Impact of model resolution and Mediterranean sea coupling on hydrometeorological extremes in RCMs in the frame of HyMeX and MED-CORDEX

Abstract

In this study, we are interested in evaluating the potential improvement of: (i) coupled RCM simulations (with the Mediterranean sea) in comparison with atmosphere only (stand-alone) RCM simulations and (ii) RCM simulations at a finer resolution in comparison with coarser resolution. For that, three different RCMs (WRF, ALADIN, LMDZ4) were run, forced by ERA-Interim reanalyses, within the HyMeX/Med-CORDEX experiments. For each RCM, different versions (coupled/stand-alone, high/low resolution) were realized. This study focuses on extreme meteorological events (hot days, droughts and heavy precipitation) and evaluates the current RCM simulations in terms of return levels associated with these events. Additionally, a large set of indicators is proposed in order to better understand the performances of RCM simulations. These indicators were applied for three variables (daily precipitation amount, mean daily 2-m air temperature and dry spell length). Results show that the differences between coupled and stand-alone RCMs are localized very near the Mediterranean sea. For hot days and droughts statistics, high resolution runs display better performances than low resolution runs. The expected improvement for extreme precipitation with higher resolution runs was not observed in this study.