Added value of high-resolution regional climate simulations for regional impact studies

We present a comparison of results from the regional climate model COSMO-CLM at a horizontal resolution of 2.8 km with observations and assess the added value of such higher resolution compared to a coarser resolution of 7 km. Such an added value is expected to result from a better resolution of orography and land use as well as from direct simulation of deep convection. The simulations are driven by ERA40 reanalyses for the years 1971 to 2000 and cover southwestern Germany and parts of eastern France. We show that 2.8 km horizontal resolution simulations yield in many, but not all, cases a better agreement of temperature, precipitation, humidity, and global radiation with observation data than simulations with 7 km resolution, especially during the summer half year. At 2.8 km resolution, the model also is well able to capture the mechanisms generating small-scale features, e. g. wind systems. However, the added value is highly dependent on region and altitude. In general, we conclude that high-resolution climate modeling allows studying the impact of climatological parameters on regional scales. It produces encouraging results and has a high potential for applications and direct use in regional and local impact models and impact studies.