Analytical Modeling of Saltwater Intrusion into Coastal Aquifers under Climate Change–Driven Sea-Level Rise

Sea-level rise (SLR) is intensifying seawater intrusion (SWI) in coastal aquifers, threatening freshwater resources worldwide. Existing analytical models largely assume steady conditions and fail to represent the transient effects of a rising sea level. This study presents a new analytical and semianalytical framework for simulating time-dependent movement of the seawater–freshwater interface (SFI) in confined and unconfined aquifers by prescribing SLR as a dynamic boundary condition. Closed-form solutions for confined aquifers and perturbation-based solutions for unconfined systems are derived and validated against existing analytical models, showing high accuracy. Application of the solutions to Mumbai and Bhubaneswar in India, using CMIP6-based SLR projections, indicates substantial inland intrusion, with greater vulnerability in unconfined aquifers. The proposed solutions provide efficient and physically based tools for rapid coastal groundwater vulnerability assessment, particularly useful in data-limited settings.