Angkor, between droughts and torrential rains

The decline of Angkor is due, at least in part, to the extreme variability of weather conditions to which the Khmer were unable to adjust their water system to be sophisticated.

Written by Abdullah Al Abbadi/Blue Line news

Bayon temple, constructed by Angkorian King Jayavarman VII in the late 12th century. The faces may be representations of Buddha, the bodhisattva Lokesvara, Jayavarman VII, or a combination. CREDIT: Mary Beth Day, University of Cambridge

From the 11 th century, Khmer civilization flourished and moved over the Tonle Sap Lake, Cambodia, and has developed the largest urban complex of the preindustrial era. Even today, many temples remain, including Angkor Wat, and the remains of a large water system. At the end of the 14 th and beginning of the 15 th century, the Khmer empire sank into oblivion. Several factors have been proposed to explain this decline: war, arrival of Theravada Buddhism, modifications of trade routes, overpopulation, ecological constraints … To see more clearly, Mary Beth Day, University of Cambridge, United Kingdom, and colleagues studied sediments to highlight changes in the environment and water management practices.

These studies confirm the thesis of the role of climate fluctuations and suggest that the Khmer failed to fight the droughts.

Angkor possessed a complex network of channels, moats, and embankments and reservoirs known as barays to collect and store water from the summer monsoons for use in rice paddy fields in case of drought. One of the the largest reservoirs is the Western Baray, a pool of eight kilometers long and two wide, at its center a temple perched on an artificial island, called the Western Mebon temple. Dug from the eleventh century, this basin contains up to 53 million cubic meters, of which 65 percent came from the Siem Reap River, and 35 percent of precipitation. The studied sediments were collected at the bottom of the basin in a core sample of two meters long (the longest ever collected), corresponding to about
1000 years of history. What have they found?

The site of the Western Baray. © NASA SPOT.

The strontium isotope ratios, sedimentation rates, sediment density and color (which reflects their content of organic compounds) show that the Western Baray received significantly less sediment from the fourteenth century, the early decline of ‘Khmer empire. The volume of water was also much lower. The analysis also corroborated the episodes of droughts (the fourteenth and fifteenth centuries) that were deduced from the study of tree rings from Vietnam. These events have alternated with periods of unusually heavy rain. From the
sixteenth century, after the fall of the empire, there was a reduction in erosion. Similarly, changing the ecology of the basin at this time, with a proliferation of plant species related to the decrease in turbidity (water was no longer used or, consequently, circulated).

In addition, traces have revealed large-scale siltation of the hydraulic system during the 12th and 14 th centuries, just before the drought. Finally, deterioration, cracks, etc.. from the time when the network was used were found.

The Western Baray and Western Mebon (an artificial island) in the foreground. © R. Clark

These changes in sedimentation, maintenance and ecology of the basin are the result of complex interactions between climatic and anthropogenic factors, such as water management and land use, such as the expansion of the urbanization. It is difficult to distinguish the role of each, but they often work hand in hand, the environmental constraints leading to behavior change. However, according to Mr. B. Day, these results show that maintenance of the hydraulic system was not adequate in terms of climate and hydrological changes. The extreme variability of weather patterns overcame adaptive capacity of the Khmer. In other words, they were overtaken by events.

Selected source for further read” live science published 2-Jan-2012

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