Uncertainty in Sahel precipitation change: a storyline approach 

<p>Future changes in Sahel precipitation are uncertain because of large differences between projections of various climate models. We assess the effect of climate change on Sahel precipitation in summer and for the end of the 21^st century. We show that uncertainty in Sahel precipitation is associated with uncertainty at simulating future changes in surface air temperature over the northern Hemisphere. We point out the Atlantic Ocean and Euro-Mediterranean surface air temperature as drivers of the Sahel precipitation change uncertainty. We use a storyline approach, a statistical method, to construct scenarios of changes in Sahel precipitation, whose differences only depend on future changes in Atlantic Ocean and Euro-Mediterranean surface air temperature. We show that uncertainty in changes in Atlantic Ocean and Euro-Mediterranean surface air temperature explains up to 50% of Sahel precipitation change uncertainty. The approach also allows selecting models to better understand uncertainty in Sahel precipitation change, focusing on the mechanisms at play. We suggest that reducing uncertainty in the future warming of the North Atlantic and the Euro-Mediterranean areas would then allow reducing uncertainty in future changes in Sahel precipitation.</p>