7:06 PM Jun 14, 1996
FLOODING DUE TO CLIMATE CHANGES
Wrong approach, new research demonstrates. Planting mangroves is better for the economy and the ecosystem - and it provides effective protection. "Foreign consultants are tramping along the coastline of Vietnam and other developing countries planning higher dikes," says Mick Kelly of the Climatic Research Unit at East Anglia University in Britain. "This will benefit no-one but the engineers and consultants. But mangroves, planted in the shallow coastal waters around deltas would provide a first line of defence against tropical storms." Some 3,000 kms of Vietnam's coastline is at risk from tropical cyclones. These storms can do extensive damage. For example, one storm in 1985 killed 900 people, sank 3,300 boats and made over half a million people homeless. From 1977 to 1986 tropical cyclones in Vietnam destroyed 400,000 hectares of crops. At present, Vietnam's coasts face between one and 12 of these storms a year, Kelly explains. But the number may increase due to global warming which could also lead to rising sea levels. Joint research by the University of East Anglia and the Mangrove Ecosystem Research Centre in Hanoi, Vietnam, shows that not only do mangroves protect artificial sea defences from storm damage, they also have many indirect economic and social benefits to coastal communities. More than 60 different species of mangrove can be found in coastal tropical and subtropical wetlands, which also support over 2,000 species of fish and plants. But in Vietnam and other countries, large areas have been cut down to make way for agriculture shrimp farms and for use as timber. Often this has led to severe environmental degradation. Now there are moves to restore and rehabilitate these wetlands. The Vietnamese and British researchers have studied three coastal areas of Nam Ha Province in northern Vietnam where rehabilitation schemes are under way to assess the benefits. The work was conducted with the help of a 35,000 grant from Britain's Economic and Social Research Council. "We are hoping for a second stage of funding from the council to continue the work," says Kelly. Quite apart from the additional physical protection they offer to sea dikes, mangroves stabilise the sea floor and trap sediment which reduces the seabed's angle of slope. This dissipates the energy of the waves breaking against the dikes. The researchers explain that planting mangroves on the seaward side of a dike system considerably reduces the need for dike maintenance. Normally this is done each year in Vietnam through the obligatory labour of the local inhabitants organised by district committees and paid for through local land taxes. "These commitments draw a heavy burned on labour-scarce households," the researchers say, and can be "a source of conflict". In addition to dike protection, mangroves provide a whole range of economic benefits. Their roots and branches below the water line provide shelter and food for fish, encourage local fisheries by offering natural spawning grounds including for fish, crabs, shrimps and shellfish. The yield is estimated at approximately 50 kg per hectare per year. Mangrove flowers attract bees which produce honey for bee-keepers. Different species flower at different times and the potential yield is estimated at a minimum of 0.21 kg per hectare per year. Honey production is possible around five years after planting. Thinning and maintenance of the mangrove stands can provide wood for fuel or timber. Overall, the cost-benefit analysis conducted by the researchers shows that the benefits of planting mangroves are four to five times greater than the costs. And this does not yet include the benefits of reduced repair costs to dikes after storms or reduced agricultural losses from the control of flooding. The direct benefits alone, leave aside dike protection, make mangrove rehabilitation cost effective. "They will benefit local people here and now as well as preserve a valuable ecosystem and provide insurance against future climatic risk," say researchers.