The source: “The End of Angkor” by Richard Stone, in Science (March 10, 2006).

Located in modern-day Cambodia, the once-sprawling city of Angkor was the center of a powerful Khmer kingdom whose rule in Southeast Asia lasted from the ninth to 15th centuries. At its height, Angkor boasted a population of several hundred thousand, an extensive system of reservoirs and waterways, and many elaborate Hindu temples such as the immense, gilded Angkor Wat. Thai armies encroached on the area in the mid-15th century, and by the 16th century the city lay abandoned for reasons unclear, Science’s Asia news editor, Richard Stone, writes. Among the theories offered for Angkor’s demise are the shift of trade southward toward the sea and the ascension of Theraveda Buddhism in the area.

Thirty years ago French research­ers proposed an alternate catalyst, a sharp decline in crop yields possibly caused by the silting of irrigation channels sped by deforestation. Then the rule of the Khmer Rouge from 1975–79 and sub­sequent chaos halted archaeological efforts in Angkor for nearly 20 years. Recent discoveries made by the Australian-led Greater Angkor Project reveal that a combination of bad engineering and geological uplift of the area’s riverbeds centuries ago may have hindered the functioning of Angkor’s engineered water system and left the city vulnerable to food shortages.

The team used satellite imagery and ground surveys to reveal a city that was far larger than previously thought. The canals, water tanks, and three large reservoirs formed the basis of a water management system that completely altered the natural landscape. Around the canal system grew a “vast low-density patchwork of homes, temples, and rice paddies” scattered over a thousand square kilometers.  

One mystery of Angkor’s watercourses is a spillway branching off from one of the canals that seems to have been purposely destroyed. Archaeologist Roland Fletcher hypothesizes that Angkor engineers tried in vain to remedy a flow problem, then tore apart the spillway to prevent it from causing further disruptions. According to Fletcher, Angkor’s water infrastructure “became so inflexible, convoluted, and huge that it could neither be replaced nor avoided, and had become both too elaborate and too piecemeal.” As a result, it became less able to accommodate events such as drought or flood. Future research into the changing climate conditions of the area will reveal whether erratic monsoons between 1300 and 1600, leading to drier weather, exacerbated Angkor’s water troubles.

The destructive combination of changing environmental conditions and poor infrastructure is not peculiar to Angkor. Archaeologists also attribute the downfall of the Mayan Empire, by ad 900, to a series of droughts coupled with overpopulation. “Angkor’s downfall,” says Stone, “may be a cautionary tale for modern societies on the knife edge of sustainability.”