The marine and coastal hazards of Mediterranean cyclones

Abstract. This study aims to contribute to the understanding of marine and coastal hazard due to cyclones in the Mediterranean region, through the reproduction of sea level and wind waves with the use of an unstructured and coupled 2D hydrodynamic-wave modelling system. The modelling system is used to produce a numerical hindcast for the period 1994–2020 which is validated against tide gauges, wave buoys and satellite-borne instruments. The sea level and wave results are analysed for 2483 Mediterranean cyclones detected through a meteorological approach based on a composite cyclone detection and tracking method. We study which portion of extreme values (i.e. values exceeding the 99^th percentile) of storm surge and significant wave height is associated to Mediterranean cyclones and we find that in the Mediterranean basin, extreme waves are more frequently associated to cyclones than extreme storm surge. Indeed, more than 50 % of extreme significant wave heights of the hindcast is associated to waves generated by cyclones in most of the Mediterranean basin. The percentage is higher than 75 % in the Western Adriatic basin and in some sub-regions of the Ionian-Meridional basin, as well as in the northwestern part of the Aegean Sea. For storm surge we find that more than 50 % of extremes values are linked to cyclones in the Western Mediterranean basin, in most of the Thyrrenian and the Ionian-Meridional basin, and in the Western Adriatic Sea. On the contrary, less than 50 % of extreme values of storm surge are associated to cyclones in the Northern and Eastern Adriatic basin, in the Ligurian Sea and in the Levantine-Aegean basin. The cyclone hazard is then evaluated through selected indicators, including peak values of storm surge and significant wave height, as well as the storm erosion potential index and the total storm wave energy which are integrated indices suitable to indicate cyclones intensity. The spatial distribution of the 99^th percentile of all hazard parameters shows that the regions characterized by high hazard values vary depending on the parameter considered. In case of maximum significant wave height and total storm wave energy, the highest values are reached in the Western Mediterranean Sea, in the open sea area between the Balearic Islands and Sardinia. In case of maximum storm surge and storm erosion power index, the highest values are observed in the Northern Adriatic basin while the Western Mediterranean is characterized by moderate values. Despite some common patterns between hazard parameters in the Mediterranean basin, the analysis of their relationships stress that there is not an high correlation among most of them. Through some case studies we show that these parameters provide complementary information enabling a more comprehensive overview of cyclone hazard.