In Detail: Use of Elevation Data for Storm Surge Coastal Flood Modelling

Worldwide, storm surges pose a threat to coastal communities. Particularly in low-lying African coastal cities, the impact of climate change induced storms and sea level rise is a threat to the vulnerable community  (Nhantumbo et al. 2023).  Especially with climate change, this hazard is likely to intensify (IPCC 2022), calling for urgent action. To identify the exposed groups, assets, and infrastructure, and to implement effective storm surge risk management, an understanding of the hazard, its timing, and geographic patterns is crucial. Hazard maps can serve as a first approximation for estimating the spatial extent of storm surges and sea level rise, as well as the exposed population and assets.

For detailed hazard maps, hydrodynamic models are often used due to the complexity of storm surges. They are influenced by factors such as storm intensity, the storm's track, bathymetry, and more. Hydrodynamic modeling therefore requires high-quality and complex parameters, such as historical data sets or detailed coastal formation data for a specific area, which are not always available or may be costly to obtain. This makes free, detailed modeling of storm surges very challenging.

Other methods, such as the bathtub approach, require fewer datasets and can serve as a first approximation for modeling the potential geographical extent of coastal flooding. This Recommended Practice outlines the steps to visualize the geographical extent of coastal flooding or sea level rise using just two datasets: a digital elevation model (DEM) and a shoreline dataset. The choice of a DEM is crucial; preferably, a high-resolution DEM should be used, as it is more likely to represent the surface accurately. However, high-resolution datasets are not always available for free. In such cases, a mid-resolution DEM, such as the Copernicus 30m DEM, which is globally accessible, should be used when open-access DEMs are the only option.

The flood masks created during this practice can be further used to identify exposed elements in specific regions. The Recommended Practice on Exposure Mapping can be applied for that (Link: https://www.un-spider.org/advisory-support/recommended-practices/recommended-practice-exposure-mapping ).