Assessment of a three-dimensional baroclinic circulation model of the Tagus estuary (Portugal)

Circulation patterns and physical regimes play a major role in estuarine ecosystems. Understanding how different drivers, like climate change, may affect the estuarine dynamics is thus fundamental to guarantee the preservation of the ecological and economical values of these areas. The Tagus estuary (Portugal) supports diverse uses and activities, some of which may be negatively affected by changes in the hydrodynamics and salinity dynamics. Numerical models have been widely used in this estuary to support its management. However, a detailed understanding of the three-dimensional estuarine circulation is still needed. In this study, a three-dimensional hydrodynamic baroclinic model was implemented and assessed using the modeling system SCHISM. The model assessment was performed for contrasting conditions in order to evaluate the robustness of the parametrization. Results show the ability of the model to represent the main salinity and water temperature patterns in the Tagus estuary, including the horizontal and vertical gradients under different environmental conditions and, in particular, river discharges. The model setup, in particular the vertical grid resolution and the advection scheme, affects the model ability to reproduce the vertical stratification. The TVD numerical scheme offers the best representation of the stratification under high river discharges. A classification of the Tagus estuary based on the Venice system regarding the salinity distribution for extreme river discharges indicates a significant upstream progression of the salt water during drought periods, which may affect some of the activities in the upper estuary (e.g., agriculture). The model developed herein will be used in further studies on the effects of climate change on the physical and ecological dynamics of the Tagus estuary