How do mangroves contribute to flood risk management?
Expert(s) |
Bregje van Wesenbeeck
Mangroves are essential for protecting tropical coastlines against high waves and flooding. New research by Deltares and TU Delft, published in Communications Earth & Environment, shows that broad mangrove forests more than 500 metres wide can reduce incoming wave energy by around 75% or more. This emphasises the importance of preserving and expanding these ecosystems.
Local conditions are important
The research, based on 216,000 simulations and global data, shows that mud flats in front of mangrove forests play a crucial role in reducing wave heights. They ensure that waves are largely weakened before they reach the mangroves. In small mangrove forests, less than 100 metres wide, wave reduction depends heavily on local factors, such as the height of the incoming waves and the density of the trees. In contrast, in wide mangrove forests, more than 500 metres wide, wave reduction is always 70% or more, regardless of local conditions.
Bregje van Wesenbeeck, ecologist at Deltares and lead author of the study, explains: ‘Our findings show that wider mangrove forests are significantly more effective in reducing wave heights. This should lead to a revision of current policy, which often only prescribes forest widths of 100 metres or less.’
New standard needed: 500 metres or more
The ability of mangroves to reduce flood risks has led to regulations in several countries. These regulations prescribe mandatory widths for mangrove green belts, ranging from 50 to 200 metres. For mangrove forests less than 500 metres wide, wave attenuation is highly dependent on local water levels, wave characteristics and forest density. For forest widths greater than 500 metres, which make up 46% of global coastal mangroves, approximately 75% or more of the incoming wave energy is reduced. A new standard that aims for wider mangrove forests could help make coastal areas safer and protect existing mangrove forests.
Our findings show that wider mangrove forests are significantly more effective in reducing wave height
Bregje van Wesenbeeck, ecologist Deltares
15,773 locations worldwide analysed
The researchers used the SWAN model to calculate the wave reduction capacity of mangroves. They selected 15,773 locations with mangrove cover and used a special method to choose 1,000 representative situations. They then ran 216,000 simulations to analyse how mangroves reduce waves. This resulted in tens of millions of data points that together provide a good picture of how mangroves can protect our coastlines.
Preserving and expanding ecosystems
These findings emphasise the importance of preserving and restoring mangrove forests. By investing in the protection of these ecosystems, we can better prepare our coastlines for the challenges of climate change.
