What happened at Angkor Wat
The great Khmer capital of Angkor, in what is now Cambodia, was for a time the largest preindustrial city in the world. Modern-day visitors to the ruins at Angkor Wat can see, in addition to the ornately carved Buddhist temple, remnants of a massive and intricate system of waterways, dikes and holding ponds.
But the city declined, finally succumbing to Thai invaders in 1431. A group of researchers say they believe they have at least a partial answer to the mystery of its collapse: Two major droughts, and some follow-up flooding, probably weakened the city's agricultural base and left it vulnerable to disease and invasion.
"The Angkor droughts were of a duration and severity that would have impacted the sprawling city's water supply and agricultural productivity, while high-magnitude monsoon years damaged its water control infrastructure," the researchers wrote in a recent Proceedings of the National Academy of Sciences.
Researchers from the United States, Australia, Japan, Vietnam and Thailand conducted tree-ring analysis in the untouched, thousand-year-old "cloud forests" of nearby Vietnam. Rings grow wider or narrower based on, among other things, rainfall. Cores that were extracted from the trees without harming them provided the guide to climate change over the last 758 years -- including severe droughts from 1362 to 1392 and from 1415 to 1440.
"Angkor at that time faced a number of problems -- social, political and cultural. Environmental change pushed the ancient Khmers to the limit and they weren't able to adapt," lead researcher Brendan Buckley, a climate scientist and tree-ring specialist at Columbia University's Lamont-Doherty Earth Observatory, said in a statement. "I wouldn't say climate caused the collapse, but a 30-year drought had to have had an impact."
At its height, Angkor was home to possibly a million people and, according to a 2007 study, covered at least 385 square miles -- more than five times the size of the District. A UNESCO World Heritage Site with its huge complex of overgrown and crumbling temples, many pockmarked with bullets from Cambodia's recent wars, Angkor may be best known to Americans as a stunning backdrop in the 2001 movie "Lara Croft: Tomb Raider."
A video of Buckley in Vietnam's "cloud mountains" and discussing the findings can be seen online at http:/