Modelling landscapes with GIS provides a powerful tool to analyze and model terrestrial ecosystems for land use planning. In order to gain realistic results, input data has to represent the natural environment as realistically as possible. While some of the fundamental data layers such as topography and soils are more or less static, climatic data is variable both in space and time. Modeling orders with GIS provides a powerful tool to analyze and model terrestrial ecosystems for land use planning. In order to gain realistic results, input data has to represent the natural environment as realistically as possible. While some of the fundamental data layers such as topography and soils are more or less static, climatic data is variable both in space and time.