Long-Term Influence of Climate Variability on Hydrological Extremes across European Alpine Rivers

Four of the largest river basins in Europe – Rhine, Rhône, Po, and Danube – are fed by Alpine water resources. Recent hydrological extremes, including catastrophic floods and prolonged droughts, have highlighted the vulnerability of these basins to climatic variability, with significant consequences for downstream populations, economies, and ecosystems. Understanding the potential drivers behind changes in streamflow patterns, particularly the relative contributions of precipitation and temperature, is essential for improving the attribution of extreme hydrological events and informing sustainable freshwater resource management. However, relatively short instrumental hydroclimatic records (i.e., precipitation, temperature and streamflow) in the European Alps limit our understanding of the long-term influence of climate variability on hydrological extremes. Here, by integrating paleo streamflow reconstructions, paleo climatic reanalysis, and climate model simulations, we examine how past and future variability in precipitation and temperature has influenced extreme hydrological events. Through advanced statistical and machine learning approaches, we quantify the relative contributions of precipitation and temperature to observed, reconstructed and projected streamflow anomalies, exploring their respective roles in triggering extreme flood and drought events. By comparing historical trends with future projections across different climate scenarios, we aim to identify the primary climatic drivers of hydrological extremes and their evolution over time. This work highlights the need for a better understanding of long-term climatic forcing mechanisms to improve attributions of hydrological extremes and develop robust adaptation strategies for the Alpine region and its vital river basins.