Impacts of Sea-Level Rise on Coastal Groundwater Table Simulated by an Earth System Model With a Land-Ocean Coupling Scheme

Sea-level rise (SLR) poses a severe threat to the coastal environment through seawater intrusion into freshwater aquifers. The rising groundwater table also exacerbates the risk of pluvial, fluvial, and groundwater flooding in coastal regions. However, current Earth system models (ESMs) commonly ignore the exchanges of water at the land-ocean interface. To address this gap, we developed a novel land-ocean hydrologic coupling scheme in a state-of-the-science ESM, the Energy Exascale Earth System Model version 2 (E3SMv2). The new scheme includes the lateral exchange between seawater and groundwater and the vertical infiltration of seawater driven by the SLR-induced inundation. Simulations were performed with the updated E3SMv2 for the global land-ocean interface to assess the impacts of SLR on coastal groundwater under a high CO₂ emission scenario. By the middle of this century, seawater infiltration on the inundated areas will be the dominant component in the land-ocean coupling process, while the lateral subsurface flow exchange will be much smaller. The SLR-induced seawater infiltration will raise the groundwater levels, enhance evapotranspiration, and increase runoff with distinct spatial patterns globally in the future. Although the coupling process is induced by SLR, we found topography and warming temperature have more control on the coupling impacts, probably due to the relatively modest magnitude of SLR during the selected future period. Overall, our study suggests significant groundwater and seawater exchange at the land-ocean interface, which needs to be considered in ESMs.