From droughts to hotter droughts: Europe’s changing hydroclimate

Study Region Europe (pan-European domain), with particular focus on northern, central, southern, eastern, and Mediterranean Europe, covering the period 1902–2024. Study Focus Warming is well established to transform droughts from precipitation-driven to 'hotter' events dominated by evaporative demand. Building on this foundation, we provide a century-scale pan-European observational synthesis of the compound hot–dry hazard and explicitly separate shifts in joint hot–dry probabilities into contributions from marginal warming and from changes in heat–dryness dependence, a decomposition not previously applied at this spatio-temporal scale. We identify a marked seasonal and regional reorganization of hydroclimate, with cold-season wetting concentrated in northern Europe and warm-season drying across the broader central, southern, and eastern European domain. A direct comparison of the Standardized Precipitation Evapotranspiration Index (SPEI) and the Standardized Precipitation Index (SPI) trends shows that across central and southern Europe, the late-summer drying signal exceeds what precipitation changes alone can explain, identifying rising evaporative demand as a substantial and spatially coherent driver of recent drying. New Hydrological Insights for the Region Since the mid-1990s, compound hot–dry months have routinely affected more than 25% of Europe, and joint hot–dry probabilities have increased significantly. An explicit probability decomposition reveals that this increase is driven primarily by the rise in marginal warm-months frequency, while changes in heat–dryness dependence are spatially heterogeneous and act as a secondary, regionally specific amplifier in water-limited southern European climates. These findings highlight the need for drought monitoring, hazard assessment, and water-resources planning frameworks that explicitly incorporate evaporative demand and compound-event behavior, rather than relying solely on precipitation-based indicators.