Future evolution of large floods in Europe

Large floods regularly cause loss of life and substantial economic damage. In a warmer climate, increased precipitation variability and extremes, combined with reduced snowmelt, are expected to alter flood characteristics, but how the dynamics of large floods across Europe will evolve under climate change remains unclear.  Many existing grid-based and catchment-based studies lack the capacity to systematically identify widespread floods associated with larger impacts. This study addresses these gaps by identifying large, spatially connected floods in Europe based on the spatio-temporal connectivity of runoff extremes, which is derived from daily routed runoff simulations driven by five CMIP5 models under various warming levels. Further, a comprehensive set of flood metrics—including frequency, timing, extent, and volume—is quantified to assess future flood changes. Additionally, the underlying drivers of these changes are investigated. We show that earlier snowmelt generally leads to earlier floods, while increasing precipitation contributions attenuates flood seasonality. In western and central Europe, projected increases in precipitation amplify flood extents and volumes, particularly for the most extreme floods. In contrast, reduced snowmelt dominates flood changes in northern Europe. Interestingly, floods of different magnitudes exhibit varied responses to global warming. For example, while the extent of average large floods in southern Europe are projected to decrease, the most extreme floods remain nearly unchanged, warranting continued attention. Overall, our findings demonstrate that the impact of climate change on the dynamics and magnitude of large floods is strongly region-specific. These insights provide essential information for regional flood risk management and could help mitigate the impacts of particularly large floods in Europe.