Spatiotemporal Analysis of Groundwater Recharge under Urbanization and Climate Variability in Milan Province, Italy

Groundwater recharge (GR) is one of the most important processes of the hydrologic cycle, especially in urbanizing regions where land use and climate variability are interacting in a very complex way. In this study, we explore the impact of these drivers on GR dynamics in Milan Province, Italy, for the period 1951-2023. Applying a 1 km2 high-resolution data set derived from the BIGBANG model in combination with CORINE-based land use data, we investigated the long-term trends in total precipitation (TP), actual evapotranspiration (AET), surface runoff (R), soil water content (SW), temperature (T), and percentage of artificial surfaces (PAS). Non-parametric trend tests (Mann-Kendall and Sen’s slope) identified significant decreasing trends in GR, AET, and SW, particularly in high PAS areas. TP had high interannual variation but was the most important positive driver of GR. In contrast, increasing PAS had a strong negative impact, as indicated through stepwise linear regression, where TP and PAS together explained over 70% of GR variability. Spatial and temporal analysis illustrate how urbanization disrupts natural recharge processes, diverting water from infiltration to runoff, thereby increasing hydrological stress.