Effects of sea-level rise and river flow variation on estuarine salinity in a changing climate: Insights from the Pamlico River Estuary, USA

Understanding the spatial distribution of estuarine salinity and its interaction with climate change is important for managing ecosystem health and water quality in estuaries. In this study, we present a numerical modeling study on the response of estuarine salinity to sea-level rise (SLR) and river flow variation under future climate change in the Pamlico River Estuary (PRE), North Carolina. For this, we developed a hydrodynamic model with 20 m spatial resolution using the Regional Ocean Modeling System (ROMS) for simulating the salinity dynamics in PRE. In the ROMS model, freshwater input from the Tar-Pamlico River is included as an upstream boundary condition, with discharge values calculated by the Soil and Water Assessment Tool Plus (SWAT+). Climate projections from four Global Climate Models were used within the SWAT+ model to simulate future runoff. These outflow results were used as input to ROMS to investigate the effect of the river flow change on estuarine salinity. Additionally, we imposed various projected values of SLR on the offshore water-level boundary of ROMS to examine the impact of SLR on estuarine salinity. We conducted a series of numerical experiments to quantify the change in salt content, saltwater intrusion length and estuarine stratification under different climate change scenarios. Our model results suggest that under future climate change, increased sea levels will increase salt content and saltwater intrusion length with PRE. The impact on estuarine stratification will differ during low flow versus high flow conditions: 1) with low flow, estuarine stratification will tend to decrease due to the enhanced tidal mixing; 2) with high flow, estuarine stratification is expected to increase as the greater river flow will inhibit the vertical mixing. Our study provides insight into estuarine response to climate change. The results from this study can serve as the scientific basis for stakeholders and decision-makers to develop adaptation strategies and sustainable plans to support coastal resilience.