Multi-model CMIP5 and CORDEX simulations of historical summer temperature and precipitation variabilities over West Africa

The mean climatology, inter-model variability and spatio-temporal patterns of temperature and precipitation over West Africa from Coupled Model Intercomparison Project 5 (CMIP5), CMIP5_SUBSET [ensemble of global climate models driving COordinated Regional climate Downscaling EXperiment (CORDEX)] and CORDEX multi-model ensembles are evaluated and intercompared for the monsoon season (June-September). We find that, while CORDEX fails to outperform the simulated mean climatology of temperature by the CMIP5 ensembles, it substantially improves precipitation and provides more realistic fine-scale features tied to local topography and landuse. This improved performance over the region is found to depend more on the internal models physics than the driving boundary conditions and results from a more consistent and realistic simulation of monsoon precipitation across the various regional climate models (RCMs). Rotated empirical orthogonal function (REOF) analysis indicates that the CORDEX ensemble captures better the spatio-temporal variability of both temperature and precipitation (first REOF mode), in particular depicting the warming and Sahel precipitation recovery in recent decades over West Africa. On the other hand, the spatial patterns and associated time series of the last two REOF modes in CORDEX mostly follow the CMIP5_SUBSET pointing towards a strong role of the boundary forcing in the RCM simulation of precipitation variability.