Abstract
Climate change poses a major challenge to coastal regions such as South Florida. The flat terrain and highly permeable aquifer increase risks of saltwater intrusion and flooding. However, integrated assessments that couple density-dependent groundwater–surface water (GW–SW) processes with projected climate forcing remain limited. We applied the density-dependent Biscayne and Southern Everglades Coastal Transport (BISECT) model, validated against daily groundwater levels and surface water stages. The BISECT was forced with bias-corrected and statistically downscaled rainfall from the best‐performing CMIP6 model (ACCESS‐CM2) and sea-level rise (SLR) projections from the NASA IPCC AR6 tool. Projected simulations were conducted for a near‐future (2051–2059) and far‐future (2091–2099) under SSP2‐4.5 and SSP5‐8.5 scenarios. Results indicate substantial climate-driven shifts in hydrological processes. Groundwater levels are projected to rise by up to 1 m, especially in low-elevation coastal and inland wetland areas by the end of this century. Groundwater recharge is expected to vary across the study area, with increases under moderate emissions but declines in some patchy areas under the far-future high-emission scenario. Both groundwater and surface-water salinity are projected to increase across scenarios, with chloride concentrations exceeding 30 g l−1 in parts of the Biscayne Aquifer, threatening municipal wellfields. Inland seawater intrusion is also projected to expand, reaching 40 g l−1 in the Everglades. These projections also change the GW–SW interactions, including reduced groundwater-driven evapotranspiration. The integrated model results demonstrated that the SLR is the main driver of groundwater rise and salinity migration, while precipitation variability controls spatial recharge patterns. These findings highlight the need for nature-based adaptive solutions to protect freshwater resources, infrastructure, and ecosystems.