Scandinavian pattern and temperature changes shape European summer droughts over the past millennium.

Recent decades have seen pronounced changes in European hydroclimate, including widespread summer drying, yet its spatiotemporal variability and underlying drivers remain uncertain. Here we present the European Last Millennial Data Assimilation (EULMDA), a new reconstruction of European hydroclimate and its main drivers covering the past millennium. EULMDA integrates five Earth System Model simulations with over one hundred moisture and temperature sensitive tree-ring records. It demonstrates high skill in reproducing instrumental variability across climate variables, including large-scale atmospheric circulation changes. We show that European warm-season drought variability is primarily governed by circulation changes associated with the Scandinavian pattern (SCAND) and long-term summer temperature changes, together explaining over half of the spatiotemporal drought variance. SCAND drives a pronounced north-south dipole in summer hydroclimate, explaining a larger fraction of Mediterranean drought variability than other major circulation modes, contributing to recent multidecadal drying in the Mediterranean alongside wetting in northern Europe. Meanwhile, summer warming intensifies drying across much of Europe. These results provide critical context for interpreting recent drought trends and insight into mechanisms shaping future hydroclimate risks.