Uniquely positioned at the dynamic interface of land and sea, mangroves form the foundation of a highly productive and biologically rich ecosystem which provides a home and feeding ground for a wide range of species, many of which are endangered.
The complex network of mangrove roots can help reduce wave energy, thus limiting erosion and shielding coastal communities from the destructive forces of tropical storms.
Mangrove cleared for prawn farming. Mangroves offer natural and low-cost risk reduction mechanisms against rising sea levels and changes in the frequency and intensity of storms.
The UNEP report, citing studies already done on this, says that mangroves can rapidly reduce wave energy as they pass through the trees. The extent of reduction in the height of relatively small waves due to this natural barrier has been found to be anywhere in the range of 13% to 66% over a 100 m wide mangrove belt. The effectiveness is largely dependent on the density of the mangrove vegetation.
Waves passing through dense aerial roots and tree canopies will be reduced most effectively. The provision of shelter by mangroves is not only important for people on land, but also for those operating at sea.
In case of storm surges, the report suggests – again citing studies – that mangroves can reduce storm surge levels by up to 50 cm per km width of mangroves. While large areas of mangroves are needed to significantly reduce peak water levels, even relatively small changes in water depth may result in large areas being saved from flooding, particularly in areas of low relief that are typical for mangroves.
The report further finds out that coastal forests such as mangroves cannot completely stop a tsunami, but they can absorb some of the energy of the flowing water and thus reduce the force of the impact, saving lives and reducing damage to property. Mangrove trees can also disrupt the huge flows of water as the wave recedes and block property and people from being swept back to the sea.