Land-atmosphere coupling and climate variability in future-climate scenarios for the European continent

We analyze the hydrological cycle characteristics and climate variability of present (1960-1990) and future (2070-2100) climate simulations for the European continent. The simulations are performed with the CHRM regional climate model, using boundary conditions from two different AGCM simulations (HadCM3 and ECHAM4). The main focus of the present analysis is the investigation of the underlying physical processes leading to the increase in summer climate variability diagnosed in numerous climate-change projections. Indeed, it has been demonstrated that future summer climate in the mid-latitudes is likely to be both characterized by enhanced droughts periods as well as by an intensification of rainfall events. First, we present a detailed validation of the present-climate experiments. Then, climate-change impacts on key physical processes relevant for the investigated issue (convection, soil moisture evolution, large-scale circulation) are analyzed thoroughly. Finally, sensitivity experiments using prescribed soil moisture content (and thus shutting down the land-atmosphere coupling) are used to shed light on the respective roles of the atmospheric and land-surface processes for the expected future changes in climate variability for the European continent.