Assessing Meteorological (1950–2022) and Hydrological (1911–2022) Trends in the Northwestern Alps: Insights from the Upper Po River Basin

This study investigates hydro-meteorological trends in five Alpine catchments within the Upper Po River basin, spanning Northwestern Italy and Southern Switzerland. We ana-lyzed climatic variables from 25 weather stations (1950–2022) alongside streamflow data from 14 river sections (1911–2022). Trends were assessed using the Mann-Kendall test to detect monotonic changes and the Theil-Sen estimator to quantify magnitude, ensuring robustness against outliers. Results reveal pronounced warming, particularly in spring maximum temperatures (+0.95 °C per decade). Conversely, average and minimum daily temperatures show lower rates (+0.50 and +0.39 °C per decade). Consequently, potential evapotranspiration increased significantly (+15.1 mm per decade), contributing to a marked decline in summer streamflow in 8 out of 14 sections. Correlation analysis con-firms that snow dynamics modulate the hydrological response: while precipitation drives discharge annually and in autumn, winter exhibits a weaker coupling, as winter precipi-tation is partially stored in the basin as snow, contributing to discharge during spring and summer. By focusing on this strategic region for European agriculture and industry, the study provides essential insights to support effective adaptation strategies.