Saltwater Intrusion Seasonality Under Climate Change: Interacting Effects of River Discharge, Sea‐Level Rise, and Bathymetry

Abstract Saltwater intrusion is a growing concern under climate change. Although previous studies emphasize intensified intrusion during low‐flow periods, changes in its seasonality remain understudied. We combine long‐term observations with coupled hydrologic–hydrodynamic modeling to examine how river discharge and sea‐level rise (SLR) affect intrusion seasonality in Pamlico River Estuary. We find that intensified discharge seasonality, with lower low flows and higher high flows, amplifies intrusion seasonality by driving landward salt‐front expansion during low‐flow periods and oceanward retreat during high‐flow periods, increasing its seasonal migration range. Moderate SLR increases intrusion magnitude while maintaining high seasonal variability. Under higher SLR, however, landward topography constrains low‐flow expansion and reduces seasonal migration. These findings provide a mechanistic framework for understanding saltwater intrusion seasonality under climate change: river discharge and SLR determine how strongly the salt front tends to migrate, while its position relative to local topography determines whether that migration remains unconstrained or limited.