Paper: Societal response to monsoonal fluctuations in NE Thailand during the demise of Angkor Civilisation

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New paper published in The Holocene

This paper investigates the possible social responses to changes in the strength of the southwest monsoon in northeastern Thailand during the currency of the Angkor civilisation. These assessments are based on hydrogen and carbon isotope records of leaf waxes (δDwax and δ13Cwax) from a 2000-year-long wetland sequence of Pa Kho in northeastern Thailand, a region that formed the northern boundary of the Angkor Kingdom. Our data indicate anthropogenic flooding of the Pa Kho wetland through the control of water through dam construction from c. AD 1300 in response to the fluctuating strength of monsoon rains. δDwax, a proxy for regional hydroclimate variability, corroborates pre-existing evidence that increased summer monsoon rains, which supported the expansion of the agrarian economy, aided the rise of the Angkorian Empire whereas extreme drought contributed to its demise. Interestingly, our δDwax record shows already a gradual decreasing monsoon intensity from c. AD 1000 onwards, although Angkor’s prosperity reached its peak at c. AD 1200. We suggest that the complex hydrological system established under royal patronage at Angkor provided a resilient buffer against short-term monsoon fluctuations. The long-term decline in monsoon rains over a ~300-year period, combined with ongoing urbanisation, may have stretched the hydrological systems to their limit. We suggest that this was a major factor that contributed to the demise of Angkor in the mid-15th century.

Source: Societal response to monsoonal fluctuations in NE Thailand during the demise of Angkor CivilisationThe Holocene

Environmental lessons from Angkor

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Another one up for climate change – analysis of tree ring data from Vietnam give us a better understanding of how climate change in the 14th and 15th centuries contributed to the collapse of Angkor in an open-access article published in the Proceedings of the National Academy of Sciences.

cambodia, angkor wat front gate
photo credit: Alex Grechman

Climate as a contributing factor in the demise of Angkor, Cambodia

PNAS, 29 March 2010

Did climate influence Angkor’s collapse?
e! Science News, 29 March 010

Angkor Wat doomed by drought, floods, suggests tree ring study
USA Today, 29 March 2010

Did Climate Influence Angkor’s Collapse? Evidence Suggests Changing Environment Can Bring Down a Civilization
Science Daily, 30 March 2010

Drought and flooding led to collapse of Angkor
LA Times, 31 March 2010

Climate blamed in fall of Angkor

Phnom Penh Post, 31 March 2010

Angkor lesson for cities

The Telegraph (Calcutta), 01 April 2010
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Combination of stresses led to fall of Angkor

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It wasn’t the silting up of the canals, or the rapid deforestation to make way for the urban complex, or the climate change, but rather a combination of all these stresses that culminated in the abandonment of Angkor in the 17th century. This was the conclusion delivered by researchers working on the Greater Angkor Project at the University of Sydney, possibly putting this archaeological mystery to rest. (But if you’ve been a faithful reader of this blog, you’d have known this already, wouldn’t you?)

Faces at Bayon
photo credit: Mendhak

Urban sprawl hastened Angkor’s collapse
24 June 2009, The Australian
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Dendrochronology sheds light on Angkor's collapse

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Stories about Angkor’s collapse makes it sound like there was one event that caused a civilisation to fall; I rather think there’s usually a confluence of factors. In Angkor, we can now add drought to the list which includes deforestation, breakdown of the water management system and attacks from neighbouring Siam. The conclusion of drought comes from a dendrochronology analysis, or the dating by tree rings, which is in itself a surprising technique because tree-ring dating is more reliable in temeperate climates where the seasonal changes produce more visible tree rings. I believe this may be first, or at the very least one of the few, instance where dendrochronology has been used in Southeast Asia (corrections, of course, are very welcome).

photo credit: Hazel Motes

Drought might have collapsed Cambodian Angkor city
AP, 18 February 2009
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Studying Angkor’s demise, archeologists warn of repeating the past

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The ecological demise of ancient and modern Angkor is discussed here as several archaeologists (including Roland Fletcher, pictured here, who has earlier spoken here, here and here) are featured talking about how the tourism explosion at Siem Reap and the elevated drain on water resources are described as an ‘ecological time bomb’.

Studying Angkor’s demise, archeologists warn of repeating the past, 17 February 2008
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Water woes pressure state of Angkor’s temples

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Angkor’s ecological time bomb is discussed in this article, making parallels between the theorised failure of the water management systems to the current pumping of underground water to support the modern city of Siem Reap. The former resulted in the fall of Angkor. Will the later result in the fall of the very monuments themselves?

Development pressures threaten Angkor Wat ruins [Link no longer active]
AP via, 13 February 2008
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Groslier's thesis on Angkor's fall gains credence


04 September 2007 (University of New South Wales) – 50 years ago, French archaeologist Bernard-Philippe Groslier’s theorised that Angkor’s sudden abandonment was due to a massive failure in the city’s water management system. The theory was not widely accepted due to lack of empirical evidence, but the map of Angkor’s spawl that broke two weeks ago has made it timely to give Groslier’s theory another relook.

Architects of Angkor’s downfall

The architects of Cambodia’s famed Angkor – the world’s most extensive medieval “hydraulic city” – unwittingly engineered its environmental collapse, says research by UNSW scientists and a team of international scholars.

This revelation, published in the Proceedings of the National Academy of Science, supports a disputed hypothesis by French archaeologist Bernard-Philippe Groslier, who 50 years ago suggested that the vast medieval settlement of Angkor was defined, sustained, and ultimately overwhelmed by over-exploitation and the environmental impacts of a complex water-management network.

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Angkor engineered its own demise

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14 Aug 2007 (News in Science) – Still more Angkor stories buzzing in the news, and I expect to be posting a few more similar stories today. This story focuses on the fall of Angkor and the failed water management system thesis.

Angkor engineered its own demise
Dani Cooper

An international team of archaeologists has used radar technology to confirm the Cambodian temple of Angkor Wat was surrounded by the pre-industrial world’s most extensive urban sprawl.

In today’s Proceedings of the National Academy of Sciences, the researchers report that NASA radar technology has helped reveal an ancient city, hidden beneath tropical vegetation.

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Angkor "killed by climate change"

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14 March 2007 ( – This isn’t exactly new news, because I posted something about this last year. Nonetheless, the story seems timely over the recent hype of climate change from Al Gore’s movie, An Inconvenient Truth.

City ‘killed by climate change’

Climate change was a key factor in the abandonment of Cambodia’s ancient city of Angkor, Australian archaeologists said today.

The city, home to more than 700,000 people and capital of the Khmer empire from about 900AD, was mysteriously abandoned about 500 years ago.

It has long been believed the Khmers deserted the city after a Thai army ransacked it, but University of Sydney archaeologists working at the site say a water crisis was the real reason it was left to crumble.

“It now appears the city was abandoned during the transition from the medieval warm period to the little ice age,” Associate Professor of Archaeology Roland Fletcher said.

Prof Fletcher said that to sustain a population of 750,000, the Khmers had a meticulously organised water management system.

But blockages found in two large structures that controlled the water system in central Angkor suggested the network had begun to break down late in the city’s history.

Prof Fletcher said the discoveries complemented previous field work that had led his team to conclude the city was abandoned when new monsoon patterns, brought about by climate change, had made the site unsustainable.

Related Books:
Uncovering Southeast Asia’s Past: Selected Papers from the 10th International Conference of the European Association of Southeast Asian Archaeologists by E. A. Bacus, I. Glover and V. C. Pigott (Eds)

Climate change could have killed Angkor

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22 July 2006 (Australian Broadcasting Corporation, citing Reuters; also featured in other news media) – A new hypothesis presented at an international conference on Angkor posits that climate change led to the relatively fast depopulation and abandonment of Angkor.

ABC, 22 July 2006

Climate change could have killed ancient city

A Sydney conference has heard that climate change led to the fall of the ancient Cambodian city of Angkor.

The theory has been presented to an international gathering under the patronage of UNESCO.

Associate Professor Fletcher believes the medieval mini ice age caused climatic instability that lead to water and sediment overwhelming Angkor’s delicately balanced infrastructure.

Related Books:
Uncovering Southeast Asia’s Past: Selected Papers from the 10th International Conference of the European Association of Southeast Asian Archaeologists by E. A. Bacus, I. Glover and V. C. Pigott (Eds)
Angkor and the Khmer Civilization (Ancient Peoples and Places) by M. D. Coe
The Civilization of Angkor by C. Higham
The Archaeology of Mainland Southeast Asia: From 10,000 B.C. to the Fall of Angkor by C. Higham