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Extreme sea levels, consisting of tides, storm surges, and mean sea levels, can cause a range of coastal hazards. The world's coastal areas are increasingly at risk due to rising mean and extreme sea levels, which can lead to the permanent submergence of land; increased coastal flooding; enhanced coastal erosion; loss of coastal ecosystem; and salinization (Oppenheimer, et al., 2019). Global projections of extreme sea levels can be used to assess the impacts of these coastal hazards and provide information on the projected changes for the coming decades. In a previous contract (C3S_422_Lot2), a Pan-European dataset with consistent projections of mean sea level, tides, surges and wave condition has been developed (Muis et al., 2020). The time series and indicator are made available via the Climate Data Store (CDS), and have been used for coastal applications such as offshore wind maintenance, port operations and planning, and coastal flood risk assessment.
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GTSMv3.0 uses the unstructured Delft3D Flexible Mesh software (Kernkamp et al., 2011). The spatially-varying resolution leads to high accuracy at relatively low computational costs. It has an unprecedented high coastal resolution globally (2.5 km, 1.25km in Europe, Figure 2-1). The resolution decreases from the coast to the deep ocean to a maximum of 25km. Grid resolution is refined in areas in the deep ocean with steep topography areas to enable the dissipation of barotropic energy through generation of internal tides. See User Guide (Yan et al., 2019) for more detailed regarding the model. GTSMv3.0 also has high temporal resolution producing output at 10-minute intervals. The 10-minutes time series are physically realistic since two types of forcing are used; that is, tidal and meteorological forcing. The tidal forcing is internally generated based on position of the earth, moon and sun. The meteorological forcing is available at hourly (or coarser) resolution, but is internally interpolated to the model timestep. Because tides vary at high-frequency and can non-linearly interact with storm surge (so the sum of the two is different from the individual components) we use an temporal resolution of 10 minutes. Especially for output stations with a wide and shallow continental shelf (such as the North Sea) lower temproal resolution, i.e. hourly resolution, can be too coarse and may miss the peak water levels.
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