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There is increasing recognition of the need to incorporate the complex and dynamic interactions between society and water in studies of water resource systems. The study of human-water dynamics requires the involvement of researchers from different disciplines, including hydrology and social science. This paper tracks recent trends in socio-hydrological research using quantitative and qualitative methods. Bibliographic metrics and network analysis are used to identify general trends and illustrate the internal connections in this small but growing interdisciplinary field. Results show that hydrologists dominate research in socio-hydrology as presently defined, with far less participation from social scientists. Research questions for socio-hydrology tend to focus on system dynamics and are often not framed in a way that engages the interests and expertise of social scientists. A qualitative analysis addresses key barriers to the interdisciplinary development of socio-hydrology and identifies research needs and directions for better integration of the human dimensions of water science. Attracting social scientists to this field requires a broader conceptualization of socio-hydrology to focus on sustainable development, risk assessment, hazard management, resilience, adaptation, and knowledge mobilization in addition to hydrology’s traditional focus on systems modeling and decision support. We propose three themes for thematic focus: systemic risk and natural hazards; sustainability science; and adaptive governance. This broader framing of socio-hydrology is inherently more interdisciplinary, brings new methods and viewpoints to the field, and ensures that place-based local values are included in studies of water system dynamics.

In the past, land consolidation projects in the Netherlands were aimed almost exclusively at increase of crop yields and farm income. Also the improvement of the water management system served agricultural purposes. Hydrological research, therefore, was directed to find optimal agrohydrological conditions. The results were translated into criteria for hydrological variables (like groundwater and surface water levels, discharge coefficients) and design rules for subsurface drainage systems. Initially the need to reduce excessive wetness was emphasized, later yield reduction due to water shortages in summer also became important. Lately the land consolidation projects have been renamed as “land development projects”. This is a result of recent developments in the rural areas, where aspects of nature conservation and outdoor recreation have become important items. Because water management measures in favour of one function often interfere with another, fixed design rules are no longer sufficient. The hydrological consequences for different interests have to be known beforehand. For the calculations of groundwater flow, analytical solutions are being replaced by numerical methods in order to cope with increasingly complex situations. Aspects of water quality are becoming more important. In addition to analyses of water samples, attention is paid to flow paths and stream velocities of groundwater, which give insight into the relation between quality and quantity. In this work, a close cooperation with agronomists and biologists has been established. A review is given of the hydrological models used for this purpose, at present and in the near future.

Intercepted rainfall may be evaporated during or after the rain event. Intercepted rain is generally determined as the difference between rainfall measurements outside and inside the forest. Such measurements are often used to discriminate between water storage and evaporation during rain as well. Two well-accepted methods underestimate water storage by a factor two as compared to direct observations. The underestimation of storage is compensated by an overestimation of evaporation during rain by a factor of three. The direct observations of water storage and evaporation appear to agree with previous direct observations. Thus, it is concluded that these observations are representative Also, our results based on methods using only rainfall measurements inside and outside the forest appear to agree with previous results, This would result in the conclusion that the common methods systematically underestimate water storage and overestimate evaporation during rain. Indeed, the systematic errors can be explained by the neglect of drainage before saturation. Water storage is better simulated assuming an exponential saturation of a larger storage capacity. A smaller evaporation can be simulated using an appropriate resistance to vapour transport. The observations in dense coniferous forest showed water storage to be the dominant process in rainfall interception, but this conclusion should not be generalized to other forests and climates. Direct observations of water storage and evaporation are recommended to build a realistic set of parameters for rainfall interception studies of the main vegetation types. (C) 1998 Elsevier Science B.V. All rights reserved.

High-elevation grasslands worldwide provide essential hydrological services including water provision, flow regulation, and erosion control. Despite their importance, hydrological research of grasslands in montane regions is usually scarce and disperse, limiting the capacity to improve water resource management. We present a systematic literature review of the hydrological function of high Andean grasslands under conserved, degraded, and restored conditions in ecosystems situated above the tree line in the tropical Andes (paramos, punas, and jalcas). Most hydrological research on these grasslands has been developed in paramos (92%), especially in Ecuador, while research in punas is scarce (6%) despite being the largest grassland extent in the region. For paramos, published literature highlights the importance of conserving grasslands to facilitate water infiltration to soils, which in turn reduces erosive processes. Water-vegetation relations for conserved paramos are well understood, indicating that about 50% of water inputs return to the atmosphere via evapotranspiration, but knowledge about hydrological functions of conserved punas and jalcas is virtually non-existent. Under changing land use, afforestation of grassland ecosystems with exotic tree species, especially pines, reduces soil water storage as well as water yield and flow regulation capacity. Impacts of grazing and agriculture on the hydrological function of paramo grasslands strongly depend on historical land management and current land use practices and are not generalizable. Short-term restoration studies indicate that more than two years are necessary to recover the hydrological function of degraded grasslands, therefore medium and long-term studies are required to determine efficient restoration periods. These knowledge gaps limit the ability to extrapolate and regionalize findings. Future directions aimed to fill them are proposed, and methods successfully used to investigate the hydrology of high Andean grasslands are highlighted. This research not only enlightens what is known about the hydrology of high Andean grasslands, but also seeks to guide future hydrological evaluations to fill identified geographical and topical knowledge gaps precluding improved management of water resources in the tropical Andes.

In the Federal Republic of Germany (West) at the present time 14 forest hydrological research projects with 34 individual catchments are being maintained. In some cases measurements have been extended to several sub-catchments. Mostly, the approaches of ungaged paired-watershed studies or single-watershed studies are used. Only in the Forest Hydrological Research Area of Krofdorf was the procedure of a watershed calibration with two control catchments and two planned experimental catchments carried out for 10 years and subsequently, during the winter of 1982–1983, reductions of forest cover density by cuttings were started. In connection with forest decline caused by air pollution and its effects on amount, timing and quality of discharge there is an increasing demand to use sound long-term quantitative and qualitative precipitation and streamflow measurements of forest catchments such as ‘benchmark-catchments’. However, for this purpose the procedures of a climatic calibration and/or watershed modelling must be realised.

The aim of hydrological research has always been, and should still be to improve our understanding of hydrologic processes. Catchment hydrological response has the potential to enhance understanding of these processes. Regionalisation of hydrological response is important in identifying watersheds with similar catchment hydrological response, thus making predictions in ungauged and poorly gauged basins to be possible. This study establishes the hydrological response of 122 catchments in Swaziland's trans -boundary basins on the basis of validated WR90 hydro-meteorological time series data. The flow duration indices (FDIs: Q10, Q50, Q90) were determined and standardised by the mean monthly streamflow, and the runoff ratio was calculated as a method to determine how catchments respond to precipitation inputs. The runoff ratio and FDIs were then plotted against aridity indices, and the plot shows that the runoff ratio is consistent with the aridity index, except for a few suspected anomalies emanating from values of Q50 and Q90. The findings indicate that the hydrological response of the catchments is diverse and somewhat characterised by regions. The diversity and the regions are associated with climate regime and topography controls. It is anticipated that the potential of using hydrological response to gain more understanding of catchments behaviour will improve and further rigorous exploration may be required.

Long-term persistence (LTP) of annual river runoff is a topic of ongoing hydrological research, due to its implications to water resources management. Here, we estimate its strength, measured by the Hurst coefficient H, in 696 annual, globally distributed, streamflow records with at least 80 years of data. We use three estimation methods (maximum likelihood estimator, Whittle estimator and least squares variance) resulting in similar mean values of H close to 0.65. Subsequently, we explore potential factors influencing H by two linear (Spearman's rank correlation, multiple linear regression) and two non-linear (self-organizing maps, random forests) techniques. Catchment area is found to be crucial for medium to larger watersheds, while climatic controls, such as aridity index, have higher impact to smaller ones. Our findings indicate that long-term persistence is weaker than found in other studies, suggesting that enhanced LTP is encountered in large-catchment rivers, were the effect of spatial aggregation is more intense. However, we also show that the estimated values of H can be reproduced by a short-term persistence stochastic model such as an auto-regressive AR(1) process. A direct consequence is that some of the most common methods for the estimation of H coefficient, might not be suitable for discriminating short- and long-term persistence even in long observational records.

Reconstruction of missing runoff data is of important significance to solve contradictions between the common situation of gaps and the fundamental necessity of complete time series for reliable hydrological research. The conventional empirical orthogonal functions (EOF) approach has been documented to be useful for interpolating hydrological series based upon spatiotemporal decomposition of runoff variation patterns, without additional measurements (e.g., precipitation, land cover). This study develops a new EOF-based approach (abbreviated as CEOF) that conditions EOF expansion on the oscillations at outlet (or any other reference station) of a target basin and creates a set of residual series by removing the dependence on this reference series, in order to redefine the amplitude functions (components). This development allows a transparent hydrological interpretation of the dimensionless components and thereby strengthens their capacities to explain various runoff regimes in a basin. The two approaches are demonstrated on an application of discharge observations from the Ganjiang basin, China. Two alternatives for determining amplitude functions based on centred and standardised series, respectively, are tested. The convergence in the reconstruction of observations at different sites as a function of the number of components and its relation to the characteristics of the site are analysed. Results indicate that the CEOF approach offers an efficient way to restore runoff records with only one to four components; it shows more superiority in nested large basins than at headwater sites and often performs better than the EOF approach when using standardised series, especially in improving infilling accuracy for low flows. Comparisons against other interpolation methods (i.e., nearest neighbour, linear regression, inverse distance weighting) further confirm the advantage of the EOF-based approaches in avoiding spatial and temporal inconsistencies in estimated series.

Remote sensing can potentially be used to monitor river ice, which is of significance for water resource utilization and hydrological research, especially on the Tibetan Plateau, over which field observations are severely limited. However, methods to monitor the river ice distribution over a large scale while overcoming snow interference have not been reported yet. To monitor river ice on the Tibetan Plateau on a large scale, we present a relative difference river ice (RDRI) identification method based on the differential spectral characteristics of river ice. The difference between the red and near-infrared (NIR) band reflectance of river ice is divided by the sum of the NIR reflectance and infrared band reflectance. The resulting values are notably different for river ice and other neighboring similar landscapes, such as snow cover. This method can overcome the interference caused by snow cover and other surrounding landscapes and enable the monitoring of river ice in different forms at different elevations on the Tibetan Plateau. The RDRI method is applied to Landsat and Sentinel-2 images. The validation results show that the mean overall accuracy and Kappa coefficient were 99.76% and 0.94, respectively. The comparison of the RDRI and normalized difference snow index (NDSI) methods indicates that the accuracies of both methods for river ice monitoring are similar in the absence of any snow disturbance. The RDRI can enable more accurate remote sensing of river ice on a large scale, which can support river ice distribution research over the Tibetan Plateau.

Soil moisture data assimilation (SMDA) has found growing application in the hydrological research community because of readily available satellite-based soil moisture (SM) data. Several past studies have explored the capability to assimilate observed SM in hydrological model to enhance streamflow prediction. However, the impact of the conceptual hydrological model (CHM) structure on the SMDA in streamflow prediction has not been investigated yet. In this study, to understand the CHM structure's role, we used three different CHMs for the SMDA: dynamic Budyko (DB), Genie Rural a 4 parametres Journalier (GR4J), and Probability Distributed Model (PDM) model. The SM obtained from Global Land Data Assimilation System (GLDAS) was assimilated using Ensemble Kalman Filter (EnKF) for 43 Model Parameter Estimation Experiment (MOPEX) basins. The GR4J model was found to be performed best from calibration and validation results, and the DB model was found to be performed least. The results show that the performance of the DB model improved during assimilation compared to its open-loop version for all the 43 basins. However, deterioration in model performance was observed for the GR4J and PDM model during assimilation for all basins except a few. The assimilated model performance was evaluated in respect of Assimilation Efficiency (AE) and ranged from 2.56 to 81.24%, −70.9 to 17.65%, and −71.38 to 24.86%, respectively, for the DB, GR4J, and PDM model. Further, we hypothesized that if the GLDAS SM is better than the model-simulated SM, then improvement in the model performance is observed due to the SMDA. The coefficient of determination (r2) between the SM simulated by all the three models without assimilation and the GLDAS SM was found for all the basins. Results indicated that the GR4J and PDM model captured SM better than the DB model. Moreover, to strengthen this hypothesis, we run the GR4J and PDM model deterministically, considering the daily GLDAS SM as the initial condition for streamflow simulation instead of the SM simulated by these models for the basins where deterioration in model performance was observed. For all the basins, it is found that the GR4J and PDM model performance deteriorated. Even though the GLDAS SM is used as every day's initial condition to simulate the streamflow, no improvement of model performance is observed. In general, our study underlines the significance of the CHM structure in the SMDA exercise.

The integration of interdisciplinary scientific and societal knowledge plays an increasing role in sustainability science and more generally, in global change research. In the field of water resources, interdisciplinarity has long been recognized as crucial. Recently, new concepts and ideas about how to approach water resources management more holistically have been discussed. The emergence of concepts such as socio-hydrology indicates the growing relevance of connections between social and hydrological disciplines. In this paper, we determine how well social sciences are integrated with hydrological research by using two approaches. First, we conducted a questionnaire survey with a sample of hydrology researchers and professionals (N = 353) to explore current opinions and developments related to interdisciplinary collaboration between hydrologists and social scientists. Second, we analyzed the disciplinary composition of author teams and the reference lists of articles pertaining to the socio-hydrology concept. We conclude that interdisciplinarity in water resources research is on a promising track but may need to mature further in terms of its aims and methods of integration. We find that current literature pays little attention to the following questions: What kind of interdisciplinarity do different scholars want? What are social scientists’ preferred roles and knowledge from a hydrology perspective?

Mixing calculations (i.e., the calculation of the proportions in which end-members are mixed in a sample) are essential for hydrological research and water management. However, they typically require the use of conservative species, a condition that may be difficult to meet due to chemical reactions. Mixing calculation also require identifying end-member waters, which is usually achieved through End Member Mixing Analysis (EMMA). We present a methodology to help in the identification of both end-members and such reactions, so as to improve mixing ratio calculations. The proposed approach consists of: (1) identifying the potential chemical reactions with the help of EMMA; (2) defining decoupled conservative chemical components consistent with those reactions; (3) repeat EMMA with the decoupled (i.e., conservative) components, so as to identify end-members waters; and (4) computing mixing ratios using the new set of components and end-members. The approach is illustrated by application to two synthetic mixing examples involving mineral dissolution and cation exchange reactions. Results confirm that the methodology can be successfully used to identify geochemical processes affecting the mixtures, thus improving the accuracy of mixing ratios calculations and relaxing the need for conservative species. Fil: Pelizardi, Flavia Paola. Universidad Nacional del Centro de la Provincia de Buenos Aires. Rectorado. Instituto de Hidrología de Llanuras - Sede Azul. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Instituto de Hidrología de Llanuras - Sede Azul; Argentina Fil: Bea, Sergio Andrés. Universidad Nacional del Centro de la Provincia de Buenos Aires. Rectorado. Instituto de Hidrología de Llanuras - Sede Azul. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Instituto de Hidrología de Llanuras - Sede Azul; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Carrera, Jesús. Consejo Superior de Investigaciones Científicas; España. Universidad Politécnica de Catalunya; España Fil: Vives, Luis Sebastián. Universidad Nacional del Centro de la Provincia de Buenos Aires. Rectorado. Instituto de Hidrología de Llanuras - Sede Azul. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Instituto de Hidrología de Llanuras - Sede Azul; Argentina

Conceptual models often suffer from the over-parameterization problem due to limited available data for the calibration. This leads to the problem of parameter nonuniqueness and equifinality, which may bring much uncertainty of the simulation result. How to find out the appropriate model structure supported by the available data to simulate the catchment is still a big challenge in the hydrological research. In this paper, we adopt a multi-model framework to identify the dominant hydrological process and appropriate model structure of a karst spring, located in Guilin city, China. For this catchment, the spring discharge is the only available data for the model calibration. This framework starts with a relative complex conceptual model according to the perception of the catchment and then this complex is simplified into several different models by gradually removing the model component. The multi-objective approach is used to compare the performance of these different models and the regional sensitivity analysis (RSA) is used to investigate the parameter identifiability. The results show this karst spring is mainly controlled by two different hydrological processes and one of the processes is threshold-driven which is consistent with the fieldwork investigation. However, the appropriate model structure to simulate the discharge of this spring is much simpler than the actual aquifer structure and hydrological processes understanding from the fieldwork investigation. A simple linear reservoir with two different outlets is enough to simulate this spring discharge. The detail runoff process in the catchment is not needed in the conceptual model to simulate the spring discharge. More complex model should need more other additional data to avoid serious deterioration of model predictions.

The availability of continuous long-term precipitation time series with uniform spatial distribution has a significant role in hydrological studies and applications from simple water budget calculation to infrastructure design. However, in numerous parts of the world precipitation observations are sparse, patchy and uneven and hence hydrological research and hydroclimate-related projects are conducted with uncertainty. Therefore, filling gaps in precipitation time series and estimating precipitation in ungauged regions are of prime importance. Satellite-based precipitation measurement methods, among rainfall measuring tools, seem to be the most promising method to provide continuous and high spatiotemporal precipitation data. Precipitation Estimation from Remotely Sensed Information using Artificial Neural Networks-Climate Data Record (PERSIANN-CDR) is one of the most commonly used precipitation retrieval algorithms, with long term data and high spatiotemporal resolutions that is employed in this study. Biases in the satellite-based precipitation data, as some studies have reported, demand the development of bias-correction models to enhance the accuracy of the satellite-based estimates. First, the performance of the PERSIANN-CDR algorithm is assessed based on 35 years of monthly, seasonal and annual observed precipitation at 49 stations as the benchmark in Fars province, Iran. Results indicate that while PERSIANN-CDR mimics the precipitation time series with a high degree of correlation, it underestimates the precipitation in the province with the Root Mean Squared Error (RMSE), Relative Mean Error (RME) and BIAS of (15.23 mm, 0.23 and 0.77), (37.68 mm, 0.24 and 0.76) and (96.07 mm, 0.24 and 0.76) for the monthly, seasonal and annual precipitation, respectively. Then, a set of bias-correction models is developed to enhance the PERSIANN-CDR estimates with the reduced monthly, seasonal and annual RMSE, RME and BIAS of (9.09 mm, −0.01 and 1.01), (19.36 mm, −0.01 and 1.01) and (41.23 mm, 0.0 and 1.0), respectively. The Bias-correction models are validated with the precipitation time series that were not used in the development phase. The validated models proved as an effective and robust tool in improving the accuracy of the PERSIANN-CDR datasets. We also demonstrate how the proposed models are used to estimate precipitation at ungauged sites and to fill in the gaps in the ground-based precipitation time series. The proposed models provide the practitioners, planners, and decision-makers with a huge precipitation data bank for various hydro-climatological projects in the study area.

Precipitation products are good choices to complement ground observations in hydrological research, but their accuracy is uncertain in different areas. This study aims to evaluate the systematic error characteristics of four major precipitation products, namely, Climate Prediction Center MORPHing technique(CMORPH), Climate Hazards Group Infrared Precipitation with Stations (CHIRPS), Global Land Data Assimilation System (GLDAS), and Tropical Rainfall Measuring Mission(TRMM) 3B42 v7, over the Yangtze River Basin in terms of estimating precipitation amounts and detecting events. The results show that the precipitation products have high spatial and seasonal heterogeneity of error characteristics, and the capability to capture rain occurrence decreases when rainfall intensity increases. GLDAS demonstrated the poorest performance, with the lowest correlation of 0.08 and the largest relative bias of over 25% underestimation. The possibility of GLDAS missing medium and heavy rains (>15 mm/d) reached 50%, and of falsely reporting light rainfall was up to 40%, while CMORPH outperformed the others with the highest consistency (0.39) against the gauge, the smallest root-mean-square error (RMSE) (10.28 mm), and the highest scores for most subregions. Generally, in this study GLDAS proved its inferiority to satellite-based precipitation products for hydrological applications over the Yangtze River Basin.

1. Rehabilitating degraded riverine landscapes in order to restore their ecosystem services require a scientific approach. The tasks include the development of methods for the assessment of ecological conditions and trends, for benchmarking of management alternatives and for the definition of ecological goals. 2. The central challenge is to develop a coherent eco-hydrological research protocol analyzing the causal effects of hydrology on geomorphic processes and ecology. 3. A major aspect is the formulation of ecological targets: historical reference conditions can be used to illustrate ecological deficiencies. However, at the planning and operational levels, they have to be substituted by a set of models which predict the responses towards management measures. 4. Large scale restoration programmes should be accompanied by hypothesis-based research in order to analyze the effects of engineering measures and advance our understanding of river-floodplain ecology. 5. A focus has to be the promotion of comprehensive management concepts, taking into account all concerned parties and assuring their active involvement. It is important to take advantage of management initiatives of various stakeholders, because governmental water policies rarely promote ecological improvement as a goal in itself. 6. Institutional frameworks should be established with the mandate to develop large-scale and comprehensive rehabilitation concepts and guaranteeing transparent planning and decision processes. It is imperative that expert panels comprising of scientists, river-engineers, planners and managers are installed, with long-term mandates, clearly defined responsibilities and authority for decision making.

The Badain Jaran Desert, located in western Inner Mongolia in northwestern China, is characterized by the coexistence of high megadunes and numerous lakes. The spatial distribution of groundwater systems and supply sources of lakes have yet to be elucidated. Ra isotopes and geochemistry of water samples from 17 lakes and their peripheral groundwater were investigated. The characteristics of the geochemical behaviors of Ra isotopes, including activities, activity ratios, main sources and sinks, and geochemistry both of groundwater and lake water, suggest that there are two groundwater flow systems in the studied area: the southern-central and the northern groundwater flow systems. The southern-central groundwater is supplied from mountains farther to the south and the northern groundwater supplied from areas farther to the north. We developed mass balance models for 228Ra in fresh and saline lakes. The equation for the saline lakes has three input terms: groundwater discharge, atmospheric deposition and diffusion from bottom sediments; and two outputs: radioactive decay and coprecipitation. The freshwater lake equation has one input term: radionuclide supply from groundwater; and two output terms: adsorption onto particles in the lake and radioactive decay. Mass balance calculations for 228Ra give discharge fluxes of 0.03 × 106–7.72 × 107 m3 yr−1 for the lakes. The flushing times of the lakes were estimated to be 0.05–9.23 yrs. The results of this study promote scientific understanding of the hydrologic cycle and water resource evaluation in the Badain Jaran Desert and provide a paradigm for radium isotope application in hydrological research in arid areas.

River ice monitoring is important for hydrological research and water resource management of the Tibetan Plateau but limited by the serious shortage of field observations, and remote sensing can be used as an effective supplementary means for monitoring river ice. However, remote sensing high-altitude river ice is scarce and a basin-scale understanding of river ice is lacking on the Tibetan Plateau. To ascertain the spatial and temporal distribution characteristics of high-altitude river ice at the basin scale, we selected the Babao River basin as the study area, which is a typical river basin located in the northeastern Tibetan Plateau. Utilizing 447 available Landsat images during the river ice period from 1999 to 2018 and the classical normalized difference snow index (NDSI) algorithm, we monitored the river ice in a long time series at the Babao River basin. The average Khat of accuracy validation reached 0.973. The average area of river ice in the river ice period of this basin showed a weak decreasing trend and was negatively correlated with air temperature. We also found that gentle slopes and high elevations are beneficial for the development of river ice. The melting of river ice supplements river discharge in spring. This study is the first to reveal the distribution characteristics and changing trend of river ice at the basin scale on the Tibetan Plateau, and the results provide a reference for river ice research in this region.

Summary Coupling surface and subsurface water flow in fully integrated hydrological codes is becoming common in hydrological research; however, the coupling of surface–subsurface solute transport has received much less attention. Previous studies on fully integrated solute transport focus on small scales, simple geometric domains, and have not utilised many different field data sources. The objective of this study is to demonstrate the inclusion of both flow and solute transport in a 3D, fully integrated catchment model, utilising high resolution observations of dissolved organic carbon (DOC) export from a wetland complex during a rainfall event. A sensitivity analysis is performed to span a range of transport conditions for the surface–subsurface boundary (e.g. advective exchange only, advection plus diffusion, advection plus full mechanical dispersion) and subsurface dispersivities. The catchment model captures some aspects of observed catchment behaviour (e.g. solute discharge at the catchment outlet, increasing discharge from wetlands with increased stream discharge, and counter-clockwise concentration–discharge relationships), although other known behaviours are not well represented in the model (e.g. slope of concentration–discharge plots). Including surface–subsurface solute transport aids in evaluating internal model processes, however there are challenges related to the influence of dispersion across the surface–subsurface interface, and non-uniqueness of the solute transport solution. This highlights that obtaining solute field data is especially important for constraining integrated models of solute transport.

Computer-based simulation models are frequently used in hydrological research and engineering but also in other fields of environmental sciences. New case studies often require existing model concepts to be adapted. Extensions may be necessary due to the peculiarities of the studied natural system or subtleties of anthropogenic control. In other cases, simplifications must be made in response to scarce data, incomplete knowledge, or restrictions set by the spatio-temporal scale of application. This paper introduces an open-source modeling framework called ECHSE designed to cope with the above-mentioned challenges. It provides a lightweight infrastructure for the rapid development of new, reusable simulation tools and, more importantly, the safe modification of existing formulations. ECHSE-based models treat the simulated system as a collection of interacting objects. Although feedbacks are generally supported, the majority of the objects' interactions is expected to be of the feed-forward type. Therefore, the ECHSE software is particularly useful in the context of hydrological catchment modeling. Conversely, it is unsuitable, e.g., for fully hydrodynamic simulations and groundwater flow modeling. The focus of the paper is put on a comprehensible outline of the ECHSE's fundamental concepts and limitations. For the purpose of illustration, a specific, ECHSE-based solution for hydrological catchment modeling is presented which has undergone testing in a number of river basins. (C) 2015 Elsevier Ltd. All rights reserved.

In hydrogeology, understanding the behavior of aquifers is an important issue. May it be for forecasting the availability of water on a long term or for estimating the impact of pollutants when injected at difierent regions, modeling of an aquifer is very useful for hydrogeologists. This paper gives an overlook of the difierent types of tests on a particularsite, namely the Hydrogeological Experimental Site (HES) of Poitiers (France). The aim is to show that the HES is a huge instrumented test bed allowing difierent types of experiments. Thus, system identification users can expect to gather large series of input-output datasets so as to experiment their own tools. Note that a large database exists concerning already-run tests, but what is interesting is that new experiments can be programmed so as to account for customized datasets. As a counterpart, the use of HES data should promote proper modeling of the underlying aquifer, thus contributing to the hydrological research field.

In the wake of changing climate the present water crisis seems to tighten its hold on the Mankind hence water resources estimation is integral part of planning, development and management of water resources of the country and the estimation of water resource is based on several hydrological and meteorological parameters. Rainfall is the main source of the ground and surface water resources. Recently due to anticipated climate change it is projected that spatial and temporal pattern of rainfall in different part of the country will be change and there will be increase in intensity of rainfall greater monsoon variability. This unprecedented change is expected to have severe impact on the on the water resource and finally on water resource estimation for future planning and management. Apart from climate change, both the ever increasing population and the rapidly changing land use patterns have left the major river basins of the India in a bleak uncertainty to keep up the required runoff. For planning and management, the climate and the hydrological modellers have begun working out runoff projections. During recent years, the Global Climate Models (GCMs) and Regional Climate Models (RCMs) driven hydrological models are in frequent use to draw such projections. But the projections have been often found to lack of reliability. Very recently, there is another emerging field of multi-model ensembles that has added feather to cap of the climate modeling community but this field is yet to be tried in many of the basin runoff-studies especially in the Indian perspective. There is a dire need for more research input assessing the future runoff as far as the Indian River basins are concerned. The climate models are being improved day by day so are the hydrological models. The multi-model ensembles are expected to bring out more reliability in the model outputs regarding the future runoff regimes of the basins than that could be brought about using individual models. The present study is a brief reviewof the model-based projections made for the some of the major river basins of the world. This attempt also seeks to bring forth the basin wise state-of-the-art research activities of such a kind so that the unexplored horizons of model based hydrological research could be taken up as newer research challenges like eg. in India there hasn’t yet been much basin scale studies conducted using multi-model ensembles. Therefore it is suggested that detailed studies to be taken up to assess the impact of climate change on the various parameters involved in estimation of water resources and asses water resource keeping in view the climate change for more realistic future planning and integrated water resource management.

In this paper are given the results of ground water mathematical modeling of the source zone Sokolovići in order to define the optimal water exploitation. After processing and analyzing the results of hydrogeological and hydrological research of source of Sarajevsko Polje, boundary conditions are selected, and after that were made calibration of mathematical models for Sokolovići zone.Given the complexity and importance of groundwater sources Sokolovići, optimization of the results of the mathematical model is also made in this paper. Optimal exploitation (optima yield) of groundwater is selected based on the three criteria: 1st the provision of river inflow in amount of that will not exceed the natural infiltration in accordance with the appropriate geometry and boundary conditions; 2nd ensuring at least minimum required flow to downstream groundwater source, in quantities that exploitation of Sokolovići water well will not compromise, and 3rd preservation of filtration stability of wells in the Sokolovići area.

Reference evapotranspiration ( ET o ) assessment at regional scale is a challenge to agricultural and hydrological research requiring the characterization of vast areas to obtain accurate meteorological variables. To account for this, a new approach considering a modified version of the Makkink equation and based on a combination of remotely sensed solar radiation ( R s ) considering the MSG satellite, and numerical weather forecast of near surface air temperature ( T 2 m ), was developed. The new approach is referred as Makkink-Advection equation (MAK-Adv). Once R s and T 2 m were validated for the semiarid conditions registered in Southern Spain with very satisfactory results (RMSE = 1.6 MJ m −2 d −1 and 1.4 °C respectively, with linear regressions with slope = 0.99 and R 2 = 0.97), the MAK-Adv approach was calibrated and validated with ET o measurements from a weighing lysimeter under near-reference conditions in Southern Spain. The new approach has provided accurate daily ET o estimations compared with lysimeter data (RMSE = 0.50 mm d −1 , RE = 12.3% and MAE = 0.39 mm d −1 ), and remains accurate during summer time (RMSE = 0.62 mm d −1 and RE = 9%), the critical period when accurate ET o data are essential for a correct agricultural water management. Once calibrated and validated, and thanks to the use of remotely sensed data, the MAK-Adv approach allowed the ET o assessment at regional scale. For a semi-arid region located in southern Spain with an area of 87,300 km 2 , a detailed spatial ET o assessment was performed, determining ET o values for the totality of the area with a resolution of about 9 km 2 allowing to evaluate the spatial and temporal variability at basin/region scale. This new approach gets over the serious limitations for a correct ET o assessment when traditional methodologies are not able to provide these data for vast areas, even with the modern weather station networks. Thus, MAK-Adv approach is especially useful for those areas with missing or inaccurate meteorological in situ observations.

Summary The Brisbane River estuary (BRE) in Australia not only plays a vital role in ecosystem health, but is also of importance for people who live nearby. Comprehensive investigations, both in the short- and long-term, into the salinity and turbidity distributions in the BRE were conducted. Firstly, the analysis of numerical results revealed that the longitudinal salinity varied at approximately 0.45 and 0.61 psu/h during neap and spring tides, respectively. The turbidity stayed at a higher level and was less impacted by tide in the upper estuary, however, the water cleared up while the tide changed from flood to ebb in the mid and lower estuary. The second investigation into the seasonal variations of salinity and turbidity in the BRE was conducted, using ten-year field measurement data. A fourth-order polynomial equation was proposed, describing the longitudinal variation in salinity dilution changes as the upstream distance in the BRE during the wet and dry seasons. From the observation, the mid and upper estuaries were vertically well-mixed during both seasons, but the lower BRE was stratified, particularly during the wet season. The estuary turbidity maximum (ETM) zone was about 10 km longer during the wet season than the dry season. Particular emphasis was given to the third investigation into the use of satellite remote sensing techniques for estimation of the turbidity level in the BRE. A linear relationship between satellite observed water reflectance and surface turbidity level in the BRE was validated with an R 2 of 0.75. The application of satellite-observed water reflectance therefore provided a practical solution for estimating surface turbidity levels of estuarine rivers not only under normal weather conditions, but also during flood events. The results acquired from this study are valuable for further hydrological research in the BRE and particularly prominent for immediate assessment of flood impacts.

Soil water is one of the most important components in hydrological cycle. The stable isotopes (e.g., deuterium, 2 H, oxygen-18, 18 O) in soil water have been increasingly used as natural tracers in the ecological, environmental and hydrological research. In view of different techniques for extracting soil water, there are significant differences in the δD and δ 18 O compositions. This paper presents a method for the accelerated solvent extraction (ASE) of soil water for stable isotope analyses by mass spectrometry. The optimum parameters of extracting soil water were as follows: dichloromethane as the extraction solvent, temperature of 100 °C, pressure of 10.3 MPa, static time of 10 min. The samples were extracted three times, and with cycle values four, four and three, respectively. The extracted water was enriched in deuterium and oxygen-18 by 2.12%–4.58% and −0.17%–0.93%, respectively, compared with the added water. The reproducibility of replicate extractions of soil water was around ±0.89% for δD and ±0.37% for δ 18 O.

An analytical Excel-based toolkit called Gas-Tracer-Interpretation (GTI) was developed for determining mean residence time (MRT) of groundwater samples and for validating conceptual model assumptions. This novel data interpretation toolkit improves data handling during analysis and resolves some problems in the interpretation of data from environmental tracers. The toolkit can assist error detection, uncertainty and ambiguity during data analysis, particularly ambiguity due to the decline in atmospheric data of CFC input functions (air-mixing ratios of tracers). The innovative interpretation methodologies are: (1) corrections of environmental tracer data are conducted in concentrations in water instead of air (atmosphere), allowing comparison of different tracer input functions under similar conditions and thereby replacing the use of unique global atmospheric data; (2) a multi-model, multi-tracer approach is adopted to improve the number of different combinations of environmental tracers and lumped-parameter models (piston flow (PM), exponential (EM), exponential-piston flow (EPM), advection-dispersion (DM) and gamma (GM)); and (3) generation of sufficient information for determination of erroneous, unclear and ambiguous outcomes. Results are linked to graphical analysis to improve data view. GTI supports the environmental tracers CFC-11, CFC-12, CFC-113, SF6, 3H, and also SF5CF3, which is included as it represents a promising environmental tracer in hydrological research. The toolkit compares modeled input functions of tracers and data from samples. The apparent recharge age and MRT are estimated by combining explicit graphical and numerical data presentation. Due to the multi-model approach, it is possible to contrast selected models and estimate the best fit for a given sample, which is particularly useful for validating conceptual model assumptions. The toolkit has been developed in Microsoft ?Excel, and hence is user-friendly such that advanced programming skills or detailed understanding of the calculations and mathematical procedures are unnecessary. Display Omitted Software for multi-tracer and multi-model residence time analysis of groundwater.Optimization approach for joint residence time analysis of matrix of tracers.New algorithm for the standardization of dissolution of gaseous components.Analysis of uncertainty, ambiguity, error, degradation and contamination.

Summary This study first focuses on comprehensive evaluating three widely used satellite precipitation products (TMPA 3B42V6, TMPA 3B42RT, and CMORPH) with a dense rain gauge network in the Mishui basin (9972 km 2 ) in South China and then optimally merge their simulated hydrologic flows with the semi-distributed Xinanjiang model using the Bayesian model averaging method. The initial satellite precipitation data comparisons show that the reanalyzed 3B42V6, with a bias of −4.54%, matched best with the rain gauge observations, while the two near real-time satellite datasets (3B42RT and CMORPH) largely underestimated precipitation by 42.72% and 40.81% respectively. With the model parameters first benchmarked by the rain gauge data, the behavior of the streamflow simulation from the 3B42V6 was also the most optimal amongst the three products, while the two near real-time satellite datasets produced deteriorated biases and Nash–Sutcliffe coefficients (NSCEs). Still, when the model parameters were recalibrated by each individual satellite data, the performance of the streamflow simulations from the two near real-time satellite products were significantly improved, thus demonstrating the need for specific calibrations of the hydrological models for the near real-time satellite inputs. Moreover, when optimally merged with respect to the streamflows forced by the two near real-time satellite precipitation products and all the three satellite precipitation products using the Bayesian model averaging method, the resulted streamflow series further improved and became more robust. In summary, the three current state-of-the-art satellite precipitation products have demonstrated potential in hydrological research and applications. The benchmarking, recalibration, and optimal merging schemes for streamflow simulation at a basin scale described in the present work will hopefully be a reference for future utilizations of satellite precipitation products in global and regional hydrological applications.

Summary Estimating areal precipitation and quantifying the associated uncertainties are important for both hydrological research and water resource management. However, many, if not all, precipitation products provide only the precipitation at reasonable spatial scales without uncertainty attached. In this paper, we promote a double smoothing technique to derive the precipitation amounts at small grid size based on gauge observations and then propose a bootstrap method to quantify the rainfall model estimation uncertainty (the uncertainty of rainfall estimation by a given model; here our model is double smoothing) by the traditional bootstrap for parameter uncertainty and the rainfall product uncertainty in term of prediction. As the residuals by the direct use of smoothing approach are heterogeneous, making the direct use of bootstrapping method invalid, we use an empirical transformation to stabilise the residuals. Furthermore, by using bootstrapping method, we can easily upscale the precipitation and the associate uncertainty to any required scales. The product is easy to use in research and practice. We demonstrate our methods by applying it to Murray Darling Basin in the eastern Australia.

Hydrograph recession analysis is widely used in hydrological research and water resources planning and management. The most common application is the forecasting of low flows, estimating groundwater resources in a catchment, rainfall runoff models and hydrograph analysis. In the rainfall runoff modelling, some authors have included the recession characteristics in their model. They used the recession parameter for hydrograph separation and modelling surface runoff. This paper presents an alternative commonly used techniques for hydrograph recession analysis, namely of an individual recession segment, the master recession and a relatively recent approach based on wavelet transform was carried out in order to separate analytically the linear component hydrographs by recession index K that is commonly used as an indicator of flow. These methods were applied to a set of measures hydrometric the North-eastern Algeria in the watershed Seybouse. The results show that all the methods tested produce reasonable and comparable results.

This study examined the effect of wildfire and salvage harvesting on runoff generation and sediment exports from three small forest catchments in south-eastern Australia. In 2006, wildfire burnt a radiata pine catchment and two adjacent natural eucalypt forest catchments which formed part of a long-term hydrological research project. Subsequently, only the pine plantation catchment was salvage harvested. The combined effect of fire and salvage harvesting in the pine catchment caused a substantial increase in runoff compared to the burnt eucalypt forest catchments and pre-fire conditions, particularly in response to high intensity, short duration summer storms. Post-fire maximum suspended sediment concentrations from fixed-interval sampling greatly exceeded pre-fire values for both eucalypt and pine catchments, while sediment (suspended and bedload) exported from the pine catchment exceeded each of the eucalypt catchments by a minimum of 180 and 33 times. However, the export increase was probably closer to 320 and 71 times based on a survey of eroded channels in the pine catchment combined with measured post-survey exports. Notably, seven summer storm events accounted for approximately 80% of the pine catchment sediment yield. Hillslope process measurements indicated that the highest runoff velocities occurred in log drag-lines formed by cable harvesting, while soil water repellency was more extensive in the harvested pine catchment than in the adjacent eucalypt catchment. The latter effect probably resulted from higher burn severity in the pines combined with reduced soil moisture due to less shading after harvesting. Runoff modelling indicated that the log drag-lines acted as an extension to the drainage network and increased peak flows at the harvested catchment outlet by 48% for a high intensity summer storm event, while substantial reductions in modelled runoff were achieved through increasing the hillslope surface roughness coefficient. It is recommended that post-fire salvage operations should avoid the formation of log drag-lines when using cable harvest techniques and maximise surface cover to limit increases to runoff, erosion and catchment sediment exports.

We examine the stages of assessment of the anthropogenic impacts on landscape-hydrological complexes and suggest the principles of this assessment built upon geosystem-hydrological research and landscape planning tools. We demonstrate the advisability of addressing water-ecological problems on the basis of a knowledge of the formation regularities of hydrological processes with the use of the method of indication and typology.

Summary Adequate assessment of uncertainty for prediction and simulation purposes is a current issue in hydrological research. This article describes the application of the Hydrologic Uncertainty Processor (HUP) proposed by Krzystofowicz in 1999 to a small semi-arid watershed in southern Italy. The version applied in this work is a precipitation-dependent HUP aimed at assessing the hydrologic uncertainty about actual streamflow at some future time, with lead times of a few hours, given the information available at the forecast time and assuming a perfectly known amount of precipitation. The processor is based on Bayes theorem and hence models the prior and likelihood functions to obtain the revised posterior distribution. A complete example of the modelling assumptions, estimation procedure and results is carried out in the present paper. In detail, we analysed a 26-km2 semi-arid basin, considering hourly forecasts over an almost continuous five-year period in 2000–2005. A distributed rainfall–runoff model suited to represent contributions of different runoff generation mechanisms to hydrologic response is used for deterministic predictions. Analysis of the resulting posterior distributions show that hydrologic uncertainty: (i) grows with the value of discharge predicted by the model; (ii) is higher when associated with high precipitation amounts; and (iii) increases with lead time of predictions. The predictive ability of the processor is investigated for several runoff events. The results indicate good processor performance for a lead time equal to the period covered by the precipitation forecast, and a significant deterioration for higher lead times that is heavily dominated by the presumption of null precipitation beyond the forecast period. Finally, the skill of the processor is assessed through a retrospective analysis in terms of the probability of detection and the false-alarm rate.

Accurate forecasting of rainfall has been one of the most important issues in hydrological research. Due to rainfall forecasting involves a rather complex nonlinear data pattern; there are lots of novel forecasting approaches to improve the forecasting accuracy. Recurrent artificial neural networks (RNNS) have played a crucial role in forecasting rainfall data. Meanwhile, support vector machines (SVMs) have been successfully employed to solve nonlinear regression and time series problems. This investigation elucidates the feasibility of hybrid model of RNNs and SVMs, namely RSVR, to forecast rainfall depth values. Moreover, chaotic particle swarm optimization algorithm (CPSO) is employed to choose the parameters of a SVR model. Subsequently, example of rainfall values during typhoon periods from Northern Taiwan is used to illustrate the proposed RSVRCPSO model. The empirical results reveal that the proposed model yields well forecasting performance, RSVRCPSO model provides a promising alternative for forecasting rainfall values.

Assessment of the potential impact of climate change on water systems has been an essential part of hydrological research over the last couple of decades. However, the notion that such assessments should also include technological, demographic and land use changes is relatively recent. In this study, the potential impacts of climate change and continued urbanisation on waste and stormwater flows in the combined sewer of central Helsingborg, South Sweden, have been assessed using a series of DHI MOUSE simulations run with present conditions as well as two climate change scenarios and three progressive urbanisation storylines. At present, overflows of untreated wastewater following heavy rainfalls are a major source of pollution to the coastal receiving waters and there is a worry that increased rainfall could exacerbate the problem. Sewer flows resulting from different urbanisation storylines were simulated for two 10-year periods corresponding to present (1994-2003) and future climates (nominally 2081-2090). In all, 12 simulations were made. Climate change was simulated by altering a high-resolution rainfall record according to the climate-change signal derived from a regional climate model. Urbanisation was simulated by altering model parameters to reflect current trends in demographics and water management. It was found that city growth and projected increases in precipitation, both together and alone, are set to worsen the current drainage problems. Conversely, system renovation and installation of sustainable urban drainage systems (SUDS) has a positive effect on the urban environment in general and can largely allay the adverse impacts of both urbanisation and climate change.

Assessment of the potential impact of climate change on water systems has been an essential part of hydrological research over the last couple of decades. However, the notion that such assessments should also include other changes is relatively recent. In this study, the potential impacts of climate change and continued urbanisation on stormwater flows to a suburban stream, Helsingborg, south Sweden, have been assessed using drainage simulations for present conditions as well as two climate (medium and high gas emission) and two water management storylines for subdivision. Climate change was simulated by altering a high-resolution rainfall record according to the climate-change signal derived from a regional climate model. Subdivision and urbanisation was simulated by altering model parameters chosen to reflect current trends in demographics and water management. The simulations were run for a 15 month period. It was found that city growth and projected increases in heavy rainfalls, both together and alone, are set to raise peak flow volumes and increase flood risk. Conversely, installation of a sustainable urban drainage system (SUDS) has a positive effect on the urban environment in general and can largely allay the adverse impacts of change road. The relative impacts of changes in climate and urbanisation are assessed for the combined sewer system which serves central Helsingborg in Semadeni-Davies et al. [Semadeni-Davies A., Hernebring, C., Svensson, G., Gustafsson, L.G., 2008. The impacts of climate change and urbanisation on drainage in Helsingborg, Sweden: combined sewer system. J. Hydrol. 350 (1-2), 100-113.

Summary The contribution of stable isotopes in meteorological, climatological and hydrological research is well known. Until this date and despite the fact that several hydrological studies of water sources in Greece have been published, no systematic isotopic study of precipitation has been performed in the country. This paper presents all the available isotopic data collected since 1960 in several Hellenic measurement stations. This data is divided in two periods: the first covers data that was collected in the past, in the frame of a preliminary survey of the isotope composition of precipitation in the Eastern Mediterranean Sea and specific hydrological studies; the second is the result of a three-year coordinated research project of the International Atomic Energy Agency, in which the authors participated, aiming at the systematic study of stable isotopes ( 2 H and 18 O) and 3 H in precipitation around the Mediterranean basin. No statistically significant behavior between the two periods of data was found. The isotopic content of precipitation presents characteristics intermediate of those of the Eastern and Western Mediterranean. The tritium concentration in precipitation declines as expected towards the pre-bomb levels, however there is an indication that tritium concentrations are higher in Northern Greece.

The Institute of Urban Water Management and Landscape Water Engineering of the Graz University of Technology (Austria) operates a hydrological research area in the City of Graz. In this urban research area precipitation and runoff data are collected by order of the municipality of Graz. At present precipitation data are measured by seven tipping bucket rain gauges. Comparative measurements have shown a deviation between the recorded and the actual precipitation intensity. This made the institute calibrate the rain gauges periodically. In the middle of the 1990s, the development of a field calibration kit was started. Based on the experiences with the first field calibration kit, a microprocessor controlled device was developed. With this calibration device, the tipping bucket rain gauges are calibrated at regular intervals. In this paper the calibration process and the current results for seven rain gauges are discussed. The calibration process is dynamic calibration and uses a peristaltic pump. Not all of the tipping buckets investigated underestimate the rain intensity in the whole measuring range. Several rain gauges have a positive relative deviation, not exceeding 22%, in the low intensity range up to 0.5 mm/min. Positive deviation can be explained by retention of water in the buckets between tips. The reason for the negative deviation is the loss of water during the tips. It leads to the underestimate of the actual intensity. The largest relative deviation in the range of underestimate exceeds 30%. In the range of extreme intensities, the larger buckets (5 cm 3 ) show a lower relative deviation than the smaller (2 cm 3 ) buckets. The gauge characteristic can change in favourable or unfavourable directions after several years. Therefore, the calibration of tipping buckets is recommended at least every 2 to 3 years.

Predicting hydrological response to rainfall or snowmelt including an estimation of prediction uncertainty is a major challenge in current hydrological research. The process-based catchment model TACD (tracer aided catchment model, distributed) was applied to the mountainous Brugga basin (40 km2), located in the Black Forest Mountains, southwest Germany. The Monte Carlo-based generalized likelihood uncertainty estimation (GLUE) framework was used to analyse the uncertainty of discharge predictions. The model input parameter sets were generated using the Latin Hypercube sampling method, which is an efficient way to sample the parameter space representatively. It was shown that the number of investigated parameters should exceed the number of varied parameters by at least a factor of 10. Even if the process basis and suitability of the model could be proven, relatively large uncertainty ranges of the discharge predictions still occurred during the simulation of floods. Prediction uncertainty varied both temporally and spatially. Incorporating additional data, i.e. sub-basin runoff and observed tracer concentrations, reduced the prediction uncertainty. However, the potential restriction of the uncertainty clearly depends on the goodness of the simulation of the additional data set. Knowledge of the uncertainty of model predictions and of the potential for experimental data to reduce it are crucial to sustainable environmental management, and should be considered more thoroughly during the planning of future field studies.

For more than ten years, scientists of the Universities of Karlsruhe, Heidelberg and Bayreuth have investigated the water dynamics as well as transport of matter in the Weiherbach catchment, a loess area of about 6.3 km2 located in the “Kraichgau” of Southwest Germany. The investigations had the following scientific objectives: to identify the processes governing water and solute dynamics on different spatial and temporal scales in a small rural loess catchment, to develop a physically based numerical model to cope with all hydrological situations, i.e. simulating the extreme cases of very small runoff and flood runoff events as well as simulating soil water flow and transport, based on the obtained understanding of processes as well as to provide a data set for hydrological research for the intensively used rural loess areas of Central Europe. Modeling approaches for the processes dominating water and mass balance on the plot, hillslope and small catchment scale were developed based on process studies, tested against observations and implemented into the physically based, distributed model CATFLOW. During the observation period rainfall-runoff activity was low. The distribution of soil types was found to be strongly influenced by erosion leading to a typical hillslope soil catena. Preferential flow in earthworm burrows turned out to be crucial for solute transport in the soil on the plot and the hillslope scale, especially for leaching of surface applied pesticides, but also for runoff generation on the catchment scale. However, pesticide as well as phosphate loads in the Weiherbach creek during rainfall-runoff events were strongly determined by losses of sewer pipelines, which drain paved farm courtyards and pesticide loss due to runoff from courtyards. Those entrance paths are difficult to model in physical terms. A simplified, effective model approach for preferential flow based on field and laboratory measurements yielded simulation results in good accordance with short term observations of tracer transport on the plot scale as well as long term observations of tracer transport on the hillslope scale. Assuming that the soil catena of each hillslope may be substituted by the same typical soil catena a long term simulation of catchment scale water dynamics yielded results in acceptable agreement with the observed rainfall-runoff dynamics, soil water dynamics as well as evapo-transpiration. However, a falsification of the developed modeling approach was not possible, because of the uncertainty of the obtained parameter values due to measurement errors and due to the enormous variability of state variables and parameters in the Weiherbach soils.

The new South African Water Act and the inclusion of a component that stipulates that some water has to be reserved to maintain the ecological functioning of rivers has stimulated a renewed interest and need for detailed hydrological data. This has occurred at a time when many of the countries rivers are already affected by impoundments, abstractions, return flows and land-use change impacts. The need to relate the ecological requirements of rivers to the characteristics of the natural flow regime and to convey the details of flow regimes to non-hydrological specialists has presented hydrologists with an exciting challenge. It is rewarding to discover that the status of hydrological research and practice in South Africa, and the methodologies that were already available, were more than capable of responding to this challenge and that the hydrological tools required to assist with the implementation of the new act were either already available or could be developed rapidly.

An overview of weather radar-related developments in South Africa, specifically aimed at hydrological research and operations, is given. Hydrometeorological applications of weather radar have their roots in the country's long-standing research effort on rainfall enhancement from summertime convective storms. This programme has developed the necessary infrastructure, expertise and related hardware and software to collect and archive high-quality radar data, analyse the information and conduct comparisons with conventional measurements on catchment scales. The high spatial and temporal resolution, and real-time nature of radar data have distinct advantages over even dense raingauge networks when catchment rainfall under convective conditions is estimated for flood hydrology. These advantages are highlighted by two case studies presented. The information gained from radar data has also provided insight into the structure of rain-producing systems, enabling the more accurate modelling of the phenomenon. Shortcomings of weather radar data for hydrological applications are described and the ongoing research efforts to address these shortcomings are highlighted. These include methods to reduce the impact of ground clutter, anomalous propagation, hail and the bright band on rainfall estimates. It also includes methods to extend the useful range of radar data for rainfall estimation, necessitated by the less-than optimal radar spacing over South Africa. Furthermore, some of the plans to optimise the use of the radar infrastructure are highlighted with specific reference to the radar networking system and how radar rainfall estimates might be integrated with satellite rainfall estimates and measurements by conventional gauges.

This paper investigates the role of the production function approach in capturing the value of hydrological services of wetland ecosystems. Hydrological research in the Hadejia-Nguru wetlands in northern Nigeria suggests that the major role of the wet season inundation of the wetlands is in recharging the underlying aquifers. This paper shows that the hydrological services extend beyond direct use values, and have a significant economic value associated with them. Whereas the direct benefits provided by the wetlands, such as floodplain agriculture, fishing and forestry, have previously been assessed, this paper synthesizes the results of two approaches to capture the value of indirect benefits derived from the role of the wetlands in replenishing and maintaining groundwater resources within the wetland area.

In 1989, in a hydrological research programme within a deacidification project in the Gardsjon area in southwest Sweden, flow paths and residence times of soil water and groundwater in microcatchments were examined to support the interpretation of the hydrochemical changes. Saturated hydraulic conductivity and soil water retention were analysed on more than 100 cylinder samples. The catchments have shallow sandy-silty till soil with a mean depth in the main catchment of 43 cm. Porosity of the mineral soil in the main catchment was high and ranged from 38 to 85%. The samples from the B-horizon had generally higher porosity. Porosity and the content of organic matter were correlated. The soil water retention was relatively high at all tensions, likely owing to the high content of organic matter. Dissolved organic substances were most probably transported from the shallow soil on the steep sides of the catchment down to the valley where it precipitated. The high porosities could be a consequence of long-term weathering, provided that the organic substances present have increased the leaching of the weathering products. Measured values of saturated hydraulic conductivity were close to log-normally distributed with a mean for all samples of 3 × 10−5 m s−1. There was a significant increase in conductivity toward the ground surface with the mean conductivity of the samples in the uppermost 10 cm of the mineral soil of 4 × 10−5 m s−1, which was about 13 times higher than the conductivity of 3 × 10−6 m s−1 at 1 m depth. From the relationship between runoff at the catchment outlet and groundwater levels, the conductivity was estimated to be 15–200 times higher in the upper soil layer than in the deeper ones. In one profile, 44–64% of the yearly lateral flow was estimated to occur above 30 cm depth. The conductivity was correlated with the content of drainable water, which indicated the importance of the largest pores for the saturated hydraulic conductivity.

Applications of 14C, 36C1 and 129I in hydrology using the AMS technique are reviewed. The small amounts of carbon needed for AMS measurement of 14C have facilitated new areas of hydrological research. Uncertainties in the natural fall-out of 36Cl and the dissolution of 36Cl-labelled chloride during groundwater migration are limitations for groundwater dating with this nuclide. Estimation of recharge by measurements of the advance of the 6Cl bomb peak through the unsaturated zone is of increasing importance in hydrology. AMS measurements of 129 I will provide an environmental monitor for nuclear pollution plumes. Some directions for future studies are suggested.

In order to determine, experimentally, the rate at which surface water quality recovers after acid deposition is reduced, a roof was built over a small catchment near Lake Gardsjon, southwest Sweden. By irrigating the catchment with chemically adjusted water, the input of S and N is reduced by at least 90%. Previous hydrological research on catchments similar to that used in the roof experiment suggested that storm runoff from the catchment is concentrated in surface-near soil layers, temporarily saturated when the water table has risen in response to rainfall. If so, it is suggested that the improvements in water quality using the roof catchment will appear first in storm runoff, because the spate-specific flow pathways will be flushed by the large throughput of the non-acidic irrigation water. The hydrological basis of this suggestion was investigated using hydrometric observations and tracer studies. Laboratory analysis of ~100 soil samples gave mean values of the saturated hydraulic conductivity of 1 × 10−4 m/s in the uppermost 20 cm of the soil layer, decreasing to 6 × 10−6 m/s in the 20 cm closest to bedrock. The variation in hydraulic conductivity roughly agreed with the one inferred from the observed relation between groundwater level and catchment runoff. A preliminary tracer experiment with injected 3H and 36Cl, conducted during a very wet period, showed particle velocities of >1 m/h in the soil. This was significantly higher than velocities estimated from hydrometric observations, being ~0.1 m/h in the A horizon and ~0.01 m/h in the less conductive B and C horizons. The greater particle velocity indicated by the tracer experiment suggested that much of the flow was concentrated in a small fraction of the pore space. The replacement of the pre-irrigation water in the catchment by irrigation water could be investigated by using 18O, because the 18O content of the irrigated water differed from that of the groundwater and soil water before the irrigation. The 18O data showed that after six months of irrigation, about one fourth of the baseflow was new water.