The Mediterranean basin is surrounded by an extended coastline characterized by a high population density. Mediterranean coastal communities are increasingly exposed to Extreme Sea Level (ESL) events, causing substantial social and economic impacts. Despite the high damaging potential shown in recent years, no clear consensus has yet emerged in the literature on how their frequency and intensity are changing. Therefore, this analysis aims to investigate how ESL events are evolving along the Mediterranean coastline and to identify the main drivers of their long-term variability. The main goal of this study is to present a new Ocean Monitoring Indicator (OMI), developed in the Copernicus Marine Service framework, designed to continuously monitor frequency and intensity changes of ESL events along the Mediterranean coastline.
The study is based on a multi-product dataset combining numerical models, satellite observations, and in-situ measurements. This multi-source approach ensures a continuous temporal coverage from 1993 to 2025 and a continuous spatial coverage of the entire Mediterranean coastal area. A robust metric, the 50-year return level (RL50), based on the non-stationary Extreme Value Analysis (EVA) methodology and particularly suited for the analysis of extreme trends, is used to quantify the ESL change along a 20-km coastal belt.
Our analysis reveals that the entire Mediterranean coastline is undergoing an increase in ESL events. In particular, the eastern part of the basin experiences the most pronounced increase, with RL50 trends exceeding 5 mm/yr in the northern Adriatic Sea, the Aegean Sea, and along the Turkish and Cypriot coastlines. The Adriatic Sea and the Aegean Sea, together with the Gulf of Gabes, are also identified as areas more exposed to ESL conditions on average. On the other hand, the western side of the basin shows a moderate increase, with RL50 trend ranging between 1 mm/yr and 4 mm/yr. The contribution analysis, aimed at quantifying the role of mean sea level change and changes in storminess, shows that the mean sea level rise drives the detected ESL trend along the entire coastline. However, in the northern Adriatic Sea a strong increase in storm surges dominates the ESL trend. This enhancement is most likely connected with changes in atmospheric circulation.
These results provide new evidence on the long-term evolution of Mediterranean ESL events and highlight the importance of considering both mean sea level change and changes in storminess when assessing future coastal hazards. The proposed comprehensive, multi-dataset OMI provides a valuable tool to support coastal risk assessment, adaptation planning, and the management of activities increasingly affected by sea level extremes. Our analysis can be extended to other coastal areas, allowing the assessment of long-term changes in ESL events and their main drivers.
 

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