Climate and human-driven shifts in groundwater–lake interactions in a semi-arid maar lake

Inland waters in semi-arid regions respond rapidly to both climate variability and human pressure, but the mechanisms linking external forcing to groundwater–surface water connectivity are still poorly understood, particularly in tropical lakes. Maar lakes are specially well suited to explore these processes because they are directly embedded in regional groundwater flow systems. We examine these interactions in Lake Alchichica (central Mexico), a semi-arid maar lake that has undergone a persistent decline in water level over recent decades. We developed a conceptual model based on a multiproxy approach combining effective precipitation, regional hydrogeochemistry, isotopic and physicochemical lake data, and groundwater level dynamics. Hydrogeochemical and isotopic patterns indicate a tight coupling between regional groundwater flow and lake water, with progressive chemical evolution along the flow path and increasing ion concentrations driven by intense evaporation. Between 2017 and 2021, groundwater levels dropped by ~38 cm, pointing to a reduction in subsurface inflows and a direct impact on the lake water balance. This decline cannot be explained by meteorological variability alone and instead suggests system-scale changes, likely associated with regional groundwater exploitation and long-term climate variations. Although groundwater chemistry has remained relatively stable, reported shifts in lake temperature and composition indicate emerging pressures on ecosystem functioning. Together, these results show how climatic and anthropogenic forcing can reshape groundwater–lake connectivity threatening lake's habitat.