Quantifying subsurface contributions to compound flooding in coastal urban areas for enhanced resilience

Coastal cities are increasingly affected by flooding due to the combined impacts of surface and subsurface water processes. Compound flood events, driven by changing groundwater levels, tidal surges, and riverine, pose substantial risks to urban infrastructure and livelihoods, particularly in low-lying coastal cities like Mumbai. Despite its critical importance, the role of groundwater dynamics in flood severity and its contribution to comprehensive flood risk assessments remain underexplored. In this study, we quantify flood risks induced by multiple drivers and their contributions to compound events. We integrate surface and subsurface flooding using MIKE+ and FEFLOW to simulate 1D-2D coupled hydrodynamic models, respectively. Mumbai serves as the study area due to its susceptibility to tidal surges, riverine, and groundwater flooding. By incorporating tidal, well, and streamflow data, our study quantifies the contribution of groundwater to surface flooding, offering a deeper understanding of the interplay between subsurface and surface water processes. Our findings lay the foundation for proactive groundwater management strategies and promote the development of resilient urban infrastructure, ultimately mitigating the impacts of flooding in vulnerable coastal areas.