Droughts in Germany: performance of regional climate models in reproducing observed characteristics

Droughts are among the most relevant natural disasters related toclimate change. We evaluated different regional climate model outputs andtheir ability to reproduce observed drought indices in Germany and its nearsurroundings between 1980-2009. Both outputs of an ensemble of sixEURO-CORDEX models of 12.5 km grid resolution and outputs from a high-resolution (5 km) Weather Research and Forecasting (WRF) run were employed. The latter model was especially tailoredfor the study region regarding the physics configuration. We investigateddrought-related variables and derived the 3-month standardized precipitationevapotranspiration index (SPEI-3) to account for meteorological droughts.Based on that, we analyzed correlations, the 2003 event, trends and droughtcharacteristics (frequency, duration and severity) and compared the resultsto E-OBS. Methods used include Taylor diagrams, the Mann-Kendall trend testand the spatial efficiency (SPAEF) metric to account for spatial agreementof patterns. Averaged over the domain, meteorological droughts were found tooccur approximately 16 times in the study period with an average duration of 3.1 months and average severity of 1.47 SPEI units. WRF's resolution and setupwere shown to be less important for the reproduction of the single droughtevent and overall drought characteristics. Depending on the specific goalsof drought analyses, computation resources could therefore be saved, since acoarser resolution can provide similar results. Benefits of WRF were foundin the correlation analysis. The greatest benefits were identified in the trendanalysis: only WRF was able to reproduce the observed negative SPEI trendsto a fairly high spatial accuracy, while the other regional climate models (RCMs) completely failed inthis regard. This was mainly due to the WRF model settings, highlighting theimportance of appropriate model configuration tailored to the target region.Our findings are especially relevant in the context of climate changestudies, where the appropriate reproduction of trends is of high importance.

Automated summary

This study evaluated the ability of different regional climate models to reproduce observed drought indices in Germany and its surroundings, finding that the high-resolution Weather Research and Forecasting (WRF) model performed the best in reproducing observed drought trends. These findings are crucial for climate change studies.