Urbanisation and groundwater recharge potential shifts in a coastal basin: A spatiotemporal ecohydrological assessment

• GIS–MCDA (AHP + WOA) applied to map GWRPZ for 2000, 2015, and 2021. • Low and Average recharge zones increased from 1.7% to 7.5% and 51.4% to 63.1%. • Above-Average zones declined from 44.4% to 27.9%, Good zones reduced below 2%. • On a cumulative basis validation achieved 91.67% accuracy and 72.86% AUC. • The framework enables GWRPZ ecohydrological planning in coastal basins with limited monitoring wells. Rapid urbanisation in coastal cities alters natural groundwater recharge processes through land-use transformation, the expansion of impervious surfaces, and modifications to drainage networks, posing challenges for groundwater sustainability under data-scarce conditions. This study presents a spatiotemporal framework for delineating Groundwater Recharge Potential Zones (GWRPZ) in the Cooum and Adyar River basins, two highly urbanised coastal catchments within the Chennai Metropolitan Area, India, for the years 2000, 2015, and 2021. The framework integrates nine hydro-environmental parameters including land use/land cover, rainfall, slope, drainage density, soil, geology, geomorphology, lithology, and lineament density using a GIS-based Multi-Criteria Decision Analysis approach with the Analytic Hierarchy Process and weighted overlay modelling. The spatiotemporal analysis indicates a progressive decline in areas characterised by above-average and good recharge potential, accompanied by an increase in average and low recharge zones, reflecting the cumulative influence of urban expansion on infiltration and subsurface recharge processes. Given the limited availability of groundwater monitoring data, model evaluation was conducted using a cumulative validation strategy based on trends in groundwater-level fluctuations across multiple periods. The validation results demonstrate a reasonable correspondence between observed groundwater responses and mapped recharge potential patterns, supporting the applicability of the framework in data-scarce urban environments. The study highlights the value of spatiotemporal recharge zoning as a decision-support tool for urban physical planning, enabling identification of recharge-sensitive zones for protection and management in rapidly transforming coastal cities.