PNNL

Abstract

Sea-level rise (SLR) poses a severe threat to the coastal environment through seawater intrusion into freshwater aquifers, making them unsuitable for drinking and irrigation. The rising ground water table also exacerbates the risk in pluvial, fluvial, and groundwater flooding. Despite the importance of the impacts of SLR on groundwater systems over coastal regions, current Earth system models commonly ignore the exchanges of water at the land-ocean interface. Therefore, the transport of sediments and nutrients from ocean to land cannot be simulated. To fill this gap, we developed a new land-ocean hydrologic coupling scheme in the Energy Exascale Earth System Model version 2 (E3SMv2) that includes the lateral exchange between seawater and groundwater and the vertical infiltration of seawater driven by the SLR-induced inundation. The coupled model was configured for simulations in the global land-ocean interface and calibrated against a global groundwater benchmark dataset. The corresponding impacts on coastal groundwater at global scales were assessed under a high CO2 emission scenario. By the middle of this century, seawater infiltration on the inundated areas is found to be the dominant mechanism in the land-ocean coupling scheme, while the lateral subsurface flow exchange is much smaller. Furthermore, topography and warming temperature have more control on the coupling process than the magnitude of SLR, which shows small spatial variation at global scales. Our results show that SLR-induced seawater infiltration will raise the groundwater levels, enhance evapotranspiration, and increase runoff with distinct spatial patterns globally in the future.