarly, a daily load reduction that could be assessed with 〉95% confidence within the HMR basin required substantial dirt road removal (50% by roaded area) and restoration of 20% of the skirun area (combined for ∼5% of the basin area) for the 11-year record but was also possible within 2–3 years following restoration. These modeling results suggest that despite considerable flow-load variability, it may be possible to detect cumulative changing land-use conditions within several years of project completion such that quantitative TMDL “crediting” may be developed. Copyright © 2012 John Wiley & Sons, Ltd.

Description: Determining catchment responses to climate signals gives insight into the potential effects of climate change. This study tested the hypothesis that a 28-year time series of water yields from four headwater catchments in the Turkey Lakes Watershed, Ontario contains signals of non-stationary climate change and naturally occurring stationary climate oscillations and that the effects of these signals are greater in catchments with lower rates of change in water loading and lower water storage capacity (small wetlands). Non-stationary trends explained 0%, 18%, 44%, and 52% of the variance in the water yields of the four catchments. Wavelet analysis using Morlet wavelets identified stationary responses at multiple temporal scales, increasing the amount of variance explained to 56%, 63%, 76%, and 81% when combining stationary and non-stationary models. The catchment with low water loading and low water storage was most sensitive to non-stationary and stationary signals, suggesting that these catchments act as sentinels to detect climatic signals. Wavelet coherence analysis revealed correlations between global climate oscillation indices and water yield. The AMO index was strongly correlated with both temperature and precipitation (R 2  = 0.46, P 〈 0.001 and R 2 of 0.34, P 〈 0.001, respectively). Temperature in the Turkey Lakes Watershed increased by 0.067 °C per year from 1981 to 2008, but approximately 0.037°C of this increase can be explained by the AMO index. While it is likely that anthropogenic climate change impacts water yields, it is important to account for multiple nested climate oscillations to avoid exaggerating its effects. Copyright © 2012 John Wiley & Sons, Ltd.

Description: The dominance of ‘old’ pre-event water in headwater storm runoff has been recorded in numerous upland catchment studies, however the mechanisms by which this pre-event water enters the stream channel are poorly understood. Understanding these processes is fundamental to determining the controls on surface water quality and associated impacts on stream ecology. Previous studies in the upland forested catchment of the Afon Hafren (River Severn) at Plynlimon, mid-Wales, identified an active bedrock groundwater system that was discharging into the stream channel during storm response. Detailed analysis showed that these discharges were small and could not account for the majority of pre-event storm water response identified at this site; pre-event storm runoff had to be sourced predominantly from further upstream. An intensive stream survey was used to determine the spatial nature of groundwater-surface water (GW-SW) interactions in the Hafren Catchment. Detailed physicochemical in-stream profiling identified a marked change in water quality indicating a significant discrete point of bedrock groundwater discharge upstream of the Hafren Transect study site. The in-stream profiling showed the importance of high spatial resolution sampling as a key to understanding processes of GW-SW interaction and how quick and cost-effective measurements of specific electrical conductance (SEC) of stream waters could be used to highlight in-stream heterogeneity. This approach is recommended for use in headwater catchments for initial characterisation of the stream channel in order to better locate instrumentation and to determine more effective targeted sampling protocols in upland catchment research. Copyright © 2012 John Wiley & Sons, Ltd.

Description: For a nationwide flood risk assessment in Germany, simulations of inundation depth and extent for all major catchments are required. Therefore, a fast two-dimensional hydraulic model is needed. From the range of existing methods, two storage cell models are evaluated to find an appropriate method for large-scale applications. The Dynamic Rapid Flood Spreading Model (Dynamic RFSM) based on irregular storage cells, and a raster-based model with inertia formulation of momentum equation are compared. Simulation performed with the fully dynamic shallow water model InfoWorks RS 2D served as a reference. The hydraulic models are applied to a test area having a very flat topography adjacent to the river Elbe. As a benchmark scenario, the outflow through a hypothetical dike breach was chosen. To investigate the impact of the grid resolution on run time and model performance, the simulation with the raster model is carried out with different grid sizes. Furthermore, the sensitivity of the Dynamic RFSM to the choice of time step was analysed. Both models were able to simulate the final inundation extent and depths with a reasonable accuracy. However, the Dynamic RFSM showed some weakness in simulating inundation extent over the flat test area. Coarsening the grid resolution reduced the run time of the raster-based model considerably and can be regarded as a promising strategy to constrain the computational efforts for a large-scale application, although the model accuracy gradually deteriorated. With similar run time, the raster-based model performed better than the Dynamic RFSM in terms of inundation extent and comparable regarding maximum inundation depth. Generally, an application at national scale appears feasible with both hydraulic modelling schemes. Copyright © 2012 John Wiley & Sons, Ltd.

Description: Current concern for the sustainable management of soil resources and the many adverse effects of increased sediment loads on streams and river systems has generated a need for more information on rates and patterns of soil loss and an improved understanding of catchment sediment budgets. Traditional measurement techniques are frequently unable to meet the requirements and fallout radionuclides have been shown to offer considerable potential for tracing the mobilisation, transfer, redistribution and storage of soil and sediment within catchments and river systems. Caesium-137 and lead-210 have been the most widely used fallout radionuclide sediment tracers, but their half-lives mean that the information that they provide is in most instances limited to the medium-term (e.g. 25-120 years). The need for information on shorter timescales has directed attention to the potential for using beryllium-7, which has a considerable shorter half-life, for tracing soil and sediment redistribution over short timescales (e.g. days-weeks). To date, however, there have been relatively few attempts to exploit this potential. This situation is likely to be in part a reflection of the emphasis of early work on 137 Cs and 210 Pb and the more recent nature of work using 7 Be. However, it may also reflect the limitations and constraints imposed by the nature of 7 Be fallout and the short half-life of this radionuclide. This contribution explores recent work in using 7 Be as a sediment tracer and the constraints imposed by its origin and behaviour. Attention is directed to fallout inputs, the application of 7 Be to tracing soil and sediment redistribution on slopes and on river floodplains, its use as a source fingerprint and other related applications. The likely future potential of 7 Be as a sediment tracer is assessed Copyright © 2012 John Wiley & Sons, Ltd.

Description: Karst depressions represent important sinks for sediment and such sediment can provide a valuable record of the impact of environmental change on soil erosion rates. However, the sediment dynamics of karst depressions are not well understood. This contribution reports a study of the small catchment of a karst depression in Southwest China, with a drainage area of 0.054 km 2 , aimed at using the sediment deposits in the depression to reconstruct the erosional response of the catchment to land use change and, more particularly, the deforestation which took place in 1979. 137 Cs and 210 Pb ex are used as both chronometers and as tracers. Five cores, collected from the bottom of a depression, with an area of 2652 m 2 , showed similar 137 Cs depth distributions, with a single 137 Cs peak, which was attributed to the 1979 deforestation. The 137 Cs activity associated with the peaks varied between 5.68 ± 0.64 Bq kg -1 and 9.19 ± 0.99 Bq kg -1 . The average depth of sediment deposition between 1979 and 2008 deduced from the depths of the 1979 137 Cs peak was 74.1 cm. The existence of relatively high 210 Pb ex activity of 66.33 ± 8.44 Bq kg -1 in the upper section (0-16 cm) of the core analyzed for 210 Pb ex suggests that recent sedimentation has been very limited. Net erosion rates on the hillslopes contributing runoff and sediment t to the depression were estimated to be 5258 t km -2  yr -1 from 1979 to 1990 and 256 t km -2  yr -1 from 1991 to 2008, respectively. The high sediment yield in the first period was associated with the severe soil erosion triggered by the 1979 deforestation, which resulted from the changes in land ownership immediately after the Cultural Revolution. Soil erosion has been very limited since 1990, because the thin soils had been totally removed from many parts of the karst slopes and the soils remaining on the other parts of the slopes have been protected by terracing or vegetation rehabilitation Copyright © 2012 John Wiley & Sons, Ltd.

Description: In the Colorado Front Range, forested catchments near the rain-snow transition are likely to experience changes in snowmelt delivery and subsurface water transport with climate warming and associated shifts in precipitation patterns. Snowpack dynamics are strongly affected by aspect: Lodgepole pine forested north-facing slopes develop a seasonal snowpack, while Ponderosa pine-dotted south-facing slopes experience intermittent snow accumulation throughout winter and spring. We tested the degree to which these contrasting water input patterns cause different near-surface hydrologic response on north- and south-facing hillslopes during the snowmelt period. During spring snowmelt, we applied lithium bromide (LiBr) tracer to instrumented plots along a north-south catchment transect. Bromide broke through immediately at 10 and 30 cm depths on the north-facing slope, and was transported out of soil waters within 40 days. On the south-facing slope, Br - was transported to significant depths only during spring storms, and remained above the detection limit throughout the study. Modeling of unsaturated zone hydrologic response using Hydrus 1-D corroborated these aspect-driven differences in subsurface transport. Our multiple lines of evidence suggest that north-facing slopes are dominated by connected flow through the soil matrix while south-facing slope soils experience brief periods of rapid vertical transport following snowmelt events and are drier overall than north-facing slopes. These differences in hydrologic response were largely a function of energy-driven differences in water supply, emphasizing the importance of aspect and climate forcing when considering contributions of water and solutes to streamflow in catchments near the snow line. Copyright © 2012 John Wiley & Sons, Ltd.

Description: The warming of the Earth's atmosphere system is likely to change temperature and precipitation, which may affect the climate, hydrology and water resources at the river basins over the world. The importance of temperature change becomes even greater in snow or glacier dominated basins where it controls the snowmelt processes during the late-winter, spring and summer months. In this study hydrologic responses of streamflow in the Pyanj and Vaksh River basins to climate change are analyzed with a watershed hydrology model, based on the downscaled atmospheric data as input, in order to assess the regional climate change impact for the snowfed and glacierfed river basins in the Republic of Tajikistan. As a result of this analysis, it was found that the annual mean river discharge is increasing in the future at snow and glacier dominated areas due to the air temperature increase and the consequent increase in snow/ice melt rates until about 2060. Then the annual mean flow discharge starts to decrease from about 2080 onward because the small glaciers start to disappear in the glacier areas. It was also found that there is a gradual change in the hydrologic flow regime throughout a year, with the high flows occuring earlier in the hydrologic year, due to the warmer climate in the future. Furthermore, significant increases in annual maximum daily flows, including the 100-year return period flows, at the Pyanj and Vaksh River basins toward the end of the 21st century can be inferred from flood frequency analysis results. Copyright © 2012 John Wiley & Sons, Ltd.

Description: Snow and frozen soil prevail in cold regions worldwide, and the integration of these processes is crucial in hydrological models. In this study, a combined model was developed by fully coupling a simultaneous heat and water model with a geomorphologically based distributed hydrological model. The combined model simulates vertical and lateral water transfer as well as vertical heat fluxes and is capable of representing the effects of frozen soil and snowmelt on hydrological processes in cold regions. This model was evaluated by using in situ observations in the Binggou watershed, an experimental watershed for cold region hydrology of the Watershed Allied Telemetry Experimental Research Project. Results showed that the model was able to predict soil freezing and thawing, unfrozen soil water content, and snow depth reasonably well. The simulated hydrograph was in good agreement with the in situ observation. The Nash Sutcliffe coefficient of daily discharge was 0.744 for the entire simulation period, 0.472 from April to June and 0.711 from June to November. This model can improve our understanding of hydrological processes in cold regions and assess the impacts of global warming on hydrological cycles and water resources. Copyright © 2012 John Wiley & Sons, Ltd.

Description: Hydropeaking due to operations of storage hydropower plants were highlighted as one of the main stresses on aquatic ecology by the European Water Framework Directive. Nevertheless, hydropower must be seen as a high value resource in the renewable energy sector. However, very few studies deal with the physical processes behind the artificial unsteady flows, as the variability of local river morphology and roughness respectively in general. Thus, the aim of the present study is to address these issues based on one-dimensional hydrodynamic-numerical modelling, In total, four Austrian rivers have been investigated, which were further divided into thirteen sub-reaches according to their bed-slope. Based on single and multiple linear regression models, it was possible to relate potential retentions of peak flow for peak duration 〈 2 hours and for bed-slopes 〈 0.005 to the spatial extent of wetted width between base and peak flow, independent of the selected ramping rate (discharge relationship between base-flow and peak flow). Moreover, the ramping velocity (rate of decreasing water level between peak-flow and base-flow) correlated positively with an increase in depth-variance during peak flow, which was related further to an increase in mean flow velocities and a higher specific discharge respectively over the 13 selected reaches. Nevertheless, within sensitivity testing, it could be proved that increases in channel roughness cause an increase in peak-flow retention and a lowering of the ramping velocities respectively for the decreasing limb. Copyright © 2012 John Wiley & Sons, Ltd.