Hydrogeological settings shape drought impacts on river flows in Corsica, France: Evidence from multi-tracer investigations, watershed typology and past-trend analysis

Study Region This study investigates 13 benchmark Mediterranean watersheds located in Corsica, France. These hard-rock watersheds are representative of contrasting hydrogeological settings ranging from coastal lowlands to mountainous granitic and metamorphic terrains, under a Mediterranean climate characterised by strong drought variability and hydroclimatic stress. Study Focus This study focuses on their hydrogeological dynamics under drought conditions, using an integrated approach combining watershed characterisation, multivariate statistical classification, tracer-based analysis ( 18 O, 2 H, 222 Rn, EC), and long-term hydrological trends assessment. Multivariate analyses are used to identify hydrogeological watershed typologies and to relate morphometric, climatic, and geological attributes to their subsurface flow processes and groundwater contributions. New Hydrological Insights for the Region Four hydrogeological watershed typologies are identified, defining a gradient from climate-dominated coastal systems with limited storage and rapid flow paths to granitic groundwater-buffered systems with higher recharge efficiency, deeper flow paths, and stronger baseflow contributions, and with intermediate behaviours controlled by mountain headwaters influence or metamorphic structural constraints. Watersheds with limited groundwater storage are highly sensitive to precipitation decline and show reduced baseflow, whereas groundwater-buffered systems exhibit higher resilience and more stable hydrological regimes over time. Overall, the results demonstrate that hydrological responses to climate variability are primarily controlled by hydrogeological conditions rather than climate forcing alone, supporting process-based watershed management strategies tailored to Mediterranean environments facing increasing drought pressure and water resource vulnerability.