The ancient city of Angkor in Cambodia was the capital of the great Khmer Empire that flourished from the 9th to the 15th century. At its height the city covered more than 385 square miles and had an advanced road system and religious structure and a trade network ahead of its time.

Angkor's hydro-engineering system, composed of canals, moats, embankments and large reservoirs, known as barays, was one of the most complex in the ancient world. Yet at the height of its power the city was eventually abandoned. The reasons for this mass exodus of nearly 750,000 people remained a mystery to archaeologists with many theories being proposed to explain the decline of Angkor. Now one team of researchers has suggested the inhabitants abandoned the city because of a prolonged drought and the state's inability to cope with climate change.

Suggested causes of the fall of the Khmer Empire have ranged from war and land overexploitation to a shift in maritime trade. But recent evidence suggests that prolonged droughts might have been the culprit. Researcher Mary Beth Day, a paleolimnologist from the University of Cambridge, along with her colleagues studied the city's reservoirs and took samples of sediments from the largest Khmer reservoir, the West Baray.

The researchers found that the rate of sediment deposited in the baray dropped to one-tenth of what it was before the city collapsed. This suggests that drought may have interfered with the empire's water management system.

"When Angkor collapsed, there was a drop in water levels," said Day. "And much less sediment was delivered to the baray at the time."

The growing population of Angkor also stressed the water system. The researchers found that the sediment being delivered to the reservoir before the city collapsed was more weathered than sediment delivered after the collapse of Angkor. In the end it didn't matter how advanced the water system of Angkor was, it couldn't handle the sudden and intense variations in climate.

"Angkor can be an example of how technology isn't always sufficient to prevent major collapse during times of severe instability," Day told LiveScience. "Angkor had a highly sophisticated water management infrastructure, but this technologic advantage was not enough to prevent its collapse in the face of extreme environmental conditions."

"It's important to understand, however, that failure of the water management network was not the sole reason for the downfall of the Khmer Empire," Day added. "The collapse of Angkor was a complex process brought about by several different factors - social, political and environmental."

The research is published online in the Jan. 2 issue of Proceedings of the National Academy of Sciences.

The collapse of one of the ancient world's most advanced cultures is a grim warning of the effects of climate change on any society. With the world experiencing major droughts in Texas, Africa and other parts of the world, history shows us how even technology isn't enough to cope with climate change.