## 7 Discussion  
Coastal risk in the Mediterranean area is rising due to growing population, commerce and infrastructure in coastal areas, and the impacts of global sea level rise and warming, associated with increased frequency of sea storms. Major coastal hazards are represented by storm surges and the coastal flooding caused by severe tropical or extra-tropical storms. Storms in the Mediterranean Sea are frequent especially during the winter months and their impact on coastal infrastructures and environment is highly hazardous. The present study analyzes the extreme sea storm event that occurred on 28 December 2020 in the Gulf of Naples. The exceptional nature of this storm is well represented by the maximum evaluated Run Up, which in the order of magnitude for the events with a return time equal to 100 years [43]. The event observed on 28 December 2020 was mainly characterized by the sea conditions, including the wind induced wave motion. The overall maximum wind speed measured by the meteorological monitoring network, although intense, was not exceptional, as it can be usually observed at least once in a year. The sea roughness, instead, was of extraordinary intensity. Particularly, the wave crests height was remarkable as the storm occurred in phase with the astronomical tidal maximum in sigitial phase. The damage on the coastal infrastructures was consequently very high. The results of our study suggest that Castel dell'Ovo western bastion played a major role by interfering with the wave motion in front of Via Partenope, thus causing waves 10-15% higher than normal when the incoming direction is between SSW to SW, as recorded on 28 December 2020. This research also highlights the importance of integrating the analysis of the entire spectrum of factors that control the entity of the storm surge phenomenon. The surge calculated as a consequence of all the factors was 1.08 m. This value, under conditions of unlimited fetch and for equal duration of the wind event, corresponds to a wave height generated by a wind of greater intensity. The analysis of the present wind event through Groen-Dorrestein nomogram, characterized by a duration of 14 h and an average wind speed (15 m s\({}^{-1}\)), suggests that a greater wave height of 1.08 m, for the same duration, is generated by a higher wind event with an average intensity of 17.5 m s\({}^{-1}\) (+20%). Our results confirm the results of modeling studies on directional storm surge in enclosed seas [49] and wind and wave setup contributions to extreme sea levels at a tropical high island [50]. Usually, surge height depends on the cosine of the angle between the wind direction and the major axis of the narrow gulf. Even though a longer fetch will produce higher storm surge, the exact relationship is complex and dependent on the local physiography, as observed for case studies of the Red Sea and the Adriatic Sea [49]. Numerical simulations of wind waves, storm-surge, and wave setup indicate that the storm  
Figure 23: Profile sections in correspondence of the damaged area of Via Partenope: the orthophoto shows the very reduced width of the cliff in Section 1, about half with respect to Section 2. The graphical section (Length Scale LS equal to 0.5 Height Scale HS) gives evidence of the complete overtopping of the cliff during the phase of maximum wave heights. Profile traces are in Figure 22.  
track and the local morphology led to local differences in extreme sea levels, in the order of 1 m along Samoa coastline [50]. In our case a relevant contribution was given by tidal rise of local sea level. Other studies have also confirmed the importance of the timing of the sea storm landfall relative to local high tide, as observed in storm surge simulations made for Sandy Hurricane which struck New York area in 2012 [51]. The present study also suggests that, in the case of artificial cost (e.g., when a seawall occupies protects the coastline), wave breaking occurs at the toe of the structure, and wave height needs to be considered independently from the runup [52].