1 Upscaling of Land Surface Parameters through Inverse SVAT-Modeling

Ongoing intensification of agriculture in West Africa has led to a change in surface and subsurface characteristics, which directly affect evapotranspiration rates. If these changed evapotranspiration rates in turn affect regional precipitation patterns, rainfed and irrigated agriculture in West Africa may face changed boundary conditions because of complex feedback mechanisms between the surface and atmosphere. The investigation of these feedback effects requires the application of regional climate models that account for soil and vegetation state through SVAT schemes. Regional climate models use land use data in resolutions of 10-250 km because of the limitation of computing resources required for fine resolution runs over the domain of interest. However, information on land surface parameters is usually available at much finer resolution. It is a fundamental and not yet satisfactorily solved problem in hydrological research how subgrid scale variability can be accounted for at coarse resolutions. We therefore investigate into the possibility to derive “effective ” parameters on grid scale (in dependence of mean and standard deviation at subgrid scale) that yield approximately the same surface heat fluxes as the corresponding aggregated fluxes on the finer scale.