What do CMIP6 models tell us about rainfall intensification in the West African Sahel?

Regional projections of rainfall changes are required for adaptation planning, especially in regions where unprecedented climatic evolution are underway, such as the West African Sahel. The potential of models to draw a realistic picture of future regional changes remains to be assessed through the lens of past evolution. Here we make sense of several rainfall regime indicators, a widespread raingauge dataset and a set of the most recent climate model simulations to identify features that deserve confidence and others that require care. We show that, at the sahelian scale, the mean intensity and occurrence of rainy days are well reproduced, yielding a good depiction of the recent rainfall intensification. However, unlike wet extremes, changes in dry extremes are not captured, pointing to model deficiencies in reproducing realistic changes in intraseasonal rainfall variability. We also show that the regional rainfall evolution of the last 35 years is very unlikely due to neither internal variability nor to natural forcing factors alone; based on a qualitative attribution analysis, aerosols turn out to account for the largest share of the recent increasing signal. The greenhouse-gases (GHG) influence makes less consensus among models, especially regarding extreme rainfall trends. This is a major concern for projections of future hydro-climatic trajectories in the region since GHG is to become the predominant climate forcing factor for the coming decades.