Cost-benefit analysis of coastal flood defence measures in the North Adriatic Sea

Abstract

Abstract. The combined effect of global sea level rise and local subsidence phenomena poses a major threat to coastal settlements. Flooding events are expected to grow in frequency and magnitude, increasing the potential economic losses and costs of adaptation. In Italy, a large share of the population and economic activities are located along the coast of the peninsula, although risk of inundation is not uniformly distributed. The low-lying coastal plain of Northeast Italy is the most sensitive to relative sea level changes. Over the last half a century, the entire north-eastern Italian coast has experienced a significant rise in relative sea level, the main component of which was land subsidence. In the forthcoming decades, sea level rise is expected to become the first driver of coastal inundation hazard. We propose an assessment of flood hazard and risk linked with extreme sea level scenarios, both under historical conditions and sea level rise projections at 2050 and 2100. We run a hydrodynamic inundation model on two pilot sites located in the North Adriatic Sea along the Emilia-Romagna coast: Rimini and Cesenatico. Here, we compare alternative risk scenarios accounting for the effect of planned and hypothetical seaside renovation projects against the historical baseline. We apply a flood damage model developed for Italy to estimate the potential economic damage linked to flood scenarios and we calculate the change in expected annual damage according to changes in the relative sea level. Finally, damage reduction benefits are evaluated by means of cost-benefit analysis. Results suggest an overall profitability of the investigated projects over time, with increasing benefits due to increased probability of intense flooding in the next future.