Influence of submonthly air-sea coupling on heavy precipitation events in the Western Mediterranean basin

Abstract : Heavy precipitation events (HPEs) can be a major cause of damage and casualties in the Mediterranean basin. With the use of atmosphere–ocean coupled regional climate models (AORCMs) and the advantage of 24 years of simulation (1989–2012), we identified regions with potential impact of submonthly air-sea coupling on HPEs among the regions hit by heavy rain during HyMeX 1st special observation period (SOP1): Valencia in Spain, the Cévennes in Southern France, Liguria in Northwestern Italy, Calabria in Southern Italy and Northeastern Italy. A first evaluation of the two AORCMs (MORCE and CNRM-RCSM4) against gridded precipitation datasets showed that 70 to 90% of the 30 most intense HPEs simulated were observed HPEs for most regions. The Cévennes, Valencia and Calabria were the only three regions to show a statistical relationship between rain differences and SST differences where the low-level jets that feed the events most frequently blow. This sensitivity of precipitation to SST changes is due to low-level wind changes related with changes in surface heat fluxes. Based on the calculation of submonthly variations in these regions during HyMeX, HPEs on the 28/09/2012 and 12/10/2012 in Valencia and on 25-26/10/2012 in the Cévennes have most probably been affected by submonthly air-sea coupling.