Compound River Floods and Sea Storms: Forcings and Impacts

Coastal areas are strategically significant from an ecological, anthropic, and economic point of view, but they are also susceptible to forces causing inundations. Multiple forcings occurring in close succession in space and time amplify the effects of a single force and form a compound event. An example is an atmospheric disturbance that extends from the sea to the mainland, causing a sea storm and a river flood due to heavy rainfall. This condition can occur in geomorphological contexts where the sea and mountains are close to each other, and the river basins are small. Most research on compound events focuses on extreme events; detailed studies of compound events not associated with extreme events and generated by non-exceptional atmospheric disturbances are scarce. Furthermore, there are very few detailed studies focusing solely on compound river floods and sea storms. Consequently, this paper is focused on compound river floods and sea storms generated by atmospheric disturbances regardless of their exceptional or non-typical typology. This analysis includes their forcings, correlation, and effects and is carried out in Calabria, a region of Southern Italy that represents an interesting case study due to its geomorphological, climatic, and hydrological peculiarities, which favor the formation of compound events, and, due to the considerable anthropization of its coastal territories, increases their risk. The main findings concern confirming that the existence of this compound event between river floods and sea storms is generated by the same atmospheric disturbance, the geomorphological conditions under which it occurs, and the main driving forces behind it. Therefore, this study is only the first step in a more in-depth analysis that will also examine the quantitative aspects of these phenomena. This analysis is essential for the planning and management of coastal areas subject to compound events and for ensuring effective mitigation measures.