The Increase of Sardinian Coastal Erosion and the Historical Climate Change Effects on Wind and Wave Height

Climate change effects on wave regime are affecting Sardinian beaches and coasts. Sardinia island is in the centre of western Mediterranean basin, and its coasts are mainly under two main opposite winds, the mistral and the sirocco, which affect north-west and south-east coasts of the island respectively. We analysed historical wind intensities and wave heights in Sardinian coasts, for detecting historical trends which can explain the alarming increase of coastal erosion of the island. In this sense, we investigated two case studies located in the two opposite quadrants of Sardinia, the Gulf of Alghero and in the Gulf of Cagliari that are in the North-West and South-East quadrants, respectively. For the wind analysis we used the values of speed and direction of the anemometer stations of Alghero and Elmas (Cagliari), for which long series of data are available. The wind most frequently detected by the station of Elmas is the sirocco, with a linear growth for the period of analysis (1943-2021) with higher values of 3, 4 and 5 m/s for 2 consecutive days of sirocco. On the other hand, in Alghero, for 2 consecutive days of mistral, there is a linear decrease for the analysis period (1957-2021) with values greater than 3, 4 and 5 m/s. For the analysis of wave data in the quadrants of Sardinian coasts we compared the ECMWF, the Copernicus and the SIMAR database. The direction and wave height values from the models were validated with observed data of the buoy wavemeters in the Gulf of Alghero and in the Gulf of Cagliari, which data are available for shorter periods.to. Annual maximum significant wave heights are increasing in both the Gulf of Cagliari and the Gulf of Alghero. In particular, the increase in wave heights is more evident in the last two decades (from 1998 to 2019). The increase of the average sea level and the intensification of extreme events in the South-East quadrant of Sardinia is accelerating the erosion of the wonderful beaches of Nora, Capoterra, Sarroch and Poetto in the Gulf of Cagliari, which reduction was dramatic (up to 70 m). Climate change effects on wind frequency and intensity and wave can affect island tourism, an important source of income for Sardinia, and in the extreme cases is leading to damage to housing, alarming resident population.