European summer drying largely driven by atmospheric circulation changes since the 1980s

Abstract In recent decades, Europe has experienced more frequent and severe droughts driven by two mechanisms: shifts in large-scale atmospheric circulation, altering the frequency and position of pressure systems, and thermodynamic changes, which cause background warming, raise evaporative demand and affect precipitation. However, the relative roles of these drivers in observed drought trends remain uncertain. Here we disentangle their contributions using nudged atmospheric circulation model simulations, which isolate the circulation-induced component of European hydroclimatic variability and trends. We show that circulation-induced effects play a substantial role in long-term summer drying. These changes account for about 55% of the observed summer soil moisture decline in mid-latitude Europe since 1980 and about 42% of increased atmospheric vapour pressure deficit. Further, we demonstrate that more frequent anticyclonic, warm and dry weather conditions linked to these circulation changes amplify the thermodynamic component of drying. Whereas our study improves our understanding of the mechanisms behind European hydroclimatic trends, these findings also highlight the high uncertainty for European hydroclimate projections because future circulation changes remain poorly constrained. If historical circulation trends were partly externally forced, circulation-driven drying may continue. If instead they arose from internal climate variability, a circulation tendency that counteracts thermodynamic drying could be expected.