Mechanisms of European Summer Drying under Climate Change

The geography of Europe as a continental landmass, located between the arid Sahara and the cold high latitudes (both are dry in terms of absolute humidity), dictates the reliance during summer of southern Europe (south of 45 degrees N) on stored water from winter and spring, and of northwestern Europe on a small concentrated low-level moisture jet from the North Atlantic. In a recent study, we explained the projected winter precipitation decline over the Mediterranean under climate change as due to shifts in upper tropospheric stationary waves and to the regional-scale land-water warming contrast. Here, based on the analysis of observations and output from models from phase 5 of the Coupled Model Intercomparison Project, we expand this theory further, documenting how the winter precipitation decline expands into southern Europe during spring, dictated by similar dynamical mechanisms, depleting soil moisture and setting the stage for drier summers via soil moisture-precipitation feedbacks. Over northwestern Europe, an anomalous anticyclonic circulation west of the British Isles displaces the low-level moisture jet northward, limiting moisture supply, and reducing low-level relative humidity and rainfall. Finally, we discuss how this comprehensive perspective of European summer climate change can help us better understand the variations across model projections, and pave the way for their reduction.