Trees Not Necessarily a Barrier Against Tsunami, Australian Scientists

Australian researchers have warned against placing too much of a trust in mangroves and tree barriers as a fail-safe protection against tsunami. Since the devastations of 2004, various governments and NGOs have promoted mangroves and trees as a guarantee against the earthquake-driven tidal waves.

Instead the stress could be on early warning systems, educating the people to recognise the signs of an imminent tsunami and well-coordinated evacuation plans.

“Following the Boxing Day Tsunami scientific studies were released which claimed that the damage to coastal communities had been less in places where there was a barrier of trees or coastal vegetation,” explains Dr Andrew Baird of the ARC Centre of Excellence for Coral Reef Studies and James Cook University.

“As a result there has been a lot of tree planting in coastal areas affected by the tsunami, in the hope it will protect coastal communities in future from such events.

“However these studies looked only at the presence or absence of vegetation and the extent of damage – and did not take account of other important variables, like the distance of a village from the shore, the height of the village above sea level or the shape of the seabed in concentrating the tsunami’s power.”

The study by Dr Alexander Kerr of the University of Guam, Dr Baird, Ravi Bhalla and V. Srinivas of the Foundation for Ecological Research, Advocacy and Learning India concludes there is, as yet, no evidence that coastal tree belts can provide meaningful protection against a tsunami or, for that matter storm surges produced by cyclones, such as the surge that followed Cyclone Nargis in Myanmar early this year which killed over 150,000 people.

As a result it would be extremely dangerous to rely on tree planting alone to shield coastal communities in the event of future tsunami or storm surges, they warn – and doing so could lead to further tragedies.

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The team’s analysis of the pattern of damage of the Boxing Day 2004 tsunami shows that many variables were at work in determining how the force of the water affected people and structures on land, and these all need to be taken into account – not just a few of them.

The findings have major implications for civil defence and emergency planning, the cost of restoring affected regions and in minimizing the death and destruction suffered by some of the poorest communities in the world.

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To fully explore what drives the flooding following tsunami like the Boxing Day Tsunami, and storm surges, like those that could accompany any of the many cyclones that hit northern Australia each year, an extensive, statistically-sound analysis needs to be carried out of all the factors which may act on the force of the waves driving inland.

These include the height of the settlement above the sea, its distance, the shape of the sea bottom and local land uses. These make the difficulty of accurately predicting tsunami damage much harder – and a problem requiring rigorous analysis for multiple factors and their interaction.

In the meantime the Japanese model of preparing for the worst including early warning systems and emergency evacuation plans could be followed, the Australian team suggests.

Mangroves should be protected for their conservation value, and for the goods and services they provide to people even if they don’t protect coastal dwellers from extreme events, Dr.Baird stressed.

Their research report Roles of coastal bio-shields and their putative role in protecting coasts from large weather related disturbance events is soon to be published by the United Nations Environment Program.

Source-Medindia
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