Filippo Giorgi, Jeremy S. Pal, Peter Gibba, Ibourahima Kebe, and Michel Nikiema
Journal of Climate


In this study, the response of the annual cycle of high intensity daily precipitation events over West Africa to anthropogenic greenhouse gas for the late 21st Century is investigated using an ensemble of high-resolution regional climate model experiments. For the present-day, the RCM ensemble substantially improves the simulation of the annual cycle for various precipitation statistics compared to the driving Earth System Models. The late 21st Century projected changes in mean precipitation exhibit a delay of the monsoon season, consistent with previous studies. In addition, these projections indicate a prevailing decrease in frequency, but an increase in the intensity of very wet events, particularly in the pre-monsoon and early mature monsoon stages, more pronounced over the Sahel and in the RCP8.5 than the Gulf of Guinea and the RCP4.5. This is due to the presence of stronger moisture convergence in the boundary layer that sustains intense precipitation once convection is initiated. The pre-monsoon season experiences the largest changes in daily precipitation statistics, particularly towards an increased risk of drought associated with a decrease in mean precipitation and frequency of wet days, and increased risk of flood associated with very wet events. Both these features can produce significant stresses on important sectors such as agriculture and water resources at a time of the year (e.g. the monsoon onset) where such stresses can have stronger impacts. The results thus point towards the importance of analyzing changes of precipitation characteristics as a function of the regional seasonal and sub-seasonal cycles of rainfall.