Understanding climate change over the southwestern Mediterranean using high-resolution simulations

The severe wintertime precipitation decline projected by global climate models (GCMs) over the Southwestern Mediterranean makes this region a major climate change hotspot. Here, we evaluate the performance of the MIT Regional Climate Model (MRCM) in simulating seasonal and inter-annual regional climatic features over Northwestern Africa and the Iberian Peninsula (NWAIP), and develop and interpret regional climate change projections over the same region under the RCP4.5 and 8.5 scenarios, at a resolution of 12 km, driven by three carefully selected GCMs. MRCM succeeds in correctly capturing the spatio-temporal patterns of precipitation when forced by ERA-Interim reanalysis data. In addition to substantial year-round warming, the MRCM ensemble projects a significant decline in precipitation during winter and spring under continued anthropogenic forcing. Even with significant climate change mitigation, the drying is relatively large, with an average of − 34% in precipitation over Morocco’s three main watersheds during spring, and − 22% during winter. Projections for the Iberian Peninsula are less severe, though drying trends are still robust. The consistency of the precipitation projections is discussed in the light of physical mechanisms acting at the regional scale. Being located downwind of a large desert, the region is particularly vulnerable to the changes in circulation projected by global models. The latter will advect dry air from the Sahara, which will suppress precipitation. The local topography also contributes to these trends. Overall, our results elucidate the physical processes responsible for winter and spring drying in the southwestern Mediterranean.