Does a convection-permitting regional climate model bring new perspectives on the projection of Mediterranean floods?

Abstract

Abstract. Floods are the primary natural hazard in the French Mediterranean area causing damages and fatalities every year. These floods are triggered by heavy precipitation events (HPEs) characterized by limited temporal and spatial extents. For a decade, a new generation of regional climate models at the kilometer scale have been developed, allowing an explicit representation of deep convection and improved simulations of local-scale phenomena such as HPEs. Convection-Permitting regional climate Models (CPMs) have been scarcely used in hydrological impact studies, and future projections of Mediterranean floods remain uncertain with Regional Climate Models (RCMs). In this paper, we use the CNRM-AROME CPM (2.5 km) and its driving CNRM-ALADIN RCM (12 km) at the hourly timescale to simulate floods over the Gardon d’Anduze catchment located in the French Mediterranean region. Climate simulations are bias-corrected with the CDF-t method. Two hydrological models, a lumped and conceptual model (GR5H), and a processed-based and distributed model (CREST), successively forced with historical and future climate simulations from the CPM and from the RCM, have been used. The CPM model confirms its ability to reproduce extreme hourly rainfall compared to the RCM. This added value is propagated on flood simulation with a better reproduction of flood peaks. Future projections are consistent between the hydrological models, but differ between the two forcing climate models. With the CNRM-ALADIN RCM, all floods are projected to increase, whereas a threshold effect is found for simulations driven by the CNRM-AROME CPM, where the magnitude of the largest floods is expected to increase while the moderate floods are expected to decrease. In addition, different flood event characteristics indicate that floods are expected to become flashier in a warmer climate, regardless of the model. This study is a first step for impact studies driven by CPMs over the Mediterranean.