of these models is SURFEX which simulates processes at the surface and in the soil, e.g. temperature and water balance, radiation balance and transfer of heat, see Figure 1. It is important to describe the surface, and its properties, as well as possible. To do this SURFEX uses
elevation data (from the GTOPO3 database of USGS), data on sand- and clay fraction in soil (from the HWSD database of FAO
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