Wednesday, 18 February 2009

Tree rings helped pinpoint time of drought

International Herald Tribune

The Associated Press
Published: February 17, 2009

BANGKOK, Thailand: A prolonged and intense drought may have contributed to the demise of Cambodia's great ancient city Angkor, an American researcher said Tuesday.

Brendan M. Buckley, speaking on the sidelines of a three-day climate conference in Vietnam, said bands on tree rings that he and his colleagues have examined show that Southeast Asia was hit by a severe drought from 1415 until 1439.

That would coincide with the time period during which many archeologists believe Angkor collapsed. From the city of famed temples, Angkorian kings ruled over most of Southeast Asia between the 9th and 14th centuries.

During that time, they oversaw construction of architectural stone marvels, including Angkor Wat, regarded as a marvel of religious architecture and designated as a World Heritage Site by UNESCO.

"Given all the stress the Khmer civilization was under due to political reasons and so forth, a drought of the magnitude we see in our records should have played a significant role in causing its demise," said Buckley, a research scientist at Columbia University's Tree-Ring Laboratory in New York.

Scientists have a historical record of droughts with the thickness of a tree's rings. Since trees grow more during wet periods, the rings will grow thicker at those times. Trees grow less in dry times so those rings will be thinner.

While the 1431 invasion from Siam, what is now Thailand, has long been regarded as a major cause of Angkor's fall, archaeologists working at the sprawling temple site have long suspected that ecological factors played a role.

The Greater Angkor Project is run by the University of Sydney in collaboration with the French archaeological group Ecole Francaise d'Extreme Orient and APSARA, the body responsible for the management of the Angkor World Heritage Park. The project concluded in 2007 that ancient Angkor had become unwieldy and that efforts to expand rice production to support a population of 1 million had led to vast deforestation, top soil degradation and erosion.

Last year, the group went further to show that the deforestation resulted in flooding and huge amounts of sediment clogging the network of canals that was at the heart of the city's vital water management system.

Dan Penny, a University of Sydney researcher who is a director at the Greater Angkor Project, said the new findings on drought will help researcher gain a greater understanding of why Angkor collapsed.

"Angkor was a civilization obsessed with managing water. It was an agrarian society," Penny said. "It's hard to imagine that a society like that could have shrugged off 20 or 30 years of drought."

However, Penny said it was likely that the drought was more of a contributing factor to the kingdom's demise than a driving force. Not only was it forced to contend with the impacts of deforestation but also attacks from the Siamese and the Cham of southern Vietnam.

"We have these droughts occurring on top of preexisting pressures," Penny said.

"Climate change was an accelerant," he said. "It's like pouring petrol on a fire. It makes a social and economic pressures that may have been endurable disastrous."

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