The impact of climate change on the storm surges of the Mediterranean Sea: Coastal sea level responses to deep depression atmospheric systems

This study aims to systematically assess the impacts of projected climate change on episodic events of sea level elevation in coastal areas of the Mediterranean, induced by severe weather conditions identified as deep depressions. We try to add new insight in the long-term, climatic timescale, identification of affected parts of the Mediterranean coastal zone correlated to low atmospheric pressure systems, indicative of the Mediterranean basin during the 21st century. To achieve this goal, an integrated quantitative assessment is proposed by combining projections from available and established, green-house gasses emission/concentration scenarios (based on Representative Concentration Pathways; RCP 4.5 and 8.5) with advanced numerical modelling and statistical post-processing for the definition of cyclonic weather impacts on characteristic coastal zone hotspots. To this end, climate projections and outputs from three Regional Climate Models (RCMs) of the Med-CORDEX initiative at the Mediterranean basin scale are used and extensively evaluated against re-analysis data. These atmospheric datasets feed a robust storm surge model (MeCSS) for the simulation of barotropic hydrodynamics (sea level elevation and currents) thoroughly validated against in situ sea level observations by tide-gauges. Our results corroborate a projected storminess attenuation for the end of the 21st century, yet local differentiations in storm surge maxima around the Mediterranean coastal zone are pinpointed. Moreover, a slight reduction of average storm-induced Mean Sea Level (MSL; component attributed solely to the meteorological residual of sea level elevation) is also apparent towards the end of the 21st century. Extreme storm surge magnitudes range between 0.35 and 0.50 m in the Mediterranean with higher values along parts of its northern coasts (Venice lagoon, Gulf of Lions, northern Adriatic and Aegean Seas, etc.) and the Gulf of Gabes in its southern part. Overall, the spatial distributions of surge maxima are estimated to remain similar to those of the past throughout the entire Mediterranean coastal zone. Differentiations between the two scenarios (RCP4.5-8.5) used are obvious, not so much related to the spatiotemporal distribution of storm surge maxima, which shows a very stable pattern, but more in terms of their magnitudes. Indicatively, a decrease of surge maxima from -30% to -2% can be observed towards the end of the 21st century, especially for RCP8.5-driven MeCSS simula