Evaluation of regional COSMO-CLM climate simulations over the eastern Mediterranean for the period 1979–2011

The Regional Climate Model (RCM) COSMO-CLM capability to reproduce the climate characteristics, including extreme values, over the Eastern Mediterranean (EM) was tested. Model configuration has been chosen based on a previously performed sensitivity analysis, aimed to ascertain the accuracy of model performances over Israel. Three simulations driven by ERA Interim reanalysis data for 1979–2011 have been performed using the 0.44˚, 0.22˚ and 0.0715˚ horizontal resolutions equivalent to about 50˚, 25˚ and 8 km, respectively. The CORDEX-MENA domain has been employed for the simulation at resolutions 0.44˚ and 0.22˚. Nested in the 0.22˚ domain the highest resolution of 0.0715˚ is performed over Israel. The model response was analysed for daily precipitation, 2m average temperature, maximum temperature, minimum temperature and a subset of climate indicators defined by the Expert Team on Climate Change Detection and Indices for temperature and precipitation. Results were inter-compared and evaluated against observations. The increased resolution was found to improve precipitation and temperature results. Extreme precipitation indices were well reproduced compared with observations, with a 13% averaged percentage bias. COSMO-CLM was able to reproduce the EM precipitation gradients, with mostly overestimations in the coastal plains and underestimations in the mountains. Extreme temperature indices related to maximum temperatures were reproduced relatively well with an averaged percentage bias of 5.7%. The ability of the model to reproduce minimum temperature observational values was found to be highly dependent on station location with respect to topography. The results in this study are considered a substantial improvement from earlier RCM evaluation studies.