The water system that helped Angkor rise may have also brought its fall

At the medieval city of Angkor, flooding after decades of scant rainfall triggered a devastating breakdown of the largest water system in the preindustrial world, new evidence suggests.

Intense monsoon rains bracketed by decades of drought in the 1400s set off a chain reaction of failures in Angkor’s interconnected water network, computer simulations indicate. The climate-induced crumbling of the system — used for irrigation, drinking water and flood control — hastened Angkor’s demise, scientists conclude online October 17 in Science Advances.

“Angkor’s critical [water] infrastructure acted to accelerate the impact of climatic disruption,” says study coauthor and geoscientist Dan Penny of the University of Sydney.

Complex infrastructure systems, from Angkor’s water network to modern electrical grids, consist of many interacting parts. Troubles in one part of a system can lead to the failure of other components.

Penny and colleagues devised a computer model of how a rapid shift to periods of intense rainfall affected Angkor’s water system at the peak of its complexity in the 1300s. A series of simulations indicated that, above a critical volume of water flow, earthen channels carrying water into the system began to erode and widen. Water was then unevenly shunted through junctions in the network, gushing into some connected channels and trickling into others.

Meanwhile, accumulating sediment further decreased the volume of water that newly parched channels could carry, intensifying the uneven flow of water through the system. A breakdown of the entire water network would soon have followed, the researchers say.

By the 1200s, Angkor, in what’s now Cambodia, was the world’s most extensive city, covering about 1,000 square kilometers (SN: 5/14/16, p. 22). The city had spent the previous several hundred years building and expanding a network of canals, embankments, reservoirs, moats and other structures devoted to water management.

But in the 1400s, Angkor’s king and many commoners mysteriously abandoned the city. Some researchers have attributed Angkor’s demise to war with a neighboring kingdom in present-day Thailand and possibly the tumultuous replacement of Hinduism by Buddhism in the region.

But the new research paints a convincing picture of climate-induced infrastructure collapse at Angkor, says archaeologist Charles Higham of the University of Otago in Dunedin, New Zealand, who was not involved in the study.

Angkor, for example, depended on consistent irrigation for rice fields. A breakdown of the water system would have undermined not only rice harvests but also weakened public beliefs that the king held supernatural powers justifying his rule, Higham suspects.