The Río de la Plata is a large fluvial–estuarine–sea system discharging into the southwestern Atlantic Ocean, which has relevant features such as high fluvial discharge, microtidal astronomical tidal scales, a relevant meteorological tide, and a strong atmospheric forcing effect, due to its large width. The objective of this study is to advance the understanding of the estuarine hydrodynamics and salt transport, as well as discussing the main characteristics of the spatiotemporal variability of the salinity field. To achieve this, the results of a 3D model of the Río de la Plata and its maritime front were used, simulating an extensive period of 10 years. In this study, the model was validated using vertical salinity profiles collected at different locations in the estuary. The temporal variability of the salinity stratification was characterised at different temporal scales: annual, monthly, and storm. At the same time, the influences of fluvial flow and winds were determined. The correlation analysis between fluvial flow and the salinity field showed that high annual fluvial flows generate an extension of the freshwater area, with larger longitudinal salinity gradients and a shift of the salinity front towards the ocean. The tendency at the monthly scale is not as clear as that observed at the annual scale. The results show that the effect of a storm coming from the northwest is quite similar to that of storms coming from the southwest, especially in the central and southern zones of the Río de la Plata, where mixing increases and stratification decreases, according to the intensity of the storm. The effect of south–southeasterly storms increases the mixing process and reduces stratification; the opposite effect was identified with respect to northeasterly storms, under the influence of which the stratified area increases. Synthesising the obtained results, a global zonification of the vertical salinity stratification for the Río de la Plata is proposed.

This work implements a dynamical downscaling approach, based on a set of nested two-dimensional hydrodynamic models, to quantify the expected changes in the total sea level climate and its components for the Uruguayan coast, using surface wind and sea level pressure projections from global climate models generated during the Phase 5 of the Coupled Models Inter-Comparison Project, considering three time horizons: historical period (1986-2005), short term (2027-2045) and long term (2082-2100), and the future scenarios RCP 4.5 and RCP 8.5. It is concluded that the main contribution to the projected changes in the area is the regional mean sea level rise, followed in importance by the effect that the increase in the water depth has on the amplitude of the tidal components. Moreover, it is concluded that changes in the meteorological residuals (or surges), associated with potential changes in the atmospheric circulation patterns, are negligible in the study area. The obtained results reinforce the need to resort to dynamic downscaling for projecting total sea level changes in areas characterized by wide and shallow continental shelfs and estuaries, as this approach allows to resolve the interactions that may arise between tides, surges and the mean sea level rise, something that cannot addressed with an approach based solely on statistical downscaling.