A Coupled Surface–Subsurface Modeling Framework for Evaluating Watershed Vulnerability to Climate and Land Use Change

High Resolution Image Download MS PowerPoint Slide Watersheds face intensifying pressures from climate and land use/land cover (LULC) dynamics. To assess systemic vulnerability, we developed an integrated framework that couples the Soil and Water Assessment Tool (SWAT) with a modified DRASTIC model. The integrated model improves aquifer vulnerability assessment accuracy compared to traditional DRASTIC methodologies. AUC values increased from baseline levels of 0.37, 0.40, 0.50, and 0.07 to 0.53, 0.80, 0.81, and 0.63 for NO 3 –, TDS, Cl –, and Ca 2+, representing relative improvements of 44%, 99%, 62%, and 845% respectively. Future projections under RCP 4.5 and 8.5 scenarios demonstrate a strong positive correlation ( R 2 = 0.75–0.81) between simulated annual runoff and annual rainfall, based on analyses of future time-series data without detrending, while urbanization-driven LULC shifts amplify TP and NH 4 + -N loads by 19–23%. Strategic land use interventions (e.g., converting 6.86% of agricultural land to forests) reduce high-vulnerability groundwater zones by 15.08%, highlighting actionable pathways for adaptive watershed management. This framework provides a transferable tool for policymakers to prioritize mitigation strategies in integrated surface–subsurface systems under climate uncertainty.