Evaporation Impacts on Residence Time and Salinity Transport in a Low-Inflow Estuary

Low-inflow estuaries are highly complex marine-dominated systems which are sensitive to climate change impacts. Residence times serve as a key metric for assessing estuarine resilience and recovery from potential contaminants. However, quantifying evaporation’s impact on residence times in low-inflow estuaries has not been considered within the literature. Here, we develop a high-resolution 3D hydrodynamic model of a small, shallow, complex, low-inflow estuary in Southern California using Delft3D. Extensive in-situ observational data including bathymetry, flow velocities, pressure, temperature, and salinity are used to calibrate and validate the numerical model. The overall model skill is strong. Tidal lag within this system is minimal, only the upper most estuary reaches experience a \(\sim \) $\sim$ 20 min delay. Changes in tidal prism and distortion are observed and modeled. The estuary is shown to be flood-dominant. Currently, residence times within the estuary range from 4 days near the inlet to 2 weeks in the inner estuary. Notably, residence times are sensitive to evaporation and increase approximately 10%, primarily driven by evaporative volume losses. This suggests that low-inflow, shallow estuaries may undergo future climate-related changes in residence times which could alter biogeochemistry and negatively impact water quality.