BANGKOK – The collapse of Cambodia's great ancient city of Angkor may have been due to a massive drought nearly 600 years ago — not just rival Siamese forces and widespread deforestation as previously suspected, a researcher said.
Brendan M. Buckley said Tuesday that bands from tree rings that he and his colleagues examined show that Southeast Asia was hit by a severe and prolonged drought from 1415 until 1439, coinciding with the 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. They oversaw construction of architectural stone marvels, including Angkor Wat, regarded as a wonder of religious architecture and designated a World Heritage Site by UNESCO.
While the 1431 invasion from Siam — what is now Thailand — has long been regarded as a main cause of Angkor's fall, archaeologists working at the sprawling temple site have suspected that ecological factors played a major part in its collapse.
"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.
The thickness of a tree's rings provides scientists with a historical record of a region's climate. Wet periods encourage tree growth, making rings thicker, while dry periods create thinner rings.
Buckley, one of the world's top tree ring experts, has spent the past 16 years taking core samples from trees across Southeast Asia to build a record of the region's climate dating back hundreds of years.
Buckley — who spoke on the sidelines of a three-day climate conference in Vietnam_ said his data helped identify at least four mega-droughts in Southeast Asia dating back 722 years.
The Greater Angkor Project — run by the University of Sydney in collaboration with the French archaeological group Ecole Francaise d'Extreme Orient and APSARA, the body responsible for management of the Angkor World Heritage Park — concluded in 2007 that ancient Angkor had become unwieldy. Efforts to expand rice production to support a population of 1 million led to vast deforestation, top soil degradation and erosion.
Dan Penny, a University of Sydney researcher who is a director at the Greater Angkor Project, said the new findings on drought will help researchers gain a greater understanding of why the kingdom collapsed.
"Angkor was a civilization obsessed with managing water. It was an agrarian society," said Penny, who also spoke at the conference. "It's hard to imagine that a society like that could have shrugged off 20 or 30 years of drought."
Penny said sediment samples show no evidence that Angkor was turned into a "dust bowl" by the drought, he said. However, the drought likely came as a final blow to a kingdom already suffering the effects of deforestation and attacks from the Siamese and the Cham of southern Vietnam, he said.
"We have these droughts occurring on top of preexisting pressures," Penny said. "Climate change was an accelerant. It's like pouring petrol on a fire. It makes a social and economic pressures that may have been endurable disastrous."