Coastal Flood Hazard Tool

By Bolelang Sibolla and Melanie Luck-Vogel, CSIR

The Intergovernmental Panel on Climate Change (IPCC) in its 5th report from 2014, points out that the climate is changing globally, leading to higher atmospheric and ocean temperatures, sea level rise and a change in general weather patterns.

Globally the sea level is to rise between 0.4 m and 1.0 m (IPCC5-Chapter 13, page 1181), threatening to flood low lying coastal areas. This is of concern as currently about 40% of the world’s population are living within 100 km of the Earth’s ocean’s coasts and many key economic infrastructure is located there.

Further, for Southern Africa, an increase in ocean storm frequency and intensity is expected. This will lead to an increase in storm surges, exacerbating the risk of flooding specifically of low-lying coastal areas, putting livelihoods and coastal economies even more at risk.

The National Oceans and Coastal Information Management System (OCIMS): Coastal Flood Hazard tool gives a first indication on which areas are at risk of flooding. It can be used for populated areas but also for currently undeveloped areas to assess whether future development might be at risk.

The certainty of coastal flood risk modelling depends heavily on spatially very detailed and accurate digital elevation models (Gesch, 2009). For the development of the OCIMS: (South African) Coastal Flood Risk Viewer we are therefore using high-resolution airborne Light Detection and Ranging (LiDAR) data as main 3D data source.

The online tool currently has two offerings based on the bathtub model : continuous flood-lines and 4 sea level rise scenarios based on the IPCC projections. The data coverage of the tool is illustrated in Figure 1. A third offering based on more rigorous dynamic flood models is in progress. The hydrodynamic modelling datasets are meant to be the result of collaborative efforts with other South African municipalities and flood modelling experts.

Figure 1:  Data Coverage