Influence of wind stress and the Isonzo/Soča River outflow on surface currents in the Gulf of Trieste

Abstract. In this study, we analysed the extreme meteo-marine event that occurred between October and November 2023 in the northern Adriatic area, focusing on its effects in the Gulf of Trieste (GoT). This event featured a strong inflow of very humid southerly winds, very intense thundershowers and storm surges on the coast, and caused several damages in the north-eastern part of Italy. The heavy rainfall in the Isonzo/Soča catchment led to two major runoff peaks with significant discharges into the GoT. These events represent an ideal case study to investigate how the interplay between local river discharges and the wind regime influence ocean currents in coastal areas.

We adopted an integrated approach to fully understand the dynamics of peculiar environmental processes, clearly emerging from the visual analysis of satellite images (Sentinel-2) collected throughout the event. Therefore, we incorporated in our analysis multiple datasets, including rainfall, wind and surface currents from both HF radars and numerical models. In this way, we could analyse the interaction between river runoff and ocean currents in the GoT, and the importance of prevailing winds such as Bora and Sirocco in modulating current dynamics. The use of rainfall time series allowed us to assess the impact of precipitation on environmental conditions, while the analysis of the wind regime helped to understand the patterns, distribution and intensity of winds in the area of interest. It was observed that the intense runoff of the Isonzo/Soča River triggered by heavy rainfall can override the effects of wind, leading to a dominance of river-induced circulation in the GoT. Such a multi-platform integrated approach proves to be a useful tool for the analysis (and, potentially, forecast) of surface ocean dynamics and possible extreme events in coastal areas.