Climate change-driven coastal flooding in the Mid Adriatic Sea and adaptation of coastal defense structures

The Adriatic Sea is highly impacted by rising sea levels and increasingly frequent extreme events due to climate change consequences. This work aims at evaluating coastal flooding caused by future extreme sea storms for five test sites along the Marche Region coast (Italy). Projections of water levels and waves to 2070, under the very high emission scenario identified by the IPCC, were used to force a modeling chain that provided the inundation extent and the water depths in the flooded areas. To define the joint probability of wave height and period, accounting for their mutual dependence, a bivariate extreme value analysis was performed. An extreme pair of wave height-peak period was computed through a copula approach that better allows to understand the correlation between wave energy and storm dynamics compared to univariate methods. Regardless of the analyzed site, coastal flooding affects all the beaches and summer facilities and extends hundred of meters inland, interesting also urban areas and strategic infrastructures. The extension of the flooding increases with increasing return periods, showing the consequences of medium-to-low probability extreme events, projected to occur once in a year by the end of the century. To face such situation, coastal defense structures need to be adapted, carefully selecting the best adaptation option to undertake. While for emerged breakwaters increasing their height always results in a reduced flooding, for submerged barriers a negative effect occurs when the freeboard approaches zero: even if the wave transmission is reduced, a large piling-up generates in the protected area, enlarging the inundation extent, as shown by numerical results.