February 17, 2009

Tree Rings Show History Of Drought In Southern Vietnam

Researchers are studying data from the tree rings of conifers in Vietnam to reveal new clues into how droughts affected ancient civilizations.

The researchers, from the US and Japan, reported their findings at a climate change conference in Dalat on Tuesday. They found that the tree ring samples collected from Fokienia hodginsii, a rare species that lives in Vietnam's cloud forests, revealed drought records for more than 700 years.

Brenden M. Buckley said he and his colleagues collected information to show that Southeast Asia underwent a severe drought from 1415 to 1439, which is the same time historians claim Angkor collapsed.

"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 the Tree Ring Laboratory at the Lamont-Doherty Earth Observatory in the United States.

"There was a very significant multi-decadal drought in the early 1400s with the worst drought year being 1417," he said.

Researchers also noted evidence of another major drought lasting at least 30 years in the mid-18th century.

"All of the kingdoms in Southeast Asia collapsed, in Thailand, Vietnam and Laos between 1750-80," said Buckley, who worked alongside Masaki Sano and Tatsuo Sweda of Ehime University of Japan to study the tree rings of Fokienia.

"Fokienia is an exceptional tree species because of the way it grows and responds to drought," he said.

Researchers presented their findings at the conference in southern Vietnam that is aimed at understanding annual monsoons and how climate change could affect the region and its economies.

"What the Fokienia trees are most keenly tuned into is the length of the monsoon. Longer the monsoon, the trees grow more," said Buckley.

Researchers said they are still unable to determine what caused the longer periods of drought, however they said it could be linked to "a recently discovered multi-decadal switch of sea surface temperatures in the Pacific," said Reuters.

"Angkor was a civilization obsessed with managing water. It was an agrarian society," said Dan Penny, a University of Sydney researcher and a director at the Greater Angkor Project.

"It's hard to imagine that a society like that could have shrugged off 20 or 30 years of drought."

"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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