By Andrew Baird, a postdoctoral fellow at the Center for Coral Reef Biodiversity at James Cook University (THE NEW YORK TIMES, 26/12/06):
SINCE the Indian Ocean tsunami two years ago today that killed more than 200,000 people, governments, donors and experts have embraced the idea that healthy mangrove forests and coral reefs could reduce the death toll from a giant wave. Former President Bill Clinton, in his role as the United Nations special envoy for tsunami recovery, recently endorsed a program that will allocate $62 million to preserve such natural barriers in 12 Asian and African countries.
But the $62 million question is, will these barriers work?
Research suggests that the level of protection offered by greenbelts has been exaggerated. And by diverting resources from more effective measures like education campaigns and evacuation plans to well-meaning but misguided reforestation, we may even contribute to a greater loss of life in future tsunamis.
There have been few scientific studies about the protective role of coastal vegetation. And while one study did suggest that a shield of mangrove forest managed to reduce tsunami damage in three villages in Tamil Nadu State in India, the forest was not the only difference between these coastal villages and those nearby that suffered major destruction.
Indeed, when my colleagues and I re-analyzed the data, we found no relationship between the death toll in each village and the area of forest in front of each one.
What actually saved these villages was being further from the coast or built on relatively high land. It was only a coincidence that they also had more forest between themselves and the ocean (of course, the further a village is from the coast, the greater potential area of forest).
Indeed, a recent paper in the journal Natural Hazards that surveyed more than 50 sites in affected regions found that coastal vegetation did not reduce tsunami damage, and that damage was actually greater in areas fronted by coral reefs.
Similarly, my colleagues and I, working in Aceh, Indonesia, found that neither reefs nor coastal forest reduced the damage caused by the tsunami. The distance the tsunami traveled inland was largely determined by the height of the tsunami and the slope of the land. In other words, where the tsunami was 30 feet high, it flooded all land lower than 30 feet above sea level, whether this reached 200 yards inland, or two miles.
Mangrove forests are, to be fair, very effective at dissipating the energy of storm waves, but a tsunami is a very different beast. Tsunamis, produced by earthquakes, have wavelengths of miles, compared to that of a few yards for typical wind-generated waves. The tsunami, for instance, that hit the Acehnese coast was eight miles thick; this wall of water rolled in for nearly an hour.
Of course, coastal forests at some point do begin to reduce tsunami damage, but we can’t expect them to offer meaningful protection against the sheer amount of energy involved in a tsunami. In 2004, the energy released by the Indian Ocean earthquake is estimated to have been the equivalent of 23,000 Hiroshima-sized atomic bombs: that’s nearly three Hiroshimas for every mile of affected coastline. Another significant concern is the enforcement of buffer zones in the name of tsunami protection. Buffer zones, to have any real effect, would need to be many miles wide and thus impossible to institute without prohibitively high social and economic costs.
Perhaps it is unsurprising then that local governments have begun to regulate these barriers in a way that is not only insufficient, but grossly unfair: luxury hotels escape enforcement while tens of thousands of impoverished fishing families in India, Sri Lanka and Thailand are prevented, in the name of tsunami protection, from rebuilding their homes in areas that have been designated buffer zones.
A more recent tsunami, on July 17, demonstrated the tragic consequences of inadequate planning. More than 18 months after the 2004 catastrophe, the Indonesian government had yet to deploy an early warning system on the island of Java. Tremors from a major earthquake were felt and the tsunami was preceded by a telltale withdrawal of the sea — yet amazingly, people did not know to seek high ground. Government officials failed to act despite precise warnings, and more than 600 people died. Clearly, education efforts in Indonesia have been inadequate.
But we can take heart in the example set by Japan. On Nov. 15, an undersea earthquake with a magnitude of 8.1 set off that nation’s tsunami early warning system. Thousands were evacuated.
While the resulting tsunami was luckily too small to cause damage, Japan’s sophisticated early warning system, intensive education campaigns, annual evacuation drills and loudspeakers for nearly every kilometer of coastline might have saved thousands of lives if the tsunami had been larger. Similarly effective measures in the Indian Ocean have yet to be developed, in part because efforts and resources remain focused on these questionable schemes to build mangrove barriers.
Certainly, coastal vegetation can provide communities with many valuable resources, and the rehabilitation of these ecosystems should be encouraged. But if the aim is to protect people from tsunamis, the science indicates that money would better be spent on early warning systems, education and evacuation planning.