The ancient civilisation based at Angkor in Cambodia collapsed in the late 16th century because of problems with a very modern ring to them, research by an international team indicates.

The Greater Angkor Project, based in Sydney, is preparing a paper arguing that extreme climate change and the failure of Angkor's complicated water systems were to blame.

The temple complex was the heart of the mighty Khmer empire and its ruins are one of the most popular attractions in South-East Asia.

The Angkor Wat temple, the centrepiece, was built in the ninth century and surrounded by huge reservoirs and canals - believed to be partly Hindu symbols and partly for irrigation.

Sydney archaeologist Professor Roland Fletcher, co-director of the team of scientists from France, Cambodia and Australia on the project, told Radio Australia's Connect Asia program: "It was actually the largest low density pre-industrial city on earth."

"It covers nearly 1,000 square kilometres, but that's all spread out, something like modern Los Angeles.

"So it was really enormous and it had somewhere in the order of, at the top end, 750,000 people in it."

Among the challenges for the authorities of Angkor were to manage the South East Asian monsoon and then a long dry season - that is, flood control and water delivery.

Professor Fletcher says this involved a massive water system, with canals as long as 40 kilometres, which "appears to have been the mechanism for holding water and using it as reserve in case monsoons were bad".

But from 1350 to 1500 AD, the region was hit by a very unstable climate, with droughts and severe monsoons mixed up.

Are there lessons from that period for modern cities?

"I would suspect there are, in the sense that what you see in Angkor is a landscape that has been completely cleared of forests in order to grow a dominant crop, so basically . . . simplification of the landscape and removing the tree cover," he said.

"On the other hand, [there is] the dependency on very big infrastructure for managing daily life - so, for instance, if you have really heavy monsoons that these canals and systems weren't designed to deal with."

"With severe monsoons, you would get severe damage to the structures, and we actually find that there is a dam up in the north that's been torn away and the big southern canals of Angkor are full of sand, which suggest very severe flooding."

For modern observers, "the situation is not absolutely equivalent - one reason being that we know a great deal more in the modern world, and we have a great deal more capacity available to us to deal with situations".

"But when you consider that Angkor was a giant low-density city, that had cleared its regional landscape of its natural vegetation cover, was dependent upon massive infrastructure and hit by climate change, it does sound a little topical.

"It does sound a little like the modern world."

(Source: abc.net.au/news)