Forecasting the 12 November 2019 Venice Acqua Alta event: the role of baroclinic compounding effects

Abstract. The northern Adriatic Sea is known to be threatened by extreme sea level events. Venice is exposed to these events, locally known as Acqua Alta, which cause the flooding of the historical city centre. Despite its relevance, a comprehensive analysis of extreme Acqua Alta events that considers all possible compounding drivers, including baroclinic contributions, is, to our knowledge, still missing. In this work, numerical results based on the Copernicus Marine Mediterranean Analysis and Forecasting System are analyzed to better understand the physical mechanisms underlying the 12 November 2019 Acqua Alta event and to assess individual processes playing a role in the event dynamics.

The novel finding of this study is the identification of the contribution of baroclinic dynamics. We estimate a net baroclinic contribution of 7 cm (4 %) to the 175 cm sea level peak. We show for the first time that internal seiches along the northern Adriatic slope contribute to the dynamics of the Acqua Alta event. Moreover, we identify a northern Adriatic density front and quantify its contribution to the time-mean positive northward sea level slope.