Modeling Relative Sea-Level Rise through Geodetic-Hydrodynamic Fusion: Quantifying Multi-Sectoral Risks in the Bengal Delta

The Bengal Delta, one of the world’s most dynamic and densely populated coastal systems, faces accelerating relative sea-level rise (RSLR) driven by complex interactions among eustatic rise, land subsidence, sediment compaction, and anthropogenic stress. This study develops an integrated geodetic-hydrodynamic modeling framework to quantify multi-sectoral risks arising from RSLR and to provide a data-driven foundation for adaptive coastal resilience planning. High-resolution InSAR and GNSS observations were combined with tide-gauge and hydrodynamic models to produce spatially explicit subsidence-adjusted RSLR projections under multiple climate scenarios. Monte Carlo ensembles and sensitivity analyses were applied to assess uncertainty in hydrodynamic responses, inundation dynamics, and salinity intrusion. Results indicate spatially variable subsidence rates ranging from 2.1 to 6.5 mm yr⁻¹, amplifying effective RSLR to 3.8-8.9 mm yr⁻¹ across the deltaic plain. By mid-century, permanent inundation is projected to expand by 24-42%, while salinity intrusion may penetrate up to 90 km inland during the dry season under high-emission scenarios. Agricultural productivity, ecosystem integrity, freshwater availability, and rural livelihoods emerge as the most vulnerable sectors. Sectoral exposure mapping reveals critical infrastructure and cropland losses concentrated in the south-central polders and estuarine tracts. This integrated geodetic-hydrodynamic fusion framework demonstrates that deltaic vulnerability cannot be explained by eustatic sea-level rise alone but results from the compounded effects of geophysical subsidence and hydrodynamic forcing. The study underscores the urgency of dynamic adaptation strategies- such as sediment management, adaptive land use zoning, and ecosystem-based coastal protection- to enhance resilience in climate-vulnerable mega deltas. The methodology offers a transferable blueprint for quantifying and managing RSLR-induced risks in other subsiding coastal systems worldwide.