Investigating Hurricane-Induced Salt Variation across the Land-Estuary-Ocean Continuum Using a Dynamically Coupled Hydrological-Ocean Model

Coastal salinity plays a pivotal role in shaping the structure and productivity of coastal ecosystems, which, in turn, provide significant socio-economic benefits to adjacent communities. However, assessing the spatiotemporal variations of salinity presents challenges due to the complex interplay of terrestrial and oceanic hydrological processes, including river discharge, winds, tides, sea level rise, and storm events. To address these challenges, we developed a dynamically coupled hydrological-ocean model designed to capture salt transport and exchange across the Land-Estuary-Ocean (LEO) continuum.

This model integrates a process-based hydrological model (WRF-Hydro) with an overland salinity module, a regional ocean model (ROMS), and a modified coupler (MCT) on the COAWST platform, representing an advanced approach to modeling hydrological and oceanic processes in tandem. Our application of this model focuses on the Cape Fear River Estuary, North Carolina, examining the impacts of Hurricane Florence (2018) on estuarine salinity dynamics and freshwater plume formation. The results reveal how runoff and wind interactions govern estuarine salinity, with initial regulation by wind-forced water level gradients transitioning to dominance by substantial runoff. Additionally, the model captures the formation and westward movement of a freshwater plume in the coastal ocean, driven by runoff, winds, and estuary geomorphology. The model also highlights potential saltwater intrusion into low-lying freshwater wetlands within the upper estuary.

By incorporating both hydrological and oceanic processes, this coupled modeling approach exemplifies the integration of soil hydraulics, plant hydraulics, and river hydraulics, as emphasized in the session. The findings demonstrate the model's utility as a holistic tool for evaluating saltwater intrusion, tracing coastal pollutants, and understanding the pathways of water and material exchanges along the LEO continuum. These insights are crucial for advancing hydrologic modeling and informing coastal management and restoration efforts, particularly in the context of human disturbances and the evolving challenges posed by climate change.