Drought is one of the main threats to food security and ecosystem productivity. During the past decades, Europe has experienced a series of droughts that caused substantial socioeconomic losses and environmental impacts. A key question is whether there are some similar characteristics in these droughts, especially when compared to the droughts that occurred further in the past. Answering this question is impossible with traditional single-index approaches and also short-term and often spatially inconsistent records. Here, using a multidimensional machine learning-based clustering algorithm and the hydrologic reconstruction of European drought, we determine the dominant drought types and investigate the changes in drought typology. We report a substantial increase in shorter warm-season droughts that are concurrent with an increase in potential evapotranspiration. If shifts reported here persist, then we will need new adaptive water management policies and, in the long run, we may observe considerable alterations in vegetation regimes and ecosystem functioning.

Department of Civil and Environmental Engineering and Department of Earth System Science University of California Irvine Irvine CA 92697 USA

Department of Hydrology T G Masaryk Water Research Institute Podbabská 2582 30 Prague 6 160 00 Czech Republic

Faculty of Environmental Sciences Czech University of Life Sciences Prague Praha Suchdol 16500 Czech Republic

Global Change Research Institute CAS Bělidla 986 4b Brno 603 00 Czech Republic

UFZ Helmholtz Centre for Environmental Research Leipzig 04318 Germany

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