ALBERT

Description: Land use change as conversion pasture to forest produces several changes on hydrological cycle. In this paper we analyze the effects on stream discharge of afforestation of a small watershed devoted to pasture using the HBV hydrological model. Streamflow data obtained over the first ten years after planting were employed to evaluate the capacity of HBV model to simulate hydrological behavior of catchment after afforestation. Obtained results indicate that the estimation of streamflow was accurate as reflected by statistics (R 2  = 0.90, NSC = 0.89 and PBIAS = 0.34). Afterwards, streamflow under pasture land use (if afforestation had not occurred) was simulated using hydro-meteorological data collected during the period of study and model parameters optimized previously, together with two parameters, pcorr and cevpfo , that were adjusted for pasture conditions. HBV model results indicate that afforestation produced a water yield reduction around 2000 mm (22% of total stream discharge) during the first ten years of planting growth. The differences between forest and pasture land cover are increasing in all seasons year by year. The greatest streamflow reduction was observed in wet period (autumn and winter) with 76% of total reduction. In summer, streamflow reduction represents only 3% of total, however, represents 24.7% of discharge in this season. Streamflow reduction was related to increase of rainfall interception (mainly in wet periods) and the increase of evapotranspiration by plantation in dry periods. This article is protected by copyright. All rights reserved.

Description: Air flows from the atmosphere into an unconfined aquifer when the water table falls during pumping tests. Pumping test results in unconfined aquifers may be significantly affected by low-permeability zones (LPZs) near the initial water table position because they restrict the downward movement of air. A transient, three-dimensional (3D) air-water two-phase flow model is employed to investigate numerically the effects of local heterogeneity on pumping test results in unconfined aquifers. Two cases of local heterogeneities are considered herein: a LPZ around the pumping well and on one side of the pumping well. Results show that the drawdown with the LPZ is significantly greater than that of the homogeneous aquifer. The differences in drawdown are the most significant at intermediate times and gradually diminish at later times. The LPZ significantly reduces air flow from the atmosphere to the aquifer. The pore air velocity in the LPZ is very low. The air pressure at the observation point under the LPZ when air begins to enter is significantly lower than the air pressure of the homogeneous aquifer at the same point. After that, the air pressure increases quickly and then increases slowly. The time for the air pressure to reach the atmospheric pressure is significantly longer. This article is protected by copyright. All rights reserved.

Description: Over the last half century, since logging for timber production became intensive, Borneo has lost much of its pristine tropical forests. The long-term consequences of associated decline in precipitation are evident, and might, in turn, cause much more severe deforestation. This article is protected by copyright. All rights reserved.

Description: Accepting the concept of standardization introduced by the standardized precipitation index (SPI), similar methodologies have been developed to construct some other standardized drought indices such as the standardized precipitation evapotranspiration index (SPEI). In this study, the authors provided deep insight into the SPEI and recognized potential deficiencies/limitations in relating to the climatic water balance it used. By coupling another well-known Palmer drought severity index (PDSI), we proposed a new standardized Palmer drought index (SPDI) through a moisture departure probabilistic approach, which allows multiscalar calculation for accurate temporal and spatial comparison of the hydro-meteorological conditions of different locations. Using datasets of monthly precipitation, temperature and soil available water capacity, the moisture deficit/surplus was calculated at multiple temporal scales and a couple of techniques were adopted to adjust corresponding time series to a generalized extreme value distribution out of several candidates. Results of the historical records (1900–2012) for diverse climates by multiple indices showed that the SPDI was highly consistent and correlated with the SPEI and self-calibrated PDSI (SC-PDSI) at most analyzed time scales. Furthermore, a simple experiment of hypothetical temperature and/or precipitation change scenarios also verified the effectiveness of this newly-derived SPDI index in response to climate change impacts. Being more robust and preferable in spatial consistency and comparability as well as combining the simplicity of calculation with sufficient accounting of the physical nature of water supply and demand relating to droughts, the SPDI is promising to serve as a competent reference and alternative for drought assessment and monitoring. This article is protected by copyright. All rights reserved.

Description: Modeled hydrologic processes are represented in a set of numerical equations, the complexity of which can be measured by the total number of variables needed. A single dominant hydrologic process could control the hydrologic response of a watershed, and so the identification of the corresponding dominant variable(s) would aid in identifying a parsimonious model and in collecting more reliable data. By accounting for both model complexity and serial correlation in the variables, a model is used to identify the dominant variables for representing watershed scale streamflow, sediment transport, and phosphorus yields. Long-term water quantity and quality data was used to show that rainfall and non-linear soil water storage were the dominant variables for weekly streamflow, suspended sediment, and particulate phosphorus. Model accuracy did not consistently improve when other statistically significant variables were included. The results suggest that improved model performance may not justify the added model complexity. As such, identification of dominant variables would be the priority for developing parsimonious hydrologic models, especially at watershed scales. This article is protected by copyright. All rights reserved.

Description: We applied graphical methods and multivariate statistics to understand impacts of an unsewered slum catchment on nutrients and hydrochemistry of groundwater in Kampala, Uganda. Data was collected from 56 springs (groundwater), 22 surface water sites and 13 rain samples. Groundwater was acidic and dominated by Na, Cl and NO 3 . These ions were strongly correlated indicating pollution originating from wastewater infiltration from on-site sanitation systems. Results also showed that rain, which was acidic, impacted on groundwater chemistry. Using Q-mode hierarchical cluster analysis, we identified three distinct water quality groups. The first group had springs dominated by Ca-Cl-NO 3 , low values of EC, pH and cations, and relatively high NO 3 values. These springs were shown to have originated from the acidic rains because their chemistry closely corresponded to ion concentrations that would occur from rainfall recharge, which was around 3.3 times concentrated by evaporation. The second group had springs dominated by Na-K-Cl-NO 3 and Ca-Cl-NO 3 , low pH but with higher values of EC, NO 3 and cations. We interpreted these as groundwater affected by both acid rain and infiltration of wastewater from urban areas. The third group had the highest EC values (average of 688 μS/cm), low pH and very high concentrations of NO 3 (average of 2.15 mmol/L) and cations. These springs were exclusively located in slum areas and we interpreted these springs as groundwater affected by infiltration of wastewater from poorly sanitized slums areas. Surface water was slightly reducing and eutrophic due to wastewater effluents, but the contribution of groundwater to nutrients in surface water was minimal because o-PO 4 was absent whereas NO 3 was lost by denitification. Our findings suggest that groundwater chemistry in the catchment is strongly influenced by anthropogenic inputs derived from nitrogen-containing rains and domestic wastewater. This article is protected by copyright. All rights reserved.

Description: We examined the water balance a forested ombrotrophic peatland and adjacent burned peatland in the boreal plain of western Canada over a three-year period. Complete combustion of foliage and fine branches dramatically increased shortwave radiation inputs to the peat surface while halting all tree transpiration at the burned site. End-of-winter snowpack was 7-25% higher at the burned site likely due to decreased ablation from the tree canopy at the unburned site. Shrub regrowth at the burned site was rapid post-fire, and shading by the shrub canopy in the burned site approached that of the unburned site within three years after fire. Site-averaged surface resistance to evaporation was not different between sites, though surface resistance in hollows was lower in the burned site. Water loss at both burned and unburned sites is largely driven by surface evaporative losses. Evaporation at the burned site marginally exceeded the sum of pre-fire transpiration and interception at the unburned site, suggesting that ET during the growing season was 2 0–40  mm greater at the the burned peatland. While the net change in water storage during the growing season was largely unchanged by fire, the lack of low-density surface peat in the burned site appears to have decreased specific yield, leading to greater water table decline at the burned site despite similar net change in storage. This article is protected by copyright. All rights reserved.

Description: The eddy covariance (EC) method was used in a 30-month study to quantify evapotranspiration (ET) and vegetation coefficient (K CW ) for a wetland on a ranch in subtropical south Florida. To evaluate the errors in ET estimates, the EC-based ET (ET C.-EC ) and the Food and Agricultural Organization (FAO) Penman-Monteith (PM) based ET (ET C.-PM ) estimates (with literature crop coefficient K C ) were compared to each other. The ET C.-EC and FAO-PM reference ET were used to develop K CW . Regression models were developed to estimate K CW using climatic and hydrologic variables. Annual and daily ET C.-EC values were 1152 mm and 3.27 mm, respectively. The FAO-PM model underestimated ET by 25% with ET C.-EC being statistically higher than ET C.-PM . The K CW varied from 0.79 (December) to 1.06 (November). The mean K CW for dry (November-April) season (0.95) was much higher than values reported for wetlands in literature, while wet (May-October) season K CW (0.97) was closer to literature values. Higher than expected K CW values during dry season were due to higher temperature, lower humidity and perennial wetland vegetation. Regression analyses showed that factors affecting the K CW were different during the dry (soil moisture, temperature, and relative humidity) and wet (net radiation, inundation, and wind speed) seasons. Separate regression models for the dry and wet seasons were developed. ET and K CW from this study, one of the first for the agricultural wetlands in subtropical environment, will help improve the ET estimates for similar wetlands. This article is protected by copyright. All rights reserved.

Description: Research on runoff processes to date has focused on the differences between the main divisions of runoff partitioning. Indeed, our major advancements in runoff theory have come with new differentiations of different forms of overland flow and subsurface stormflow. These studies of ‘how runoff processes are different’ have resulted in our current summaries of runoff regimes conceptually (e.g. the Variable Source Area (VSA) concept) and codified in our models (e.g. TOPMODEL and its derivatives). This article is protected by copyright. All rights reserved.

Description: Supraglacial channels are an important mechanism for surface water transport over the ablation zone of western Greenland. The first assessment of the spatio-temporal distribution of surface melt channels and their relationship to supraglacial lakes over the Jakobshavn Isbrae region of Western Greenland was analyzed using Landsat ETM + panchromatic images during the 2007 melt season. A total of 1188 melt channels were delineated and show an increase in the number of melt channels throughout the season, reaching a peak on August 9. Water-filled melt channels advanced to maximum elevation of 1647 m on August 9, and attained a minimum average slope of 0.009 on July 8. The ablation zone demonstrates two hydrologic modes, where crevasse and moulin terminating channels dominate at elevations 〈800 m and higher order channel networks 〉800 m. Development of higher order networks is interrupted by flow divergence due to partitioning of melt water into vertical infiltration through moulins and crevasse fields prevalent at lower elevations. Tributary and Connector networks between 800 to 1200 m in elevation are correlated with fewer lake occurrences, relatively lower surface velocities (~50 ma -1 ) and ice flow dominated by internal deformation over basal sliding. High order channels are associated with lake basins that exceed melt water storage capacity. Evolution of channel networks is coupled to changes in melt water production, runoff, and ice dynamics with implication for the englacial and subglacial environments. This article is protected by copyright. All rights reserved.

Description: This paper reviews the use of the Generalised Likelihood Uncertainty Estimation (GLUE) methodology in the 20 years since the paper by Beven and Binley (1992) in Hydrological Processes, which is now one of the most highly cited papers in hydrology. The original conception, the on-going controversy it has generated, the nature of different sources of uncertainty and the meaning of the GLUE prediction uncertainty bounds, are discussed. The hydrological, rather than statistical, arguments about the nature of model and data errors and uncertainties that are the basis for GLUE are emphasised. The application of the IHDM model to the Gwy catchment at Plynlimon presented in the original paper is revisited, using a much larger sample of models, a wider range of likelihood evaluations and new visualisation techniques. It is concluded that there are good reasons to reject this model for that data set. This is a positive result in a research environment in that it requires improved models or data to be made available. In practice, there may be ethical issues of using outputs from models for which there is evidence for model rejection in decision making. Finally some suggestions for what is needed in the next 20 years are provided. This article is protected by copyright. All rights reserved.

Description: A short-term flood inundation prediction model has been formulated based on the combination of the super-tank model, forced with downscaled rainfall from a global numerical weather prediction model, and a one-dimensional hydraulic model. Different statistical methods for downscaled rainfall have been explored, taking into account the availability of historical data. It has been found that the full implementation of a statistical downscaling model considering physically based corrections to the numerical weather prediction model output for rainfall prediction performs better compared with an altitudinal correction method. The integration of the super-tank model into the one-dimensional hydraulic model demonstrates a minimal requirement for the calibration of rainfall-runoff and flood propagation models. Updating the model with antecedent rainfall and regular forecast renewal has enhanced the model's capabilities as a result of the data assimilation processes of the runoff and numerical weather prediction models. The results show that the predicted water levels demonstrate acceptable agreement with those measured by stream gauges and comparable to those reproduced using the actual rainfall. Moreover, the predicted flood inundation depth and extent exhibit reasonably similar tendencies to those observed in the field. However, large uncertainties are observed in the prediction results in lower, flat portions of the river basin where the hydraulic conditions are not properly analysed by the one-dimensional flood propagation model. This article is protected by copyright. All rights reserved.

Description: This study aims to analyse the combined impacts of future discharges and sea levels on erosion-sedimentation potential, and its seasonal changes, in a ~43 km long coastal river reach of South-West Finland. To our knowledge, this kind of combined study has not been performed before. In addition to surveying the present erosion-sedimentation conditions, the daily erosion-sedimentation potential is simulated with a one dimensional hydrodynamic model for the 1971–2000 and 2070–2099 periods by applying four discharge scenarios. Different sea level stages are also employed in the simulations. All scenarios forecast increasing autumn and winter discharges, but diminishing summer discharges. This indicates increasing river channel erosion, particularly during winters and autumns. Although discharge changes have altogether a greater influence on erosion-sedimentation potential, the importance of sea level changes on sedimentation is noticeable in the estuary. The rising sea level scenarios increase the sedimentation potential. In total, by 2070–2099 the erosion potential may increase in most parts of the study area. This article is protected by copyright. All rights reserved.

Description: Northern peatlands are a large source of atmospheric methane (CH 4 ) and both a source and sink of atmospheric carbon dioxide (CO 2 ). The rate and temporal variability in gas exchanges with peat soils is directly related to the spatial distribution of these free-phase gases within the peat column. In this paper we present results from surface and borehole ground penetrating radar (GPR) surveys – constrained with direct soil and gas sampling – that compare the spatial distribution of gas accumulations in two raised bogs: one in Wales (UK), the other in Maine (USA). Although the two peatlands have similar average thickness, physical properties of the peat matrix differ, particularly in terms of peat type and degree of humification. We hypothesize that these variations in physical properties are responsible for the differences in gas distribution between the two peatlands characterized by: 1) gas content up to 10.8 % associated with woody peat and presence of wood layers in Caribou Bog (Maine), and 2) a more homogenous distribution with gas content up to 5.7 % at the surface (i.e. 〈 0.5 m deep) in Cors Fochno (Wales). Our results highlight the variability in biogenic gas accumulation and distribution across peatlands and suggest that the nature of the peat matrix has a key role in defining how biogenic gas accumulates within, and is released to the atmosphere from, peat soils. This article is protected by copyright. All rights reserved.

Description: The confounding effects of step change invalidate the stationarity assumption of commonly used trend analysis methods such as the Mann-Kendall test technique, so previous studies have failed to explain inconsistencies between detected trends and observed large precipitation anomalies. The objectives of this study were to: 1) formulate a trend analysis approach that considers nonstationarity due to step changes; 2) use this approach to detect trends and extreme occurrences of precipitation in a mid-latitude Eurasian steppe watershed in north China; and 3) examine how runoff responds to precipitation trends in the study watershed. Our results indicate that annual precipitation underwent a marginal step jump around 1995. The significant annual downward trend after 1994 was primarily due to a decrease in summer rainfall; other seasons exhibited no significant precipitation trends. At a monthly scale, July rainfall after 1994 exhibited a significant downward trend, whereas precipitation in other months had no trend. The percentage of wet days also underwent a step jump around 1994 following a significant decreasing trend, although the precipitation intensity exhibited neither a step change nor any significant trend. However, both low- and high-frequency precipitation events in the study watershed occurred more often after than before 1994, probably as either a result or an indicator of climate change. In response to these precipitation changes, the study watershed had distinctly different precipitation-runoff relationships for observed annual precipitations of less than 300 mm, between 300 and 400 mm, and greater than 400 mm. This article is protected by copyright. All rights reserved.

Description: Hydrological models are useful tools to analyze present and future conditions of water quantity and quality. The integrated modeling of water and nutrients needs an adequate representation of the different discharge components. In common with many lowlands, groundwater contribution to the discharge in the North German lowlands is a key factor for a reasonable representation of the water balance especially in low flow periods. Several studies revealed that the widely used SWAT model performs poorly for low flow periods. This paper deals with the extension of the groundwater module of the SWAT model to enhance low flow representation. The current two-storage concept of SWAT was further developed to a three-storage-concept. This was realized due to modification of the groundwater module by splitting the active roundwater storage into a fast and a slow contributing aquifer. The results of this study show that the groundwater module with three storages leads to good prediction of the overall discharge especially for the recession limbs and the low flow periods. The improved performance is reflected in the signature measures for the mid segment (PBIAS: −2:4% vs. −15:9%) and the low segment (PBIAS: 14:8% vs. 46:8%) of the flow duration curve. The three-storage groundwater module is more process oriented than the original version due to the introduction of a fast and a slow groundwater flow component. The three-storage version includes a modular approach, since groundwater storages can be activated or deactivated independently for subbasin and HRU level. This article is protected by copyright. All rights reserved.

Description: The ecological condition and biodiversity values of floodplain wetlands are highly dependent on the hydrological connectivity of wetlands to adjacent rivers. This paper describes a method for quantifying connectivity between floodplain wetlands and the main rivers in a wet tropical catchment of northern Australia. We used a 1-D hydrodynamic model to simulate time-varying water depths across the stream network (i.e. rivers, streams and man-made drains). The timing and duration of connectivity of seven wetlands (4 natural and 3 artificial) with the two main rivers in the catchment were then calculated for different hydrological conditions. Location and areal extent of the wetlands and the stream network were identified using high resolution laser altimetry (LiDAR) and these data formed key inputs to the hydrodynamic model. The model was calibrated using measured water depths and discharges across the floodplain. An algorithm was developed to identify contiguous water bodies at daily time steps and this gave the temporal history of connection and disconnection between wetlands and the rivers. Simulation results show that connectivity of individual wetlands to both rivers varies from 26 to 365 days during an average hydrological condition. Location, especially proximity to a main river, and wetland type (natural stream or artificial drain) were identified as key factors influencing these levels of connectivity. Some natural wetlands maintain connection with the river for most or all of the year, whereas the connectivity of some artificial wetlands varies from 26 to 36 days according to their patterns of network connection to adjacent rivers – a result that has important implications for the accessibility of these types of wetland to aquatic biota. Using readily available river gauge data, we also show how connectivity modelling can be used to identify periods when connectivity has fallen below critical thresholds for fish movement. These connectivity patterns within the floodplain network are central to the setting of river flows that will meet environmental requirements for biota that use floodplain wetlands during their life history. This article is protected by copyright. All rights reserved.

Description: Pumping tests are one of the most commonly used in-situ testing techniques for assessing aquifer hydraulic properties. Numerous researches have been conducted to predict the effects of aquifer heterogeneity on the groundwater levels during pumping tests. The objectives of the present work were 1) to predict drawdown conditions and estimate aquifer properties during pumping tests undertaken in radially symmetric heterogeneous aquifers and 2) to identify a method for assessing the transmissivity field along the radial coordinate in radially symmetric and fully heterogeneous transmissivity fields. The first objective was achieved by expanding an existing analytical drawdown formulation which was valid for a radially symmetric confined aquifer with two concentric zones around the pumping well to an N concentric zone confined aquifer having a constant transmissivity value within each zone. The formulation was evaluated for aquifers with three and four concentric zones to assess the effects of the transmissivity field on the drawdown conditions. The specific conditions under which aquifer properties could be identified using traditional methods of analysis were also evaluated. The second objective was achieved by implementing the Inverse Solution Algorithm (ISA) which was developed for petroleum reservoirs to groundwater aquifer settings. The results showed that the drawdown values are influenced by a volumetric integral of a weighting function and the transmissivity field within the cone of depression. The weighting function migrates in tandem with the expanding cone of depression. The ability of the ISA to predict radially symmetric and log-normally distributed transmissivity fields was assessed against analytical and numerical benchmarks. The results of this investigation indicated that the ISA method is a viable technique for evaluating the radial transmissivity variations of heterogeneous aquifer settings. This article is protected by copyright. All rights reserved.

Description: Stormwater management increasingly recognises the need to emulate, to the maximum extent possible, the flow regime of receiving waters in their pre-development state. Hydrological models play a central role in assessing the catchment-scale impacts of alternative stormwater management strategies. However, because of the complexity of physical processes involved in urban hydrology, particularly subsurface flows, the predictive performance of such models is often low. We investigated how the structure of hydrological models influenced the prediction of urbanisation and stormwater management impacts on baseflow. We calibrated three conceptual models of the same reference catchment and compared the modelled flow regime from different stormwater management scenarios, using each of the three model structures. Scenarios were assessed using six metrics, characterising the whole streamflow regime and in particular baseflow. While the three models of the reference catchment represented the observed hydrograph well, the most complex structure, developed using a thorough diagnostic of the catchment behaviour, better captured the change in hydrological regime during dry years. Predictions of baseflow changes due to urbanisation varied significantly according to the model structure. Similarly, the models showed distinct responses to the stormwater management scenarios applied, especially for scenarios involving infiltration of stormwater at source. Our results confirm the importance of predicting the consequences of land use changes with conceptual models that are consistent with the hydrological behaviour of the study catchment. Future work should help quantify the uncertainties due to model structure, and thus provide practical guidance to the use of catchment models for assessing stormwater management strategies. This article is protected by copyright. All rights reserved.

Description: Although fire-induced soil water repellency (SWR) and its effects on soil hydrology and geomorphology have been studied with detail, very few studies have considered the effect of rock fragments resting on the soil surface or partly embedded in soil. In this research, we have studied the effect of rock fragments on the strength and spatial distribution of fire-induced SWR at different fire severities. A fire-affected area was selected for this experiment and classified into different zones according to fire severity (unburned, low, moderate and high) and rock fragment cover (low, 〈20%, and high, 〉60%). During 7 days after fire, SWR and infiltration rates were assessed in the soil surface covered by individual rock fragments and in the midpoint between two adjacent rock fragments (with maximum spacing of 20 cm). SWR increased with fire severity. Rock fragments resting on the soil surface increased the heterogeneity of the spatial distribution of fire-induced SWR. SWR increased significantly with rock fragment cover in bare areas under moderate and high fire severity, but quantitatively important changes were only observed under high fire severity. In areas with a low rock fragment cover, water repellency from soil surfaces covered by rock fragments increased relative to bare soil surfaces, with increasing SWR. In areas with a high rock fragment cover, SWR increased significantly from non-covered to covered soil surfaces only after low-severity burning. Rock fragment cover did not affect infiltration rates, although it decreased significantly in soil surfaces after high-severity burning in areas under low and high rock fragment cover. This article is protected by copyright. All rights reserved.

Description: Extremely low water level events have frequently occurred in the middle-lower Yangtze River (MLYR) in recent years (2006–2011). Most of these drought events coincided with the initial operation of the Three Gorges Dam (TGD). The TGD was therefore the focus of controversy about the causes of the hydrological droughts of the rivers and lakes of the region. We quantified the effects of the TGD's operation on water levels from 2006 to 2011 using a newly developed hydrodynamic model. The operation of the TGD significantly exacerbated the severe hydrological droughts that occurred in late September to November due to water impoundment, but it increased water levels from April to early June in the MLYR due to the drawdown of TGD water levels. Evidence suggests that the recent extremely low water levels were mainly due to the remarkable decline in inflows to the MLYR resulting from precipitation changes and possible human activities. Nevertheless, it should be noted that the effects of the TGD on downstream rivers and lakes will be intensified in the foreseeable future. This article is protected by copyright. All rights reserved.

Description: Water availability is one of the key environmental factors that control ecosystem functions in temperate forests. Changing climate is likely to alter the ecohydrology and other ecosystem processes that affect forest structures and functions. We constructed a multi-year water budget (2004–2010) and quantified environmental controls on an evapotranspiration (ET) in a 70-year-old mixed-oak woodland forest in northwest Ohio, USA. ET was measured using the eddy-covariance (EC) technique along with precipitation (P), soil volumetric water content (VWC), and shallow groundwater table fluctuation. Three biophysical models were constructed and validated to calculate potential ET (PET) for developing predictive monthly ET models. We found that the annual variability in ET was relatively stable and ranged from 578 mm in 2009 to 670 mm in 2010. In contrast, ET/P was more variable and ranged from 0.60 in 2006 to 0.96 in 2010. Mean annual ET/PET_FAO was 0.64 while mean annual PET_FAO/P was 1.15. Annual ET/PET_FAO was relatively stable, varying from 0.60 in 2005 to 0.72 in 2004. Soil water storage and shallow groundwater recharge during the non-growing season were essential in supplying ET during the growing season when ET exceeded P. Spring leaf area index (LAI), summer photosynthetically active radiation (PAR), and autumn and winter air temperatures (T a ) were the most significant controls of monthly ET. Moreover, LAI regulated ET during the whole growing season and higher temperatures increased ET even during dry periods. Our empirical modeling showed that the interaction of LAI and PET explained 〉90% of the variability in measured ET. Altogether we found that increases in T a and shifts in P distribution are likely to impact forest hydrology by altering shallow groundwater fluctuations, soil water storage, and ET and, consequently, alter the ecosystem functions of temperate forests. This article is protected by copyright. All rights reserved.

Description: Subsurface stormflow is thought to occur mainly in humid environments with steep terrains. However in semi-arid areas, preferential flow through macropores can also result in a significant contribution of subsurface stormflow to catchment runoff for varying catchment conditions. Most hydrological models neglect this important subsurface preferential flow. Here we use the process-oriented hydrological model Hillflow-3D, which includes a macropore flow approach, to simulate rainfall-runoff in the semi-arid Parapuños catchment in Spain, where macropore flow was observed in previous research. The model was extended for this study to account for sorptivity under very dry soil conditions. The results of the model simulations with and without macropore flow are compared. Both model versions give reasonable results for average rainfall situations, although the approach with the macropore concept provides slightly better results. The model results for scenarios of extreme rainfall events (〉 13.3 mm per 30 min) however show large differences between the versions with and without macropores. These model results compared to measured rainfall-runoff data show that the model with the macropore concept is better. Our conclusion is that preferential flow is important in controlling surface runoff in case of specific, high intensity rainfall events. Therefore preferential flow processes must be included in hydrological models where we know that preferential flow occurs. Hydrological process models with a less detailed process description may fit observed average events reasonably well but can result in erroneous predictions for more extreme events. This article is protected by copyright. All rights reserved.

Description: The central route of the South-North Water Transfer Project (CTP) is designed to divert approximately 9.5 billion m 3 of water per year from the Han River, a major tributary of the Yangtze River, to the Hai River Basin in the North China. The main purpose of this study is to assess the impact of CTP on groundwater table in the Hai River basin. Our study features a large-scale distributed hydrological model that couples a physically based groundwater module (GWM), which is subbasin-based, with a conceptual surface water module (SWM), which is grid-based. There are several grids in each subbasin and water exchange among grid are considered. Our model couples SWM and GWM, and calculates human water use at the same time. The simulation results indicate that even with the water supply by CTP, the groundwater table will continue to decline in the Hai River basin. However, the CTP water can evidently reduce the decline rate, helping alleviate groundwater over-exploitation in Hai River region. This article is protected by copyright. All rights reserved.

Description: Complexity-reduction modelling can be useful for increasing the understanding of how the climate affects basin soil moisture response upon historical times not covered by detailed hydrological data. For this purpose, here is presented and assessed an empirical regression-based model, the European Soil Moisture Empirical Downscaling (ESMED), in which different climatic variables, easily available on the web, are addressed for simplifying the inherent complexity in the long-time studies. To accommodate this simplification, the Palmer Drought Severity Index, the precipitation, the elevation and the geographical location were used as input data in the ESMED model for predicting annual soil moisture budget. The test area was a large region including central Europe and Mediterranean countries and the spatial resolution was initially set at 50 km. ESMED model calibration was made according with the soil moisture values retrieved from the Terrestrial Water Budget Data archive by selecting randomly 285 grid points (out of 2606). Once parameterized, ESMED model was performed at validation stage both spatially and temporally. The spatial validation was made for the grid points not selected in the calibration stage while the comparison with the soil moisture outputs of the GLDAS-NOAH10 simulations upon the period 1950-2010 was carried out for the temporal validation. Moreover, ESMED results were found to be in good agreement with a root-zone soil moisture product obtained from active and passive microwave sensors from various satellite missions. ESMED model was thus found to be reliable for both the temporal and spatial validation and, hence, it might represent a useful tool to characterize the long-term dynamics of soil moisture-weather interaction. This article is protected by copyright. All rights reserved.

Description: Tundra snow cover is important to monitor as it influences local, regional, and global scale surface water balance, energy fluxes, as well as ecosystem and permafrost dynamics. Observations are already showing a decrease in spring snow cover duration at high latitudes but the impact of changing winter season temperature and precipitation on variables such as snow water equivalent (SWE) is less clear. A multi-year project was initiated in 2004 with the objective to quantify tundra snow cover properties over multiple years at a scale appropriate for comparison with satellite passive microwave remote sensing data and regional climate and hydrological models. Data collected over seven late winter field campaigns (2004 to 2010) show the patterns of snow depth and SWE are strongly influenced by terrain characteristics. Despite the spatial heterogeneity of snow cover, several inter-annual consistencies were identified. A regional average density of 0.293 g/cm 3 was derived and shown to have little difference with individual site densities when deriving SWE from snow depth measurements. The inter-annual patterns of SWE show that despite variability in meteorological forcing, there were many consistent ratios between the SWE on flat tundra and the SWE on lakes, plateaus, slopes. A summary of representative inter-annual snow stratigraphy from different terrain categories is also presented. This article is protected by copyright. All rights reserved.

Description: The main objective of this paper is to provide comparative-quantitative examinations on capabilities of 2DH and pseudo-3D modelling approaches for simulating spatial and temporal variability of the flow and salinity in Lake Urmia, Iran. The water quality in the lake has been an environmentally important subject partly because this shallow hyper saline aquatic ecosystem is considered to be one of the largest natural habitats of a unique multi-cellular organism, Artemia urmiana . This brine shrimp is the major food source for many of the protected and rare shorebirds that visit the lake. Artemia urmiana can grow and survive in certain ranges of salinity and their disappearance could lead to an alteration of existing equilibria. The lake has also experienced considerable man-made changes during the past 3 decades. A newly built crossing embankment almost divided the lake into two northern and southern halves. A relatively small opening of 1.25kmin the new embankment provides water connections between the two halves. As a result, the flow and salinity regimes have been significantly changed. This might have had adverse serious impacts on the lake ecosystem. In the current study the 2DH hydrodynamic model has been found to provide reasonable predictions for the flow regime in the lake, while its salinity predictions have not been consistent with the field observations.Thepseudo-3D model has produced results fairly close to the salinity measurements and its temporal and spatial variations. The pseudo-3Dmodelhas been used for evaluating the embankment effects on the lake hydrodynamics and on the salinity conditions. The effectiveness of introducing a different number or length of openings in the embankment for restoring the pre-embankment conditions has also been examined. These remedy options have been found not to offer substantial improvements to the lake existing ecosystem. This article is protected by copyright. All rights reserved.

Description: Subsurface flow and heat transport near Freienbrink, NE Germany, was simulated in order to study groundwater-surface water exchange between a floodplains aquifer and a section of the lowland River Spree and an adjacent oxbow. Groundwater exfiltration was the dominant process and only fast surface water level rises resulted in temporary infiltration into the aquifer. The main groundwater flow paths are identified based on a 3D groundwater flow model. To estimate mass fluxes across the aquifer-surface water interfaces, a 2D flow and heat transport modelling approach along a transect of 12 piezometers was performed. Results of steady-state and transient water level simulations show an overall high accuracy with a Spearman coefficient ρ = 0.9996 and RMSE = 0.008 m. Based on small groundwater flow velocities of about 10 -7 to 10 -6  ms -1 mean groundwater exfiltration rates of 233 l m -2 d -1 are calculated. Short periods of surface water infiltration into the aquifer do not exceed 10 days and the infiltration rates are in the same range. The heat transport was modelled with slightly less accuracy (ρ = 0.8359 and RMSE = 0.34 °C). In contrast to the predominant groundwater exfiltration, surface water temperatures determine the calculated temperatures in the upper aquifer below both surface water bodies down to 10 m during the whole simulation period. These findings emphasize prevailing of heat conduction over advection in the upper aquifer zones, which seems to be typical for lowland streams with sandy aquifer materials and low hydraulic gradients. Moreover, this study shows the potential of coupled numerical flow and heat transport modelling to understand groundwater-surface water exchange processes in detail. This article is protected by copyright. All rights reserved.

Description: Particles eroded from hillslopes and exported to rivers are recognized to be composite particles of high internal complexity. Their architecture and composition is known to influence their transport behaviour within the water column relative to discrete particles. To-date, hillslope erosion studies consider aggregates to be stable once they are detached from the soil matrix. However, lowland rivers and estuaries studies often suggest that particle structure and dynamics are controlled by flocculation within the water column. In order to improve the understanding of particle dynamics along the continuum from hillslopes to the lowland river environment, soil particle behaviour was tested under controlled laboratory conditions. Seven flume erosion and deposition experiments, designed to simulate a natural erosive event, and five shear cell experiments were performed using three contrasting materials: two of them were poorly developed and as such can not be considered as soils, whilst the third one was a calcareous brown soil. These experiments revealed that soil aggregates were prone to disaggregation within the water column and that flocculation may affect their size distribution during transport. Large differences in effective particle size were found between soil types during the rising limb of the bed shear stress sequence. Indeed, at the maximum applied bed shear stress, the aggregated particles median diameter was found to be three times larger for the well-developed soil than for the two others. Differences were smaller in the falling limb, suggesting that soil aggregates underwent structural changes. However, characterization of particles strength parameters showed that these changes did not fully turn soil aggregates into flocs, but rather into hybrid soil aggregate-floc particles. This article is protected by copyright. All rights reserved.

Description: Submarine groundwater discharges (SGD) were investigated in a marine watershed in south-eastern Korea using water budget analysis and a 222 Rn mass balance model. Multi-layered TOPMODEL added hydrological assumption was used to estimate groundwater components in the water budget analysis. Field observations of soil moisture, rainfall, runoff and groundwater fluctuations were used for calibration and validation of the hydrologic model. Based on observed hydrological data and terrain analyses, parameters for the hydrologic model were delineated and used to describe several hydrologic responses in the watershed. SGD estimations by 222 Rn mass balance method were also performed at Il-Gwang bay in July, 2010, and May, June, July and Nov. 2011. The estimated groundwater through hydrologic modeling and water balance analysis was 1.3x10 6  m 3 /year, which rapidly increased during typhoon season due to heavy rainfall and permeable geologic structure. The estimated groundwater was approximately 3.7-27.1 % of SGD as evaluated by 222 Rn mass balance method ranges 3.44 and 17.45 m 3  m -2  year -1 . Even though SGD is predominantly influenced by tide fluctuation, the head gradient (difference) from hydrologic processes associated with heavy rainfalls can also extra significant influences. Comprehensive understanding of SGD evaluation can be improved through a simultaneous application of both these approaches. This article is protected by copyright. All rights reserved.

Description: Fallout radionuclides 137 Cs and 210 Pb are well established as tracers of surface and sub-surface soil erosion contributing sediment to river systems. However without additional information it has not been possible to distinguish sub-surface soil erosion sources. Here we use the fallout radionuclide 7 Be (half-life 53 days) in combination with 137 Cs and excess 210 Pb to trace the form of erosion contributing sediment in large river catchments in eastern Australia; the Logan River (area 3,700 km 2 ), Bowen River (9,400 km 2 ) and Mitchell River (4,700 km 2 ). We show that the combination of 137 Cs, excess 210 Pb and 7 Be can discriminate horizontally-aligned sub-surface erosion sources (rilled and scalded hillslopes and the floors of incised drainage lines and gully ‘badland’ areas) from vertical erosion sources (channel banks and gully walls). Specifically, sub-surface sources of sediment eroded during high rainfall and high river flow events have been distinguished by the ability of rainfall-derived 7 Be to label horizontal soil surfaces, but not vertical. Our results indicate that in the two northern catchments erosion of horizontal sub-surface soil sources contributed almost as much fine river sediment as vertical channel banks, and several times the contribution of hillslope topsoils. This result improves on source discrimination provided previously and indicates that in some areas erosion of hillslope soils may contribute significantly to sediment yield, but not as topsoil loss. We find that in north-eastern Australia scalded areas on hillslopes and incising drainage lines may be sediment sources of comparable importance to vertical channel banks. Previous studies have used the combination of 137 Cs, excess 210 Pb and 7 Be to estimate soils losses at the hillslope scale. Here we show that with timely and judicious sampling of soil and sediment during and immediately after high flow events 7 Be measurements can augment fallout 137 Cs and 210 Pb to provide important erosion source information over large catchments. This article is protected by copyright. All rights reserved.

Description: The hydrology of tropical dry forests have been poorly characterised when compared to their humid temperate and wet tropical counterparts. Despite accounting for more than 42% of all tropical forests and roughly 19% of the Earth's total forest, tropical dry forest represent less than 1% of the forest hydrology literature. The need for substantial hydrological research in tropical dry forests is extremely important, given that many tropical dry forest regions are currently water stressed due to high population densities and rapid land use change. Furthermore, future climate change scenarios are expected to have significant implications for the hydrological functioning of these catchments and will likely enhance pressures on already limited water resources. This paper provides an overview on the state of hydrological knowledge, particularly runoff generation, of tropical dry forests. We further highlight the research gaps and identify research priorities for tropical dry forests, and issue a call for increased hydrological research efforts in these forests. This article is protected by copyright. All rights reserved.

Description: We use two hydrological models of varying complexity to study the Juncal River Basin in the Central Andes of Chile with the aim to understand the degree of conceptualization and the spatial structure that are needed to model present and future streamflow. We use a conceptual semi-distributed model based on elevation bands (WEAP), frequently used for water management, and a physically oriented, fully-distributed model (TOPKAPI-ETH) developed for research purposes mainly. We evaluate the ability of the two models to reproduce the key hydrological processes in the basin with emphasis on snow accumulation and melt, streamflow and the relationships between internal processes. Both models are capable of reproducing observed runoff and the evolution of MODIS snow cover adequately. In spite of WEAP's simple and conceptual approach for modeling snowmelt, its lack of glacier representation and snow gravitational redistribution as well as a proper routing algorithm, this model can reproduce historical data with similar goodness-of-fit as the more complex TOPKAPI-ETH. We show that the performance of both models can be improved by using measured precipitation gradients of higher temporal resolution. In contrast to the good performance of the conceptual model for the present climate, however, we demonstrate that the simplifications in WEAP lead to error compensation which results in different predictions in simulated melt and runoff for a potentially warmer future climate. TOPKAPI-ETH, using a more physical representation of processes, depends less on calibration and thus is less subject to a compensation of errors through different model components. Our results show that data obtained locally in ad-hoc short-term field campaigns are needed to complement data extrapolated from long-term records for simulating changes in the water cycle of high elevation catchments, but that these data can only be efficiently used by a model applying a spatially distributed physical representation of hydrological processes. This article is protected by copyright. All rights reserved.

Description: Land use/cover (LULC) and climate change are two main factors affecting watershed hydrology. In this paper, individual and combined impacts of LULC and climate change on hydrologic processes were analyzed applying the model Soil and Water Assessment Tool (SWAT) in a coastal Alabama watershed in USA. Temporally and spatially downscaled Global Circulation Model (GCM) outputs predict a slight increase in precipitation in the study area, which is also projected to experience substantial urban growth in the future. Changes in flow frequency and volume in the 2030s (2016–2040) compared to a baseline period (1984–2008) at daily, monthly and annual time scales were explored. A redistribution of daily streamflow is projected when either climate or LULC change was considered. High flows are predicted to increase, while low flows are expected to decrease. Combined change effect results in a more noticeable and uneven distribution of daily streamflow. Monthly average streamflow and surface runoff are projected to increase in spring and winter, but especially in fall. LULC change does not have a significant effect on monthly average streamflow, but the change affects partitioning of streamflow, causing higher surface runoff and lower baseflow. The combined effect leads to a dramatic increase in monthly average streamflow with a stronger increasing trend in surface runoff and decreasing trend in baseflow. This article is protected by copyright. All rights reserved.

Description: The fresh groundwater lenses (FGLs) of small islands can be highly vulnerable to climate change impacts, including sea-level rise (SLR). Many real cases of atoll or sandy islands involve two-layer hydrogeological conceptualizations. In this paper, the influential factors that effect FGL in two-layer small islands subject to SLR are investigated. An analytical solution describing FGLs in circular islands, composed of two geological layers, is developed for the simplified case of steady-state and sharp-interface conditions. An application of the developed model is demonstrated to estimate the FGL thickness of some real-world islands by comparison with existing FGL thickness data. Furthermore, numerical modeling is applied to extend the analysis to consider dispersion effects and to confirm comparable results for both cases. Sensitivity analyses are used to assess the importance of land-surface inundation (LSI) caused by SLR, relative to other parameters (i.e. thickness of aquifer layers, hydraulic conductivity, recharge rate, and land-surface slope) that influence the FGL. Dimensionless parameters are used to generalize the findings. The results demonstrate that LSI has a considerable impact on a FGL influenced by SLR, as expected, although the FGL volume is more sensitive to recharge, aquifer thickness and hydraulic conductivity than SLR impacts, considering typical parameter ranges. The methodology presented in this study provides water resource managers with a rapid-assessment tool for evaluating the likely impacts of SLR and accompanying LSI on FGLs. This article is protected by copyright. All rights reserved.

Description: Mapping groundwater discharge zones at broad spatial scales remains a challenge, particularly in data sparse regions. We applied a regional scale mapping approach based on thermal remote sensing to map discharge zones in a complex watershed with a broad diversity of geological materials, land cover and topographic variation situated within the Prairie Parkland of northern Alberta, Canada. We acquired winter thermal imagery from the USGS Landsat archive to demonstrate the utility of this data source for applications that can complement both scientific and management programs. We showed that the thermally determined potential discharge areas were corroborated with hydrological (spring locations) and chemical (conservative tracers of groundwater) data. This study demonstrates how thermal remote sensing can form part of a comprehensive mapping framework to investigate groundwater resources over broad spatial scales. This article is protected by copyright. All rights reserved.

Description: Obtaining representative meteorological data for watershed-scale hydrological modeling can be difficult and time consuming. Land-based weather stations do not always adequately represent the weather occurring over a watershed, because they can be far from the watershed of interest, have gaps in their data series, or recent data is not available. This study presents a method for using the Climate Forecast System Reanalysis (CFSR) global meteorological data set to obtain historical weather data and demonstrates the application to modeling five watersheds representing different hydroclimate regimes. CFSR data are available globally for each hour since 1979 at a 38 km resolution. Results show that utilizing the CFSR precipitation and temperature data to force a watershed model provide stream discharge simulations that are as good as or better than models forced using traditional weather gaging stations, especially when stations are more than 10 km from the watershed. These results further demonstrate that adding CFSR data to the suite of watershed modeling tools provides new opportunities for meeting the challenges of modeling un-gaged watersheds and advancing real-time hydrological modeling. This article is protected by copyright. All rights reserved.

Description: River water temperature is a very important variable in ecological studies, especially for the management of fisheries and aquatic resources. Temperature can impact on fish distribution, growth, mortality and community dynamics. River evaporation has been identified as an important heat loss and a key process in the thermal regime of rivers. However, its quantification remains a challenge, mainly due to the difficulty of making direct measurements. The objectives of this study were to characterize the evaporative heat flux at different scales (brook vs. river) and to improve the estimation of the evaporative heat flux in a stream temperature model at the hourly timescale. Using a mass-balance approach with floating minipans, we measured river evaporation at an hourly timescale in a medium-sized river (Little Southwest Miramichi) and a small brook (Catamaran Brook) in New Brunswick, Canada. With these direct measurements of evaporation, we developed mass transfer equations to estimate hourly evaporation rates from microclimate conditions measured 2 m above the stream. During the summer 2012, river evaporation was more important for the medium-sized river with a mean daily evaporation rate of 3.0 mm day -1 in the Little Southwest Miramichi River compared to 1.0 mm day -1 in Catamaran Brook. Evaporation was the main heat loss mechanism in the two studied streams and was responsible for 42 % of heat losses in the Little Southwest Miramichi River and 34 % of heat losses in Catamaran Brook during the summer. This article is protected by copyright. All rights reserved.

Description: Although catchment storage is an intrinsic control on the rainfall-runoff response of streams, direct measurement remains a major challenge. Coupled models that integrate long-term hydrometric and isotope tracer data are useful tools that can provide insights into the dynamics of catchment storage and the volumes of water involved. In this study, we use a tracer-aided hydrological model to characterize catchment storage as a dynamic control on system function related to streamflow generation, which also allows direct estimation of the non-stationarity of water ages. We show that in a wet Scottish upland catchment dominated by runoff generation from riparian peats (histosols) with high water storage, non-stationarity in water age distributions are only clearly detectable during more extreme wet and dry periods. This is explained by the frequency and longevity of hydrological connectivity and the associated relative importance of flow paths contributing younger or older waters to the stream. Generally, these saturated riparian soils represent large mixing zones that buffer the time variance of water age and integrate catchment-scale partial mixing processes. Although storage simulations depend on model performance, which is influenced by input variability and the degree of isotopic damping in the stream, a longer-term storage analysis of this model indicates a system which is only sensitive to more extreme hydroclimatic variability. This article is protected by copyright. All rights reserved.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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.