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Over the past decades, a number of water sciences and management programs have been developed to better understand and manage the water cycles at multiple temporal and spatial scales for various purposes, such as ecohydrology, global hydrology, sociohydrology, supply management, demand management, and integrated water resources management (IWRM). At the same time, rapid advancements have also been taking place in tracing, mapping, remote sensing, machine learning, and modelling technologies in hydrological research. Despite those programs and advancements, a water crisis is intensifying globally. The missing link is effective interactions between the hydrological research and water resource management to support implementation of the UN Sustainable Development Goals (SDGs) at multiple spatial scales. Since the watershed is the natural unit for water resources management, watershed science offers the potential to bridge this missing link. This study first reviews the advances in hydrological research and water resources management, and then discusses issues and challenges facing the global water community. Subsequently, it describes the core components of watershed science: (1) hydrological analysis; (2) water-operation policies; (3) governance; (4) management and feedback. The framework takes into account water availability, water uses, and water quality; explicitly focuses on the storage, fluxes, and quality of the hydrological cycle; defines appropriate local water resource thresholds through incorporating the planetary boundary framework; and identifies specific actionable measures for water resources management. It provides a complementary approach to the existing water management programs in addressing the current global water crisis and achieving the UN SDGs.

Snow depth mirrors regional climate change and is a vital parameter for medium- and long-term numerical climate prediction, numerical simulation of land-surface hydrological process, and water resource assessment. However, the quality of the available snow depth products retrieved from remote sensing is inevitably affected by cloud and mountain shadow, and the spatiotemporal resolution of the snow depth data cannot meet the need of hydrological research and decision-making assistance. Therefore, a method to enhance the accuracy of snow depth data is urgently required. In the present study, three kinds of snow depth data which included the D-InSAR data retrieved from the remote sensing images of Sentinel-1 synthetic aperture radar, the automatically measured data using ultrasonic snow depth detectors, and the manually measured data were assimilated based on ensemble Kalman filter. The assimilated snow depth data were spatiotemporally consecutive and integrated. Under the constraint of the measured data, the accuracy of the assimilated snow depth data was higher and met the need of subsequent research. The development of ultrasonic snow depth detector and the application of D-InSAR technology in snow depth inversion had greatly alleviated the insufficiency of snow depth data in types and quantity. At the same time, the assimilation of multi-source snow depth data by ensemble Kalman filter also provides high-precision data to support remote sensing hydrological research, water resource assessment, and snow disaster prevention and control program.

With the start of the COVID-19 pandemic and the resulting contact restrictions, conducting field trips to hydrological research basins became close to impossible. Hydrological field knowledge is an essential part of hydrological education and research. In order to impart this knowledge to students of hydrological engineering subjects in times or situations where on-site exploration is not possible, the VR4Hydro tool was developed. VR4Hydro is a virtual reality platform built from 360° panoramas that allows users to interactively explore the Gersprenz River basin in Germany. The following study seeks to investigate the applicability of performing virtual field trips in the context of hydrological education by evaluating user experience. Sixteen students of the subject engineering hydrology were asked to document their experiences with VR4Hydro using a qualitative approach by answering a series of multiple-choice questions as well as long-answer text questions. The analysis and discussion of the results showed that virtual excursions generally met with great interest among users. The majority rated the virtual tour as a valuable addition to traditional teaching methods. All students found the tool particularly appealing in cases where external circumstances did not allow for a real excursion. The findings of this study show that the application of virtual field trips (VFT) in hydrological engineering can be a valuable supplement to real field trips to improve the interest and learning outcome of students.

The Mekong River basin (MRB) is a transboundary basin that supports livelihoods of over 70 million inhabitants and diverse terrestrial-aquatic ecosystems. This critical lifeline for people and ecosystems is under transformation due to climatic stressors and human activities (e.g., land use change and dam construction). Thus, there is an urgent need to better understand the changing hydrological and ecological systems in the MRB and develop improved adaptation strategies. This, however, is hampered partly by lack of sufficient, reliable, and accessible observational data across the basin. Here, we fill this long-standing gap for MRB by synthesizing climate, hydrological, ecological, and socioeconomic data from various disparate sources. The data— including groundwater records digitized from the literature—provide crucial insights into surface water systems, groundwater dynamics, land use patterns, and socioeconomic changes. The analyses presented also shed light on uncertainties associated with various datasets and the most appropriate choices. These datasets are expected to advance socio-hydrological research and inform science-based management decisions and policymaking for sustainable food-energy-water, livelihood, and ecological systems in the MRB.

Forecasting discharge (Q) and water level (H) are essential factors in hydrological research and flood prediction. In recent years, deep learning has emerged as a viable technique for capturing the non-linear relationship of historical data to generate highly accurate prediction results. Despite the success in various domains, applying deep learning in Q and H prediction is hampered by three critical issues: a shortage of training data, the occurrence of noise in the collected data, and the difficulty in adjusting the model’s hyper-parameters. This work proposes a novel deep learning-based Q–H prediction model that overcomes all the shortcomings encountered by existing approaches. Specifically, to address data scarcity and increase prediction accuracy, we design an ensemble learning architecture that takes advantage of multiple deep learning techniques. Furthermore, we leverage the Singular-Spectrum Analysis (SSA) to remove noise and outliers from the original data. Besides, we exploit the Genetic Algorithm (GA) to propose a novel mechanism that can automatically determine the prediction model’s optimal hyper-parameters. We conducted extensive experiments on two datasets collected from Vietnam’s Red and Dakbla rivers. The results show that our proposed solution outperforms current techniques across a wide range of metrics, including NSE, MSE, MAE, and MAPE. Specifically, by exploiting the ensemble learning technique, we can improve the NSE by at least $$2\%$$ 2 % . Moreover, with the aid of the SSA-based data preprocessing technique, the NSE is further enhanced by more than $$5\%$$ 5 % . Finally, thanks to GA-based optimization, our proposed model increases the NSE by at least $$6\%$$ 6 % and up to $$40\%$$ 40 % in the best case.

The Matusagaratí wetland in the Panamanian Darien is one of the largest and most biologically diverse wetland ecosystems in Central America. Despite this, no hydrological studies have been conducted in the area due to its remoteness and difficult access. The aim of this research is to define the relationship between surface water and groundwater through the field and laboratory data obtained from the first monitoring network installed in the Matusagaratí wetland. Variations registered in the isotopic relationships in surface water and groundwater show that the wetland receives contributions from rainfall as well as fluvial and estuarine water. There are areas of the wetland where one of these sources predominates, and others where they mix. In the wetland sector downstream the Tuira river, the groundwater presents a combination of freshwaters coming from Filo del Tallo and those coming from the Tuira river, whose high salinity reflects the estuary's influence. Meanwhile, in the upstream sector of the wetland, the groundwater is a mixture of river water and rainwater on the river´s levee but behind it, rainwater predominates. In all cases, groundwater has Rare Earth Elements patterns like those of the Tuira river, highlighting the importance of river flooding as a source and support system for the wetland groundwater. Hydrological research such as this, presents a valuable opportunity to provide sound scientific information to promote sustainable management and environmental conservation of this unique wetland that is rapidly being transformed to cattle pasture and palm and rice cultivation. Fil: Carol, Eleonora Silvina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigaciones Geológicas. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Centro de Investigaciones Geológicas; Argentina Fil: Alvarez, Maria del Pilar. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Instituto Patagónico para el Estudio de los Ecosistemas Continentales; Argentina Fil: Candanedo, Indra. Universidad Tecnologica de Panamá.; Panamá Fil: Saavedra, Sidney. Universidad Tecnologica de Panamá.; Panamá Fil: Arcia, Manuel. Universidad Tecnologica de Panamá.; Panamá Fil: Franco, Ana. Universidad Tecnologica de Panamá.; Panamá

Drought is a complex natural hazard that has been recurrently occurred in many regions across the globe. Therefore, precise drought characterization and its regional monitoring are key challenges for advanced water management and hydrological research. In this research, we provided a novel method to improve annual average time series data for the Standardized Drought Index (SDI)-type drought monitoring tools. We proposed multi-auxiliary information-based estimation strategy that improves annual moving average/total precipitation time series records. Therefore, we incorporated a minimum and maximum temperature as auxiliary variables under multi-auxiliary regression estimator. In summary, this study propagates a new drought index named: the Precision-Weighted Standardized Precipitation Index (PWSDI). We evaluated the performance of PWSDI for 10 meteorological stations in Pakistan. We found that improved estimates of temporal precipitation time series are good candidates for modelling and monitoring hydrological drought at the regional settings under SDI procedure.

Understanding of flood dynamics forms the basis for the leading water resource management and flood risk mitigation practices. In particular, accurate prediction of river flow during massive flood events and capturing the hysteretic behavior of river stage-discharge are among the key interests in hydrological research. The literature demonstrates that data-driven models are significant in identifying complex and hidden relationships among dependent variables, without considering explicit physical schemes. In this regard, we aim to discover the extent to which data-driven models can recognize the hidden relationships among different hydrological variables, in order to generate accurate predictions of the river flow. A secondary aim involves the detection of whether data-driven models can digest the internal features of training inputs to extrapolate severe flood records beyond the training domain. To achieve these aims, we developed a recurrent neural network (RNN) model of two hidden layers to capture the hidden relationships among the inputs, and investigated the model's predictive capability using quantitative and qualitative analyses. The quantitative analysis comprised of a comparison between model predictions, and another set of precise independent records obtained through an advanced hydroacoustic system for reference. A qualitative approach was adopted to visualize the hysteretic behavior of the stage-discharge relations of the model records, with the high-resolution records of the hydroacoustic system. The findings display the potential of data-driven models for accurately predicting river flow. Consequently, the qualitative analysis revealed moderate correlations of stage-discharge loops as compared to the reference records. Additionally, the model was tested against severe destructive flood records generated from the East Asian monsoon and tropical cyclones. Its findings suggest that data-driven models cannot extrapolate new features beyond their training dataset. Overall, this study discusses the competence of RNNs in providing reliable and accurate river flow predictions during floods.

The Bokanjac–Policˇnik system, as a complex set of mutually interrelated Dinaric karst catchments and sub-catchments, is a highly vulnerable and limited groundwater source for the wider Zadar area in northern Dalmatia, Croatia. Based on hydrogeological, hydrochemical, and hydrological research, including the prediction of groundwater discharge by the end of the twenty-first century, a complex study was performed with the following main aims: (1) groundwater protection in the present state, (2) assessment of future groundwater protection, and (3) prediction of drinking water availability and quality under the predicted climate change conditions. Long- term prediction of changes in groundwater quantity, as well as investigations of trends in groundwater quality, will allow us to protect this essential natural resource with respect to possible negative trends. The results showed that a significant decrease in the quantity of available groundwater is possible and that extraction will have to be well planned because any decrease in the groundwater pressure in this area will cause a further decrease in quality, especially regarding the possibility of seawater intrusions into the aquifer. The results of this study were incorporated in sanitary protection zones.

West Africa plays key roles in global climate and shows one of the strongest variations in hydro-climatic conditions. As it turns out, the region appears to be underrepresented in the existing compendium of Earth science and hydrology-focused journal papers when it comes to significant discussion on terrestrial hydrology and freshwater science. This prominent gap is largely precipitated by increasing number of constraints that include lack of considerable and robust investments in gauge measurements for meteorological and hydrological applications, poor funding of research institutions and other disincentives, among other factors. In this manuscript, the challenges and problems in large-scale terrestrial hydrology-focused investigation in West Africa are reviewed. Using a dossier of some recent contributions in the field of remote sensing hydrology, this review also highlights some of the progress in terrestrial hydrology and the opportunities that exist for hydro-geodetic research in West Africa that leverage on sustained investments in satellite geodetic missions. It is noted that West Africa is still a pristine environment for hydrology-focused research and can benefit from recent advancements in sophisticated space agency programs such as the Gravity Recovery and Climate Experiment, which undoubtedly has revolutionized terrestrial hydrology research around the world for nearly two decades. Given the poor density of gauge stations and limited ground observations, hydrological research in West Africa is expected to benefit more from independent space observations and multi-resolution data. This is because the lack of sufficient in-situ data for the parameterizations and adequate initialization of outputs from hydrological models and reanalysis data for hydrological applications results in poor representation of the West African land surface and hydrological state variables. To further improve our contemporary understanding of West Africa’s terrestrial hydrology, the continued evaluation/validation of these observations and space-borne measurements is advocated.

Air temperature is one of the most important meteorological factors that affect melting of glaciers, distribution of snowfall and rain at higher altitudes in the Himalaya. However, studies on spatio-temporal variability of air temperature in the central Himalaya are limited. In the present study, seasonal and annual characteristics (July 2011 to December 2015) of near-surface temperature and lapse rate in the Dokriani glacier catchment (DGC) of the central Himalaya are investigated using data from three automatic weather stations (AWSs). An attempt is also made to quantify 0 °C isotherm and temperate sustainability over the glacierized area. The results reveal that the average near-surface temperature lapse rate (NSTLR) of the catchment varies from 4.6 to 7.5 °C km−1 during all measurement seasons, suggesting that the standard environmental lapse rate (SELR, 6.5 °C km−1) is not a promising input for realistic glacio-hydrological modeling. The seasonal variability of the NSTLR indicates that the monsoon (warm and humid period) lowers the temperature lapse rate in this catchment due to the presence of high moisture content in the air. The steepest lapse rate is investigated during the pre-monsoon season due to clear and drier weather conditions. In addition to this, the results reveal strong variability in NSTLR at diurnal and sub-diurnal levels, with high variability in the day time and low in the night-time hours. A higher air temperature is examined in the ablation zone of the Dokriani Glacier during the monsoon season (i.e., JJAS: June, July, August, September), while other seasons (pre-monsoon, post-monsoon, winter) show both higher as well as lower temperatures. A large variation in 0 °C isotherm is also observed ranging from 5000 to 5500 m asl during 2012–2015. The present work emphasizes that the study of monthly, seasonal, and annual variability of the NSTLR are very important for glacio-hydrological research in the central Himalaya.

Computer-based simulation models are frequently used in hydrological research and water environment decision-making. New case studies often require existing models to be adapted. Extensions may be necessary due to the peculiarities of the studied natural system. This paper introduces the object-oriented framework called FSFM designed to cope with abovementioned challenges. The modeling framework provides an easy-to-use and flexible infrastructure for the rapid development of new, reusable simulation tools by introducing dependency injection and reflection mechanism. So, it is very suitable for building new models only by substituting a few components. In addition, the CASC2D-SED-Govers model engine is developed based on the modeling framework, and it was tested on the arsenic area based on two rainfall events. It is concluded that the modeling framework in this paper is efficient for building new models in the level of fine-grained component. This paper focuses on decomposition of the model and design methods of the plug and play of the component in the modeling framework.

The 12th International Conference on Salt Lake Research was held in Langfang City, China from July 14 to 18, 2014. Fifteen manuscripts of presentations have been retained for publication in this special issue. They are very diverse, covering the biology, physics, chemistry and geology of salt lakes, the history of hydrological research on the Dead Sea, the effects of socioeconomic and environmental policies by stakeholders on human populations, and the increasing salinization of freshwater lakes around the world.

In a case study in Tao River Basin, China, we derived a high spatial-resolution regional distribution of evapotranspiration (ET) using the single crop coefficient method and Budyko equation. We then further analyzed the spatio-temporal characteristics of this diverse eco-hydrological basin from 2001–2010. The results suggest that the single crop coefficient method based on leaf area index captures better spatial and temporal dynamics of the regional ET than did the Budyko Equation method. The rising temperature was the main reason for the increasing ET in the Tao River Basin during 2001–2010. Areas with high ET efficiency were distributed mainly in the areas where the vegetation coverage was high, and a lower runoff coefficient responded. The estimated spatial patterns of ET allowed an improved understanding of the eco-hydrological processes within the Tao River Basin and the method used might be generalized as a reference for future regional-scale eco-hydrological research.

Seasonal and interannual changes in the Earth’s gravity field are mainly due to mass exchange among the atmosphere, ocean, and continental water sources. The terrestrial water storage changes, detected as gravity changes by the Gravity Recovery and Climate Experiment (GRACE) satellites, are mainly caused by precipitation, evapotranspiration, river transportation and downward infiltration processes. In this study, a land data assimilation system LDAS-G was developed to assimilate the GRACE terrestrial water storage (TWS) data into the Community Land Model (CLM3.5) using the POD-based ensemble four-dimensional variational assimilation method PODEn4DVar, disaggregating the GRACE large-scale terrestrial water storage changes vertically and in time, and placing constraints on the simulation of vertical hydrological variables to improve land surface hydrological simulations. The ideal experiments conducted at a single point and assimilation experiments carried out over China by the LDAS-G data assimilation system showed that the system developed in this study improved the simulation of land surface hydrological variables, indicating the potential of GRACE data assimilation in large-scale land surface hydrological research and applications.

Central Asia contains one of the largest internal drainage basins in the world, and its continental location results in limited availability of both surface and groundwater. Since the twentieth century, water resources of the region have been exploited beyond sustainable levels. From small Mongolian headwater streams to the mighty Aral Sea, surface waters have been partially desiccated. Demands from the agricultural, energy and raw material sectors as well as population growth have not only increased water abstractions, but also left a diverse and strong pollution footprint on rivers, lakes and groundwater bodies. Such changes in water quantity and quality have not only led to a degradation of aquatic and riparian ecosystems, but also they have placed the region’s socioeconomic development at risk. Because of the complexity of Central Asia’s water problems, integrated assessment and management approaches are required. Despite some shortcomings in practical implementation, the widespread adoption of the Integrated Water Resources Management and water–food–energy nexus approaches may be keys to a more sustainable future. This thematic issue aims to provide documentation of the current state of scientific knowledge, ranging from hydrological research to water quality investigations, and offers an assessment of ecosystems and the services provided by them. Reviews and case studies on different management options conclude the thematic issue by providing insights into field-tested solutions for the region’s water challenges.

The arid region of northwest China is a large area with complex topography. Hydrological research is limited by scarcity and uneven distribution of rain gauges. Satellite precipitation products provide wide coverage and high spatial–temporal resolutions, but the accuracy needs to be evaluated before application. In this paper, the reliability of four satellite precipitation products (CMORPH [Climate Prediction Center’s morphing technique], PERSIANN [Precipitation Estimation from Remotely Sensed Information using Artificial Neural Networks], TRMM [Tropical Rainfall Measuring Mission] 3B42, and TRMM 3B43) were evaluated through comparison with ground data or reported values on daily, monthly, and annual scales from 2003 to 2010. Indices including frequency bias index, probability of detection, and false alarm ratio were used to evaluate recorded precipitation occurrences; relative mean bias, the correlation coefficient, and the Nash coefficient were used to assess precipitation amount. Satellite precipitation products were more accurate in the warm than in the cold season, and performed better in northern Xinjiang than in other regions during the cold season. CMORPH and PERSIANN tended to overestimate precipitation. TRMM 3B42 and TRMM 3B43 performed best because the former most accurately detected precipitation occurrences on a daily scale, and both produced accurate space–time distribution of precipitation and the best consistency with rain gauge observations. Only a few monthly precipitation values for TRMM 3B42 and TRMM 3B43, and annual precipitation values for TRMM 3B42 were with satisfactory precision. TRMM3B42 and TRMM 3B43 are therefore recommended, but correction will be needed before application. Factors including elevation, relative relief, longitude, and latitude had significant effects on the performance of satellite precipitation products, and these factors may be helpful in correcting satellite precipitation.

It is theoretically and practically significant to conduct snowmelt runoff simulations and hydrological research for high-elevation regions. The Lhasa River basin, an ungauged basin, is a typical alpine headwater region where snowmelt runoff contributes significantly to its stream flow. In this study, the snowmelt period, defined by the snow cover curves obtained at different altitudinal zones based on Moderate-Resolution Imaging Spectroradiometer (MODIS) and Digital Elevation Model data, occurred from March 6 to July 12 in the basin. The snowmelt processes were simulated with the Snowmelt Runoff Model (SRM) in 2002 and 2003 for calibration and validation, respectively. The coefficients of determination (R2) were 0.86 and 0.87 for calibration and validation, respectively, and the Nash–Sutcliffe coefficients were both 0.80, which indicate reasonable performances in simulating hydrological processes in the Lhasa River basin. The simulated snowmelt at altitudes below 5,000 m accounts for most of the snowmelt. And the simulated snowmelt runoff contributed 3–6 % to the total runoff. The sensitivity of individual parameters was analysed and ranked as follows: α and γ > CS > CR > Tcrit. In short, the SRM based on MODIS remotely sensed data performed well for the ungauged Lhasa River basin.

Over the course of hydrological research projects often a large number of heterogeneous data sets are acquired from sources as diverse as boreholes, gauging stations or satellite imagery. This data then need to be integrated into models for the simulation of hydrological processes. We propose a framework for exploration of geoscientific data and visually guided preparation of such models. Data sets from a large number of sources can be imported, combined and validated to avoid potential problems due to artefacts or inconsistencies between data sets in a subsequent simulation. Boundary conditions and domain discretisations for surface and subsurface models can be created and tested regarding criteria indicating possible numerical instabilities. All data sets including simulation results can be integrated into a user-controlled 3D scene and aspects of the data can be enhanced using a number of established visualisation techniques including thresholding and user-defined transfer functions. We present the application of this framework for the preparation of a model for simulation of groundwater flow in a river catchment in southwest Germany investigated in the scope of the WESS project.

An understanding of soil moisture heterogeneity across spatial scales has been considered to be critical to eco-hydrological research and particularly important for vegetation restoration in semi-arid areas. This study aimed to investigate the spatial variance of deep soil moisture at multiple scales in the semi-arid Loess Plateau of China. The relative importance of the related factors and the dominant driver of soil desiccation were especially discussed. The impact factors in this study are related to slope positions, land use types and precipitation. To understand the relative importance of these factors to soil moisture, the experiment was conducted at three spatial scales (slope, small catchment and region) according to the impact scope of each factor. The soil moisture to a depth of 4 m had been obtained by in situ sampling in nine catchments along the precipitation gradients from south to north across the semi-arid area of the Loess Plateau. The terrain, soil and vegetation properties were investigated synchronously. The common characteristics of soil moisture spatial variance were extracted by comparing the soil moisture profile in the plots/catchments with different climate and terrain properties. At slope scale, the deep soil moisture (>100 cm) was heterogeneous in grasslands, while relatively homogeneous in planted shrub/forest lands. At catchment scale, the influence of slope position on soil moisture was not significant compared with the influence of land use types. The deep soil moisture difference between slope positions was less than 4% in grasslands and less than 1.5% in planted shrub/forest lands, while reaching 9.7% between land use types. In the catchments, the soil moisture of different land use types commonly ranked as farmland > grassland > planted forest land, despite the climate difference in each catchment. At regional scale, precipitation was a significant factor influencing soil moisture spatial variance, but the influence was rather slow compared with the influence of afforestation. The land use type was the dominant factor of soil moisture spatial heterogeneity, rather than the slope positions and precipitation change. The afforestation was the major driver of soil desiccation in the semi-arid Loess Plateau of China. In consideration of the soil moisture conservation and the vegetation sustainable development, we suggested that abandoning slope farmland to natural grassland was a more effective measure for ecological recovery in the semi-arid Loess Plateau of China.

Eco-hydrological research in arid inland river basins has been a focus of geologists and ecologists as it is crucial for maintaining the sustainable development of socio-economy, particularly in ecologically vulnerable areas. Based on the research work carried out in the Tarim River basin of Xinjiang, northwestern China, this paper summarizes synthetically the climate change and associated responses of water resources in the mountainous area, land use and land cover in the oasis, and plants responding to environmental stresses in the desert area of the river basin. Research gaps, challenges, and future perspectives in the eco-hydrological studies of the Tarim River basin are also discussed.

Changing trends in runoff and water balance under a warming atmosphere are a major subject of interest in recent climatic and hydrological research. Forest basins represent the most complex systems including critical hydrological processes. In this study, we investigate the relationship between annual total runoff (Q), precipitation (P), and mean temperature (T) using observed data collected from 829 (forest) site years around the world. It is shown that the strong linear relationship between annual P and Q is a function of mean T. By empirically perturbing observed annual Q and P with T, a set of ΔQ-zero lines are derived for different mean T. To evaluate the extent to which the future changes in annual P and T alter Q, the future projections of ΔP and ΔT under a warming scenario (A1B) from five coupled AOGCMs (Atmosphere-Ocean General Circulation Models) are compared with the empirical ΔQ-zero lines derived in this study. It is found that five AOGCMs show different distributions with respect to the ΔQ-zero lines, which can be attributed to the contrasting dominant sensitivities of various influencing factors to water balance partitioning among models. The knowledge gained in this empirical study is helpful to predict water resources changes under changing climate as well as to interpret hydrologic simulations in AOGCM future projections.

WOS: 000280242500023 The objectives of this paper were to determine evapotranspiration (ET) from an oak-beech dominated forest ecosystem in Belgrad Forest near Istanbul, Turkey by using catchment water balance method and compare it with potential evapotranspiration (PET) computed by using Thornthwaite method. Data, in this study, were derived from a long-term hydrological research conducted in Belgrad Forest. Long-term stream flow measurements (1979-1995) were conducted with concrete sharp-crested V-notch weirs instrumented with automatic water level recorders in two close experimental watersheds. ET values of the watersheds were determined by using water balance equation. Average annual ET values from the old growth oak-beech forest ecosystem during the monitoring period of 17 years were around 833.20 mm for W-I and 752.07 mm for W-IV whereas PET estimated according to Thornthwaite method was found to be 726.14 mm. In other words, 79.68%, and 71.93% of mean annual precipitation evaporated from W-I and W-IV, respectively while 69.45% of precipitation evaporated according to Thornthwaite method. PET estimated with Thornthwaite method differed significantly only from W-I whereas W-I and W-IV had similar ET values. Istanbul UniversityIstanbul University This long-term study was financially supported by Istanbul University, Unit of Scientific Research Projects. The authors are grateful to Emeritus Professors of the Department of Watershed Management, A. N. Balci and Necdet Ozyuvaci, for their valuable contributions throughout the study period.

Digital elevation models (DEM) are becoming increasingly important as tools in hydrological research and water resources management. Since error and uncertainty are inherently associated with spatial data, a complete evaluation of a DEM is of utmost importance before it is put into subsequent analysis. The present paper offers an innovative approach for quality assessment of contour interpolated DEMs of different resolutions. Five most frequently cited interpolation methods viz., TIN with linear interpolation, Inverse Distance Weighing, Thin Plate Spline, Ordinary Kriging and TOPOGRID were selected for gridding of contours at five different resolutions i.e., 30m, 45m, 60m, 75m and 90m. In order to compare the quality of interpolated DEMs, a qualitative and quantitative evaluation of inter-polated DEMs for their vertical, horizontal and shape accuracy were carried out. It was found that different interpolation methods produced DEMs with different levels of artifacts. The analyses of vertical accuracy suggested that the variations were not pronounced in nature. However, the quantitative comparisons for horizontal and shape accuracy showed that there was a high level of disparity with significant differences among the interpolated DEMs.

Previous studies have shown chironomids to be excellent indicators of environmental change and training sets have been developed in order to allow these changes to be reconstructed quantitatively from subfossil sequences. Here we present the results of an investigation into the relationships between surface sediment subfossil chironomid distribution and lake environmental variables from 42 lakes on the Tibetan Plateau. Canonical correspondence analysis (CCA) revealed that of the 11 measured environmental variables, salinity (measured as total dissolved solids TDS) was most important, accounting for 10.5% of the variance in the chironomid data. This variable was significant enough to allow the development of quantitative inference models. A range of TDS inference models were developed using Weighted Averaging (WA), Partial Least Squares (PLS), Weighted Averaging–Partial Least Squares (WA–PLS), Maximum Likelihood (ML), Modern Analogues Technique (MAT) and Modern Analogues Techniques weighted by similarity (WMAT). Evaluation of the site data indicated that four lakes were major outliers, and after omitting these from the training set the models produced jack-knifed coefficients of determination (r2) between 0.60 and 0.80, and root-mean-squared errors of prediction (RMSEP) between 0.29 and 0.44 log10 TDS. The best performing model was the two-component WA–PLS model with r2jack = 0.80 and RMSEPjack = 0.29 log10 TDS. The model results were similar to other chironomid-salinity models developed in different regions, and they also showed similar ecological groupings along the salinity gradient with respect to freshwater/salinity thresholds and community diversity. These results therefore indicate that similar processes may be controlling chironomid distribution across salinity gradients irrespective of biogeographical constraints. The performance of the transfer functions illustrates that chironomid assemblages from the Tibetan Plateau lakes are clearly sensitive indicators of salinity. The models will therefore allow the quantification of long-term records of past water salinity for lacustrine sites across the Tibetan Plateau, which has important implications for future hydrological research in the region.

Knowledge of soil water dynamics on hillside is important for a landscape sustainable development guarantee. The mathematical modelling of the hillside soil water dynamics is a very effective and relatively accurate hydrological simulation method. This accuracy closely relates to the determination of a representative input data and characteristics in the mathematical model (Stekauerova, 2002; Mikulec, Stekauerova, 2003). Therefore, experimental hydrological research of hillside is very important. The objective of this work was to observe a hillside soil hydrological response to the infiltration experiment. The infiltration method with one cylinder was used. Soil water content in two verticals was measured by TRIME method. Soil water content data were evaluated and graphs that represent soil water dynamics on hillside in time were constructed.

Few citizens of the world would have trouble understanding the terms springs, ground water, geology, or hydrology. Newer water terms that are more familiar include bottled water, spring water, sparkling water, or mineral water, all of which now come in vessels of different shapes, sizes, colors and labels. It is interesting to note that a glass of cold, refreshing tap water will cost about 1 cent, whereas the same glass of sparkling cold bottled water will cost 50 or more times that price, and is even more than a gallon of gasoline. On the other hand, the term karst is not as well known, and it is the most pertinent objective of this congress to bring about a better knowledge and understanding of karst. “The past is a key to the future.” A wise statement; however, serving as an editor of the international journal of Environmental Geology gives frequent reminders that some younger and perhaps a few older scientists, particularly those in the consulting area, are not well aware of the stepping stones inherited from the past. This is evidenced by the use of phrases such as, “development of a new concept, method, or solution” which was published many years before. A suggestion: “do the homework” and adequately reference research while preparing project proposals, and acknowledge primary contributors on the subject. Sometimes a list of carefully selected references is more important to a fellow scientist than the paper itself. Historically, the use of karst spring waters dates back to the earliest civilizations. Cuneiform tablets provided the first written records of hydrological research that describes an expedition in 852 bc by the Assyrian King Salmanassar III to the headwaters of the Tigris. The source of the Tigris is a karst spring. Inscriptions near the entrance to the cave from which the spring discharges state that it is the source of water to the Tigris and immortalizes Salmanassar III. It is the first known reference to the formation of stalagmites. Other examples from the Bible include the principal sources of water for the ancient city of Palmyra in Syria where a spring called Efca discharges water that is warm (33°C), sulphurus, and radioactive. It was believed by some to have curative powers. In Biblical times, karst-caves or systems provided water in Sinai and at Shobek, Kirhareshet, Lachish, Jerusalem, Hazor, and Gezer. In China, a book, Annotation on Water Scripture, by Li Daoyuan, published during the second century ad describes hot springs, and the water from Lisban Spring, in China, is recorded in 1134 bc as being used for medical purposes by many monarchies. In Europe, one of the most famous springs is Bath in England. It is the site of an early spa during Roman times, where soldiers enthusiastically visited these hot springs for rest and relaxation. This source became contaminated and represents one of the earliest recorded problems with pollution of spring waters. Hot springs were famous throughout the Roman Empire, and many remain today as health resorts. In 2004, Dorothy Crouch, in her books, Water Management in Ancient Greek Cities (1993) and Geology and Settlement Greco-Roman Pattern presents two of the most comprehensive texts on interrelationships between water supplies and development of civilization in karst. The books illustrate that many of the basic hydrogeologic concepts of karst were developed by early philosophers of ancient Greece and were used in the sighting, planning, and construction of Syracuse Corinth, Delphi, Miletus, Ephesus, plus five other sites that were studied and compared representing 1400 years of urbanization by the Greeks and Romans.

To meet these challenges, a number of novel research programs and networks focusing on entire catchments or landscapes have recently been established such as CUASHI (Toran and Hooper 2004) or TERENO (Zacharias et al. 2011). ‘‘Catchment Research’’ is the second Topical Issue (TI) in Environmental Earth Sciences with a focus on international hydrological research. Most of the material has been provided by the Water Earth System Science Competence Cluster (WESS) founded by the Universities of Tubingen, Stuttgart, and Hohenheim together with the Helmholtz Centre for Environmental Research, UFZ (Grathwohl et al. 2013). The TI ‘‘Catchment Research’’ is a follow-up of the IWAS issue (Kalbus et al. 2012) which was dealing with Integrated Water Resources Management in different climate-hydrological sensitive areas in the world. ‘‘Catchment Research’’ is organized in three sections, starting with results from the initial period of the WESS project, followed by invited studies from catchment research in Europe, Asia and South America. The last part of the volume presents overview and technical papers on the development of terrestrial observatories, in particular, the TERENO network. A ‘‘News and Views’’ contribution concerning the networking and community efforts of the Water Science Alliance initiative is provided at the end of this issue (Krueger and Teutsch 2013). The first section of ‘‘Catchment Research’’ consists of contributions from the Water Earth System Science Competence Cluster. Grathwohl et al. (2013) provide a comprehensive overview of the WESS research concept and field sites. Studies presented put emphasis on experimental investigations in various sub-catchments of the Neckar River basin, e.g., using fluorometry (Lemke et al. 2013), assessing hyporheic exchange processes (Osenbruck et al. 2013), and delineating subsurface heterogeneity underneath the river bed (Doro et al. 2013). David et al. (2013) are investigating the influence of sewer overflows to accumulation patterns in river bed sediments. The second Editorial to the EES Topical Issue ‘‘Catchment Research’’.

Statistical analysis of parameters and residuals of conceptual hydrological models has received little effort in the hydrological research, certainly by orders of magnitude less than on many other problems like development and comparison of automatic calibration methods, optimisation algorithms, etc. Much more work is required than is presently undertaken to investigate the properties of model residuals. There is a need of an easily understandable and applicable statistical analysis scheme. In this article, a procedure is presented through which two basic issues of model evaluation are accounted for. First, different techniques used for parameter analysis are discussed. Second, methodology of residual analysis is discussed and the general behaviours of residuals are examined. To illustrate the procedure, a simple water balance model was applied to the Stabbybacken River Basin in central Sweden.

It is increasingly clear that there is a need to assist National Hydrological Agencies in Africa to improve their hydrometric data collection capabilities and at the same time to halt the decline in hydrometric standards. This has to be achieved in a cost-effective and sustainable way and, at the same time reinforce existing systems with new technology and equipment and strengthen the institution capacity of these agencies. The Southern African Development Community-Hydrological Cycle Observation System (SADC-HYCOS) will provide the framework, methodologies and tools to achieve this goal. This paper provides the first opportunity to inform the global hydrological community of the aims and activities of the SADC-HYCOS project. Significant advances will be made in the installation of real time data collection platforms and transmission system, the development and implementation of a regional database, the improvement and/or development of data exchange and dissemination systems using a regional electronic network and Internet links, the development of hydrometeorological products from the database and establishing a large scale training programme relating to activities during the life-time of the project. SADC-HYCOS will promote the collection, processing and exchange of hydrological data and information within the region and raise the profile of the regional hydrological issues, hydrological research, operational hydrology, availability of data and information to a global audience.

The effect of regional, subregional and local groundwater flow systems on mesotrophic fen ecosystems was studied in the polders of the Vecht River plain that borders the Pleistocene ice-pushed moraine of Het Gooi. Variation in the vegetation and in the habitat factors (groundwater and peat soil) of fens depends whether or not the fens are connected to the outflow of the regional groundwater system. Changes in the regional groundwater flow system, caused by changes in the water management of the polders, are probably responsible for the deterioration of mesotrophic fens. Drastic measures will have to be taken to restore the hydrology on a regional scale if the mesotrophic fens are to be saved from extinction. Hydrological research that integrates the results of regional and local studies is essential if the ecology of fen ecosystems is to be understood.

This article is an attempt to give a brief review on the status of groundwater studies in Egypt, their results, and the present plans for groundwater development that are usually based on the hydrogeological characteristics of the groundwater resources as well as on the environmental control of the discharge area. In terms of groundwater hydrology, Egypt can be divided into the following groundwater provinces: (1) the Western Desert, (2) the Eastern Desert, (3) the Nile Valley including the delta, (4) the Sinai Peninsula, (5) the Northern Coastal Zone, and (6) Wadi El-Natrun. The studies of volume and nature of groundwater and the environmental impact studies that were carried out in each of these provinces differed according to the importance given to development of projects in areas of interest and to the availability of funds. Recent studies and the surveys conducted for groundwater hydrological research by local and international organizations are described separately for each province. Special reference is made to groundwater hydro-geological setting, groundwater resources evaluation, and present and future utilization. The New Valley is the largest Egyptian irrigated agricultural development project that is solely dependent on groundwater resources. An outline showing its nature, objective, and size is included as an example of groundwater development.

Although practice of hydrology can be traced back to as early as 5000 to 6000 years ago in ancient Mesopotamia, Egypt and China, the study of hydrology emerged as a discipline in the 17th century when Pierre Perrault, Edme Mariotte and Edmond Halley conducted their experimental work on the hydrologic cycle. For quite a long period, hydrological education and research programs were offered primarily as an engineering discipline in universities in the United States and many East Asian countries. With our increasing understanding of the mechanisms of spatial and temporal distributions of water over large watersheds, and even the globe, and the capabilities of computer modeling of complicated hydrological processes, the study of hydrology has now extended to and interacted with meteorology, geophysics, environmental science, and mathematical statistics, and has established its own right as a branch of geoscience. Recognizing the geoscience nature of hydrology, a hydrology section in TAO was established in 2006 and has since received an increasing number of papers contributing to this growing field. This issue marks the first TAO special issue in hydrology. It focuses on two topics watershed management and climate change impacts in hydrology, both involving spatial scales which are characteristic of hydrology. This special issue is composed of seven papers on watershed management addressing water quality, groundwater, coastal inundation, hill-slope runoff, and surface and ground water interaction and five papers on climate change impacts on sea level rise, extreme rainfall frequency, runoff regime, river discharge, and water quality management. Case studies were carried out in different countries including Taiwan, United States, China, Japan, and Vietnam and in vastly different terrain ranging from Tampa Bay in Florida, USA, coastal lowlands in Taiwan, river basins in Japan and Central Vietnam, to the Tibetan Plateau in China. Hydrological research is multi-faceted, and, with our improved knowledge of hydrological processes and growing concern of the global influence of hydrological changes, new issues will arise continuously. It is the editors’ belief that this special issue will serve as a stepping stone in addressing hydrologic issues that not only are of global concern but also fundamental for universal applications. We are grateful to the TAO editorial office for their superb support and assistance during the review and editing process. Our sincere appreciations also extend to all contributing authors and reviewers for their enthusiasm and dedication, which have made this special issue a reality.

Dr. Samuel Mandel, most recently a retired professor of hydrogeology from Hebrew University of Jerusalem, was born in Austria in 1918. After completing high school, he studied chemistry atthe University ofVienna. In 1938, his studies were interrupted due to the annexation of Austria by Germany. He escaped from Austria and went to Palestine as an illegal immigrant, workipg as a labourer in the Dead Sea potash plant. During World War II, he joined the British Army and served in Lebanon, Egypt, and Greece. After the war, he studied physics and geology in Jerusalem and then specialized in hydrology at the University of Grenoble, France. In 1961, he receive a Ph.D. from the Israel Institute of Technology for his work on the Cenomanian-Turonian limestone aquifer of western Israel. Tahal Consulting Engineers, Ltd., employed Dr. Mandel as the chief of groundwater investigations and later as the head of the Department of Hydrological Research. During his years in Tahal, he worked in many developing countries in exploration, assessment, and utilization of groundwater for domestic and irrigation supplies. With this varied experience, in 1966 he joined the Ground Water Research Centre of the Hebrew University of Jerusalem. When Israel's Ministry of Foreign Affairs started the UNESCO-sponsored "International PostGraduate Diploma Course in Groundwater" at the university in 1968, Prof. Mandel was appointed as the Course Director, a position that he held for more than 20 years. This course became very popular among mid-level hydrogeologists, especially those from developing countries. In 1969, I was fortunate to get admission to this course and to become one of Prof. Mandel's students. Prof. Mandel was a devoted field hydrogeologist and a great teacher. "Coastal aquifers" was his favourite subject, and he supervised the construction of a parallel-plate Hele-Shaw model to demonstrate seawater intrusion to his students. Even after the advent of computer modeling in groundwater studies, he insisted that his students should always keep in mind the basic principles of hydrogeology, realize the importance of good quality field work, and avoid over-simplification of natural conditions while modeling. In the classroom, his casehistories included his personal experiences on projects from various countries such as M~xico, Uruguay, Nepal, Iran, Israel, and Korea. Prof. Mandel had a special skill of making his lectures interesting and engrossing by adding witty comments and remarks from time to time. He liked to refer to the water table or piezometric head as the "pulse" of the aquifer, which his students should monitor in order to prevent the aquifer from becoming "ill." He loved his students and was always prepared

The International Hydrological Decade (1965–75) has stimulated hydrological research of many kinds. One project is concerned with a small catchment area in Yorkshire