A previously undetected resonant mechanism influencing the Adriatic sea-level dynamics

Severe coastal floods affected the northern Adriatic Sea in December 2019, despite the absence of clear warnings from operational forecasting systems. This study investigates the physical mechanisms underlying these events using a combination of several approaches, including analysis of in situ wind and sea-level observations, atmospheric reanalysis products, simulations performed with a high-resolution hydrodynamic model, and a simplified analytical model. The results reveal a previously unrecognised wind-induced resonance mechanism. Specifically, a quasi-periodic wind forcing, associated with a sequence of successive cyclones over the Adriatic region, efficiently excited the basin’s fundamental barotropic mode. This resonant response led to a substantial amplification of sea-level oscillations, contributing significantly to the observed flooding. The findings identify a new type of resonance, complementing the four resonance mechanisms previously described in the Adriatic-related literature, and highlight the importance of accounting for resonance effects in coastal flooding assessment and forecasting.