Mangroves are Not the Answer to Tsunamis
Three surviving palms mark the location
of what was a substantial mangrove forest
on Pulau Raya.
We helped the population of Pulau Raya to deal with the loss of 115 out of a population of 350. Most were children who had gone to the school on that Sunday for some kind of event.
Tragically the school building was built behind the only remaining mangroves on the north coast of the island. Most mangroves had been cleared over the years for shrimp ponds. The majority of the residents saw the sea withdraw dramatically from the shore and they ran for high ground but the residents and kids in the vicinity of the school did not. The mangroves blocked their view of the ocean and they were almost all killed.
Tsunamis give some warning regardless of our attempts at electronic systems. The water drains out to sea. If people are aware they can run and many may reach high ground. If they can't see the ocean, those running from the sea can warn them. Island Aid reluctantly must agree that planting green belts along tsunami coastlines is a dangerous practice unless they are several km in width. Even in that case a large tsunami will just convert them into a wall of deadly debris.
The latest findings ARC support the idea that planting mangroves is not an blanket solution at all in the quest for strategies to mitigate tsunami damage.
Mangroves no defence v tsunamis
http://media.jcu.edu.au/story.cfm?id=565
Coastal mangroves and green belts offer little or no protection against the deadly might of a tsunami, according to a controversial new scientific report, just published in the international journal, "Estuarine and Coastal Shelf Science".
Research from the ARC Centre of Excellence for Coral Reef Studies (CoECRS) at James Cook University, the University of Guam (UoG), and the Wildlife Conservation Society-Indonesia Programme (WCS-IP) has overturned claims that death rates were lower in villages shielded by mangroves during the 2004 Boxing Day tsunami.
The researchers' findings challenge current advice by the United Nations Environment Program, non-government organisations, and other scientists that 'green belts' and buffer zones should be incorporated into reconstruction efforts to protect villages from future tsunamis.
In fact, the ecologists warn, these green belts may give a false sense of security, leading to greater loss of life should such a tragedy recur in future.
When Dr Alex Kerr of UoG, Dr Andrew Baird of CoECRS and Dr Stuart Campbell of WCS-IP, reanalysed data from a recent Indian study, they found it was height above sea-level and distance from the shore that protected the inhabitants of some villages, rather than vegetation.
"Our re-analysis revealed that the distance of a village from the coast and the height of the village above sea level explained 87% of the variation in mortality among villages. Once these two variables were taken into account, vegetation area provides less than a 1% increase in explanatory power," says Dr Kerr.
"The apparent link between vegetation area and mortality was actually due to the fact that more vegetation grows at higher elevations above sea-level - and the greater the distance from the sea, the greater the area of vegetation.
"In short, if you had hamlets of equal elevation and distance from the sea, differences in vegetation area would make little difference to the death toll from a tsunami."
JCU's Dr Baird says the new analysis means there is genuine danger in overstating the protective capacity of vegetation in the event of another tsunami.
"Mangrove forests provide coastal communities with many valuable goods and services. However, expecting them to provide protection from tsunamis is unrealistic," he said.
"Following the Krakatoa eruption the resulting tsunamis penetrated eight kilometres through primary rainforest.
"Right now buffer zones are being enforced through a combination of government legislation, and a refusal of aid to people that wish to move back to their homes, in the belief they may provide protection from some future huge event. These buffer zones are only between 100 and 500 m, yet they may dispossess over a million people in India and Sri Lanka," Dr Baird said.
"It's a beautiful idea that green belts can stop a tsunami, and its aims are commendable. But it isn't true, and it won't work.
Logically, the safest course is to build farther from the sea or on higher ground. However, this cannot be considered in isolation from the social economic and emotional cost of shifting entire communities and their livelihoods, the researchers say.
"Tsunamis are catastrophic but, fortunately, they are rare - and a well-organised early-warning and evacuation plan may be far more effective in saving lives," Dr Baird said.
"Even if property is destroyed, this may still be preferable to the social dislocation and potential conflict involved in removing entire communities from their coastal existence."
Dr Baird adds that a further dimension of the problem is the fact that in many cases these buffer zones are being used by developers and local authorities as a pretext for moving communities, so they can then build tourist facilities on the vacated shoreline.
Research from the ARC Centre of Excellence for Coral Reef Studies (CoECRS) at James Cook University, the University of Guam (UoG), and the Wildlife Conservation Society-Indonesia Programme (WCS-IP) has overturned claims that death rates were lower in villages shielded by mangroves during the 2004 Boxing Day tsunami.
The researchers' findings challenge current advice by the United Nations Environment Program, non-government organisations, and other scientists that 'green belts' and buffer zones should be incorporated into reconstruction efforts to protect villages from future tsunamis.
In fact, the ecologists warn, these green belts may give a false sense of security, leading to greater loss of life should such a tragedy recur in future.
When Dr Alex Kerr of UoG, Dr Andrew Baird of CoECRS and Dr Stuart Campbell of WCS-IP, reanalysed data from a recent Indian study, they found it was height above sea-level and distance from the shore that protected the inhabitants of some villages, rather than vegetation.
"Our re-analysis revealed that the distance of a village from the coast and the height of the village above sea level explained 87% of the variation in mortality among villages. Once these two variables were taken into account, vegetation area provides less than a 1% increase in explanatory power," says Dr Kerr.
"The apparent link between vegetation area and mortality was actually due to the fact that more vegetation grows at higher elevations above sea-level - and the greater the distance from the sea, the greater the area of vegetation.
"In short, if you had hamlets of equal elevation and distance from the sea, differences in vegetation area would make little difference to the death toll from a tsunami."
JCU's Dr Baird says the new analysis means there is genuine danger in overstating the protective capacity of vegetation in the event of another tsunami.
"Mangrove forests provide coastal communities with many valuable goods and services. However, expecting them to provide protection from tsunamis is unrealistic," he said.
"Following the Krakatoa eruption the resulting tsunamis penetrated eight kilometres through primary rainforest.
"Right now buffer zones are being enforced through a combination of government legislation, and a refusal of aid to people that wish to move back to their homes, in the belief they may provide protection from some future huge event. These buffer zones are only between 100 and 500 m, yet they may dispossess over a million people in India and Sri Lanka," Dr Baird said.
"It's a beautiful idea that green belts can stop a tsunami, and its aims are commendable. But it isn't true, and it won't work.
Logically, the safest course is to build farther from the sea or on higher ground. However, this cannot be considered in isolation from the social economic and emotional cost of shifting entire communities and their livelihoods, the researchers say.
"Tsunamis are catastrophic but, fortunately, they are rare - and a well-organised early-warning and evacuation plan may be far more effective in saving lives," Dr Baird said.
"Even if property is destroyed, this may still be preferable to the social dislocation and potential conflict involved in removing entire communities from their coastal existence."
Dr Baird adds that a further dimension of the problem is the fact that in many cases these buffer zones are being used by developers and local authorities as a pretext for moving communities, so they can then build tourist facilities on the vacated shoreline.
Photographs available at: http://www.coralcoe.org.au/news_stories/greenbelts/imagegallery.html
Article: Kerr, A. M., Baird, A. H. & Campbell, S. J. 2006 Comment on Kathiresan & Rajendran, Coastal mangrove forests mitigated tsunami. Estuarine, Coastal and Shelf Science 67, 539-541.
ARC Centre of Excellence for Coral Reef Studies website: http://coralcoe.org.au
posted by Island Aid at
5:45 pm
0 Comments:
Post a Comment
Subscribe to Post Comments [Atom]
<< Home