Mangrove forests can be an effective coastal defence in the Pearl River Delta, China

Coastal vegetation can reduce extreme water levels during storm events, but the controlling factors and processes in complex estuary or delta systems are still unclear. This limits an effective implementation of nature-based coastal defences in delta mega-cities in low-lying coastal areas. Here we have numerically modelled how mangroves can offer coastal protection to the large coastal cities located in the Pearl River Delta (China), such as Guangzhou and Shenzhen, during strong typhoons, like Hato (2017). Water level attenuation by mangroves is effective during extreme water level conditions and differences in mangrove forests' properties drive their coastal protection function. The local (within-wetland) attenuation of extreme water levels is more effective with wide vegetation patches and higher vegetation drag. Narrower vegetation patches can still provide non-local (upstream) water level attenuation if located in the upper estuary channels, but their design needs to avoid amplification of water levels in other delta areas.