Runoff simulations on the macroscale with the ecohydrological model SWIM in the Elbe catchment-validation and uncertainty analysis

This study presents an example where the hydrological processes of the ecohydrological model SWIM (Soil and Water integrated Model) are thoroughly analysed. The model integrates hydrology, vegetation, erosion and nutrient dynamics. It is process-based and has to be calibrated. The hydrological validation of the model is of prime importance, because all other ecological processes are related to the water cycle. On the other hand, these ecological processes influence the water cycle in turn, and therefore they were considered in the modelling process and in the sensitivity and uncertainty analysis. The validation was multi-scale, multi-site and multi-criteria: the validation strategy followed a bottom-up approach in which the model was firstly calibrated for 12 mesoscale sub-basins, covering the main subregions of the German part of the Elbe basin, and the information gained from the mesoscale was then used to validate the model for the entire macroscale basin. Special attention was paid to the use of spatial information (maps of water table) to validate the model in addition to commonly used observations of water discharge at the basin outlet. One main result was that investigations in smaller catchments have to accompany macroscale model applications in order to understand the dominant hydrological processes in the different areas of the entire basin and at different scales. The validation was carried out in the German part of the Elbe river basin (similar to80258 km(2)). It is representative of semi-humid landscapes in Central Europe, where water availability during the summer season is a limiting factor for plant growth and crop yield. Copyright (C) 2005 John Wiley Sons, Ltd.