Monday, August 13, 2007

Lack of water doomed Angkor

Computer rendering of Angkor era

Illustrations by Tom Chandler/Monash University

An artist's impression of life in Angkor, Cambodia's medieval capital.

Khmer warriors of Angkor's heyday rode elephants into battle, as seen in this computer illustration based on relief sculptures at an Angkor temple.

Although the city thrived for six centuries, Angkor was no stranger to strife.

A Thai royal document, for example, records the invasion and sacking of the city in the mid-1400s. Modern looting still threatens Angkor temples, many of which are beyond the UN World Heritage site boundaries that protect Angkor Wat.

Suburbia in 13th-century century Angkor was a low-density place, with houses perched on mounds to protect the structures from seasonal floods.

Small artificial ponds stored water that could be use to flood rice paddies.

Neighborhood temples, surrounded by miniature moats, echoed the structure of Angkor Wat.

As Angkor's population expanded, it would have needed to clear forest to create more neighborhoods like this one. Archaeologists speculate that resulting floods and erosion ruined the waterworks the city depended on, possibly leading to its collapse.


Lack of water doomed Angkor

Overpopulation and deforestation filled the Cambodian city's canals with sediment, researchers say.

August 14, 2007
By Thomas H. Maugh II
Los Angeles Times Staff Writer

The medieval Khmer city of Angkor in Cambodia was the largest preindustrial metropolis in the world, with a population near 1 million and an urban sprawl that stretched over an area similar to modern-day Los Angeles, researchers reported Monday.

The city's spread over an area of more than 115 square miles was made possible by a sophisticated technology for managing and harvesting water for use during the dry season -- including diverting a major river through the heart of the city.

But that reliance on water led to the city's collapse in the 1500s as overpopulation and deforestation filled the canals with sediment, overwhelming the city's ability to maintain the system, according to the report in the Proceedings of the National Academy of Sciences.

The hydraulic system became "not manageable, no matter how many resources were thrown at it," said archeologist Damian Evans of the University of Sydney in Australia, the lead author of the paper.

But during the six centuries that the city thrived, it was unparalleled, particularly because it was one of the very few civilizations that sprang up in a tropical setting, said archeologist Vernon L. Scarborough of the University of Cincinnati, who was not involved in the research.

Just one section of the city, called West Baray, "was 900 times larger than the entire 9-square-kilometer hillock on which sat Tikal, the largest city in Central America," he said.

"The scale is truly unparalleled," added archeologist William A. Saturno of Boston University, who also was not involved. "Forest environments are not good ones for civilizations . . . because they require intensively manipulating the environment. Angkor is the epitome of this, and it is going to be the model for how tropical civilizations are interpreted."

Old and new technologies

The new data come from an unusual agglomeration of both old and new technologies. The core data came from a synthetic aperture radar unit flown on the space shuttle in 2000 and managed by NASA's Jet Propulsion Laboratory in La CaƱada Flintridge.

The radar pierced low-lying clouds and vegetation to give an accurate picture of soil density, local structures and moisture in soil, which reflects growing conditions. The images revealed, for example, the characteristic moat-enclosed local temples and artificial ponds used for water storage and irrigation.

This information was supplemented with photographs taken from ultralight aircraft flown over the city at low speeds and altitudes.

Finally, the researchers used motor scooters to traverse the city and closely examine sites revealed on the radar images. But so many sites have been revealed, Evans said, that the researchers are only partway through this process.

The group, collectively called the Greater Angkor Project, released a partial map three years ago. The new one released Monday contains, among other things, an additional 386 square miles of urban area, at least 74 long-lost temples and more than 1,000 newly recognized artificial ponds.

Angkor was the capital of the Khmer Empire, which got its start in AD 802 when the god-king Jayavarman II declared the region's independence from Java. At its height, the empire covered not only Cambodia but also parts of modern-day Laos, Thailand and Vietnam.

It is perhaps best known for Angkor Wat, the magnificent temple built by King Suryavarman II in the early 12th century.

Angkor has been studied for more than a century, but early scholars were so overwhelmed by the artworks and architecture, as well as the political successions, that they ignored the archeology, said coauthor Roland Fletcher of the University of Sydney.

In the late 1960s, French archeologist Bernard-Philippe Groslier began a more formal study of the ruins, but that work was halted for more than 20 years by the war that broke out in 1970.

After the war, archeologist Christophe Pottier of the Ecole Francaise d'Extreme-Orient in Siem Reap, another coauthor, renewed the work, beginning what eventually grew into the current project.

Disputes over history

In the process, the researchers have begun solving many of the disputes that have arisen over the city's history, Evans said.

"The debate has always been . . . was it large enough, was the manipulation of the landscape intensive enough to cause environmental problems?" Evans said. "The answer is definitively yes."

Other arguments have been based on the assumption that Khmer hydraulic engineering technology was rather rudimentary, he said. "What our research has shown is that it was extremely sophisticated and highly complex," he said.

Many of the reservoirs and walls of canals were constructed of compacted earth, he said, but junctions and other crucial points in the system were "quite sophisticated stone structures."

The Khmer built, for example, a massive stone structure to divert the Siem Reap River from its old bed through the center of the city. Other sites have stone structures built into the walls to manage the inflow and outflow of water, he said.

The system was complex enough that the Khmer could have grown rice throughout the year and not just during the rainy season, Evans said. It is not yet clear if they did so, however.

"The intentional movement of earth to create the whole water system is just really mind-boggling," Saturno said. "It was an enormous undertaking" that required not just administrative skills, but also engineering know-how and massive amounts of physical labor.

But in the end, maintenance became too labor-intensive, Evans said. As trees were removed from the landscape, sediment began accumulating in the canals at a rate more rapid than it could be removed. Many dike walls collapsed, although it is not yet known when that occurred.

"We're going now and excavating [the sites] on the ground, and trying to get a grip on when they happened -- whether they were a precursor of the decline, a symptom or the system gradually falling into ruin after they left," he said.


Urban Sprawl Might Have Doomed Angkor Wat

Artist's impression of settled areas in and around Angkor Wat complex. Credit: Tom Chandler, Monash University

13 August 2007
By Ker Than,
LiveScience Staff Writer

A new map made from satellite data reveals Cambodia's Angkor Wat temple was the center of one of the largest cities of the pre-industrialized world.

The research also sheds light on the extent of the city's sprawl and on its mysterious downfall, factors that could be linked in a way that bears on today's extensive and suburbanized metropolises.

Using ground-sensing radar provided by NASA, researchers found evidence that the ancient Cambodian capital took up an area of nearly 400 square miles (1,000 square kilometers). For comparison, Philadelphia covers 135 square miles, while Phoenix sprawls across more than 500 square miles, not including the huge suburbs. Each has about 1.5 million residents in the city limits.

"In terms of population, however, Angkor would only have had a few hundred thousand people," said study team member Damian Evans, an archaeologist at the University of Sydney in Australia. "There were cities with much larger populations—for example, in China—before, during and after the Angkor period."

The new radar technique, which senses differences in plant growth and soil moisture content created by topographical differences, also identified more than 1,000 new manmade ponds and more than 70 long-lost temples.

The work, detailed in the Aug. 14 issue of the journal for the Proceedings of the National Academy of Sciences, provides fresh evidence for an idea put forward more than 50 years ago— that Angkor relied on a complex irrigation system consisting of linked ponds and that the city's downfall might have been the result of land overexploitation.

The Khmer capital

Angkor was the capital city of the Khmer empire from the 9th to the 16th centuries. The now-crumbling and decadent temple, Angkor Wat , was constructed in the 12th century at the bidding of one of its kings.

The new maps show that Angkor's water system consisted of canals in the North that funneled water into massive reservoirs in the city's center where the temple resided. "From there, a series of distributor canals dispersed the water through the southern parts of Angkor and down towards the lake," Evans explained.

In the 1950s, the late archaeologist Bernard-Philippe Groslier speculated that traces of a hydraulic network were part of an ancient irrigation network that ferried water to farmers in the city's suburbs. Groslier also argued that the breakdown of the network, triggered perhaps by overexploitation of the landscape, was implicated in Angkor's downfall.

Supporting Groslier's hypothesis, the new maps and excavations reveal breaches in dykes and attempts to patch up the system. Whether such phenomena were the cause, a symptom or a result of Angkor's decline remains to be determined, Evans said.

Modern lessons

"Our research shows that Angkor was certainly extensive enough, and that land-use was certainly intensive enough, to have impacted profoundly on the regional ecology," Evans told LiveScience.

Angkor was surrounded by a vast expanse of rice fields that would have required extensive forest clearance. Over time, the intense farming could have led to serious ecological problems, including those associated with deforestation, overpopulation, topsoil degradation and erosion.

The consequence of overexploiting the environment isn't the only lesson Angkor's fate has for modern society, Evans said. Angkor required a massive infrastructural network of canals and roads to keep it running.

"This increasingly complex elaborate system would have been very difficult and expensive to maintain," Evans said. "This is obviously something to bear in mind, considering that many cities in our contemporary world are expansive, low-density urban sprawls as Angkor appears to have been."


Vast ancient settlement found at Angkor Wat

Aerial photos of remnants of Angkor settlement. Occupation mounds and ponds (upper left). Canals and embankments (upper right). Roadway and canal (lower left). Village temple area (lower right) (Image: Proceedings of the National Academy of Sciences) - Click on the photo to zoom in

The new map of Angkor Wat combines data from ground-sensing radar with aerial photographs and extensive fieldwork (Image: Proceedings of the National Academy of Sciences) - Click on the photo to zoom in

13 August 2007 news service
Emma Young, Sydney, Australia

A huge urban sprawl once surrounded Cambodia’s famous Angkor Wat temple, according to a newly created map. The scale of the settlement makes it more plausible that the inhabitants of Angkor brought on their own society's collapse through environmental degradation.

The new map uses data from high-resolution, ground-sensing radar and aerial photographs to augment extensive fieldwork. By detecting slight variations in vegetation and ground moisture due to underlying ruins, the radar reveals in unprecedented detail the location of temples - including 94 newly identified temple sites plus another 74 that have yet to be checked on the ground - ponds, roads and canals.

Researchers in the Greater Angkor Project at the University of Sydney in Australia, together with colleagues in Australia, Cambodia and France, used the techniques to survey the entire watershed of the Angkor region.

The area covers nearly 3000 square kilometres, most of which is now blanketed with dense vegetation. Earlier maps suffered from problems with the resolution of aerial photographs and radar data, and from difficulties with accessing remote regions.

Urban sprawl

The researchers found that about two thirds of this region was once occupied, making it by far the biggest pre-industrial settlement yet documented. The main urban district of about 1000 square kilometres was surrounded by suburbs that seem to spread far beyond the north-western and south-eastern borders of the study site.

In fact, says Damian Evans of the University of Sydney, “there is just no obvious boundary” for the settlement. The population of the area was probably around half a million, he adds, though earlier estimates of a million inhabitants - suggested in the 1970s - could still be correct.

Such extensive settlement may help explain why Angkor, which thrived between the 9th and 16th centuries, had been overwhelmed by vegetation by the time European explorers first encountered the site in the 1860s.

The main theory for Angkor’s abandonment is that the creation of an extensive water management system caused environmental damage that ultimately led to the failure of the system, leading to food shortages. That scenario now seems even more likely.

Canal system

“This new map lays out definitively what the system would have looked like - and shows that it was capable of significantly impacting on the local environment,” says Evans.

Local people cleared land, creating a complex system to move water from a region of high ground spanning about 500 square kilometres to storage reservoirs in the centre, and on, via canals, to irrigate about another 500 square kilometres of land to the south. This system would have allowed the society to produce surplus rice to feed workers engaged in building monuments such as Angkor Wat.

The new map also reveals apparent failures of the canal system, with multiple dykes at certain sites. “There is massive redundancy in the canal network - and that gives us an indication that things were going wrong,” says Evans.

Researchers have not yet dated these sites to confirm that they coincide with Angkor’s collapse, however. Nor is it clear what exactly might have gone wrong. “We have evidence of a huge water-management system that had the capacity to impact significantly on the environment," says Evans. "But at the moment, the actual evidence that it did so is pretty thin on the ground.”

Journal reference: Proceedings of the National Academy of Sciences
(DOI: 10.1073/pnas.0702525104)

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