Mangroves: a bio-shield against tropical storms

CASE STUDY: MANGROVES

Mangroves: a bio-shield against tropical storms

Mangrove forests, which in most places are no more than a couple of hundred metres wide, are found along tropical coasts. They act as a first and vital line of defence against storm and wave damage. In the wake of the Indian Ocean tsunami in 2004 and Cyclone Nargis in 2008, it became clear that the damaged caused was exacerbated by the over-felling of mangroves, inappropriate coastal development and a lack of preparedness. Global warming is responsible for rising sea levels and other more extreme weather events such as tropical cyclones and floods. It is therefore crucial that decision makers and practitioners develop coastal management plans that prioritize mangrove conservation and development to mitigate these climate change impacts.

When Cyclone Nargis made landfall on Myanmar’s Ayeyarwady Delta in May 2008, 84,500 people were killed (United States Agency for International Development [USAID], 2008). This huge mortality has been blamed on insufficient warnings (Human Rights Watch, 2010), though other factors are also important. Among these is the large-scale agricultural expansion into the natural habitats of low-lying areas, which left them exposed to waves. The most extensive flooding (271,000 hectares or 57 per cent of the area) occurred in the townships of Labutta and Bogalay, which are home to 389,000 people (United Nations Institute for Training and Research [UNITAR], n.d.). Around half of the flooded area comprised reclaimed land where mangroves had been cleared, mostly since 1989 for paddy fields (Water Resources Management ES4OD, n.d.), with some later converted for salt production. Cyclone Nargis generated a 3–4-metre-high surge, which easily flooded the largely unprotected paddies and salt pans. Elsewhere in the world, intact coastal wetlands reduce the height of hurricane surges by 4.7–7.9 cm per kilometre (Day and others, 2007). Although wave attenuation varies from site to site, 20 km of wetlands have the potential to reduce storm surges by 0.94–1.58 m.

With the clearing of the Ayeyarwady Delta’s mangroves in the past two decades, this buffer has been lost. Prior to Cyclone Nargis, the last severe hurricane or cyclone in central Myanmar occurred in 1982. Given predicted sea level rise and the increased frequency of extreme weather events, post-Nargis reconstruction efforts should reconsider agricultural expansion into the delta and instead focus on recovering coastal wetlands to buffer storm surges, while also supporting locally-based coastal resource management and social development to improve communities’ resilience. Such restoration efforts could also inform resilience-building in other heavily populated Asian deltas.