Impact of Climate Change on the Hydrodynamics of the Ria de Arousa (NW Spain)

Ria de Arousa, one of the Rias Baixas, presents very high economic value for the Galician communities due to its importance for aquaculture, but the changes associated with climate change are expected to have an impact on its hydrodynamics and consequently on the production of cultivated species. The main objective of this work is to study the impact of climate change on the circulation and hydrography of the Ria de Arousa, considering the SSP5-8.5 scenario defined by IPCC. To achieve this goal, the Delft3D hydrodynamic model was implemented three-dimensionally using the results obtained from the CMIP6 MPI-ESM1-2-HR climate model as boundary conditions. Future changes in the hydrodynamic and hydrographic circulation of this coastal system were analysed. The model results were used to assess the impact of climate change on water temperature, salinity, and density patterns of the Ria de Arousa, as well as on stratification, Brunt–Väisälä frequency, and residual circulation. During summer, the water temperature is higher at the surface and lower at the bottom, likely due to the intrusion of water from the Eastern North Atlantic Central Water (ENAWC). In the future, this pattern will continue, albeit with higher temperatures, as the water temperature is expected to increase by around 2.2 °C by 2100. During winter, the water temperature at the bottom is warmer than at the surface, indicating a thermal inversion typical of this season. In the future, the water temperature will also increase, although the increase will be lower compared to summer, with a value of approximately 0.5 °C. Salinity will decrease in the summer and increase in the winter, especially in the areas closest to the rivers. Density analysis shows vertical homogeneity in the water column during winter and stratification during summer. During winter, the Brunt–Väisälä frequency (N) is higher in the region closest to the river’s mouth and lower near the ocean. In the summer, the N value decreases with depth. In the future, the density will increase in winter and decrease in summer, and stratification is expected to decrease. Regarding the residual circulation, it was observed that it will strengthen in the summer and weaken in the winter due to a decrease in freshwater runoff. However, the positive circulation pattern observed in the present will be maintained in the future.