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

European summer hydroclimate has shifted markedly in recent decades, including widespread drying across many regions. However, major uncertainties remain regarding their spatiotemporal variability and underlying drivers. Here, we present the European Last Millennial Data Assimilation (EULMDA), a new reconstruction of European hydroclimate and its main drivers over the past millennium. EULMDA combines five Earth System Model simulations with more than 100 tree-ring records sensitive to moisture and temperature, and shows strong skill in reproducing instrumental variability in multiple climate fields, including large-scale circulation changes. For the warm season, we identify two dominant controls on European drought variability: circulation fluctuations linked to the Scandinavian pattern (SCAND) and long-term summer temperature changes. Together, these factors account for more than half of the spatiotemporal drought variance. The 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. Taken together, these dynamic and thermodynamic processes have shaped European hydroclimate throughout the past millennium, providing critical context for interpreting recent drought trends and insight into mechanisms shaping future hydroclimate risks.