Time invariant boundary data of regional climate models COSMO-CLM and WRF and their application in COSMO-CLM

Basic time invariant boundary parameters, such as topography, land use, soil texture, and derived vegetation and soil properties as defined in the regional climate models Consortium for Small-scale Modeling in Climate Mode (CCLM), and the Weather Research and Forecasting Model (WRF), are investigated in terms of their applicability. The focus is on the comparison of the four available data sets and the investigation of their influences on actual CCLM simulations. Several runs of the CCLM model with National Centers for Environmental Prediction (NCEP) and ERA40 boundary forcings in the Mediterranean Coordinated Regional Climate Downscaling Experiment indicate that the investigated data sets are suitable for the considered region. The variations introduced by the different time invariant boundary data are within the range of the variations resulting from different driving reanalysis data, but lower than the differences obtained in intermodel evaluations, e. g., in Prediction of Regional scenarios and Uncertainties for Defining European Climate Change Risks and Effects (PRUDENCE) and Ensembles-based predictions of climate changes and their impacts (ENSEMBLES). The variation in the monthly mean values resulting from differences in the land use, topography, and soil data are up to 1.1 K in the area average monthly mean temperature and up to 17% of the observed value of the area average monthly precipitation. The study indicates that CCLM would benefit from further improvements of the time invariant boundary data, especially the soil texture data.