New model of storm surge mitigation by coastal wetlands in 11 major river deltas

Date: 2 July 2018

Introduction: A study by Rebecca Van Coppenolle shows that, among others, the Niger and Mississippi delta benefit strongly from 'nature-based' protection of land and people.

Low-lying river deltas worldwide are vulnerable to coastal flooding, and the risk is growing as coastal population density and projected storm surge intensity increase. However, tidal wetlands such as salt marshes and mangroves can help—they reduce wave strength and slow storms down, potentially lessening storms’ effects. Drawing on global datasets, GCE researchers Rebecca Van Coppenolle and Stijn Temmerman (Global Change Ecology Centre, research group Ecosystem Management) created a simple GIS model to evaluate tidal wetlands’ ability to mitigate storm surge risk in 11 of the world’s largest river deltas. They worked together with Christian Schwartz, former GCE-member who now works at Utrecht University. Results were published in the scientific journal Estuaries and Coasts.

Rebecca: “We used the model to calculate the inland area and number of people in the path of a storm with and without wetlands present in order to come up with a measure of flood risk mitigation provided by wetlands. Our results show large differences in the amount of protection afforded by existing tidal wetlands worldwide. The three deltas with the highest degree of protection in terms of both land (>80%) and people (>70%) were the Mahakam (Indonesia), the Chao Praya (Thailand), and the Niger (Nigeria), followed by the Mississippi (U.S.).”

While this type of model cannot predict local-level storm surge effects, it provides large-scale insights into how mangroves and salt marshes contribute to “nature-based” storm surge mitigation. In deltas where historic conversion for human land use has been limited and large tidal wetlands still exist, such as in the Mississippi, Niger, and Ganges-Brahmaputra deltas, the ongoing conservation of existing wetlands should be a priority. Deltas where large areas of wetland have already been lost, on the other hand, would likely benefit from a focus on restoring native ecosystems instead of relying only on flood defense structures.

Deltas are often home to large populations that are exposed to flood risks (here Guayaquil, a 3 million people city in the Guayas delta in Ecuador), but conservation of large tidal wetlands (here mangroves) that naturally occur in deltas can temper storm surges and reduce flood risks