DROUGHTS and flooding may have been decisive factors in the mysterious collapse of the ancient Khmer capital of Angkor, according to a new study released this week.

In a paper published Monday in the journal Proceedings of the National Academy of Sciences of the United States of America, researchers Brendan Buckley, Daniel Penny and their collaborators argue that climate variation strained the city’s complex and fragile infrastructure beyond repair, leaving it unable to support its population.

“The lack of textual records dating after the 13th century has created a historical [gap] and divergent, unresolved claims about the causes, rate and timing of Angkor’s decline and fall,” Buckley and his colleagues wrote. “Historians and archaeologists have, with a few notable exceptions, only rarely considered the role played by environment and climate in the history of Angkor.”

The researchers based their argument on an analysis of growth rings from cypress trees discovered in Vietnam that were almost 1,000 years old.

By looking at the varying widths of the growth rings, Buckley and his colleagues determined that Angkor was subject to two major droughts – one in the mid 1300s, and another in the early 1400s – that coincided with the period in which the Khmer imperial capital is believed to have begun an accelerated decline.

These droughts, which likely had a severe impact on Angkor’s agricultural productivity, were followed closely by unusually intense monsoon seasons that led to floods and damage to the system of canals and baray upon which residents depended for water management.

“What our study demonstrates ... is that decades of weakened summer monsoon rainfall, punctuated by abrupt and extreme wet episodes that likely brought severe flooding that damaged flood-control infrastructure, must now be considered an additional, important, and significant stressor occurring during a period of decline,” the researchers wrote.

Buckley said the research was part of a broader project looking at medieval droughts in Asia, and described his recognition of its relevance to Angkorean history as “one of these serendipitous kinds of things”. It was only when he was dating the tree rings, he said, that he realised they bore such a close relation to the period of Angkor’s decline.

Research in Siem Reap was conducted in part by scientists from the Greater Angkor Project (GAP), a research group run out of the University of Sydney. GAP deputy director Dougald O’Reilly said the study built on the insight of French archaeologist Bernard-Philippe Groslier, who argued in 1979 that the famed Angkorean canals were part of a hydraulic system that was not in place simply for religious reasons.

The new study, O’Reilly added, lends depth and context to the emerging understanding among archaeologists that Angkor’s demise was more complicated than traditional theories have suggested. In the past, scholars have ascribed the decline to conflict with the Thai kingdom of Ayutthaya and the flight of the empire’s elite to what is now Phnom Penh.

“The work that Buckley and Penny and [their collaborators] have done is really another piece of the puzzle that shows us that the decline of Angkor was a much more nuanced situation,” O’Reilly said.

Though Buckley was careful to note that a number of factors were likely involved in Angkor’s ultimate failure, he said the city may have been undone in part by its own feats of engineering.

“It just may have been ... [that] they weren’t able to cope with the vulnerability that they had because their system was so immovable,” Buckley said. “They didn’t have the ability to adapt very nimbly to these sorts of changes in their environment.”

With changing sea and river levels an issue of concern today in Southeast Asia, Buckley said, the importance adaptability in the face of a changing climate is a lesson that might be drawn from Angkor’s experience.

“Nature’s still dominant, and we don’t really control it like we’d like to,” he said. “The question is, how able are you and how nimble are you in adapting and adjusting to it, and that’s going to be the critical issue.”

ADDITIONAL REPORTING BY SAM RITH