Comparaison du climat et de la variabilité interannuelle de la pluie simulée au Sahel par les modèles climatiques régionaux

The purpose of this study is to evaluate the performance of a set of regional climate models (RCMs) in simulating the mean climatology and the interannual variability of rainfall over the Sahel. We analyzed and compared RCMs outputs within the framework of the ENSEMBLES project. The RCMs are in the same horizontal resolution and are driven by the same lateral boundary condition, the ERA-Interim, which is the latest version of the European Centre for Medium Range Weather Forecasts (ECMWF) reanalysis. The analysis focuses on the period of the monsoon peak (June-July-August [JJA]) over the Sahel. Temperature and precipitation distributions are reasonably well simulated although a few cold and dry biases are present around the Guinean coast and regions of steep topography. All RCMs, except HIRHAM, replicate reasonably well the interannual rainfall anomalies over the Sahel in both sign and magnitude. HIRHAM misses the occurrence of individual anomaly as well as the overall variability. This deficiency can be linked to a simulated weak low-level southwest monsoon flux and a strong harmattan flux from the Sahara desert propagating over the Sahel during observed wet years.