The world’s coastal areas are increasingly at risk of coastal flooding due to sea-level rise (SLR). We present a novel global dataset of extreme sea levels, the Coastal Dataset for the Evaluation of Climate Impact (CoDEC), which can be used to accurately map the impact of climate change on coastal regions around the world. The third generation Global Tide and Surge Model (GTSM), with a coastal resolution of 2.5 km (1.25 km in Europe), was used to simulate extreme sea levels for the ERA5 climate reanalysis from 1979 to 2017, as well as for future climate scenarios from 2040 to 2100. The validation against observed sea levels demonstrated a good performance, and the annual maxima had a mean bias (MB) of -0.04 m, which is 50% lower than the MB of the previous GTSR dataset. By the end of the century (2071–2100), it is projected that the 1 in 10-year water levels will have increased 0.34 m on average for RCP4.5, while some locations may experience increases of up to 0.5 m. The change in return levels is largely driven by SLR, although at some locations changes in storms surges and interaction with tides amplify the impact of SLR with changes up to 0.2 m. By presenting an application of the CoDEC dataset to the city of Copenhagen, we demonstrate how climate impact indicators derived from simulation can contribute to an understanding of climate impact on a local scale. Moreover, the CoDEC output locations are designed to be used as boundary conditions for regional models, and we envisage that they will be used for dynamic downscaling.

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The physics of extreme high-water during coastal storms covers a wide range of scales, from tides and storms propagating over long distances to the shape of local bays, reefs and islands all contributing to what is potentially extreme high-water. Traditionally, modelling of storm-surges is mostly performed at a regional scale, sometimes extended with nested more detailed models to account for local effects. With the development of more and more accurate global tide and surge models this division may shift. In this study we show the recent advances of the Global Tide Surge Model, since our previous report [9] of version 1, including Self-Attraction and Loading (SAL) representation, dissipation of internal waves, grid refinements near the coast and bathymetry at the South Pole. An open question is now, how to incorporate local effects with a global model. One option is to mimic the traditional approach and use the global model as a template for a regional model. Another option is to bypass the regional model and directly nest a detailed model in the global one. We will show an example of the first in this paper. An example of the second is planned as a collaborative initiative between Deltares and Risk Frontiers. An important question is what level is needed at the various scales needed to obtain accurate results. We will present both cases at the conference.@en