As a result of the pronounced topography, river basins in mountain regions are characterised by strong three-dimensional variations of all land surface features - soil type, soil depth, vegetation - and of all meteorological elements. In the assessment of possible impacts of climatic variations on the water flow and on water resources, a model has to be employed which takes account of these spatial variabilities.
A river basin model was developed for the whole alpine/pre-alpine basin of the river Thur/Andelfingen (1, 703sq.km.) and the 12 sub-basins. These basins are located in the north-eastern part of the Swiss portion of the Rhine basin and have an elevation range from 350 to 2,500masl. A considerable part of the Thur basin is high mountain terrain, some of it above the tree-line: much of the basin is under snow cover during the winter season.
In the hydrologic distributed modelling presented here, the digital terrain model (DTM) and land use information, as provided by a geographic information system (GIS), were introduced based on the principle of hydrologic sub-areas (hydrotopes), the assumption being of hydrologically similar behaviour within these hydrotopes. For the spatial interpolation of the meteorological input variables, various methods were employed. The structures of the model components for snow accumulation and melt, interception, soil water storage and uptake, evapotranspiration, runoff generation, and flow routing are described, including a discussion on assessing the time dependency of the various parameters.
The results for each of the hydrologic components are presented with respect to the different sub-areas and altitudinal zones.