Manfred Fink

A neural network approach for the optimisation of watershed management

Abstract Managing a catchment for drinking water supply with a high proportion of agricultural land use is a difficult task if one has to maintain a reasonable balance between water quality demand and consequent restrictions for the farming industry. In this paper, we present a neural net-based method for finding good approximations to solutions of this problem. This method is capable of ‘inverting’ a hydrological model to identify land use scenarios that match best the leaching criteria defined for establishing a certain water quality level in the stream. The method not only allows simulation land use scenarios like hydrologic models do, but can search systematically for land use scenarios that fulfill specified criteria without worrying about the complexity of combinatorial optimisation.

Assessment of spatial transferability of process‐based hydrological model parameters in two neighbouring catchments in the Himalayan Region

Abstract Estimating the hydrological regime of ungauged catchments in the Himalayan region is challenging due to a lack of sufficient monitoring stations. In this paper, the spatial transferability of the model parameters of the process‐oriented J2000 hydrological model was investigated in 2 glaciated subcatchments of the Koshi river basin in eastern Nepal. The catchments have a high degree of similarity with respect to their static landscape features. The model was first calibrated (1986–1991) and validated (1992–1997) in the Dudh Koshi subcatchment. The calibrated and validated model parameters were then transferred to the nearby Tamor catchment (2001–2009). Sensitivity and uncertainty analyses were carried out for both subcatchments to discover the sensitivity range of the parameters in the two catchments. The model represented the overall hydrograph well in both subcatchments, including baseflow, rising and falling limbs; however, the peak flows were underestimated. The efficiency results according to both Nash–Sutcliffe (ENS) and the coefficient of determination (r2) were above 0.84 in both catchments (1986–1997 in Dudh Koshi and 2001–2009 in Tamor). The ranking of the parameters in respect to their sensitivity matched well for both catchments while taking ENS and log Nash–Sutcliffe (LNS) efficiencies into account. However, there were some differences in sensitivity to ENS and LNS for moderately and less‐sensitive parameters, although the majority (13 out of 16 for ENS and 16 out of 16 for LNS) had a sensitivity response in a similar range. The generalized uncertainty likelihood estimation results suggest that the parameter uncertainty are most of the time within the range and the ensemble mean matches very good (ENS: 0.84) with observed discharge. The results indicate that transfer of the J2000 parameters to a neighbouring catchment in the Himalayan region with similar physiographic landscape characteristics is viable. This indicates the possibility of applying a calibrated process‐based J2000 model to other ungauged catchments in the Himalayan region, which could provide important insights into the hydrological system dynamics and provide much needed information to support water resources planning and management.

Hydrological Drought Risk Assessment in an Anthropogenically Impacted Tropical Catchment, Central Vietnam

Seasonal meteorological and hydrological droughts are a recurrent phenomenon in water-abundant tropical countries and are expected to become more frequent in the future. Unusual water shortage in recent years has severely affected societies living in South East Asia in general and Vietnam in particular. Preparedness, however, is absent and site-appropriate water management measures and strategies are not available. While drought-related research and water management in recent years have been addressed in water scarce sub-tropical regions, the US and Europe, more limited research has been focused on drought risk in tropical catchments. In this study, the drought characteristics of a large tropical catchment in Central Vietnam, the Vu Gia Thu Bon, were analysed in an integrated assessment framework. Daily precipitation and runoff time series for the VGTB catchment were analysed applying statistical methods to compare historical meteorological and hydrological drought, in addition to low flow frequency and seasonality. The role of tropical catchment characteristics, storage and climate variability in seasonal drought evolution were analysed by applying statistical analyses and the spatially distributed J2000 rainfall-runoff model. To assess anthropogenic impacts on hydrological drought, human interventions in the hydrological system due to hydropower development were quantified with the HEC-ResSim Reservoir operation model and the implications of low flows for salt water intrusion in the delta were simulated by the hydrodynamic Mike 11 model. It can be concluded that such an integrated model-data analysis which accounts for both landscape controls and anthropogenic impacts on the local hydrological system is a useful approach for drought management in tropical countries.

Hydrological and Agricultural Impacts of Climate Change in the Vu Gia-Thu Bon River Basin in Central Vietnam

This paper summarizes some of the climate (change) impact modeling activities conducted in the Land use and Climate Change interactions in Central Vietnam (LUCCi) project. The study area is the Vu Gia-Thu Bon (VGTB) river basin in Central Vietnam, which is characterized by recurrent floods during the rainy season, but also water shortages during the dry season. The impact modeling activities, such as the validation of the models are hindered by the scarcity of hydrometeorological data and an unfavorable distribution of the observation network, i.e., station data is available only for the lowlands. In total, two different process-based and distributed hydrological models are applied in concert with climate change and land use projections. Based on that, the magnitudes and return periods of extreme flows are estimated. The modeling results suggest increases of extreme high flows due to climate change. A multi-objective agro-economical model was developed for a typical irrigation scheme in the region in order to optimize the area for cropping, irrigation-techniques and schedules. The model results suggest the irrigation technique Alternate Wetting and Drying, which has the potential to increase the benefits for the farmers and help to mitigate greenhouse gases at the same time. In addition, the regional-scale crop model GLAM is applied for groundnut under rainfed conditions, which is capable to identify regions suitable for cropping in the future. The paper further synthesizes recommendations for local stakeholders in Central Vietnam.

Hydrological system analysis and modelling of the Kara River basin (West Africa) using a lumped metric conceptual model

ABSTRACT This paper discusses the analysis and modelling of the hydrological system of the basin of the Kara River, a transboundary river in Togo and Benin, as a necessary step towards sustainable water resources management. The methodological approach integrates the use of discharge parameters, flow duration curves and the lumped conceptual model IHACRES. A Sobol sensitivity analysis is performed and the model is calibrated by applying the shuffled complex evolution algorithm. Results show that discharge generation in three nested catchments of the basin is affected by landscape physical characteristics. The IHACRES model adequately simulates the rainfall–runoff dynamics in the basin with a mean modified Nash-Sutcliffe efficiency measure of 0.6. Modelling results indicate that parameters controlling rainfall transformation to effective rainfall are more sensitive than those routing the streamflow. This study provides insights into understanding the catchment’s hydrological system. Nevertheless, further investigations are required to better understand detailed runoff generation processes. EDITOR M.C. Acreman; ASSOCIATE EDITOR N Verhoest

Analyzing Hydro-Climatic Data to Improve Hydrological Understanding in Rural Rio de Janeiro, Southeast Brazil

The rural area of Rio de Janeiro (RJ) state has experienced increased pressure on water resources, due to an increasing population linked with the growth of the industrial and agricultural sectors. High interannual variability of rainfall causes frequent extreme events leading to droughts, floods, and landslides. Therefore, it is crucial to understand how climate affects the interaction between the timing of extreme rainfall events, hydrological processes, vegetation growth, soil cover, and soil erosion. Ecohydrological modeling can contribute to a better understanding of spatial–temporal process dynamics to develop adaptation strategies. However, prior to modeling, it is crucial to evaluate the reliability of the climate and hydrological data. This study aims to homogenize the climatic data and to analyze the hydro-climatic time series needed for further hydrological studies (e.g., ecohydrological modeling) and to contribute to a better understanding of long-term hydro-climatic patterns in a mesoscale watershed, the Muriae River Basin. The analyses include homogeneity assessment, statistical analyses, and trend detection for a time period of over 50 years. The assessment provides important insights into long-term hydro-climatic patterns, such as an increase of the annual mean temperature, a decrease of the annual relative humidity, and an increase of the frequency of intense rainfall events.

Distributed Assessment of Sediment Dynamics in Central Vietnam

Central Vietnam is located within the Southeast Asia monsoon . It is affected by extreme climatic phenomena, like Typhoon storm events. This combined with the deeply weathered bedrock, typical for subtropical regions, resulting in higher vulnerability for erosion and therefore resulting high sediment rates. Additionally, local human activities and the effects of global climate change amplify this higher vulnerability. The presented analysis contains the assessment of sheet erosion by means of the J2000-S eco-hydrological model, where the effect of climate and land use scenarios were analyzed. The results show that land use change has a higher effect then the climate chance on sheet erosion in the analyzed future period. Additionally, the landslide activity in the area was assessed, using a landslide inventory and bivariate statistical analysis. A landslide susceptibility map was the result of this assessment.