Coastal trees would have somewhat reduced Indonesia's tsunami death toll
New research shows that the death toll of the devastating 2004 Boxing Day tsunami would have been 5% smaller in Indonesia’s west coast of Aceh if forest or dense tree cover had shielded coastal settlements
Published in the prestigious Proceedings of the National Academy of Science (PNAS) of the USA, the paper summarizes research undertaken by the ReGrin project that the World Agroforestry Centre started in 2005 together with the University of Hohenheim in Germany, and Indonesian partners.
Meine van Noordwijk, Chief Science Advisor with the World Agroforestry Centre explains how directly after the Tsunami, public debate focused on criticism of the earlier clearing of protective mangroves and on planting trees to reduce risks of loss of lives and physical damage in a possible future recurrence of a Tsunami.
“Mangroves had been scarce along Aceh’s West coast with its sandy beaches,” said van Noordwijk. “There wasn’t much hard evidence to show that having more trees would have reduced the impact and that trees should be replanted as a recovery measure to reduce future vulnerability.”
To add to this, varying opinions about how close to the coast resettlement should take place, meant there was confusion about how to organize rehabilitation efforts.
The Centre’s ReGrin project (Rebuilding Green Infrastructure with Trees People Want) set about investigating green infrastructure in the form of trees that would provide both economic benefits as well as offering resilience to natural disasters. A detailed reconstruction of the role coastal vegetation had played was part of the analysis, supporting activities aimed at recovery and prevention.
While it’s now nearly seven years since the Tsunami hit, scientific analysis of the event continues. There is a keen interest in developing lessons for all coastal zones that might be vulnerable to the impacts of future earthquakes.
The study published in PNAS provides quantitative evidence that can be used to guide future actions. Using spatial analysis of the measured destructive impact of tsunami waves over a distance of 100 km along the west coast of Aceh, the researchers concluded that coastal vegetation, such as trees or rubber plantations, would have shielded the settlements and helped reduce casualties and property damage by 3 to 8%.
The authors also believe that thick vegetation behind settlements likely led to a rise in casualties and destruction, possibly due to backwash containing debris from the initial waves, a fact corroborated by eyewitness accounts.
For scientists working in this area, the research establishes a sound basis upon which to build information on the protective value of coastal vegetation, particularly the buffer and filter roles of trees in extreme wave events.
“The effectiveness of trees in reducing wave energy probably depends on their branching structure,” says van Noordwijk. “But trees that absorb more energy are more likely to be washed out and actually become a hazard.”
“The study helps us to better appreciate some of the nuances behind what it means to promote the right tree for the right place.”
The full paper is available online: Influence of coastal vegetation on the 2004 tsunami wave impact in West Aceh
More information on the the ReGrin project website
Image: A mural from Meulaboh, Aceh depicting survivors’ recollections of the Tsunami