ALBERT

Description: This study investigated the surface water-groundwater interactions of three semi-arid floodplain wetlands of the lower River Murray (SE Australia) using a combination of hydrometric, natural tracer and geophysical methods. The current management objective for these wetlands is to mimic the natural surface water flow regime by engineering wetting and drying cycles for the benet of the biota. However, the impact this will have on groundwater processes and wetland salinization is unknown. This study found that when inundated, two of the wetlands were groundwater recharge features, whereas the other was a groundwater through flow system. After these wetlands were dried, there was a reversal of the hydraulic gradients and all three wetlands became groundwater discharge features. The transformation of these wetlands to groundwater discharge features after the removal of surface water means that there is an increased risk of salinization when wetting and drying cycles are reintroduced. In arid/semi-arid regions of the world where wetlands are in direct contact with saline groundwater, extreme caution should be applied when altering the management of the surface hydrology of the wetlands because increases in salinity can impact upon biodiversity. Copyright © 2009 John Wiley & Sons, Ltd.

Description: Heavily compacted lands, typical of traditional surface mine reclamation techniques, have been shown to hinder tree growth, increase levels of flooding, and produce suboptimal water quality. Utilizing loose-dumped spoil, in accordance with the Forestry Reclamation Approach (FRA), has demonstrated success with regards to promoting tree growth and survival; however, additional information is needed to assess the potential of FRA to ameliorate other environmental concerns related to water quantity. To better understand the hydrologic characteristics of loose-dumped spoil, key hydrograph parameters (discharge volume, peak discharge, discharge duration, lag time, and response time) were monitored for three common spoil types: (1) predominately brown weathered sandstone, (2) predominately gray weathered sandstone, and (3) a mixture of both sandstones and shale. Although spoil types were found to differ hydrologically, these differences were relatively minor. Measured discharge volumes were low (averaging 12% of rainfall for all events and treatments), peak discharge rates were small (between 2·5 × 10-5and 3 × 10-3 m3/s), and the duration of discharge was long (6 days on average). From a hydrologic perspective, the results of this study indicate that mine spoils need not be segregated for reclamation as long as the spoil is placed in accordance with the loose-dumped techniques as outlined in the FRA. Copyright © 2009 John Wiley & Sons, Ltd.

Description: Coring and acoustic surveying (3.5 kHz) in both rivers and lakes in Central Amazonia provide additional insights into the Late Quaternary hydrological and sedimentological development of the Amazon River and its tributaries. Erosion and accumulation phases were found to be linked to Quaternary sea level changes. The low sea level phase during the last glacial maximum caused deep incision of the Amazon River and erosion in major tributaries such as the Rio Negro, 1500 km upstream from the Amazon mouth. A 3.5-kHz profiling suggests a lowering of the water level by at least 30 m at Manaus. During that phase, the slope of the Amazon valley must have increased, resulting in an increase in bed load transport capacity. The subsequent sea level rise caused a backwater effect far upstream, with silting up of the Amazon valley and the tributary inflows. Former river systems changed into Ria lakes. The floodplains of the Amazon River, the várzea, were formed approximately 5000 years ago when the sea level approached its present-day level. Copyright © 2009 John Wiley & Sons, Ltd.

Description: A 9-year sediment transport monitoring programme on the Niger River was used to study the relationship between suspended sediment concentration and river discharge. During annual floods, this relationship shows the hysteresis normally observed on tropical rivers. This paper presents an attempt to model the time evolution of suspended sediment concentrations during floods using only water discharge data. Two models have been developed. The first model is an empirical model based on a statistical approach using two relationships, one for the rising stage period and one for the recession period of the annual flood. The second one, a lumped conceptual model, uses the respective contributions of two sediment reservoirs. The first reservoir is limited in size and period of functioning and represents hillslope erosion observed during the runoff season. The second reservoir is unlimited in terms of both its size and period of operation and represents sediment contributions from bank erosion and remobilization of sediment deposits in the channel network. Both models have been applied to the Banankoro gauging station on the upper Niger River (for the hydrological years from 1991/1992 to 1999/2000) and are able to simulate the time evolution of sediment concentration during the annual cycle, with a reasonable degree of accuracy. For annual sediment yield, the models do not provide a better estimate than a simple regression with annual water volume. However, the two models are able to simulate the evolution of the sediment flux during the flood. Copyright © 2009 John Wiley & Sons, Ltd.

Description: The confluence of the rivers Negro and Solimões gives birth to the Amazon River near Manaus (Brazil). At their confluence, these two rivers with their very different physical and geochemical characteristics provide an interesting example of the mixing of waters along a reach of approximately one-hundred kilometres. The purpose of this article is to describe and explain the spatial configuration of the Solimões-Negro Rivers mixing zone, based on a systematic sampling survey carried out in September 1997, using a special sampler and an acoustic Doppler current profiler (Acoustic Doppler Current Profiler). The waters of the Negro River differ from those of the Solimões River in their lower velocity (0.3 vs 1 m s-1), conductivity (8 vs 80 μS cm-1 at 25° C), turbidity (5 vs 80 NTU), pH (5.5 vs 7.0) and higher temperatures (by 1 °C). Due to their higher density, the waters of the Solimões River slide under those of the Negro River, and consequently, Negro River waters are located at the surface, close to the left bank, and Solimões River waters are located at the bottom, close to the right bank. The contact between the waters of the two rivers changes from a clearly defined vertical boundary to a diffuse horizontal boundary, as they move downstream. The complete mixing process takes more than 30 h and 100 km. Copyright © 2009 John Wiley & Sons, Ltd.

Description: The inner delta of the River Niger receives runoff from both the River Niger and the River Bani (249 000 km2) and is divided into a northern part (15 000 km2) and a southern part (58 000 km2). The average input and output discharges are approximately 1490 and 900 m3 s-1 (1955/1996), respectively. The annual average water loss is approximately 40% (24-48%). The losses are greater in the northern (10·5 km3) than in the southern delta (8·2 km3), but this situation was reversed in 1984. The correlation between the output and input discharges is high for the northern part of the delta, but very low for the southern part, where the change in flooded area is likely to be limited. The average flooded area, calculated using a method based on the hydrological balance, is estimated to be about 10 000 km2 (north) and 14 000 km2 (south), which is consistent with the estimates provided by the previous authors. Copyright © 2009 John Wiley & Sons, Ltd.

Description: The main purpose of the research described in this contribution was to apply a conceptual hydrological model to predict runoff volumes when El Niño southern oscillation (ENSO) events occur. Statistical analysis was used to assess the impact of ENSO events on rainfall and runoff variables across the Chopim River basin. A conceptual model was calibrated and validated to simulate the rainfall-runoff processes within the basin. An extended runoff volume prediction procedure was applied to derive forecasts of runoff volumes for different lead times for the different rainfall data series. Copyright © 2009 John Wiley & Sons, Ltd.

Description: Soil conservation practices have been widely implemented on the Loess Plateau to reduce severe soil erosion in north-central China over the past three decades. However, the hydrologic impacts of these practices are not well documented and understood. The objective of this study was to examine how water yield has changed after implementing soil conservation practices that resulted in changes in land use and land cover in a small agriculture-dominated watershed, the LuErGou Watershed in Tianshui City, Gansu Province, China. We collected 23 years of hydro-meteorological data along with three land use surveys of 1982, 1989, and 2000. The land use survey in 2000 suggested that the soil conservation efforts resulted in a 16D6%, 4%, and 16% increase in area of grassland, forested land, and terraces respectively over the two periods from 1982 to 1988 (baseline) and 1989 to 2003 (soil conservation measures implemented). Rainfall-runoff regression models developed for both time periods at the annual and monthly time steps were used to examine the significance of change in water yield in the second time period. The averaged annual run-off coefficient over 1989-2003 did not change significantly (at the α = 0D05 level) as compared to that in the period 1982-1988. However, we found that soil conservation practices that included re-vegetation and terracing reduced water yield during wet periods. This study highlights the importance of the precipitation regime in regulating hydrologic effects of soil conservation measures in a semi-arid environment. We concluded that adequately evaluating the effects of land use change and soil conservation measures on water yield must consider the climatic variability under an arid environment. Copyright © 2009 John Wiley & Sons, Ltd.

Description: The pre-calibrated and validated physically based watershed model, water erosion prediction project (WEPP) was used as a modelling tool for the identification of critical watersheds and evaluation of best management practices for a small hilly watershed (Karso) of India. The land use/ cover of the study area was generated using IRS-1C LISS-III (linear imaging self scanner) satellite data. The watershed and sub-watershed boundaries, drainage, slope and soil map of the study area were generated using ARC/INFO geographic information system (GIS). The WEPP model was finally applied to the Karso watershed which lies within Damodar Barakar catchment of India to identify the critical sub-watersheds on the basis of their simulated average annual sediment yields. Priorities were fixed on the basis of ranks assigned to each critical sub-watershed based on the susceptibility to erosion. The sub-watershed having the highest sediment yield was assigned a priority number 1, the next highest value was assigned a priority number 2, and so on. Subsequently, the model was used for evaluating the effectiveness of best management practices (crop and tillage) for conservation of soil for all the sub-watersheds. On the basis of this study, it is realized that cash crops like soyabean should be encouraged in the upland portion of the sub-watersheds, and the existing tillage practice (country plough/ mould board plough) may be replaced by a field cultivation system for conservation of soil and water in the sub-watersheds. Copyright © 2009 John Wiley & Sons, Ltd.

Description: Floodplains during non-flood periods are less well documented than when flooding occurs, but non-flood periods offer opportunities to investigate vegetation controls on water and nutrient cycling. In this study, we characterized water uptake and nutrient concentration patterns from 2005 to 2007 under an oak savanna located on the floodplain of the Cedar River in Muscatine County, Iowa. The water table ranged from 0.5 to 2.5 m below ground surface and fluctuated in response to stream stage, plant water demand and rainfall inputs. Applying the White method to diurnal water table fluctuations, daily ET from groundwater averaged more than 3.5 mm/day in June and July and approximately 2 mm/day in May and August. Total annual ET averaged 404 mm for a growing season from mid-May to mid-October. Savanna groundwater concentrations of nitrate-N, ammonium-N, and phosphate-P were very low (mean 〈0.18, 〈0.14, 〈0.08 mg/l, respectively), whereas DOC concentrations were high (7.1 mg/l). Low concentrations of N and P were in contrast to high nutrient concentrations in the nearby Cedar River, where N and P averaged 7.5 mg/ l and 0.13, respectively. In regions dominated by intensive agriculture, study results document valuable ecosystem services for native floodplain ecosystems in reducing watershed-scale nutrient losses and providing an oasis for biological complexity. Improved understanding of the environmental conditions of regionally significant habitats, including major controls on water table elevations and water quality, offers promise for better management aimed at preserving the ecology of these important habitats. Copyright © 2009 John Wiley & Sons, Ltd.

Description: Hydrological modelling depends highly on the accuracy and uncertainty of model input parameters such as soil properties. Since most of these data are field surveyed, geostatistical techniques such as kriging, classification and regression trees or more sophisticated soil-landscape models need to be applied to interpolate point information to the area. Most of the existing interpolation techniques require a random or regular distribution of points within the study area but are not adequate to satisfactorily interpolate soil catena or transect data. The soil landscape model presented in this study is predicting soil information from transect or catena point data using a statistical mean (arithmetic, geometric and harmonic mean) to calculate the soil information based on class means of merged spatial explanatory variables. A data set of 226 soil depth measurements covering a range of 0-6.5 m was used to test the model. The point data were sampled along four transects in the Stubbetorp catchment, SE-Sweden. We overlaid a geomorphology map (8 classes) with digital elevation model-derived topographic index maps (2-9 classes) to estimate the range of error the model produces with changing sample size and input maps. The accuracy of the soil depth predictions was estimated with the root mean square error (RMSE) based on a testing and training data set. RMSE ranged generally between 0.73 and 0.83 m ± 0.013 m depending on the amount of classes the merged layers had, but were smallest for a map combination with a low number of classes predicted with the harmonic mean (RMSE = 0.46 m). The results show that the prediction accuracy of this method depends on the number of point values in the sample, the value range of the measured attribute and the initial correlations between point values and explanatory variables, but suggests that the model approach is in general scale invariant. Copyright © 2009 John Wiley & Sons, Ltd.

Description: A long-term stream water quality monitoring network was established in the city of Atlanta, Georgia during 2003 to assess baseline water quality conditions and the effects of urbanization on stream water quality. Routine hydrologically based manual stream sampling, including several concurrent manual point and equal width increment sampling, was conducted ∼12 times annually at 21 stations, with drainage areas ranging from 3.7 to 232 km2. Eleven of the stations are real-time (RT) stations having continuous measures of stream stage/ discharge, pH, dissolved oxygen, specific conductance, water temperature and turbidity, and automatic samplers for stormwater collection. Samples were analyzed for field parameters, and a broad suite of water quality and sediment-related constituents. Field parameters and concentrations of major ions, metals, nutrient species and coliform bacteria among stations were evaluated and with respect to watershed characteristics and plausible sources from 2003 through September 2007. Most constituent concentrations are much higher than nearby reference streams. Concentrations are statistically different among stations for several constituents, despite high variability both within and among stations. Routine manual sampling, automatic sampling during stormflows and RT water quality monitoring provided sufficient information about urban stream water quality variability to evaluate causes of water quality differences among streams. Fecal coliform bacteria concentrations of most samples exceeded Georgia's water quality standard for any water-usage class. High chloride concentrations occur at three stations and are hypothesized to be associated with discharges of chlorinated combined sewer overflows, drainage of swimming pool(s) and dissolution and transport during rainstorms of CaCl2, a deicing salt applied to roads during winter storms. One stream was affected by dissolution and transport of ammonium alum [NH4Al(SO4)2] from an alum-manufacturing plant; streamwater has low pH (〈5), low alkalinity and high metals concentrations. Several trace metals exceed acute and chronic water quality standards and high concentrations are attributed to washoff from impervious surfaces.

Description: Flood vulnerability assessment plays a key role in the area of risk management. Therefore, techniques that make this assessment more straightforward and at the same time improve the results are important. In this briefing, we present an automated calculation of a flood vulnerability index implemented through a web management interface (PHP) that enhances the ability of decision makers to strategically guide investment. To test the applicability of this methodology using this website, many case studies are required in order to cover the full range of cases in terms of scale such as river basin, subcatchment and urban area. This requires prompt solutions with large amounts of data and this has led to the development of this automated tool to help organize, monitor, process and compare the data of different case studies. The authors aim to create a network of knowledge between different institutions and universities in which this methodology is used. It is also hoped to encourage collaboration between the members of the network on managing flood vulnerability information and also promoting further studies on flood risk assessment at all scales. Copyright © 2009 John Wiley & Sons, Ltd.

Description: Shallow and bedrock groundwater from granitic aquifers were investigated for the hydrogeochemistry of major and minor constituents in an agricultural area. Nitrate concentrations were observed up to 49 mg/l as NO3-N, with 22% of samples exceeding the drinking water standard, which could pose a significant threat because most residents rely on groundwater as their drinking water source. Principal component analysis revealed three principal components (PCs): (1) nitrate contamination, contributed by major cations, Cl-, SO42- and NO3-, (2) reduction processes positively involving Fe, Mn and B, and negatively involving dissolved oxygen and NO3- and (3) natural mineralization, involving HCO3- and F-. Cluster analysis, performed on the PC scores, resulted in seven sample groups, which were successfully identified by total depth, elevation and land use. The nitrate-contaminated groups had mixed land uses, with locally concentrated residential areas. Uncontaminated groundwater groups were found in the natural environment, including high-altitude spring water and bedrock groundwater with a higher degree of natural mineralization. Shallow groundwater groups in paddy fields in lowlands were affected by reducing environments, of which one group was characterized by high Fe, Mn and B, and negligible nitrate. Groundwater with intermediate nitrate and lower Cl- and SO42- was found primarily in hilly terrains with orchards and vegetable gardens, indicating lower contaminant loadings than lowland areas. Higher concentrations of F- and nitrate were observed in the nitrate-contaminated water, which seemed unlikely to be explained by groundwater mixing. The strong acidity generated from nitrification may infiltrate deeper into the aquifer, induce accelerated weathering of bedrock and result in the coexistence of F- and nitrate, which may be an evidence of intense nitrate loading, leading to soil acidification. Multivariate statistical analysis successfully delineated hydrochemical characteristics of groundwater attained by natural and anthropogenic processes in an agriculturally stressed area with complex topographic land use patterns. Copyright © 2009 John Wiley & Sons, Ltd.

Description: The water quality of urban drainage ditches in lowlands in the Rhine-Meuse delta was analysed with principal component analysis (PCA) during a dry period and a rain storm, and related to the seepage of polluted river water and effective impervious area (EIA). This was done in order to test the hypothesis that seepage of river water and storm water runoff from impervious areas strongly determine the water quality of urban drainage systems along large lowland rivers. Our analysis revealed that upward seepage of groundwater originating from rivers Rhine and Meuse was positively correlated with nitrate, potassium, sodium and chloride and negatively correlated with alkalinity, calcium, magnesium and iron. EIA was correlated with very few environmental variables (i.e. phosphate, pH and iron in the dry period and iron during the rain storm). Nickel and zinc concentrations generally exceeded the maximum allowable concentrations (MAC), while lead and phosphorus concentrations were just above the nutrient standards and MAC in a few locations during the rain storm. To optimize water quality in urban water systems, attention should be paid to all sources of pollution and not only to EIA. The impact of local groundwater seepage originating from large rivers in lowlands on the chemistry of urban water systems is often underestimated and should be taken into account when assessing water quality and improving water quality status. Copyright © 2009 John Wiley & Sons, Ltd.

Description: Digital elevation models (DEMs) are data sources for distributed rainfall-runoff modelling in terms of providing the channel network for a watershed of interest. Assigning flow directions over flat regions is an important issue in the field of DEM processing and extraction of drainage features. Existing methods cannot fully incorporate the information of known drainage features and terrain surrounding the flat region. This study presented a hydrological correction method that integrates topographic information from different sources to interpolate a convergent surface. It employs radial basis function interpolation to determine elevation increment at every position, utilizes data of digital channel network, incorporates elevation in the surrounding terrain, and ensures a convergent channel network while minimizing the impact of correction on the original DEM. The method can be easily implemented in geographic information system (GIS) environment. It was applied to the DEM of the Heshui Watershed, China. The extracted channel network was visually inspected and quantitatively assessed through analysing the flow direction raster. Results showed that the channel network generated by the hydrological correction was consistent with the known drainage features and contained less parallel channels comparing with the results from two existing methods. Copyright © 2009 John Wiley & Sons, Ltd.

Description: The article presents a detailed review on the issues and constraints of hydrodynamic modelling of floods in data-poor countries with large flood-prone rivers. A one-dimensional (1D) hydrodynamic model is used to simulate the river flows with limited available data in the delta region of Mahanadi River basin in India. The shuttle radar topography mission digital elevation models (SRTM DEM) was analyzed and compared with the elevations derived from available topomaps and measured river cross-sections. Subsequently, the SRTM-derived river cross-section elevation values are refined for use in the hydrodynamic model. The 1D hydrodynamic model is set up and calibrated using the refined cross-sections derived from SRTM DEM along with the measured ones and all available river discharge as well as water-level data at different gauging sites for the monsoon period (June-September) of the year 2004. The calibrated set up is validated using both discharge and water-level data for the same period for the years 2001 and 2002. The performance of the calibration and validation results of the hydrodynamic model is evaluated for all the years using different performance indices. The model-simulated discharge and water levels are found to be in close agreement with the observed ones. The study demonstrates the usefulness of using the SRTM DEM to derive river cross-sections for use in hydrodynamic modelling studies. Copyright © 2009 John Wiley & Sons, Ltd.

Description: Researchers have found that obtaining optimal solutions for groundwater resource-planning problems, while simultaneously considering time-varying pumping rates, is a challenging task. This study integrates an artificial neural network (ANN) and constrained differential dynamic programming (CDDP) as simulation-optimization model, called ANN-CDDP. Optimal solutions for a groundwater resource-planning problem are determined while simultaneously considering time-varying pumping rates. A trained ANN is used as the transition function to predict ground water table under variable pumping conditions. The results show that the ANN-CDDP reduces computational time by as much as 94-5% when compared to the time required by the conventional model. The proposed optimization model saves a considerable amount of computational time for solving large-scale problems. Copyright © 2009 John Wiley & Sons, Ltd.

Description: The detection and estimation of trends in the presence of noise, periodicities, or discontinuous patterns is important in hydrology and climate research studies. The basic idea of currently available trend estimation techniques (tests) is that the trends should be smooth and monotonic; however, hydro-climatologic variables contain multiple signals, and have segments of increasing and decreasing trends. As a result, estimating trends in time series is an essential but arcane art and it is therefore important to continue developing the theory and practice of trend analysis. In this paper, a new technique is proposed based on the continuous wavelet transform (CWT). CWT permits the transformation of observed time series into wavelet coefficients according to time and scale simultaneously. These coefficients can be used to detect and estimate trends or to reconstruct signals that are of interest. The proposed CWT method was first tested on computer-generated data exhibiting both periodic and noise components. It was then applied to observed monthly minimum streamflow observations extracted from the Reference Hydrometric Basin Network (RHBN) for five different eco-zones in Canada. It was concluded that the proposed wavelet transform (WT) based method provides a very flexible and accurate tool for detecting and estimating complicated signals. The results from monthly minimum observations indicate that short period fluctuations are decreasing, while multi-annual variability is increasing in Canada. And finally, a persistent ∼55-year signal is well correlated with the Pacific Decadal Oscillation in all records, which indicates that trends are not controlled by a single factor. Copyright © 2009 John Wiley & Sons, Ltd.

Description: Forest disturbance has a significant impact on hydrology due to its effect on the forest canopy, which is important for precipitation interception, transpiration, site micrometeorology, and snow accumulation and ablation. This study examines the impact of mountain pine beetle infestation and subsequent forest death on snow ablation. Dead stands experience needle loss and canopy reduction due mainly to the loss of small branches and stems, which has a subsequent impact on micrometeorological conditions. Ablation is driven largely by incoming short-wave radiation, which in dead stands is greater than in alive stands, but does not reach that available in clearcuts. Long-wave radiation emission in dead stands is lower than that in alive stands, reducing its contribution to snowpack warming and ablation. Turbulent flux contributions to snow ablation are limited in forest stands relative to clearcuts, although they are slightly greater in dead than alive stands due to the more open forest structure. Additional studies are required to refine the basic energy balance model and incorporate all processes affecting the snow ablation energy balance. Copyright © 2009 John Wiley & Sons, Ltd.

Description: Mean transit times were estimated for a small headwater catchment in Japan (the Fukuroyamasawa Experimental Watershed) using the step shift in input chloride (Cl-) concentrations that occurred immediately after an episode of forest clear-cutting. Measured Cl- concentrations in stream water began to decrease immediately after clear-cutting, and this trend continued for 6 years. Before clear-cutting, the input Cl- concentrations were controlled by wet and dry deposition processes, and most of the dry Cl- deposition was collected by the forest canopy and reached the ground as throughfall and stemflow. After clear-cutting, dry deposition was no longer collected by the canopy in this way, thus causing a sharp decrease in input Cl- concentrations. By comparing measured Cl- concentrations in stream water with estimates based on the input and evaporative Cl- concentrations, it was shown that the decrease in stream water Cl- concentrations was caused mainly by this step shift in the Cl- input. It was proposed that the change in Cl- concentrations after forest cutting could be used to represent the replacement of 'old' water that existed before cutting by 'new' water that was supplied after cutting. The breakthrough curve for the new water fraction gave an approximately exponential distribution of transit times in flow-corrected time. The mean flow-corrected transit time was estimated as 1068 days (runoff: 3497 mm). It was therefore concluded that the step change in input Cl- concentrations immediately following forest clear-cutting could be successfully used to estimate transit times for the entire catchment. Copyright © 2009 John Wiley & Sons, Ltd.

Description: The radiation balance in forests is modified by the presence of a (temporally snow-covered) canopy much more than it is in open areas. The primary effects of the forest canopy are absorption of incoming shortwave radiation, as well as absorption and emission of longwave radiation. In this study, data from a mobile net radiation sensor moving along a 10-m bar in a coniferous sub-alpine stand of central Switzerland were analysed to assess the role of intercepted snow in comparison with other governing factors for winter-time radiation processes in a coniferous sub-alpine forest. The four winters investigated (2003-2007) covered a broad range of weather and snow conditions including several periods with intercepted snow lasting up to 19 days. For cloudless days, the data show that canopy albedo is elevated by the presence of intercepted snow. For transmissivity, the impact of intercepted snow is less distinct. Our analysis showed that the fraction of diffuse radiation and solar elevation are the main factors affecting shortwave transmissivity. Only after compensating for these effects, could intercepted snow be associated with increased transmissivities. Part of this analysis was carried out with the help of a physically based radiative transfer model. The model results suggest that multiple reflections are relevant to understanding the complex interactions between the factors affecting transmissivity. Finally, snow interception load can be derived reasonably well (R2 = 0.65) from radiation measurements in this sub-alpine forest. Copyright © 2008 John Wiley & Sons, Ltd.

Description: Transient storage constitutes a key element in the hydrologic cycle of watersheds. Both in-channel slow moving water (dead zones) and hyporheic zones can contribute to transient storage, which retains water and solutes, increases residence time and influences solute transport in streams. Beaver dams and other in-stream obstructions throughout low-order streams attenuate streamflow and provide dead zone storage in pools. In this article, we report the results of four tracer tests in nested stream reaches in Cherry Creek (Wyoming, USA) covering ~2.5 km of stream length to explore how the degree of beaver dam obstructions and their impoundments influence water transient storage and downstream solute transport in low-order streams in the Rocky Mountain region of the American West. Travel-time parameters for the tracer tests increased linearly with beaver dam number (N) and pond size (V). Linear regression of the travel time to the peak concentration (Tp), the leading (Tl) and tailing edge (Tt) of the dye cloud and the duration of the dye cloud (Td) versus N and V were all significant (R2 = 0.99). Slopes of the linear regressions of Tt versus N and V, were three times larger than those for Tl, suggesting that longer residence times may be caused, in part, by transient storage in the stream system. One-dimensional transport with inflow and storage (OTIS) modelled cross-sectional area of transient storage zone (As) and dispersion coefficients (D) increased linearly with N and V and reach length. Two transient storage metrics, Fmean and Fmed200, also showed a general increase with N and V, although the relationship was not as strong. This suggests that in-channel dead zones associated with beaver dams provide opportunities for generating transient water storage. The linear relationship between dispersion coefficient and reach length suggests the dispersion process might be analogous to the hydrodynamic dispersion in groundwater settings. Copyright © 2009 John Wiley & Sons, Ltd.

Description: The freshwater flux from the Greenland Ice Sheet (GrIS) to the ocean is of considerable importance to the global eustatic sea level rise. A physical modelling approach using SnowModel, a state-of-the-art snow-evolution modelling system that includes four submodels (MicroMet, EnBal, SnowPack, and SnowTran-3D), was used to quantify the 1995-2007 GrIS surface mass-balance (SMB), including freshwater flux. Meteorological observations from 26 meteorological stations located on the GrIS (Greenland Climate Network; GC-Net stations) and in coastal Greenland (Danish Meteorological Institute (DMI) WMO-stations) were used as model inputs. The GrIS minimum surface melt extent of 29% occurred in 1996, while the greatest extent of 51% was present in 2007. The 2007 melt extent was 20% greater than the average for 1995-2006. The year 2007 had the highest GrIS surface runoff (523 km3 y-1) and the lowest SMB (-3 km3 y-1); the only year with a negative GrIS SMB. Runoff in 2007 was approximately 35% greater than average for 1995-2006. From 1995 through 2007 overall, precipitation decreased while ablation increased, leading to an increased average SMB loss of 127 km3. The modelled GrIS SMB was merged with previous estimates of GrIS subglacial runoff (from geothermal melt) and GrIS calving to quantify GrIS freshwater flux to the ocean, indicating an average negative mass-balance of 265 (±83) km3 y-1. This study further suggests an average GrIS freshwater flux of approximately 786 km3 y-1 to the ocean, of which 45% occurs from iceberg calving and geothermal bottom melting. The average annual GrIS freshwater flux equals 2.1 ± 0.2 mm w.eq. y-1 in eustatic sea level rise, indicating a cumulative flux of 28 mm w.eq. from 1995 through 2007. The average GrIS net loss contributes to a net sea level rise of 0.7 ± 0.2 mm w.eq. y-1, and a cumulative net increase of 10 mm w.eq. Copyright © 2009 John Wiley & Sons, Ltd.

Description: Roughness elements at the soil surface (e.g. crop residues, rock fragments, vegetation, geotextiles) strongly reduce the erosivity of overland flow (both interrill and concentrated overland flow) and hence soil detachment rates. Common methods for shear stress partitioning that allow the calculation of effective flow shear stress in the presence of roughness elements originate from river hydraulics but seem invalid for overland flow. An alternative method to estimate the effective flow shear stress in the presence of a soil surface cover has been presented and tested for soil detachment by concentrated runoff on soil surfaces covered by crop residues by Knapen et al., (2008). In this method, the estimation of effective flow shear stress is based on the recalculation of the hydraulic radius for covered soil surfaces using flow hydraulics on uncovered surfaces. However, the applicability of this method for roughness elements different from crop residues and under field conditions needs to be tested to confirm its validity. Therefore, runoff data from three experimental studies (conducted on geotextile and grassed-covered soil surfaces) are analysed in this study. The results show that effective flow shear stress, calculated using this method, is not only a good soil detachment predictor for soil surfaces covered with crop residues but also for the tested soil surfaces with a vegetation or geotextile cover. However, the geotextile experiments point to one of the shortcomings of the method. At high flow shear stress levels, vortex erosion due to flow turbulence is reported for the thickest geotextiles. These flow turbulences are not accounted for since the method is based on average flow characteristics. Copyright © 2009 John Wiley & Sons, Ltd.

Description: Excessive fine sediment deposition on the river channel bed together with colmation of finer sediments within the hyporheic are now linked to the degradation of the aquatic habitats of gravel bed rivers in permeable catchments. Previous studies of chalk rivers (associated with outcrops of calcareous rock) have demonstrated the important role of aquatic vegetation in trapping fine sediment on the river channel bed. This research investigated the spatio-temporal patterns and composition of fine sediment stored in two vegetated river reaches, in the Frome and Piddle catchments, Dorset (UK), with contrasting hydrological regimes, in order to establish the importance of aquatic vegetation in controlling the magnitude and timing of sediment storage in chalk rivers. Monthly mapping of macrophyte and sediment cover at the two sites (Maiden Newton and Snatford Bridge, 2003-2004) revealed a cyclical pattern of sediment storage related to the growth and die-back of aquatic vegetation peaking at 66.8 kg m-2 in July 2003 at Maiden Newton, and 23.5 kg m-2 in October 2003 at Snatford Bridge. Sediment was stored within gravels and beneath vegetation in the margins and mid-channel locations at both sites. Significantly more sediment was stored beneath vegetation than within gravels. The spatio-temporal pattern of sediment storage at the reach scale and the composition of the stored sediments reflected the growth patterns and functional form (flexibility) of the dominant macrophytes Ranunculus penicillatus subsp. pseudofluitans (water crowfoot) and Rorippa nasturtium aquaticum (watercress). Finally, the paper discusses the implications of reach-scale patterns in sediment storage for contaminant storage. Copyright © 2009 John Wiley & Sons, Ltd.

Description: Spatial distribution of evapotranspiration (ET) over a complex terrain is estimated using a new approach of the conventional two-source energy balance (TSEB) model by considering the effect of topography (difference in slope and aspect). We name this approach topography considered two-source energy balance (T2SEB) model. The novelty of this model is the estimation of incoming shortwave solar radiation considering slope, aspect, altitude, latitude, longitude, and the day of calculation in the TSEB model, so that the new model should have wider applicability than existing models over topographically complex areas. In this study, high spatial resolution Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) data and meteorological data are used. ET over a complex terrain of Nagoya, Japan, on three different dates, 4 November 2005, 25 May 2004 and 30 October 2003, is estimated using both TSEB and T2SEB models. To validate both models, estimated results are compared with ground observation data at the flux tower site. Moreover, estimated results from TSEB and T2SEB models are compared in five different locations of different topography within the study area. Variation of net radiation absorbed by the surface (Rn) with topographical variables is also studied with the help of scatter plots. Estimated results for all three dates agreed within ±75 W m-2 with calculated values from both models at the flux tower site. TSEB underestimated/overestimated ET in sunlit/shaded areas in hilly areas. The T2SEB model estimated ET in hilly areas better than the TSEB model. Copyright © 2009 John Wiley & Sons, Ltd.

Description: For an experimental field site at the River Leith, United Kingdom, the spatial and temporal distribution of nitrate was observed along the upwelling flow path from groundwater to surface water. The study was carried out during baseflow conditions for two successive years. For two contrasting stream reaches, the physical and chemical characteristics of streambed sediment cores were analysed together with observations of hydraulic head, dissolved oxygen, redox and nitrogen speciation using an array of nested streambed piezometers. Pressure head gradients in the streambed piezometers showed that upwelling flows dominated the exchange between groundwater and surface water throughout the observation period. Infiltration of surface water into the streambed was not evident at depths below 10 cm. Pore water collected from sediment cores and streambed piezometers showed spatially variable redox conditions and nitrogen speciation within up to 100 cm depth in the streambed. In particular, nitrate concentrations along upwelling flow paths appeared to follow two opposite trends, with both decreasing and increasing nitrate concentrations being observed at different points in the experimental reach. The observed changes of nitrate concentrations in the upwelling groundwater are restricted to the loose superficial sediments that overlay the sandstone bedrock and do not appear to coincide with surface water-groundwater mixing in the streambed. The magnitude of variation in nitrate concentration along the upwelling flow path to the streambed appears to be governed by the sediment structure and characteristics in the two contrasting field sites. The results suggest that changes in redox status and pore water nitrate concentrations in the hyporheic may occur at depths greater than surface water infiltration into the streambed and may call for new conceptual understanding of hyporheic nutrient transformations. Copyright © 2009 John Wiley & Sons, Ltd.

Description: Attention has been given to baseflow in large rivers, but up to now, no study on baseflow for the Yangtze River in combination with extreme drought and extensive human activities has been carried out. Discharge data in 2000-2005 and in the extreme drought years, 1978 and 2006, at stations along the main stream, lakes and distributaries of the Yangtze River were collected to analyse the features of baseflow in 2006 by using baseflow separation technique, HYSEP. It can be seen that the baseflow relative to the streamflow in 2006 was greater than those in other years. The variation of baseflow discharge in the Upper Yangtze River Stream (UYRS) was larger than that in the Mid-Lower Yangtze River Stream (MLYRS). Human activities in MLYRS are more intensive than that in the UYRS and the baseflow discharge was greater. The baseflow is influenced by the extreme climate and human activities along the Yangtze River with the former being the dominant factor in 2006. The contribution of human interference to baseflow discharge was about 10% in 2006. © 2009 John Wiley & Sons, Ltd.

Description: Earlier efforts have been geared towards modelling the hydrological water balance of the Mackenzie River basin and its sub-basins using a coupled land surface-hydrological model for the Canadian cold region known as WATCLASS. The goal of this current study is to effectively inter-compare the resulting total water storage anomalies estimated from the gravity recovery and climate experiment (GRACE) satellite analysis with those estimated from the atmospheric-based water balance approach as well as the model output from WATCLASS over the 1.8 × 106 km2 Mackenzie River basin in Canada. Since the success of the parameter estimation stage of the coupled land surface-hydrological model, WATCLASS over this large catchment, was entirely based on a goodness of fit between the simulated and observed flows, it is often desirable to assess the reliability of the generated state variables prior to concluding on the overall efficiency of this model in reproducing the relevant hydrological processes over this region. A major challenge here lies in finding suitable dataset with which this comparison can be made to further assess the ability of the model in accurately reproducing other mass fluxes. The outcome of this inter-comparison reveals the potential application of the GRACE-based approach as a veritable tool required for the closure of the hydrological water balance of the Mackenzie River basin as well as serving as a dependable source of data for the calibration of traditional hydrological models. Copyright © 2009 John Wiley & Sons, Ltd.

Description: The hydrological component of the soil and water assessment tool (SWAT) model is adapted for two Ethiopian catchments based on primary knowledge of the coherence spectrum between rainfall and stream flow data. Spectrum analysis using the available nearby climatic data is made to limit the temporal and spatial scales (inverse rate coefficients) subject to the calibration of compartmentalized runoff models. The exclusion of unwarranted time scales in the calibration implies that the model efficiency (r2 values) decrease only moderately between calibration and validation, and the optimization is focused on warranted problems. On the basis of the available data for the two Ethiopian catchments, the implication is that only periods longer than about 50 days can be reliably evaluated in the model. The model structure of SWAT for the surface runoff and groundwater flow response is modified to make the time scales consistent with the results of the spectrum analysis. An optimization algorithm is developed to constrain and combine the model parameters with the spectrum analysis results. Copyright © 2009 John Wiley & Sons, Ltd.

Description: The present study aims to develop a hybrid multi-model using the soft computing approach. The model is a combination of a fuzzy logic, artificial neural network (ANN) and genetic algorithm (GA). While neural networks are low-level computational structures that perform well dealing with raw data, fuzzy logic deal with reasoning on a higher level by using linguistic information acquired from domain experts. However, fuzzy systems lack the ability to learn and cannot adjust themselves to a new environment. Moreover, experts occasionally make mistakes and thus some rules used in a system may be false. A network type structure of the present hybrid model is a multi-layer feed-forward network, the main part is a fuzzy system based on the first-order Sugeno fuzzy model with a fuzzification and a defuzzification processes. The consequent parameters are determined by least square method. The back-propagation is applied to adjust weights of network. Then, the antecedent parameters of the membership function are updated accordingly by the gradient descent method. The GA was applied to select the fuzzy rule. The hybrid multi-model was used to forecast the flood level at Chiang Mai (under the big flood 2005) and the Koriyama flood (2003) in Japan. The forecasting results are evaluated using standard global goodness of fit statistic, efficient index (EI), the root mean square error (RMSE) and the peak flood error. Moreover, the results are compared to the results of a neuro-genetic model (NGO) and ANFIS model using the same input and output variables. It was found that the hybrid multi-model can be used successfully with an efficiency index (EI) more than 0.95 (for Chiang Mai flood up to 12 h ahead forecasting) and more than 0.90 (for Koriyama flood up to 8 h ahead forecasting). In general, all of three models can predict the water level with satisfactory results. However, the hybrid model gave the best flood peak estimation among the three models. Therefore, the use of fuzzy rule base, which is selected by GA in the hybrid multi-model helps to improve the accuracy of flood peak. Copyright © 2009 John Wiley & Sons, Ltd.

Description: In urban areas with a high building density, features such as roads, buildings and river dykes significantly affect flow dynamics and flood propagation. This should therefore be accounted for in the model set-up. While 2D hydraulic models of densely urban areas are at the forefront of current research into flood inundation mechanisms, these models are constrained by inadequate parameters of topography and insufficient data. In order to solve these problems, topographic information obtained from digital elevation model (DEM) is directly programmed into the urban inundation model for a densely urban area, without exchanging the input data. In this paper, the extraction of building area is described using a tight coupling approach within a GIS environment, and its influence on the extent of flood inundation with a high building density is estimated. Copyright © 2009 John Wiley & Sons, Ltd.

Description: In this study, monthly and annual Upper Blue Nile Basin rainfall data were analyzed to learn the rainfall statistics and its temporal and spatial distribution. Frequency analysis and spatial characterization of rainfall in the Upper Blue Nile Basin are presented. Frequency analysis was performed on monthly basin rainfall. Monthly basin average rainfall data were computed from a network of 32 gauges with varying lengths of records. Monthly rainfall probability distribution varies from month to month fitting Gamma-2, Normal, Weibull and Log-Normal distributions. The January, July, October and November basin rainfall fit the Gamma-2 probability distribution. The February, June and December ones fit Weibull distribution. The March, April, May and August rainfall fit Normal distribution. The September rainfall fits Log-Normal distribution. Upper Blue Nile Basin is relatively wet with a mean annual rainfall of 1423 mm (1960-2002) with a standard deviation of 125 mm. The annual rainfall has a Normal probability distribution. The 100-year-drought basin annual rainfall is 1132 mm and the 100-year-wet basin annual rainfall is 1745 mm. The dry season is from November through April. The wet season runs from June through September with 74% of the annual rainfall. October and May are transition months. Monthly and annual rainfalls for return periods 2-, 5-, 10-, 25-, 50- and 100-year dry and wet patterns are presented. Spatial distribution of annual rainfall over the basin is mapped and shows high variation with the southern tip receiving as high as 2049 mm and the northeastern tip as low as 794 mm annual average rainfall. Copyright © 2009 John Wiley & Sons, Ltd.

Description: The Yiluo River is the largest tributary for the middle and lower reaches of the Yellow River below Sanmenxia Dam. Changes of the hydrological processes in the Yiluo River basin, influenced by the climatic variability and human activities, can directly affect ecological integrity in the lower reach of the Yellow River. Understanding the impact of the climatic variability and human activities on the hydrological processes in the Yiluo River basin is especially important to maintain the ecosystem integrity and sustain the society development in the lower reach of the Yellow River basin. In this study, the temporal trends of annual precipitation, air temperature, reference evapotranspiration (ET0) and runoff during 1961-2000 in the Yiluo River basin were explored by the Mann-Kendall method (M-K method), Yamamoto method and linear fitted model. The impacts of the climatic variability and vegetation changes on the annual runoff were discussed by the empirical model and simple water balance model and their contribution to change of annual runoff have been estimated. Results indicated that (i) significant upwards trend for air temperature and significant downwards trend both for precipitation and ET0 were detected by the M-K method at 95% confidence level. And the consistent trends were obtained by the linear fitted model; (ii) the abrupt change started from 1987 detected by the M-K method and Yamamoto method, and so the annual runoff during 1961-2000 was divided into two periods: baseline period (1961-1986) and changeable period (1987-2000); and (iii) the vegetation changes were the main cause for change of annual runoff from baseline period to changeable period, and climatic variability contributed a little to the change of annual runoff of the Yiluo River. Copyright © 2009 John Wiley & Sons, Ltd.

Description: By applying wavelet-based empirical orthogonal function (WEOF) analysis to gridded precipitation (P) and empirical orthogonal function (EOF) analysis to gridded air temperature (T), potential evapotranspiration (PET), net precipitation (PPET) and runoff (Q), this paper examines the spatial, temporal and frequency patterns of Alberta's climate variability. It was found that only WEOF-based precipitation patterns, possibly modulated by El Nino Southern Oscillation (ENSO) and Pacific Decadal Oscillation(PDO), delineated Alberta into four major regions which geographically represent northern Alberta Boreal forests, southern Alberta grasslands and Aspen Parklands and the Rocky Mountains and Foothills. The leading mode of wavelet-based precipitation variability WPC1 showed that between 1900 and 2000, a wet climate dominated northern Alberta with significant 4-8, 11 and 25-year periodic cycles, while the second mode WPC2 showed that between 1960 and 2000, southern Alberta grasslands were characterized by decreasing precipitation, dominated by 11-year cycles, and the last two modes WPC3 and WPC4 were characterized by 4-7 and 25-year cycles and both delineated regions where moisture from the Pacific Ocean penetrated the Rocky Mountains, accounted for much of the sub-alpine climate. These results show that WEOF is superior to EOF in delineating Alberta precipitation variability to sub-regions that more closely agree with its eco-climate regions. Further, it was found that while WPC2 could not explain runoff variations in southern Alberta, WPC1, WPC3 and WPC4 accounted for runoff variability in their respective sub-regions. Copyright © 2009 John Wiley & Sons, Ltd.

Description: How much data is needed for calibration of a hydrological catchment model? In this paper we address this question by evaluating the information contained in different subsets of discharge and groundwater time series for multi-objective calibration of a conceptual hydrological model within the framework of an uncertainty analysis. The study site was a 5D6-km2 catchment within the Forsmark research site in central Sweden along the Baltic coast. Daily time series data were available for discharge and several groundwater wells within the catchment for a continuous 1065-day period. The hydrological model was a sitespecific modification of the conceptual HBV model. The uncertainty analyses were based on a selective Monte Carlo procedure. Thirteen subsets of the complete time series data were investigated with the idea that these represent realistic intermittent sampling strategies. Data subsets included split-samples and various combinations of weekly, monthly, and quarterly fixed interval subsets, as well as a 53-day 'informed observer' subset that utilized once per month samples except during March and April - the months containing large and often dominant snow melt events-when sampling was once per week. Several of these subsets, including that of the informed observer, provided very similar constraints on model calibration and parameter identification as the full data record, in terms of credibility bands on simulated time series, posterior parameter distributions, and performance indices calculated to the full dataset. This result suggests that hydrological sampling designs can, at least in some cases, be optimized. Copyright © 2009 John Wiley & Sons, Ltd.

Description: The results of a study evaluating the recharge/discharge conditions of an unconfined stressed granitic aquifer situated in a semi-arid region of Andhra Pradesh, Southern India are presented. Over the last three decades, excessive withdrawal of groundwater has drastically lowered the water table to the bedrock. The watershed studied was divided into four zones based on geomorphology and hydrogeological conditions. Using environmental chloride data pertaining to groundwater, soil depth profiles, and some hydrogeologic and hydrochemical observations, a recharge model for the watershed was developed. The model revealed that the bulk of the vertical recharge in the western elevated land occurs through preferred pathways and that a small fraction occurs through the soil matrix. In addition, the watershed has a poor hydrogeologic fabric, as indicated by the small range of matrix flow recharge (1 to 1.5% of rainfall) among the four zones. The dominating preferential flow was high (∼16% of the annual average rainfall) in the valley fills, but decreased to 5-5.5% in the plains. Furthermore, although the bulk of the recharge occurs vertically, considerable lateral movement of groundwater down the slope indicates that sequential hydrochemical changes occur. Distinct geomorphological features that exist in the watershed support the proposed model. Situations similar to those described above may exist in numerous watersheds in the granitic hard rock region; therefore, information obtained from investigations conducted in this watershed can aid in the development of plans enabling the sustainable exploitation of watersheds that have not yet been developed, as well as implementation of appropriate rainwater conservation measures in over-exploited watersheds. Copyright © 2009 John Wiley & Sons, Ltd.

Description: In the shallow groundwater areas of the North China Plain (NCP), precipitation infiltration and evapotranspiration in the vertical direction are the main processes of the water cycle, in which the unsaturated zone plays an important role in the transformation process between precipitation and groundwater. In this paper, two typical sites in Cangzhou (CZ) and Hengshui (HS) of Hebei province with shallow water tables were selected to analyse the relationship among precipitation, soil water and groundwater. At each site, precipitation, soil water at depths 10, 20, 30, 50, 70, 100, 150, 200, 300 cm, and groundwater were sampled to analyse the stable isotope compositions of hydrogen and oxygen. The soil water potentials at the corresponding depths were observed. Although the climates at the two sites are similar, there are some differences in the infiltration process, soil water movement and groundwater recharge sources. Evaporation occurred at the upper depths, which led to the decrease of soil potential and the enrichment of heavy isotopes. At the CZ site, precipitation infiltrated with piston mode, and an obvious mixture effect existed during the infiltration process. Preferential flow may exist in the soil above 100 cm depth. However, at the HS site soil water moved in piston mode, and groundwater was mainly recharged by precipitation. When precipitation recharged the groundwater it experienced a strong evaporation effect. The results of the soil water movement mechanism provides the transformation relationship among precipitation, soil water and groundwater in the middle and eastern NCP. Copyright © 2009 John Wiley & Sons, Ltd.

Description: Previous experimental studies of capillary barriers have identified highly hysteretic soil moisture retention characteristics in the materials used. In this study, numerical modelling is used to analyse the role of soil moisture hysteresis in capillary barrier functioning. Comparisons between published experimental results and model simulations indicate that soil moisture hysteresis was a necessary inclusion in the modelling approach to adequately reproduce pore water pressure distributions and the timing of breakthrough occurrences. Under hypothetical intermittent infiltration and evaporation conditions, the predicted volumetric water content in the moisture retention layer was significantly different for hysteretic and non-hysteretic models. The hysteresis effect was found to be dependent on the nature of infiltration-evaporation cycling, although the predicted volume of flow through the hysteretic barrier was lower than that of the non-hysteretic case, regardless of the nature of the cyclic upper boundary conditions. For practical engineering designs, where the water leakage through the barrier is the primary concern, the inclusion of soil moisture hysteresis in numerical modelling is needed. Copyright © 2009 John Wiley & Sons, Ltd.

Description: Although river ice is a major component of the cryosphere and is particularly important to many river processes, including extreme events, its full geographical coverage has never been documented. Recognizing that the freeze-up and breakup of river ice is closely linked to the timing of 0 °C air temperatures, this study analyses the spatial extent of river networks relative to the location of three 0 °C isotherm periods. These were defined to represent a suite of ice-affected conditions that would be experienced for 6, 3 or 0·5 month periods, the briefest interval possibly leading only to a very thin and transient ice cover or simply border/frazil ice formation. Four different GIS databases were used to represent the river networks. The percentages of the total Northern Hemisphere land mass (average river network) influenced by cold temperatures conducive to ice formation were 52, 45 and 25 (56, 47 and 28), respectively. The related southern position of the isotherms ranged from 33°N, 35°N and 50°N in central North America to a nearly consistent 27°N for Eurasia, reflecting the influence of the high-elevation central plateau region. Also identified are the lengths of major rivers that fall within the three 0 °C isotherm boundaries. Included are some of the world's largest rivers including the Lena, Mackenzie, Ob, Yellow, Yukon and Yenisey rivers, although their percentage of ice-affected coverage varied for the three isotherm periods from a consistent 100% for the Lena and Yukon rivers to as little as 23% at the 6-month interval for the Yellow River. Copyright © 2009 Her Majesty the Queen in right of Canada.

Description: Storm events are major transporters of faecal microbial contaminants, but few studies have reported storm loads or concentration dynamics in relation to discharge or other pollutants, notably fine sediment. Episodically, high loads of faecal contamination during storm flows impact downstream uses of water bodies, particularly contact recreation and shellfish harvesting. We examined the storm dynamics of Escherichia coli, turbidity and discharge in the mixed land use Motueka catchment (2047 km2; 60% forest and 19% pasture) to gain insights into E. coli sources and transport. We also explored different approaches for calculating E. coli loads. Discharge and field turbidity were recorded continuously, and E. coli concentrations were sampled during events, over a 13-month period near the mouth of the Motueka River. E. coli loads were estimated by interpolation, averaging estimators and by using linear regression with smearing correction of the log-transformed variables: discharge, turbidity, and both turbidity and discharge. The annual E. coli load was dominated (~98%) by export during events. Comparison of monthly monitoring with the intensive storm monitoring campaign suggests that simple stratification of the sampling into storm and baseflow would greatly improve export estimates. E. coli peak concentrations always preceded discharge and turbidity peaks (which had similar timing). Turbidity can be a useful surrogate for faecal microbes in smaller catchments, but in the Motueka turbidity was no better for predicting E. coli concentration than discharge. Runoff from grazed pasture and direct deposition from livestock are probably the ultimate E. coli sources in the Motueka catchment. However, in-channel stores seem to dominate E. coli dynamics during events and account for the typical feature of bacterial concentrations peaking ahead of discharge and turbidity. This study demonstrates the importance of storm events to faecal microbial loads and shows that E. coli concentration dynamics may contrast with those of turbidity. © 2009 John Wiley & Sons, Ltd.

Description: Spatial and temporal patterns of areal snowcover depletion (SCD) were studied over a small (〈0.6 km2) alpine cirque within the Canadian Rocky Mountains using a combined approach of daily acquisition of remotely sensed imagery, together with meteorological observations and snowmelt modelling. Digital terrestrial photographs were georeferenced using a novel software tool together with a high-resolution digital elevation model and used to derive measurements of fractional snowcovered area (SCA) over the cirque. Manual snow surveys carried out in the pre-melt period were used to describe the initial frequency distribution of snow water equivalent (SWE) values over the cirque, and indicated a lognormal distribution of SWE when surveys were stratified by terrain features. Rates of snowmelt were simulated using a physically based snowmelt energy balance model, Snobal, driven by observed meteorological conditions at a nearby station, which were adjusted for slope orientation and exposure by making corrections to observed incoming shortwave and longwave radiation components in the cold regions hydrological model platform. Simulated melt rates were then applied to the approximated SWE distributions to model the decline in SCA over the spring. The model was found to perform well for the simulation of snowmelt based on point observations of SWE at the meteorological station, and produced a close correspondence between simulated and observed SCD curves representing two opposing slopes within the cirque. The results show that both the pre-melt distributions of SWE and the spring melt rates exhibit considerable spatial variability between distinct slope units within the cirque, and that this variability has a significant impact on simulated SCD. Assuming a unimodal pre-melt frequency distribution and conditions of spatially uniform snowmelt over complex terrain such as this can lead to large errors in the simulation results. It is suggested that modelling applications intended to represent snowmelt dynamics and areal SCD in similar alpine environments consider the effects of spatial variation in SWE distribution and melt energetics between slopes. Copyright © 2009 John Wiley & Sons, Ltd.

Description: An extensive dataset (230 precipitation gauges and 79 stream gauges) was used to analyse rainfall-runoff relationships in 10 subregions of a 482000 km2 area in the south-eastern USA (Maryland, Virginia, North Carolina, South Carolina and Georgia). The average annual rainfall and runoff for this study area between 1938 and 2005 were 1201 and 439 mm, respectively. Average runoff/rainfall ratios during this period varied between 0.24 in the southernmost Coastal Plain subregion to 0.64 in the Blue Ridge Province. Watershed elevation and relief are the principal determinants governing the conversion of rainfall to runoff. Temporal rainfall variation throughout the south-eastern USA ranges from ∼40% above and below normal while the variation for runoff is higher, from -75% to +100%. In any given year there can exist a ±25-50% error in predicted runoff deviation using the annual rainfall-runoff regression. Fast Fourier Transform and autoregressive spectral analysis revealed dominant cyclicities for rainfall and runoff between 14 and 17 years. Secondary periodicities were typically between 6-7 and 10-12 years. The inferred cyclicity may be related to ENSO and/ or Central North Pacific atmospheric phenomena. Mann-Kendall analyses indicate that there were no consistent statistically significant temporal trends with respect to southeastern US rainfall and runoff during the study period. The results of U-tests similarly indicated that rainfall between 1996 and 2005 was not statistically higher or lower than during earlier in the study period. Copyright © 2008 John Wiley & Sons, Ltd.

Description: Land-cover/climate changes and their impacts on hydrological processes are of widespread concern and a great challenge to researchers and policy makers. Kejie Watershed in the Salween River Basin in Yunnan, south-west China, has been reforested extensively during the past two decades. In terms of climate change, there has been a marked increase in temperature. The impact of these changes on hydrological processes required investigation: hence, this paper assesses aspects of changes in land cover and climate. The response of hydrological processes to land-cover/climate changes was examined using the Soil and Water Assessment Tool (SWAT) and impacts of single factor, land-use/climate change on hydrological processes were differentiated. Land-cover maps revealed extensive reforestation at the expense of grassland, cropland, and barren land. A significant monotonic trend and noticeable changes had occurred in annual temperature over the long term. Long-term changes in annual rainfall and streamflow were weak; and changes in monthly rainfall (May, June, July, and September) were apparent. Hydrological simulations showed that the impact of climate change on surface water, baseflow, and streamflow was offset by the impact of land-cover change. Seasonal variation in streamflow was influenced by seasonal variation in rainfall. The earlier onset of monsoon and the variability of rainfall resulted in extreme monthly streamflow. Land-cover change played a dominant role in mean annual values; seasonal variation in surface water and streamflow was influenced mainly by seasonal variation in rainfall; and land-cover change played a regulating role in this. Surface water is more sensitive to land-cover change and climate change: an increase in surface water in September and May due to increased rainfall was offset by a decrease in surface water due to land-cover change. A decrease in baseflow caused by changes in rainfall and temperature was offset by an increase in baseflow due to land-cover change. Copyright © 2009 John Wiley & Sons, Ltd.

Description: This paper gives an overview on the regional hydrological impact of the heatwave, which affected Europe in the summer of 2003. We investigated the small, glacierized Goldbergkees basin in the Austrian Alps, which is situated directly beneath the high Alpine Sonnblick observatory (3106 m a.s.l.). We analysed the long-term air temperature time series and quantified the extreme anomaly of the mean summer (JJA) air temperature for 4.4 times the standard deviation of the long-term mean (1886-2000). The mean summer air temperature was 4.7°C. In 2003, the solid fraction of precipitation was only 35%. This was the lowest value observed from 1927 to 2005. To quantify the impact of the warm temperatures on the Goldbergkees glacier positive degree-day sums were calculated. The 'hot' conditions of the summer of 2003 rapidly melted the snow covering the glacier and finally melted the ice beneath. The winter balance of the Goldbergkees did not show anomalies. The specific net balance of Goldbergkees was -1.8 m water equivalent (w.e.) for the 2002/2003 period and has been the most negative observed. Snowmelt was accelerated by low albedo, which was a result of Sahara dust-falls. The hydrological response unit (HRU)-based model PREVAH was applied to simulate hourly runoff, which was observed at the outlet of this small and topographically heterogeneous basin. All components contributing to runoff were separated. The model was driven using hourly meteorological data gained from the Sonnblick observatory. Snow- and icemelt were modelled based on an advanced temperature index-based approach. The model was validated using observed glacier mass balance data. The maximum simulated icemelt rate was 2.7 mm/h (4.9 mm/h assigned to the glacier surface). During August 2003, glaciermelt contributed 81% to the total runoff. Copyright © 2008 John Wiley & Sons, Ltd.

Description: The seasonal snow cover duration depends on climatic conditions, vegetation and topography. Conventional approaches of snow cover monitoring, based on point measurements or remote sensing techniques, are not suitable for meso-scale spatial and temporal observations, or for analyses of the snow extent. However, these meso-scale analyses are the basis for an understanding of ecological, hydrological and climatic systems in high mountains. Therefore, new approaches are required to monitor and to analyse the meso-scale spatial snow cover distribution. In the presented study, we used 30 point measurement data and terrestrial images, which were taken by two digital cameras. The micro-scale point measurements show the snow cover duration in several topographical positions. The terrestrial images monitor the variation of snow extent on a northwest and southeast-facing slope. They provide a spatial resolution of 10 m, and due to bad weather conditions, a temporal resolution of 5 days. Both, the micro- as well as meso-scale data enabled statistical analyses of the impact of topography on snow cover duration. The combination of terrestrial images and point measurements facilitated the verification of the representativeness of point measurements as well as their extrapolation capabilities. One important conclusion of the presented study is that snow cover duration can be explained just partly by topographical features. Copyright © 2008 John Wiley & Sons, Ltd.

Description: We evaluated sources and pathways of groundwater recharge for a heterogeneous alluvial aquifer beneath an agricultural field, based on multi-level monitoring of hydrochemistry and environmental isotopes of a riverside groundwater system at Buyeo, Korea. Two distinct groundwater zones were identified with depth: (1) a shallow oxic groundwater zone, characterized by elevated concentrations of NO3- and (2) a deeper (〉10-14 m from the ground surface) sub-oxic groundwater zone with high concentrations of dissolved Fe, silica, and HCO3-, but little nitrate. The change of redox zones occurred at a depth where the aquifer sediments change from an upper sandy stratum to a silty stratum with mud caps. The δ18O and δ2H values of groundwater were also different between the two zones. Hydrochemical and δ18O-δ2H data of oxic groundwater are similar to those of soil water. This illustrates that recharge of oxic groundwater mainly occurs through direct infiltration of rain and irrigation water in the sandy soil area where vegetable cropping with abundant fertilizer use is predominant. Oxic groundwater is therefore severely contaminated by agrochemical pollutants such as nitrate. In contrast, deeper sub-oxic groundwater contains only small amounts of dissolved oxygen (DO) and NO3-. The 3H contents and elevated silica concentrations in sub-oxic groundwater indicate a somewhat longer mean residence time of groundwater within this part of the aquifer. Sub-oxic groundwater was also characterized by higher δ18O and δ2H values and lower d-excess values, indicating significant evaporation during recharge. We suggest that recharge of sub-oxic groundwater occurs in the areas of paddy rice fields where standing irrigation and rain water are affected by strong evaporation, and that reducing conditions develop during subsequent sub-surface infiltration. This study illustrates the existence of two groundwater bodies with different recharge processes within an alluvial aquifer. © 2009 John Wiley & Sons, Ltd.

Description: Stream-subsurface exchange strongly influences the transport of contaminants, fine particles, and other ecologically relevant substances in streams. We used a recirculating laboratory flume (220 cm long and 20 cm wide) to study the effects of particle size, overlying velocity, and biofilm formation on stream-subsurface exchange of particles. Sodium chloride was used as a non-reactive dissolved tracer and 1- and 5-μm fluorescent microspheres were used as particulate tracers. Surface-subsurface exchange was observed with a clean sand bed and a bed colonized by an autotrophic-heterotrophic biofilm under two different overlying velocities, 0·9 and 5cm s-1. Hydrodynamic interactions between the overlying flow and sand bed resulted in a reduction of solute and particle concentrations in the water column, and a corresponding accumulation of particles in both the sediments and in the biofilm. Increasing overlying velocity and particle size resulted in faster removal from the overlying water due to enhanced mass transfer to the bed. The presence of the biofilm did not affect solute exchange under any flow condition tested. The presence of the biofilm significantly increased the deposition of particles under an overlying velocity of 5 cm s-1, and produced a small but statistically insignificant increase at 0·9 cm-1. The particles preferentially deposited within the biofilm matrix relative to the underlying sand. These results demonstrate that hydrodynamic transport conditions, particle size, and biofilm formation play a key role in the transport of suspended particles, such as inorganic sediments, particulate organic matter, and pathogenic microorganisms in freshwater ecosystems, and should be taken into consideration when predicting the fate and transport of particles and contaminants in the environment. © 2009 John Wiley & Sons, Ltd.

Description: In this study, the nature of basin-scale hydroclimatic association for Indian subcontinent is investigated. It is found that, the large-scale circulation information from Indian Ocean is also equally important in addition to the El Niño-Southern Oscillation (ENSO), owing to the geographical location of Indian subcontinent. The hydroclimatic association of the variation of monsoon inflow into the Hirakud reservoir in India is investigated using ENSO and EQUatorial INdian Ocean Oscillation (EQUINOO, the atmospheric part of Indian Ocean Dipole mode) as the large-scale circulation information from tropical Pacific Ocean and Indian Ocean regions respectively. Individual associations of ENSO & EQUINOO indices with inflow into Hirakud reservoir are also assessed and found to be weak. However, the association of inflows into Hirakud reservoir with the composite index (CI) of ENSO and EQUINOO is quite strong. Thus, the large-scale circulation information from Indian Ocean is also important apart form the ENSO. The potential of the combined information of ENSO and EQUINOO for predicting the inflows during monsoon is also investigated with promising results. The results of this study will be helpful to water resources managers due to fact that the nature of monsoon inflow is becoming available as an early prediction. Copyright © 2009 John Wiley & Sons, Ltd.

Description: The Puget Sound basin in northwestern Washington, USA has experienced substantial land cover and climate change over the last century. Using a spatially distributed hydrology model (the Distributed Hydrology-Soil-Vegetation Model, DHSVM) the concurrent effects of changing climate (primarily temperature) and land cover in the basin are deconvolved, based on land cover maps for 1883 and 2002, and gridded climate data for 1915-2006. It is found that land cover and temperature change effects on streamflow have occurred differently at high and low elevations. In the lowlands, land cover has occurred primarily as conversion of forest to urban or partially urban land use, and here the land cover signal dominates temperature change. In the uplands, both land cover and temperature change have played important roles. Temperature change is especially important at intermediate elevations (so-called transient snow zone), where the winter snow line is most sensitive to temperature change - notwithstanding the effects of forest harvest over the same part of the basin. Model simulations show that current land cover results in higher fall, winter and early spring streamflow but lower summer flow; higher annual maximum flow and higher annual mean streamflow compared with pre-development conditions, which is largely consistent with a trend analysis of model residuals. Land cover change effects in urban and partially urban basins have resulted in changes in annual flow, annual maximum flows, fall and summer flows. For the upland portion of the basin, shifts in the seasonal distribution of streamflows (higher spring flow and lower summer flow) are clearly related to rising temperatures, but annual streamflow has not changed much. Copyright © 2009 John Wiley & Sons, Ltd.

Description: Climate changes brought on by increasing greenhouse gases in the atmosphere are expected to have a significant effect on the Pacific Northwest hydrology during the 21st century. Many climate model simulations project higher mean annual temperatures and temporal redistribution of precipitation. This is of particular concern for highly urbanized basins where runoff changes are more vulnerable to changes in climate. The Rock Creek basin, located in the Portland metropolitan area, has been experiencing rapid urban growth throughout the last 30 years, making it an ideal study area for assessing the effect of climate and land cover changes on runoff. A combination of climate change and land cover change scenarios for 2040 with the semi-distributed AVSWAT (ArcView Soil and Water Assessment Tool) hydrological model was used to determine changes in mean runoff depths in the 2040s (2030-2059) from the baseline period (1973-2002) at the monthly, seasonal, and annual scales. Statistically downscaled climate change simulation results from the ECHAM5 general circulation model (GCM) found that the region would experience an increase of 1.2 °C in the average annual temperature and a 2% increase in average annual precipitation from the baseline period. AVSWAT simulation shows a 2.7% increase in mean annual runoff but a 1.6% decrease in summer runoff. Projected climate change plus low-density, sprawled urban development for 2040 produced the greatest change to mean annual runoff depth (+5.5%), while climate change plus higher-density urban development for 2040 resulted in the smallest change (+5.2%), when compared with the climate and land cover of the baseline period. This has significant implications for water resource managers attempting to implement adaptive water resource policies to future changes resulting from climate and urbanization. Copyright © 2008 John Wiley & Sons, Ltd.

Description: We investigated the accumulation and biogeochemical cycling of organic matter beneath Ranunculus plants in a lowland river. Organic carbon accumulated beneath the plants at a mean rate of 20 mmol C m-2 h-1. Annual gross primary production for both Ranunculus and its biofilm, and the microphytobenthos, could account for 26% of the carbon accumulated. The remainder was attributable to organic carbon in both suspended particulate matter (77%) and that associated with sands saltating along the bottom (33%). Maximum carbon oxidation occurred in spring and early summer and declined thereafter. The efflux of CO2 was greater than the carbon equivalents due to reduction of O2, NO3- and SO42- measured at the surface, which suggested a significant contribution to carbon oxidation from the subsurface and some oxidation via alternative electron acceptors. The peak in carbon oxidation could not be accounted for by either rising temperature or primary production but tracked the quality of recently deposited allochthonous organic matter. The ratio of carbon oxidation to total organic carbon accumulation suggested that 19% of the organic matter deposited was remineralised on an annual basis, although this reached 58% in June. We calculate that a total of 3.6 mol N m-2 y-1 was mineralised in the sediment, of which 11% could be accounted for by the measured efflux of NH4+. The remainder could be accounted for by the N demand from primary production (67% macrophytes/biofilm; 36% phytobenthos). Copyright © 2009 John Wiley & Sons, Ltd.

Description: Interception loss has an important influence on the water yield of forested areas. Nevertheless, in most studies stemflow is not measured, therefore the question of how to determine the feasibility of optimizing interception and stemflow parameters simultaneously by matching daily simulated throughfall to fortnightly measurements of cumulative throughfall is an important one. By applying a daily empirical interception model, a goodness fit of 2.2 mm/day is obtained between observed and simulated cumulative throughfall. However, by applying the simple but robust Linking Test, it was shown that the parameters are non-unique and falsely linked, i.e. inter-relationships between different vegetation parameter sets give similar throughfall but non-unique net precipitation. The Linking Test investigates the causes of obtaining falsely linked parameters and shows that objective equifinality is not the source of the problem. Objective equifinality occurs when an inappropriate objective function is used. The Linking Test also shows that falsely linked parameters are not caused by measuring throughfall on a non-daily basis (termed frequency sampling equifinality). By expanding the interception model to the second degree, it was found that the non-uniqueness is due to the inherent nature of interception and stemflow functions that behave similarly and therefore can easily compensate each other (termed similarity equifinality). It is also shown that a simple daily empirical exponential interception model developed for conifers in the uplands of the United Kingdom is suitable to model interception in Pinus radiata plantations in the Mediterranean climate of southern Australia by using only daily gross precipitation data and two parameters. Copyright © 2009 John Wiley & Sons, Ltd.

Description: Snow accumulation and ablation rule the temporal dynamics of water availability in mountain areas and cold regions. In these environments, the evaluation of the snow water amount is a key issue. The spatial distribution of snow water equivalent (SWE) over a mountain basin at the end of the snow accumulation season is estimated using a minimal statistical model (SWE-SEM). This uses systematic observations such as ground measurements collected at snow gauges and snow-covered area (SCA) data retrieved by remote sensors, here MODIS. Firstly, SWE-SEM calculates local SWE estimates at snow gauges, then the spatial distribution of SWE over a certain area using an interpolation method; linear regressions of the first two order moments of SWE with altitude. The interpolation has been made by both confining and unconfining the spatial domain by SCA. SWE-SEM is applied to the Mallero basin (northern Italy) for calculating the snow water equivalent at the end of the winter season for 6 years (2001-2007). For 2007, SWE-SEM estimates are validated through fieldwork measurements collected during an 'ad hoc' campaign on March 31, 2007. Snow-surveyed measurements are used to check SCA, snow density and SWE estimates. Copyright © 2009 John Wiley & Sons, Ltd.

Description: Grid-based distributed hydrological models are considered to be a very effective flood modelling tool for basin-wide flood risk analysis because of their capabilities of simulating river and surface inundations at high spatio-temporal resolutions by taking advantages of grid-based data from meteorological models, radar and satellite remote sensing. Selecting an appropriate grid size is critically important for any application of a grid-based model, which requires proper understanding of effects of grid sizes on simulated outcomes. The paper presents the outcomes of a study conducted to analyse the effects of grid resolution on simulated river peak flows and surface inundation in two selected river basins using a process-based distributed hydrological model. The outcomes show that grid resolution significantly affects the simulated river peak flows and surface inundation characteristics. In both cases, it has been found that the effects are mainly caused by changes of the topographic parameters as a result of changes of grid sizes. The reduction of average surface slope with the increase of grid size affects the simulated surface inundation extents and heights. There is a threshold resolution of digital elevation model (DEM) in the simulated flood inundation and beyond that the model outcomes become arbitrary. Averaged topographic values at coarse resolution beyond this threshold level do not represent any characteristics of locally elevated topographic features such as dykes, highways, etc. and their influence on flood inundation characteristics can be no more captured by the model. Copyright © 2008 John Wiley & Sons, Ltd.

Description: This paper evaluates the optimal spatial flood protection for people living with the threat of floods in the lower Mekong River region with respect to hydrology and economics. A hydrological numerical simulation contributes to an understanding of the relationship between flood control policy and inundation areas. The numerical simulation consists of a dynamic wave model in channels and a non-uniform flow model in inundation areas, which estimate the temporal and spatial dynamic distributions of water depth. In economics, an overlapping generations model expresses the economy's growth process considering flood magnitude and flood protection. This economic model is composed of industrial and agricultural production functions which are affected by flood control policies. The hydrological and economic models are verified by remote sensing images and data from the economic development of Thailand, respectively. Combining these two models, we can identify the area to protect and accept floods for regional development. Wide areas along the rivers should be flooded due to the benefits from fertilization for inundation agriculture in Cambodia. The conservation area should be about 2000 km2, and the spatial distribution of flooding should be identified. In the beginning of an economic growth period, there is little difference in the production of an inundation area in the range of 0-2000 km2. As the inundation area becomes larger, the production rate is larger in the stable growth period. This study explains that inundation agriculture should be maintained in riverside areas which supply much of the agricultural production in Cambodia. Copyright © 2008 John Wiley & Sons, Ltd.

Description: Knowledge of the internal renewable water resources of a country is strategic information which is needed for long-term planning of a nation's water and food security, among many other needs. New modelling tools allow this quantification with high spatial and temporal resolution. In this study we used the program Soil and Water Assessment Tool (SWAT) in combination with the Sequential Uncertainty Fitting program (SUFI-2) to calibrate and validate a hydrologic model of Iran based on river discharges and wheat yield, taking into consideration dam operations and irrigation practices. Uncertainty analyses were also performed to assess the model performance. The results were quite satisfactory for most of the rivers across the country. We quantified all components of the water balance including blue water flow (water yield plus deep aquifer recharge), green water flow (actual and potential evapotranspiration) and green water storage (soil moisture) at sub-basin level with monthly time-steps. The spatially aggregated water resources and simulated yield compared well with the existing data. The study period was 1990-2002 for calibration and 1980-1989 for validation. The results show that irrigation practices have a significant impact on the water balances of the provinces with irrigated agriculture. Concerning the staple food crop in the country, 55% of irrigated wheat and 57% of rain-fed wheat are produced every year in water-scarce regions. The vulnerable situation of water resources availability has serious implications for the country's food security, and the looming impact of climate change could only worsen the situation. This study provides a strong basis for further studies concerning the water and food security and the water resources management strategies in the country and a unified approach for the analysis of blue and green water in other arid and semi-arid countries. Copyright © 2008 John Wiley & Sons, Ltd.

Description: Evapotranspiration (ET) is one of the basic components of the hydrologic cycle and is essential for estimating irrigation water requirements. In this study, an artificial neural network (ANN) model for reference evapotranspiration (ET0) calculation was investigated. ANNs were trained and tested for arid (west), semi-arid (middle) and sub-humid (east) areas of the Inner Mongolia district of China. Three or four climate factors, i.e. air temperature (T), relative humidity (RH), wind speed (U) and duration of sunshine (N) from 135 meteorological stations distributed throughout the study area, were used as the inputs of the ANNs. A comparison was conducted between the estimates provided by the ANNs and by multilinear regression (MLR). The results showed that ANNs using the climatic data successfully estimated ET0 and the ANNs simulated ET0 better than the MLRs. The ANNs with four inputs were more accurate than those with three inputs. The errors of the ANNs with four inputs were lower (with RMSE of 0.130 mm d-1, RE of 2.7% and R2 of 0.986) in the semi-arid area than in the other two areas, but the errors of the ANNs with three inputs were lower in the sub-humid area (with RMSE of 0.21 mm d-1, RE of 5.2% and R2 of 0.961. For the different seasons, the results indicated that the highest errors occurred in September and the lowest in April for the ANNs with four inputs. Similarly, the errors were higher in September for the ANNs with three inputs. Copyright © 2008 John Wiley & Sons, Ltd.

Description: Concentration-discharge relationships have been widely used as clues to the hydrochemical processes that control runoff chemistry. Here we examine concentration-discharge relationships for solutes produced primarily by mineral weathering in 59 geochemically diverse US catchments. We show that these catchments exhibit nearly chemostatic behaviour; their stream concentrations of weathering products such as Ca, Mg, Na, and Si typically vary by factors of only 3 to 20 while discharge varies by several orders of magnitude. Similar patterns are observed at the inter-annual time scale. This behaviour implies that solute concentrations in stream water are not determined by simple dilution of a fixed solute flux by a variable flux of water, and that rates of solute production and/or mobilization must be nearly proportional to water fluxes, both on storm and inter-annual timescales. We compared these catchments' concentration-discharge relationships to the predictions of several simple hydrological and geochemical models. Most of these models can be forced to approximately fit the observed concentration-discharge relationships, but often only by assuming unrealistic or internally inconsistent parameter values. We propose a new model that also fits the data and may be more robust. We suggest possible tests of the new model for future studies. The relative stability of concentration under widely varying discharge may help make aquatic environments habitable. It also implies that fluxes of weathering solutes in streams, and thus fluxes of alkalinity to the oceans, are determined primarily by water fluxes. Thus, hydrology may be a major driver of the ocean-alkalinity feedback regulating climate change. Copyright © 2009 John Wiley & Sons, Ltd.

Description: A simple hydrologic drainage network for the Greenland Ice Sheet is modelled from available digital elevation models (DEMs) of bedrock, and surface topography and assumptions of hydrostatic water pressure, uniform hydraulic conductivity, and no conduit flow within the ice sheet. As such, it is a first-order model best suited for broad-scale hydrological assessment. Results identify 293 distinct hydrologic basins (185-117 000 km2) together with their 'realized' (wet) and 'unrealized' (dry) drainage patterns. Intersection with 1991-2000 Polar MM5 (PMM5) mesoscale climate model hindcasts of meltwater runoff suggest that these basins route varying amounts of water to the ice edge, ranging from 0 to 16 km3 annually and totalling 242 km3/year for the entire ice sheet. Regionally speaking, average annual volumetric meltwater production (km3/year) is highest in southwest and lowest in northeast Greenland, with greater hydrologic activity in western regions than in eastern regions for a given latitude. The extent to which meltwater truly reaches the ice margin as modelled is difficult to test. However, the simulated flow outlet locations show qualitative agreement with the locations of 460 observed meltwater outlets (proglacial lakes, streams, and rivers; and sediment plumes into fjörds) mapped continuously along the ice sheet perimeter. On average, about 36% of the modelled drainage network was activated (i.e. received water) over the 1991-2000 study period. Remaining areas, barring dynamic changes to ice-surface topography, would presumably activate if surface melt penetrates deeper into the ice sheet interior. Both new datasets are freely available for scientific use at the National Snow and Ice Data Center (ftp://sidads.colorado.edu/ pub/DATASETS/parca/nsidc-0372-hydrologic-outlets; ftp://sidads.colorado.edu/pub/DATASETS/parca/ nsidc-0371-hydrologic-sub-basins). Copyright © 2009 John Wiley & Sons, Ltd.

Description: Some previous global and regional studies have indicated teleconnection between the extreme phases of the Southern Oscillation (SO) and Turkish climate and hydrologic variables; however, they failed to suggest a strong correlation structure. In this study, categorised Southern Oscillation index (SOI) and Multivariate ENSO (El Nino Southern Oscillation) index (MEI) series were used to examine the far-reaching effects of the SO on temperature, precipitation and streamflow patterns in Turkey. These SO indicators were categorised into five subgroups according to their empirical distributions. Correlations between the categorised SO indicators and three analysis variables were computed using the Spearman's rho from lag-0 to lag-4. Significance of calculated correlations was tested at the 0.01 level for station-based analysis and at the 0.05 level for regional analysis. Temperature records demonstrated significant correlations with the categorised SOI and MEI in nearly half of the entire stations. For some categories, precipitation and streamflow were found to be correlated with the SO indicators in some stations mainly in western Turkey. Regional analyses of temperature and precipitation revealed a clear and strong correlation structure with the categorised SO indicators on a large portion of Turkey. This was not concluded by the earlier pertinent studies. Besides, this study showed that significant correlations were obtained not only for the SO extreme phases (namely, El Nino and La Nina) but also for neutral and moderate phases of the SO. Plausible explanations for the observed teleconnection are presented. Copyright © 2009 John Wiley & Sons, Ltd.

Description: Phosphorus (P) concentrations in sediments and in surface and interstitial water from three gravel bars in a large river (Garonne River, southern France) were measured daily, downstream of a wastewater treatment plant for a city of 740 000 inhabitants (Toulouse). Measurements were made of vertical hydraulic gradient (VHG), total dissolved phosphorus (TDP), soluble reactive phosphorus (SRP) and total phosphorus (TP) in water and of three extractable forms of phosphorus (water extractable, NaOH extractable and H2SO4 extractable) in hyporheic sediments from the gravel bars. Dissolved phosphorus was the major contributor to TP (74-79%) in both interstitial and surface waters on all sampling dates, and in most cases surface water P concentrations were significantly higher than interstitial concentrations. Hyporheic sediment TP concentrations ranged between 269 and 465 μg g-1 and were highest in fine sediment fractions. Acid-extractable P, a non-bioavailable form, represented at least 95% of sediment TP. A positive relationship was observed between VHG and TP in two of the gravel bars, with wells that were strongly downwelling having lower TP concentrations. These results suggest that in downwelling zones, hyporheic sediments can trap surface-derived dissolved P, and that much of this P becomes stored in refractory particulate forms. Bioavailable P is mainly present in dissolved form and only occupies a small fraction of total P, with particulate P comprising the majority of total P. Copyright © 2009 John Wiley & Sons, Ltd.

Description: Groundwater warming below cities has become a major environmental issue; but the effect of distinct local anthropogenic sources of heat on urban groundwater temperature distributions is still poorly documented. Our study addressed the local effect of stormwater infiltration on the thermal regime of urban groundwater by examining differences in water temperature beneath stormwater infiltration basins (SIB) and reference sites fed exclusively by direct infiltration of rainwater at the land surface. Stormwater infiltration dramatically increased the thermal amplitude of groundwater at event and season scales. Temperature variation at the scale of rainfall events reached 3 °C and was controlled by the interaction between runoff amount and difference in temperature between stormwater and groundwater. The annual amplitude of groundwater temperature was on average nine times higher below SIB (range: 0.9-8.6 °C) than at reference sites (range: 0-1.2 °C) and increased with catchment area of SIB. Elevated summer temperature of infiltrating stormwater (up to 21 °C) decreased oxygen solubility and stimulated microbial respiration in the soil and vadose zone, thereby lowering dissolved oxygen (DO) concentration in groundwater. The net effect of infiltration on average groundwater temperature depended upon the seasonal distribution of rainfall: groundwater below large SIB warmed up (+0.4 °C) when rainfall occurred predominantly during warm seasons. The thermal effect of stormwater infiltration strongly attenuated with increasing depth below the groundwater table indicating advective heat transport was restricted to the uppermost layers of groundwater. Moreover, excessive groundwater temperature variation at event and season scales can be attenuated by reducing the size of catchment areas drained by SIB and by promoting source control drainage systems. Copyright © 2009 John Wiley & Sons, Ltd.

Description: It is difficult to analyse the crytic period of the hydrological process, because hydrological time series is probably characterized by heteroscedasticity. To find out the crytic period, a model is constructed as follows: (1) after using zero-mean transformation for the data, to do Augmented Dickey-Fuller stationary test for the sequence, to build the corresponding AR(p) model and then to do ARCH effects test and white noise test for residual series; (2) for those time series that cannot pass through ARCH test, using logarithm transformation to reduce the heteroscedasticity, and then to redo step (1) until they pass through ARCH test and stationary test; (3) using periodogram analysis to determine all the possible the prime periods and further to put forward three kinds of tests to determine significance level of those prime periods. As examples, the hydrological processes of streamflow from 1784 to 1997 for the gauging stations of Alaer and Xinquman along Tarim River are analysed. After reducing their heteroscedasticity, AR(4) and AR(2) models are developed, respectively. Our results show that the streamflows from the two gauging stations have the same cryptic period of 42.7 years. Furthermore, the reliability for the crytic period model is testified by variance analysis, which shows that the crytic period model is useful and reliable. Copyright © 2009 John Wiley & Sons, Ltd.

Description: Taking northern Xinjiang, China, as an example, this study first compares the standard MODIS Terra and Aqua snow cover classifications, and then compares the accuracy of the standard MODIS daily and 8-day snow cover products with the new daily and multi-day snow cover combination of MODIS Terra and Aqua observations using in situ measurements. Under clear sky in both products, the agreement of land classification from MODIS Terra and Aqua daily and 8-day snow cover products is close to 100% for a entire water year. In contrast, the agreement of snow classification from MODIS Terra and Aqua is high only in the winter months, decreasing in the rest of the period. The high agreement mainly concentrates in land or snow-dominated areas, and major disagreements take place in the transitions zones from snow to land. The disagreement (mainly snow-land) in the 8-day products is higher than that in the daily products. In addition, both MODIS Terra and Aqua cloud masks tend to map more areas in the transition zones as cloud. Under clear sky conditions, the three daily products have similar accuracy of snow and land classification, and the 8-day standard products and the multi-day combination product also have similar accuracy of snow and land classification. This further suggests that the algorithm in the combination of Terra and Aqua snow cover products is valid. Moreover, in the actual weather/cloud conditions, the combination products from Terra and Aqua reduce cloud blockage and improve snow classification accuracy against either MODIS Terra or Aqua (51% against 44% and 34% for daily and 92% against 87% and 78% for 8-day, respectively), although Terra snow product (daily or 8-day) has slightly better accuracy than the Aqua snow product. The new combination products can provide better mapping of spatiotemporal variation of snow cover/glacier and for snow-melting modeling. Copyright © 2008 John Wiley & Sons, Ltd.

Description: The objective of this research was to characterise annual precipitation extremes in a Mediterranean vineyard region. The number of exceptional events (P 〉 95th percentile) and annual extreme events (P 〉 99th percentile), as well as their strength, erosive character and return period were analysed for 2000-2004. The erosive character was evaluated according to the R-factor (kinetic energy × maximum intensity in 30-min periods). Soil and nutrient losses caused by these events were evaluated by combining field sampling and a hydrological model to estimate total runoff in a vineyard plot. The results show a clear increase in the number of very wet days and extreme events (P 〉 95th percentile), which represented up to 88% of annual rainfall. The severity of the extreme events (TS = D precipitation event P 〉 99th percentile) reached values higher than 50 mm almost every year. These values were far exceeded in 2000, when one extraordinary event recorded 50% of the annual rainfall, with TS of 189 mm, about 80% of total rainfall being lost as runoff. Annual erosivity was driven not only by extreme events, but also by short events of less depth but high intensity. During some of the years analysed, rainfall erosivity was two or three times the average in the area. Most soil and nutrient losses occurred in a small number of events: one or two events every year were responsible for more than 75% of the annual soil and nutrient losses on average. Antecedent soil moisture conditions, runoff rates, and events with a return period higher than two years were responsible for the higher erosion rates. Apart from an exceptional event recorded in 2000, which produced more than 200 Mg ha-1 soil losses, annual soil losses up to 25 Mg ha-1 were recorded, which are much higher than the soil loss tolerance. Copyright © 2008 John Wiley & Sons, Ltd.

Description: Backflow from the Yangtze River to Poyang Lake occurs frequently due to their different flood seasons. Based on the reasons for and time period of backflow, this study estimated the spatial-temporal extent and the change of water clarity influenced by sediments within the backflow and northern Poyang Lake using time-series Moderate Resolution Imaging Spectroradiometer (MODIS) images. The results revealed that the sediments from backflows together with dredging activities in the northern Poyang Lake not only affected the northern Poyang Lake, but also influenced the central and southern Poyang Lake and the Poyang Lake national nature reserve, and resulted in great decline of water clarity in the regions influenced, which could seriously affect the lake ecosystem. The results indicated that MODIS images have potential for monitoring the distribution of sediments from backflows and dredging activities. However, the potential is limited because of the frequent cloud cover in the study area and the characteristics of backflow itself. The dredging activity combined with backflows might have great negative impacts on the Poyang Lake ecosystem, and it would be worthwhile to explore the possible impacts in order to develop scientific knowledge to support the decisions, which need to be made by the responsible authorities for deciding how to rationally manage this unique lake ecosystem Copyright © 2008 John Wiley & Sons, Ltd.

Description: Tributaries may either ameliorate or exacerbate the geomorphic and ecologic impacts of flow regulation by altering the flux of water and sediment into the flow-regulated mainstem. To capture the effects of tributary influences on a flow regulated river, long-term discharge and cross-sectional data are used to assess the geomorphic and hydrologic impacts of impoundment. In addition, the use of the short-lived cosmogenic radioisotope 7Be (half-life 53.4 days) to link sediment transport dynamics to benthic macroinvertebrate community structure is evaluated. It is found that the 7Be activity of transitional bed load sediment is highly seasonal and reflects both variations in activity of sediment sources and limited sediment residence time within the junction. Benthic communities also exhibit a strong seasonal variability. In the spring, neither the 7Be activity of the sediment, nor benthic communities exhibit clear relationships with sample site location. In contrast, during the late summer the ratio of Ephemeroptera (mayflies)/Trichoptera (caddisflies) decreased significantly below tributary junctions. This decrease in benthic community ratio was driven by increases in caddisfly abundance and was strongly correlated with the presence of recently 7Be tagged transitional bedload sediment. These observations are probably associated with the presence of coarse, stable, and unembedded substrate downstream of tributaries and the rapid turnover of sediment that may also be associated with a rapid flux in nutrients or seston. The results show that tributaries are impacting the flow-regulated mainstem and that these impacts are reflected in the benthic community structure and in the 7Be activity of transitional bed load sediment. Moreover, the observed reduction in competence and capacity of the mainstem following flood control suggests that these spatial discontinuities may be a consequence of impoundment. Copyright © 2008 John Wiley & Sons, Ltd.

Description: Surface waters associated with peatlands, supersaturated with CO2 and CH4 with respect to the atmosphere, act as important pathways linking a large and potentially unstable global repository of C to the atmosphere. Understanding the drivers and mechanisms which control C release from peatland systems to the atmosphere will contribute to better management and modelling of terrestrial C pools. We used non-dispersive infra-red (NDIR) CO2 sensors to continuously measure gas concentrations in a beaver pond at Mer Bleue peatland (Canada); measurements were made between July and August 2007. Concentrations of CO2 in the surface water (10 cm) reached 13 mg C1-1 (epCO2 72), and 26 mg C1-1 (epCO2 133) at depth (60 cm). The study also showed large diurnal fluctuations in dissolved CO2 which ranged in amplitude from ∼1.6 mg C1-1 at 10 cm to ∼0.2 mg C1-1 at 60 cm depth. CH4 concentration and supersaturation (epCH4) measured using headspace analysis averaged 1.47 mg C1-1 and 3252, respectively; diurnal cycling was also evident in CH4 concentrations. Mean estimated evasion rates of CO2 and CH4 over the summer period were 44.92 ±7.86 and 0.44 ± 0.25 μg C m-2s-1, respectively. Open water at Mer Bleue is a significant summer hotspot for greenhouse gas emissions within the catchment. Our results suggest that CO2 concentrations during the summer in beaver ponds at Mer Bleue are strongly influenced by biological processes within the water column involving aquatic plants and algae (in situ photosynthesis and respiration). In terms of carbon cycling, soil-stream connectivity at this time of year is therefore relatively weak. Copyright © 2008 John Wiley & Sons, Ltd.

Description: Streambank erosion is often the dominant source of sediment leaving modified watersheds. Mass failure of high, steep banks is one of the most serious forms of streambank erosion. The risk of a given bank experiencing mass failure is a function of bank height, angle, and soil strength, which is governed by soil moisture. Two methods for bank dewatering were tested in adjacent sections of streambank bordering a deeply incised channel in northern Mississippi: a low-cost pump system and subsurface horizontal drains. Pore water pressures (both positive and negative pressures, or matric suction) were continuously monitored for 2 years at the pumped site, at an adjacent untreated control section, and for 1 year at the site stabilized with horizontal drains. Resulting data were used to calculate a time series of the factor of safety using a computer model. Over the course of two wet seasons, average bank retreats for the control and pumped plots were 0.43 and 0.21 m, respectively. More limited monitoring revealed that the site with passive drains retreated about 0.23 m. At the pumped site pore water pressure was 3-4 kPa lower than at the control site during the most critical periods. Accordingly, computed factors of safety were above the failure threshold at the pumped site, but fell below unity at the control site on 11 occasions over the period of observation. Similarly, the drained site displayed generally lower pore water pressure and higher safety factors except for two events when drains were evidently overwhelmed with the volume of local surface and subsurface flows. These results suggest, but do not prove, that bank dewatering promoted lower rates of bank retreat and higher levels of stability since the three sites had slight differences in soils, geometry and boundary conditions. Initial cost of the dewatering treatments were significantly less than orthodox bank stabilization measures, but operation and maintenance requirements may be greater.

Description: In conjunction with available climate data, surface runoff is investigated at 12 gauges in the Quesnel watershed of British Columbia to develop its long-term (1926-2004) hydroclimatology. At Quesnel itself, annual mean values of air temperature, precipitation and runoff are 4.6 °C, 517 and 648 mm, respectively. Climate data reveal increases in precipitation, no significant trend in mean annual air temperature, but an increasing trend in mean minimum temperatures that is greatest in winter. There is some evidence of decreases in winter snow depth. On the water year scale (October-September), a strong positive correlation is found between discharge and precipitation (r = 0.70, p 〈 0.01) and a weak negative correlation is found between precipitation and temperature (r = -0.36, p 〈 0.01). Long-term trends using the Mann-Kendall test indicate increasing annual discharge amounts that vary from 8 to 14% (12% for the Quesnel River, p = 0.03), and also a tendency toward an earlier spring freshet. River runoff increases at a rate of 1.26 mm yr-1 m-1 of elevation from west to east along the strong elevation gradient in the basin. Discharge, temperature and precipitation are correlated with the large-scale climate indices of the Pacific Decadal Oscillation (PDO) and El-Niño Southern Oscillation (ENSO). Copyright © 2009 John Wiley & Sons, Ltd.

Description: Many civil infrastructures are located near the confluence of two streams, where they may be subject to inundation by high flows from either stream or both. These infrastructures, such as highway bridges, are designed to meet specified performance objectives for floods of a specified return period (e.g. the 100 year flood). Because the flooding of structures on one stream can be affected by high flows on the other stream, it is important to know the relationship between the coincident exceedence probabilities on the confluent stream pair in many hydrological engineering practices. Currently, the National Flood Frequency Program (NFF), which was developed by the US Geological Survey (USGS) and based on regional analysis, is probably the most popular model for ungauged site flood estimation and could be employed to estimate flood probabilities at the confluence points. The need for improved infrastructure design at such sites has motivated a renewed interest in the development of more rigorous joint probability distributions of the coincident flows. To accomplish this, a practical procedure is needed to determine the crucial bivariate distributions of design flows at stream confluences. In the past, the copula method provided a way to construct multivariate distribution functions. This paper aims to develop the Copula-based Flood Frequency (COFF) method at the confluence points with any type of marginal distributions via the use of Archimedean copulas and dependent parameters. The practical implementation was assessed and tested against the standard NFF approach by a case study in Iowa's Des Moines River. Monte Carlo simulations proved the success of the generalized copula-based joint distribution algorithm. Copyright © 2009 John Wiley & Sons, Ltd.

Description: Soil microtopography is a dynamic soil property which affects most soil-surface and water interaction processes. The importance of soil microtopography has been recognized for a long time, but only limited reports are available in the literature. In this study, the potential of using consumer-grade cameras and close-range photogrammetry procedures to quantify soil microtopography at plot-scale level (〈1 m2) were assessed. Five fabricated gypsum surfaces with different degrees of roughness were used to simulate the soil surface conditions with different soil aggregates. The surfaces digital elevation model (DEM) was generated using the photogrammetry system (PHM) involving a consumer-grade camera, and pin-microrelief meter (PM). The DEM generated using the PHM was assessed for accuracy, roughness indices (RI), depression area percentage (DA%), depression storage capacity (DSC), and micro-rills delineation in comparison with the PM. The accuracy was evaluated using the root mean square error (RMSE) in the x-, y-, and z-directions. Visual comparison between the 3D-visions of the DEM showed strong agreement between the DEM generated by the PHM and the PM, and between the PHM and the 2D images for the different gypsum surfaces. The average RMSE in the x-. y-, and z-direction were 2.08, 1.52, and 0.82 mm for the rough surface, and 4.42, 1.65, and 3.22 mm for the smooth surface. The RIs calculated from the two methods were highly correlated. The small discrepancy between the two methods was discussed. The micro-rills delineation was also similar for the two methods regarding the network density. The grid size did not effect the RI calculation, and has a strong influence on the DA%, DSC, and the delineated micro-rills orders. Results suggest that a consumer-grade camera and close-range photogrammetry have the potential to quantify the soil microtopography. Copyright © 2009 John Wiley & Sons, Ltd.

Description: In cold regions, the response and related antecedent mechanisms that produce flood flows from rainfall events have received limited study. In 2007, a small watershed at Cape Bounty, Melville Island, Nunavut, was studied in detail during the melt season. Two rainfall events on June 30 and July 22, totalling 9.2 and 10.8 mm, respectively, represented significant contributions to seasonal discharge and sediment transport in a year with a low winter snowpack. The precipitation events elevated discharge and suspended sediment concentrations to twice the magnitude of the nival melt, and generated the only measurable downstream lacustrine turbidity current of the season. In two days, rainfall runoff transported 35% of the seasonal suspended sediment load, in contrast to 29% transported over the nival freshet. The magnitude and intensity of the rain events were not unusual in this setting, but the rainfall response was substantial in comparison with equivalent past events. Exceptional temperatures of July 2007 generated early, deep permafrost thaw, and ground ice melt. The resultant increase in soil moisture amplified the subsequent rainfall runoff and sediment transport response. These results demonstrate the importance of antecedent moisture conditions and the role of permafrost active layer development as an important factor in the rainfall runoff and sediment transport response to precipitation events. Copyright © 2009 John Wiley & Sons, Ltd.

Description: This paper presents a new approach to modelling flash floods in dryland catchments by integrating remote sensing and digital elevation model (DEM) data in a geographical information system (GIS). The spectral reflectance of channels affected by recent flash floods exhibit a marked increase, due to the deposition of fine sediments in these channels as the flood recedes. This allows the parts of a catchment that have been affected by a recent flood event to be discriminated from unaffected parts, using a time series of Landsat images. Using images of the Wadi Hudain catchment in southern Egypt, the hillslope areas contributing flow were inferred for different flood events. The SRTM3 DEM was used to derive flow direction, flow length, active channel cross-sectional areas and slope. The Manning Equation was used to estimate the channel flow velocities, and hence the time-area zones of the catchment. A channel reach that was active during a 1985 runoff event, that does not receive any tributary flow, was used to estimate a transmission loss rate of 7.5 mm h-1, given the maximum peak discharge estimate. Runoff patterns resulting from different flood events are quite variable; however the southern part of the catchment appears to have experienced more floods during the period of study (1984-2000), perhaps because the bedrock hillslopes in this area are more effective at runoff production than other parts of the catchment which are underlain by unconsolidated Quaternary sands and gravels. Due to high transmission loss, runoff generated within the upper reaches is rarely delivered to the alluvial fan and Shalateen city situated at the catchment outlet. The synthetic GIS-based time area zones, on their own, cannot be relied on to model the hydrographs reliably; physical parameters, such as rainfall intensity, distribution, and transmission loss, must also be considered. Copyright © 2009 John Wiley & Sons, Ltd.

Description: Much of the nonlinearity and uncertainty regarding the flood process is because hydrologic data required for estimation are often tremendously difficult to obtain. This study employed a back-propagation network (BPN) as the main structure in flood forecasting to learn and to demonstrate the sophisticated nonlinear mapping relationship. However, a deterministic BPN model implies high uncertainty and poor consistency for verification work even when the learning performance is satisfactory for flood forecasting. Therefore, a novel procedure was proposed in this investigation which integrates linear transfer function (LTF) and self-organizing map (SOM) to efficiently determine the intervals of weights and biases of a flood forecasting neural network to avoid the above problems. A SOM network with classification ability was applied to the solutions and parameters of the BPN model in the learning stage, to classify the network parameter rules and to obtain the winning parameters. The outcomes from the previous stage were then used as the ranges of the parameters in the recall stage. Finally, a case study was carried out in Wu-Shi basin to demonstrate the effectiveness of the proposal. Copyright © 2009 John Wiley & Sons, Ltd.

Description: Presented here is a model framework based on a land surface topography that can be represented with various degrees of resolution and capable of providing representative channel/floodplain hydraulic characteristics on a daily to hourly scale. The framework integrates two models: (1) a water balance model (WBM) for the vertical fluxes and stores of water in and through the canopy and soil layers based on the conservation of mass and energy, and (2) a routing model for the horizontal routing of surface and subsurface runoff and channel and floodplain waters based on kinematic and diffusion wave methodologies. The WBM is driven by satellite-derived precipitation (TRMM_3B42) and air temperature (MOD08_M3). The model's use of an irregular computational grid is intended to facilitate parallel processing for applications to continental and global scales. Results are presented for the Amazon Basin over the period Jan 2001 through Dec 2005. The model is shown to capture annual runoff totals, annual peaks, seasonal patterns, and daily fluctuations over a range of spatial scales (〉1, 000 to 〈4D7M km2). For the period of study, results suggest basin-wide total water storage changes in the Amazon vary by approximately +/-5 to 10 cm, and the fractional components accounting for these changes are: root zone soil moisture (20%), subsurface water being routed laterally to channels (40%) and channel/floodplain discharge (40%). Annual variability in monthly water storage changes by +/-2.5 cm is likely due to 0D5 to 1 month variability in the arrival of significant rainfall periods throughout the basin. Copyright © 2009 John Wiley & Sons, Ltd.

Description: The impacts of climate change on storm runoff and erosion in Mediterranean watersheds are difficult to assess due to the expected increase in storm frequency coupled with a decrease in total rainfall and soil moisture, added to positive or negative changes to different types of vegetation cover. This report, the second part of a two-part article, addresses this issue by analysing the sensitivity of runoff and erosion to incremental degrees of change (from a20 to C20%) to storm rainfall, pre-storm soil moisture, and vegetation cover, in two Mediterranean watersheds, using the MEFIDIS model. The main results point to the high sensitivity of storm runoff and peak runoff rates to changes in storm rainfall (2D2% per 1% change) and, to a lesser degree, to soil water content (a1D2% per 1% change). Catchment sediment yield shows a greater sensitivity than within-watershed erosion rates to both parameters: 7D8 versus 4D0% per 1% change for storm rainfall, and a4D9 versus a2D3% per 1% change for soil water content, indicating an increase in sensitivity with spatial scale due to changes to sediment connectivity within the catchment. Runoff and erosion showed a relatively low sensitivity to changes in vegetation cover. Finally, the shallow soils in one of the catchments led to a greater sensitivity to changes in storm rainfall and soil moisture. Overall, the results indicate that decreasing soil moisture levels caused by climate change could be sufficient to offset the impact of greater storm intensity in Mediterranean watersheds. Copyright © 2009 John Wiley & Sons, Ltd.

Description: The goal of this research was to compare hyporheic activity in recently restored and adjacent un-restored reaches of the Truckee River downstream from the Reno/Sparks metropolitan area. The installation of rocky riffles and raised channel bed elevations in the restored reaches may have increased the degree of surface-subsurface interaction. A fluctuating chloride concentration signal served as the tracer, induced by the variable influx of higher salinity water several miles upstream from the study reach. The solute transport model, OTIS, was used in conjunction with the hydrodynamic model, DYNHYD5, to estimate transient storage parameters under unsteady flow conditions. The model was calibrated to chloride concentrations measured over a period of three days at six in-stream locations representing restored and un-restored reaches. An automated parameter estimation algorithm (SCE-UA) was used to optimize parameters for multiple reaches simultaneously and generate a distribution of parameter estimates. Results suggest that the transient storage zone cross-sectional area (As) is larger in the restored reaches than in the unrestored reaches, but the exchange coefficient (α) is smaller, leading to increased hyporheic residence time and hydrologic retention in the vicinity of channel reconstructions. Scenarios were used to simulate the potential effects of increased subsurface residence time on denitrification and in-stream NO3-N concentrations. Monte Carlo analysis was performed to assess uncertainty in the simulation results and show the potential for greater nutrient retention in the lower Truckee River as a result of channel restoration. Copyright © 2009 John Wiley & Sons, Ltd.

Description: Snowmelt runoff in the mountainous eastern part of Turkey is of great importance as it constitutes 60-70% in volume of the total yearly runoff during spring and early summer months. Therefore, determining the amount and timing of snowmelt runoff especially in the Euphrates basin, where large dams are located, is an important task in order to use the water resources of the country in an optimal manner. The HBV model, being one of the well-known conceptual hydrological models used more than 45 countries over the world, is applied for the first time in Turkey to a small basin of 242 km2 on the headwaters of Euphrates river for 2002-2004 water years. The input data are provided from the automatic snow-meteorological stations installed at various locations and altitudes in upper Euphrates basin operating in real-time. Since ground-based observations can only represent a small part of the region of interest, spatially and temporally distributed snow cover data are acquired through the use of Moderate Resolution Imaging Spectroradiometer (MODIS) optical satellite. In the first part of the study, an automatic model parameter estimation method, Shuffled Complex Evolution, University of Arizona (SCE-UA), is utilized to calibrate the HBV model parameters with a multi-variable criteria using runoff as well as snow-covered area (SCA) to ensure the internal validity of the model. Results show that calibrations against SCA in addition to discharge simulate discharge nearly as well as calibrations against discharge only, but further suggest that longer time periods and more study catchments should be included to achieve more comprehensible conclusions. In the second part of the study, the calibrated HBV model is applied to forecast runoff with a 1-day lead time using gridded input data from Mesoscale Model 5 (MM5) for the 2004 snowmelt period. Promising results indicate the possible operational use of runoff forecasting driven by numerical weather prediction data for flood mitigation, reservoir operation and dam safety. Copyright © 2009 John Wiley & Sons, Ltd.

Description: Climate change is expected to effect storm runoff and erosion processes in Mediterranean watersheds at multiple spatial scales. Models are typically applied to estimate these impacts; however, the scarcity of spatially distributed data for parameterization, calibration and validation often prevents application of these models, particularly for larger catchments. This report, the first part of a two-part article, presents an application and evaluation of the MEFIDIS model for two Mediterranean mesoscale watersheds (115 and 290 km2) in a data-scarce environment. A multi-scale assessment method was used that combines quantitative validation and qualitative evaluation, consisting of three steps: (1) calibration at the small (field) scale using results from rainfall simulation experiments; (2) calibration and validation for catchment-scale results while changing catchment-scale parameters only (channel roughness and a parameter controlling the distribution of saturated areas); and (3) qualitative evaluation of within-watershed erosion processes using empirical estimates of sediment delivery ratio and gully location. The results indicate that calibrating MEFIDIS at the field scale can provide reasonable results for catchment runoff and sediment export and for within-watershed erosion processes. Copyright © 2009 John Wiley & Sons, Ltd.

Description: In-channel rock vane structures are widely used in stream restoration as a way to reduce stream channel erosion and create pool or riffle features. When these structures change hydraulic gradients they may affect ecological stream functions, such as hyporheic exchange flow (HEF) patterns. A study of constructed in-channel structure controls on HEF was conducted in the third-order Batavia Kill, New York using stream and hyporheic temperature amplitude analysis and computational fluid dynamics (CFD) hydraulic simulations. Temperature monitors were installed in the water column and channel bed at six locations around each of seven in-channel restoration structures (three cross-vanes and four J-hooks) at baseflow in 2007. Elevation surveys of the structures were then used to simulate HEF using CFD. The results indicate a pattern of pronounced upwelling in the run section just below the structure, upwelling transitioning to downwelling within the pool, and pronounced downwelling in the glide out of the pool. This pattern is consistent with natural riffle pool sequences. The direction of HEF inferred from the temperature amplitude analysis agreed with the direction of flow simulated with CFD at 80% of the locations, and the few disagreements were expected due to model limitations. CFD simulation demonstrated that increasing stream flows result in changes in HEF spatial patterns and magnitude at each structure. This work illustrates how CFD simulations can guide design of in-channel restoration structures for HEF function. Copyright © 2009 John Wiley & Sons, Ltd.

Description: The extensive snow measurement network of the Sonnblick region (Hohe Tauern, Austrian Alps) is used to describe temporal trends of snow-depth as well as its relation to climate change for a high-elevated site of the European Alps (2400-3100 m.a.s.l.). Spatial representativeness of single snow stakes, with readings back to 1928, is derived for maximum snow-depth in May using a spatially dense snow depth probing from glacier mass balance measurements. Long-term trends of snow depth show a significant reduction in the contribution of snow accumulation from core-winter (1 December to 1 March) compared to early and late-winter periods. Largest values of snow-depth since 1928 were measured in the 1940s and 1950s. Comparison of monthly changes in snow-depth with precipitation measurements underlines the high influence of wind drift on snow-depth during winter season from 1 October to 30 April. Whereas inter-annual variability of maximum snow-depth is better explained by low elevation precipitation measurements than by local (high elevation) precipitation measurements, the longer-term mean of local precipitation measurements, however, fits well to the snow-depth measurements, if a mean snow-density of about 400 kg m-3 is assumed (which matches field observations). Both maximum snow-depth and winter season precipitation show a clear decreasing trend for inter-annual variability. A statistical relationship between air temperature and fraction of solid precipitation is used for estimation of temporal trends in the fraction of solid precipitation at measurement sites. For summer a decrease of about 1% of solid precipitation per decade was found for the lowest elevated sites whereas fraction of solid precipitation in winter remains stable. Relation between snow-depth and climate is investigated by means of local climate data of Sonnblick-Observatory (SBO) and by means of the North-Atlantic Oscillation Index (NAOI). Whereas winter air-temperature is significantly correlated with the NAOI, for winter precipitation and snow depth on 1 May no correlation was found with NAOI. Copyright © 2008 John Wiley & Sons, Ltd.

Description: For most of the global land area poleward of about 40° latitude, snow plays an important role in the water cycle. The (seasonal) timing of runoff in these areas is especially sensitive to projected losses of snowpack associated with warming trends, whereas projected (annual) runoff volume changes are primarily associated with precipitation changes, and to a lesser extent, with changes in evapotranspiration (ET). Regional studies in the USA (and especially the western USA) suggest that hydrologic adjustments to a warming climate have been ongoing since the mid-twentieth century. We extend the insights extracted from the western USA to the global scale using a physically based hydrologic model to assess the effects of systematic changes in precipitation and temperature on snow-affected portions of the global land area as projected by a suite of global climate models. While annual (and in some cases seasonal) changes in precipitation are a key driver of projected changes in annual runoff, we find, as in the western USA, that projected warming produces strong decreases in winter snow accumulation and spring snowmelt over much of the affected area regardless of precipitation change. Decreased snowpack produces decreases in warm-season runoff in many mid- to high-latitude areas where precipitation changes are either moderately positive or negative in the future projections. Exceptions, however, occur in some high-latitude areas, particular in Eurasia, where changes in projected precipitation are large enough to result in increased, rather than decreased, snow accumulation. Overall, projected changes in snowpack and the timing of snowmelt-derived runoff are largest near the boundaries of the areas that currently experience substantial snowfall, and at least qualitatively, they mirror the character of observed changes in the western USA. Copyright © 2008 John Wiley & Sons, Ltd.

Description: Wind-induced snow transport has remarkable effects on the snow cover spatial variability and on the temporal dynamics of snowmelt runoff. For accurate snow cover modelling, valid atmospheric forcing fields are essential. Since it is impossible to generate appropriate wind fields by a simple spatial interpolation of station data, a new approach was developed: A modified version of the Penn State University-National Centre for Atmospheric Research (MM5) model was used to generate wind fields with 200-m resolution. Because of the high computational costs of MM5, it was not practicable to include the wind field generation as an operational part of the snow cover modelling. Therefore, an archive consisting of 220 wind fields was generated prior to the simulation of the snow transport processes. These fields represent the most relevant synoptic situations for wind-induced snow transport occurring at our test site. The criteria to generate which wind field to use in a specific snow model time step are mean wind speed and direction at the 700 hPa level derived from German Weather Service/Deutscher Wetterdienst (DWD) Lokalmodell (LM) analysis data. The wind field library provided physically derived wind speed and direction fields that were used to drive a snow transport model (SnowTran-3D) in a high Alpine area in the Berchtesgaden National Park, Germany. In complex Alpine terrain, the procedure provides an alternative to simple interpolation methods, yielding improved physical realism at reasonable computational expense. Copyright © 2008 John Wiley & Sons, Ltd.

Description: To determine the distribution of water balance components in space and time, models are applied with a wide range of spatio-temporal discretizations - from lumped to distributed in the spatial scale and from annual to daily (or shorter) time-steps in the temporal scale. We present a comparative case study where we compare the simulation results of two conceptual water balance models using different spatio-temporal discretizations. Such a comparison enables to assess if different models with different discretizations may still yield similar results in space and time. The study focuses on the mountainous catchment of the river Gail (app. 1300 km2) in southern Austria for the period 1971-1990. The first model uses a semi-distributed discretization and daily data, whereas the second model uses a spatially distributed discretization (1 × 1 km raster) and monthly data. Both models use precipitation and temperature data as input. Parameters of the daily model were calibrated with runoff data of several gauges as part of a study focusing specifically on the Gail catchment. The distributed parameters of the monthly model were estimated regionally for establishing the water balance of the Hydrological Atlas of Austria. Both models perform equally well for runoff simulations. For simulation of temporal dynamics the models agree well for the main inputs and outputs of the system, with slightly lower agreements for sub-components - such as snowmelt for instance. In the spatial domain the correlation between the models is significantly lower. Differences are mainly related to different calibration approaches and are not dependent on the spatio-temporal discretization. Overall, the two water balance models yield consistent results, suggesting that the usage of monthly data is not inferior to the usage of daily data. Copyright © 2008 John Wiley & Sons, Ltd.

Description: Snow covered area (SCA) observations from the Landsat Enhanced Thematic Mapper (ETM+) were used in combination with a distributed snowmelt model to estimate snow water equivalent (SWE) in the headwaters of the Rio Grande basin (3,419 km2) - a spatial scale that is an order of magnitude greater than previous reconstruction model applications. In this reconstruction approach, modeled snowmelt over each pixel is integrated over the time of ETM+ observed snow cover to estimate SWE. Considerable differences in the magnitude of SWE were simulated during the study. Basin-wide mean SWE was 2.6 times greater in April 2001 versus 2002. Despite these climatological differences, the model adequately recovered SWE at intensive study areas (ISAs); mean absolute SWE error was 23% relative to observed SWE. Reconstruction model SWE errors were within one standard deviation of the mean observed SWE over 37 and 55% of the four 16-km2 intensive field campaign study sites in 2001 and 2002, respectively; a result comparable to previous works at much smaller scales. A key strength of the technique is that spatially distributed SWE estimates are not dependent upon ground-based observations of SWE. Moreover, the model was relatively insensitive to the location of forcing observations relative to commonly used statistical SWE interpolation models. Hence, the reconstruction technique is a viable approach for obtaining high-resolution SWE estimates at larger scales (e.g. 〉 1000 km2) and in locations where detailed hydrometeorological observations are scarce. Copyright © 2009 John Wiley & Sons, Ltd.

Description: The objective of this work was to develop a hypothetical reality of hydrologic response to be used as an error-free synthetic dataset in a larger ongoing study. The hypothetical reality was generated via rigorous simulation of a real system with a comprehensive physics-based model. The simulation was conducted with the Integrated Hydrology Model (InHM); the system is the Tarrawarra catchment located in southeastern Australia. Parameterization of the Tarrawarra boundary-value problem was based on the best available information, which, for example includes rainfall, discharge, and soil-water content data for the last six months of 1996. The InHM-simulated near-surface hydrologic response for the Tarrawarra boundary-value problem compares well (albeit not perfectly) with both the integrated and distributed observations from the catchment. The Tarrawarra-like hypothetical reality of wet season hydrologic response generated in this study is rich enough to be employed as an error-free synthetic dataset for quantitatively evaluating the capabilities/limitations of competing (underlying) modelling techniques. Copyright © 2009 John Wiley & Sons, Ltd.

Description: Evapotranspiration (ET) is one of the major processes in the hydrological cycle, and its reliable estimation is essential to water resources management. Numerous equations have been developed for estimating ET, most of which are complex and require numerous items of weather data. In many areas, the necessary data are lacking, and simpler techniques are required. Evaporation pans are used throughout the world because of the simplicity of technique, low cost, and ease of application. In this study, the radial basis function (RBF) network is applied for pan evaporation to evapotranspiration conversions. The adaptive pan-based RBF network was trained using daily Policoro data from 15 May 1981 to 23 December 1983. The RBF network obtained, Christiansen, FAO-24 pan, and FAO-56 Penman-Monteith equations were verified in comparison with lysimeter measurements of grass evapotranspiration using daily Policoro data from 25 February to 18 December 1984. Based on summary statistics, the RBF network ranked first with the lowest RMSE value (0.433 mm day-1). The RBF network obtained on the basis of the daily data from Policoro, Italy and pan-based equations were further tested using mean monthly data collected in Novi Sad, Serbia, and Kimberly, Idaho, USA. The overall results favoured use of the RBF network for pan evaporation to evapotranspiration conversions. The use of the RBF network is very simple and does not require any knowledge of ANNs. Users require only code (RBF network), Epan data and corresponding Ra data. Copyright © 2009 John Wiley & Sons, Ltd.

Description: Soil water repellency may be characterized in terms of the delayed infiltration time of a water droplet resting on the soil surface, which is, water drop penetration time (WDPT), or repellency persistence. Such repellency persistence varies nonlinearly with soil water content (θg), although no models have been proposed to reproduce the variation of WDPT with θg in soils. Dynamic factor analysis (DFA) is used to identify two common patterns of unexplained variability in a scattered dataset of WDPT versus θ g measurements. A four-parameter lognormal distribution was fitted to both common patterns obtained by DFA, and these were combined additively in a weighted multiple linear bimodal model. We show how such an empirical model is capable of reproducing a large variety of WDPT versus θg curve shapes (N = 80) both within a wide range of measured WDPTs (0-17000 s) and for samples with organic matter content ranging from 21.7 to 80.6 g (100 g)-1. Copyright © 2009 John Wiley & Sons, Ltd.

Description: The study investigates the capability of coarse resolution synthetic aperture radar (SAR) imagery to support flood inundation models. A hydraulic model of a 98-km reach of the River Po (Northern Italy) was calibrated on the October 2000 high-magnitude flood event with extensive and high-quality field data. During the June 2008, low-magnitude flood event a SAR image was acquired and processed in near real time (NRT) in order to provide adequate data for quick verification and recalibration of the hydraulic model. Copyright © 2009 John Wiley & Sons, Ltd.

Description: Many reservoirs around the world are being operated based on rule curves developed without considering the evacuation of deposited sediment. Current reservoir simulation and optimization models fall short of incorporating the concept of sustainability because the reservoir storage losses due to sedimentation are not considered. This study develops a new model called Reservoir Optimization-Simulation with Sediment Evacuation (ROSSE) model. The model utilizes genetic algorithm based optimization capabilities and embeds the sediment evacuation module into the simulation module. The sediment evacuation module is implemented using the Tsinghua university flushing equation. The ROSSE model is applied to optimize the rule curves of Tarbela Reservoir, the largest reservoir in Pakistan with chronic sedimentation problems. In the present study, rule curves are optimized for maximization of net economic benefits from water released. The water released can be used for irrigation, power production, sediment evacuation, and for flood control purposes. Relative weights are used to combine the benefits from these conflicting water uses. Nine sets of rule curves are compared, namely existing rule curves and proposed rule curves for eight scenarios developed for various policy options. These optimized rule curves show an increase of net individual economic benefits ranging from 9 to 248% over the existing rule curves. The shortage of irrigation supply during the simulation period is reduced by 38% and reservoir sustainability is enhanced by 28% through increased sediment evacuation. The study concludes that by modifying the operating policy and rule curves, it is possible to enhance the reservoir's sustainability and maximize the net economic benefits. The developed methodology and the model can be used for optimization of rule curves of other reservoirs with sedimentation problems. Copyright © 2008 John Wiley & Sons, Ltd.