Wolfgang-Albert Flügel

Combining GIS with regional hydrological modelling using hydrological response units (HRUs): an application from Germany

The concept of hydrological response units (HRUs) and their delineation and application to the Brol catchment (A=216 km2) in Germany is presented. HRUs are object orientated physiographic entities and can be used as model entities within the MMS/PRMS hydrological catchment model. Applying the HRU concept to the Brol catchment altogether 23 different HRUs were delineated from a DEM (50×50 m grid size), three classified pedo-topo-geological associations and four dominant land-use classes by means of GIS-overlay analyses. MMS/PRMS was then run with these HRUs using a 20-year daily data hydrometeorological time series. The model parameterization was carried out in such a way that rainfall input not consumed by evapotranspiration was routed to a common conceptual subsurface storage. The latter was drained by interflow laterally towards the shallow groundwater aquifer in the valley floors, which in turn seeped into the drainage channel network. The model fit between simulated and observed discharge was good (r=0.91) and it was found that the model was sensitive to parameters related to the land-use controlling evapotranspiration and direct overland flow. Future research activities will concentrate on applying the HRU concept and MMS/PRMS model in drainage basins of different climates in an object oriented way. Special attention will be given to integrating the spatial distributed precipitation into the HRU delineation and the flow routing linkages of the HRU subcells within the catchment which must be included in the present holistic approach.

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.

Land use characterisation and change detection analysis for hydrological model parameterisation of large scale afforested areas using remote sensing

Abstract The impact of large scale land use changes such as afforestation on the hydrological system behaviour of river basins is of major interest to water resources managers. Particularly in semi-arid areas, where water is strongly limited, the continuous assessment and monitoring of the hydrological system components are necessary. Their analysis and prognostic hydrological modelling requires both the determination of updated land use patterns and an estimation of their spatial dynamics over time. In this study optical remote sensing data were used in order to provide such hydrological model input parameters at different scales. Therefore, Landsat TM data from 1995 to 1999 have been utilized for various scale depended land use maps within the semi-arid Umzimvubu catchment, South Africa. The classification results were compared due to the temporal changes as a consequence thereof the afforestation. Based on an complex accuracy estimation during all processing steps, significant changes of the land use patterns could be quantified. In addition, the Leaf Area Index (LAI) distribution has been calculated for the Mooi river subcatchment based on the transformation of the normalized difference vegetation index derived from Landsat TM data to LAI utilizing an empiric equation.

Upstream-downstream linkages of hydrological processes in the Himalayan region

Understanding the upstream-downstream linkages in hydrological processes is essential for water resources planning in river basins. Although there are many studies of individual aspects of these processes in the Himalayan region, studies along the length of the basins are limited. This study summarizes the present state of knowledge about linkages in hydrological processes between upstream and downstream areas of river basins in the Himalayan region based on a literature review. The paper studies the linkages between the changes in the physical environment of upstream areas (land use, snow storage, and soil erosion) and of climate change on the downstream water availability, flood and dry season flow, and erosion and sedimentation. It is argued that these linkages are complex due to the extreme altitudinal range associated with the young and fragile geology, extreme seasonal and spatial variation in rainfall, and diversity of anthropogenic processes. Based on the findings, the paper concludes that integrated systems analysis is required to understand the holistic complexity of upstream-downstream linkages of hydrological processes in the river basin context. The integrated land and water resources management (ILWRM) approach can be instrumental in developing adaptive solutions to problems and can also enable stakeholders of upstream and downstream areas with various interests and needs to work together for the better utilization and management of land and water resources. As a part of this, the specific circumstances of the upstream communities, who live in fragile and inaccessible mountain areas with limited resource opportunities, should be taken into account so that incentive mechanisms can be established to encourage and acknowledge their contribution.

River salination due to dryland agriculture in the Western Cape Province, Republic of South Africa

Abstract River salination due to dryland agriculture was studied between 1985 and 1986 in the 150-km2 large catchment of the Sandspruit river, a tributary of the Berg river in the semi-arid Western Cape Province of South Africa. The study included investigations of all major water bodies within the catchment and aimed to identify and quantify their salinity dynamics. The following results can be presented: 1) The mean annual rainfall is about 400 mm, and has a salt concentration from the ocean of 37 mg/L. 2) Groundwater recharge of the shale aquifer only occurred during the winter season when salts from the soil and the weathered shale were transported into the groundwater. 3) The main salt output occurred between July and September and is associated with floods. A linear regression model was established to estimate salt output from the catchment by using the water level measured at the gauging station. 4) The total salt output in 1986 was 8052 Mg (tons), but bulk atmospheric deposition accounted only for a third of this amount. The remainder salt output was delivered by groundwater and interflow from the weathered shale and the soils within the catchment.

Does a weekend effect in diurnal temperature range exist in the eastern and central Tibetan Plateau

The ‘weekend effect’ method (defined here as the average for Saturday through Monday minus the average for Wednesday through Friday) has been used to identify fingerprints of anthropogenic emissions. Based on daily maximum and minimum temperature series from the China Meteorological Administration homogenized dataset, the weekend effect in diurnal temperature range (DTR) at 71 stations with elevations above 2000 m asl in the eastern and central Tibetan Plateau (TP) during 1961–2004 is examined, and principal component analysis (PCA) is performed to cluster series into four subregions with similar weekend effect variability. The DTR demonstrates a much stronger negative weekend effect in autumn and shows larger positive values in winter, which provides a strong evidence of anthropogenic activity in this region, especially in the central TP. Analysis by topographic type and degree of urbanization shows a clear weekly cycle which cannot be explained by a microclimate effect. We hypothesize that the interaction with anthropogenic aerosols from local emissions and transported by atmospheric circulation may account for the weekly cycle in the TP. More caution should be paid to the driving mechanism of the weekend effect in the most remote and clear regions in the world.

INTEGRATED PROCESS STUDIES AND MODELLING SIMULATIONS OF HILLSLOPE HYDROLOGY AND INTERFLOW DYNAMICS USING THE HILLS MODEL

Abstract Interflow is of major importance for runoff generation and groundwater recharge in mountainous and hilly catchments. However, integrated process studies and model simulation of the hydrological dynamics of hillslope drainage by interflow are still scarce. Therefore, such a study has been carried out on the Kiefer-Hang test hillslope in the catchment of the Sieg River, located in the middle mountain range of the Rheinische Schiefergebirge in Germany. The overall objective was to analyse and to simulate soil moisture, interflow and groundwater recharge with a high resolution in time and space. For the simulation study the two-dimensional HILLS numerical hillslope model was selected, parameterized and calibrated by detailed field surveys. The simulations were undertaken using measured hydro–meteorological data with 5-minute intervals. The process analyses of the study revealed the hydrological dynamics of the test slope, and the results of the simulations proved the ability of the HILLS model to simulate interflow. However, some extreme storms and dry weather periods were simulated poorly because: (i) the soil-physics is simplified in the model as compared to the complex structure of the test slope, and (ii) HILLS in its present version does not account for feedback from the level of the adjacent Breidenbach Creek.

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.

Land cover changes assessment using object‐based image analysis in the Binah River watershed (Togo and Benin)

In this study, land cover changes between 1972 and 2013 were investigated in the Binah River watershed (North of Togo and Benin) using remote sensing and geographic information system technologies. Multitemporal satellite images—Landsat MSS (1972), TM (1987), and OLI-TIRS (2013)—were processed using object-based image analysis and post–classification comparison methods including landscape metrics and changes trajectories analysis. Land cover maps referring to five main land cover classes, namely, agricultural land, forest land, savannah, settlements, and water bodies, were produced for each acquisition date. The overall accuracies were 76.64% (1972), 83.52% (1987), and 88.84% (2013) with respective Kappa statistics of 0.69, 0.78, and 0.86. The assessment of the spatiotemporal pattern of land cover changes indicates that savannah, the main vegetation type, has undergone the most dominant change, decreasing from 67% of the basin area in 1972 to 56% in 1987 and 33% in 2013. At the same time, agricultural land has significantly increased from 15% in 1972 to 24% in 1987 and 43% in 2013, while some proportions of agricultural land were converted to savannah relating to fallow agriculture. In total, more than 55% of the landscape experienced changes between 1972 and 2013. These changes are primarily due to human activities and population growth. In addition, agricultural activities significantly contributed to the increase in the number of patches, degree of division, and splitting index of forest and savannah vegetations and the decrease in their effective mesh sizes. These results indicate further fragmentation of forest and savannah vegetations between 1972 and 2013. Further research is needed to quantitatively evaluate the influences of individual factors of human activities and to separate these from the impacts of climate change-driven disturbances.

An Information System for Integrated Land and Water Resources Management in the Kara River Basin ( Togo and Benin )

A prerequisite for integrated land and water resources management (ILWRM) is a holistic river basin assessment. The latter requires information and data from different scientific disciplines but also appropriate data management systems to store and manage historical and real time data, set up protocols that facilitate data and information access and sharing among different stakeholders, and triggering further collaboration among different institutions in support of watershed-based assessment, management and planning. In West Africa in general and especially in the transboundary Volta River basin where different environmental data are collected and managed by different agencies in different countries and also where data access and dissemination are very challenging and difficult tasks, comprehensive river basin information systems are required. This paper presents the Oti River Basin Information System (OtiRBIS), a web-based data storage, management and analysis platform that addresses these needs and facilitates ILWRM implementation in the Kara river basin.