Improvements in the Precipitation Distribution of West Africa with a Convection-Permitting Simulation at Climate Scales

Two sets of 10-years of a convection-permitting regional model on the whole of Africa are being run at the Met Office. The regional model (CP4A) is forced at its boundaries with a 25km global model (N512) with present-day AMIP forcing and future climate RCP8.5 forcing. The first 5 years of CP4A show a large improvement in the mean West African monsoon with a reduction in the dry bias compared to the global N512 models (~25km resolution). It also shows a better precipitation distribution with more short lasting strong rainfall events. It is in good agreement with observations on a 25km scale. It further shows a better timing of the afternoon convection peak compared to N512 and a better representation of wet and dry spells. There are remaining biases in the model, including an underestimation of the number of wet days by 10-30 %, an underestimation of rainfall at night/morning and too much rainfall on orography. However, these results make us confident that this model will give further information on locally-driven future changes of the West-African monsoon that the current global models fail to represent.