Impact of hydrogeological regime changes on the Bakhtegan-Tashk lake system under groundwater overextraction

Study region: The Bakhtegan–Tashk Lake (BTL) system in southern Iran has experienced severe desiccation. Prolonged drought, declining surface inflows, and intensive groundwater extraction have changed the hydrological regime and disrupted groundwater–surface water (GW–SW) interactions. Study focus: This study investigates the groundwater–surface water (GW–SW) interaction as a key factor influencing the desiccation of BTL. Hydrogeological assessments, water-budget analysis, and statistical cross-correlation were employed to evaluate the dynamics between lake water bodies and groundwater levels from 87 observation wells during 2009–2020. The lake water balance indicated that surface inflows from precipitation and rivers were nearly offset by evaporation losses, emphasizing the lake’s dependency on groundwater inflows for its long-term sustainability. New hydrological insights for the region: Results revealed an annual groundwater outflow of approximately 10.5 MCM from the lake toward adjacent aquifers in recent years, signifying a reversal in the natural flow regime. Cross-correlation analysis confirmed temporal lags and weakened hydraulic connectivity between the lake and groundwater system, driven by overexploitation and reduced recharge. These findings demonstrate that human-induced hydrogeological regime changes have disrupted natural GW–SW exchanges, accelerating lake desiccation. The study enhances understanding of groundwater–lake interactions in semi-arid environments and provides essential insights for improving GW–SW modeling and sustainable groundwater management in the BTL basin and similar regions.