Climatic and socioeconomic drivers of changing flood and drought magnitudes in Europe from 1951 to 2020

Hydrological extremes display long-term trends and natural oscillations in response to climatic and socio-economic factors. Knowing how and why these extremes are shifting is crucial for increasing water resilience in Europe. This work analyses trends in floods and droughts in European catchments with an upstream area below 100 km² between 1951 and 2020. Using hight-resolution climatic and socioeconomic data, the OS LISFLOOD hydrological model and non-stationary extreme value analysis, we disentangle the effects of four drivers on flood and drought magnitudes: dynamics in climate – encompassing climate variability and climate change – land use changes, water demand changes and reservoir construction. We map combined floods and droughts changes into four trajectories: wetting, drying, accelerating, decelerating. The trajectories and their links to different drivers are aggregated at different spatial levels, revealing patterns from local to regional scales in changes of flood and drought magnitudes. We find that on average, flood magnitude rose by 1.5% and drought magnitude fell by 1.3% across Europe since the 1950s, with multidecadal variations. Climate dynamics lead to heterogenous patterns, with an overall wetting of north-western Europe, and a drying in the Mediterranean region. Diverse land use changes (e.g., urbanization, reforestation) have generally increased flood and drought hazard (intensification), while water demand primarily intensified droughts (drying). Reservoirs, conversely, have smoothed extremes and decelerated the hydrological cycle. Our work delivers insights into the intricate connections between climate, society, and water at a refined resolution in European river basins, enabling the development of effective strategies for enhancing resilience to extreme water events under global changes.