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Does increased RCM resolution lead to a better representation of heavy precipitation?

The present contribution is part of a study developed in the framework of the Euro-CORDEX initiative. The main objective is to compare several regional climate models (RCMs) at different target spatial scales over the Alpine area. For this purpose, downscaled precipitation is evaluated at two horizontal resolutions (0.11º corresponding to approx. 12 km, and 0.44º corresponding to approx. 50 km) in simulations from the Euro-CORDEX RCM ensemble, all of them using the ERA-Interim reanalysis as boundary conditions.

We focus on the European Alps because of their special climate characteristics and their high vulnerability to changes in climate. In this region, a high-resolution gridded observational data set recently became available. It has been constructed by MeteoSwiss within the EURO4M project and provides daily precipitation at a horizontal resolution of 5 km. These gridded observations were spatially averaged to match the Euro-CORDEX grid cells.

The comparison will not only be accomplished in terms of validation against observations in both resolutions. Also the ability of the high-resolution RCM simulations (0.11°) to represent observed precipitation is assessed at their skillful scale by aggregating the 0.11° grid to the 0.44° resolution and evaluating the added value with respect to the low resolution (0.44°) runs. The study will especially consider heavy precipitation characteristics and will assess the effect of model resolution on the tails of the probability distribution function. Additionally, the analysis might include preliminary results concerning the resolution effect in statistical downscaling methods.