The marine and coastal hazards of Mediterranean cyclones

Assessing the coastal hazards of extreme ocean and weather conditions, remains a difficult task for the scientific community since several limits need to
be overcome. The physical knowledge of extreme events, a precise representation of the input data, as well as reproducing correct and accurate numerical simulations are some of them.

In this work we consider a dataset of more then 1100 cyclones which took place in the period 1994-2020 in the Mediterranean basin. The aim is to evaluate their impact - in terms of sea level and waves - in both the open sea and the coastal regions through a coupled hydrodynamic-wave numerical model. The adopted modelling system consists in the SHYFEM (System of HydrodYnamic Finite Element Modules) hydrodynamic model, two-way coupled with the WW3 (WAVEWATCH III) wave model, thus accounting for the wave-current interaction in deep and shallow waters. An unstructured mesh is used to cover the whole Mediterranean sea with a mesh size varying from 10 km in the open sea to less than 1 km at the coasts. Wind and mean sea level pressure are considered as meteorological forcing at very high horizontal resolution thanks to the Copernicus European Regional ReAnalysis (CERRA) system. The numerical results are extensively validated against tide gauges, wave buoys, and satellite-borne instruments showing a good performance for specific storm events and mean conditions in different areas of the Mediterranean Sea. Then, sea level and wave results are used to compute some storm impact indicators for every cyclone of the entire dataset. These quantitative indexes allow a first classification of Mediterranean cyclones from an ocean and coastal impact point of view.