Filippo Giaroli

Coastal regions around the world are increasingly threatened by natural phenomena that manifest themselves with more and more strength, and due to climate change driven by global warming, extreme events have become more frequent and intense. Locally, sea-level variations and wind waves are the most affecting components of many coastal hazards. Sea-level variation is mainly due to two different contributions, the tidal excursion and the storm surge, that is the sea-level rise under low-pressure conditions. Often, storm surge and wind waves are studied separately, without considering the joint occurrence in which they happen, and this involves an underestimation of the problem because the elevation due to one component can be increased by the presence of the other. Indeed, the two phenomena are characterised by relatively low temporal and spatial scale in respect to global phenomena as they are strictly related to the atmospheric condition of the surrounding environment.

The objective of my research project is to develop new datasets of storm surge levels up to the end of the XXI century using the update atmospheric conditions datasets of the sixth Assessment Report of the IPCC (AR6), to evaluate how this natural phenomenon is expected to evolve in the future due to the climate change. These datasets will be then coupled with wind waves projections to analyse how these phenomena are correlated and to estimate the joint hazard for costal regions. The analysis is carried out in the whole Mediterranean Sea, with a high definition, up to 10 km resolution in coastal areas to provide a good level of knowledge of the phenomenon in all the area of study, necessary to estimate the level of risk.

First, a non-structured mesh, which allow to reach the desired resolution in all the Mediterranean domain, has been developed using the Python package named OceanMesh. The mesh is then used as computational grid in Delft3D Flexible Mesh software to estimate the sea levels in each point. The wind and pressure input are the future atmospheric conditions under AR6 scenario obtained from the Global Climate Model CMIP6 (Coupled Model Intercomparison Project 6). The joint behaviour between storm surge and wind waves is then investigated using Copula models.

The main result is to develop a storm surge model at high spatial resolution for the entire Mediterranean Sea which provide sea level elevation in all the computational grid points. The model provides both datasets related to the past and future projections, so it is possible to estimate the differences between past and future related to the climate change. The future storm surge projections will be analysed together with wind waves projections to understand how the frequency of joint extreme events is expected to change in the future.