The Khmer Empire, also known as the Angkor Civilization, was a state-level society in southeastern Asia between the 9th and 15th centuries AD. The empire was marked by enormous monumental architecture, an extensive road system, a complex hydrologic system built to take advantage of a monsoonal climate, and extensive trade partnerships between India and China and the rest of the world.
But after several hundred years of prosperity and growth, the system abruptly collapsed about 1431. Why that happened has always been a puzzle. But recent evidence gathered by scholars and published in 2012 suggests that climate change, complicated with economic and political factors, overwhelmed the abilities of the state to cope.
Factors Contributing to the Collapse
Several major factors have been cited as contributors to the demise of Angkor: war with the neighboring polity of Ayuddhaya; conversion of the society to Theravada Buddhism; increasing maritime trade which removed Angkor's strategic lock on the region; over-population of its cities; and climate change bringing an extended drought to the region. The difficulty in determining the precise reasons for Angkor's collapse lies in the lack of historical documentation. Much of Angkor's history is detailed in Sanskrit carvings from the polity's temples as well as reports from its trade partners in China. But documentation during the late 14th and early 15th centuries within Angkor itself fell silent.
At its height in the 9th century, Angkor included most of modern-day Cambodia, central Thailand, southern Viet Nam and parts of Laos and included a population of hundreds of thousands. Its principal cities--Angkor, Koh Ker, Phimai, Sambor Prei Kuk--were engineered to take advantage of the rainy season, when the water table is right at ground surface and rain falls between 45 and 75 inches a year; and the dry season, when the water table drops up to five meters (16 feet) below the surface.
To counteract the ill effects of that, the Angkorians constructed a vast network of canals and reservoirs, even permanently changing the hydrology in Angkor itself. Modern archaeological investigations into the hydrologic elements has indicated that the culprit which brought down the Angkor elites was primarily climate change.
- Read more about Angkor's Water Management System
The West Baray Reservoir
Four main reservoirs (called baray in the Khmer language) were built in the city of Angkor: north, east, west and Baray of Lolei. All of them were rectangular in shape and aligned with the longest side pointing east/west. The largest of these was the West Baray, which measures 8 kilometers (5 miles) long by 2 km (1.2 mi) wide. Believed to have been built in the mid-11th century AD, the West Baray still holds water and today people fish there; if it were filled to capacity, it would hold 53 million cubic meters (69 million cubic yards) of water.
Evidence for a Long Term Drought
Researchers used sediment core analysis of soils taken from the southwest corner of the baray to gather isotopic and elemental data and investigate local environmental changes (detailed in Day et al.). The sediment core had charcoal within it, allowing researchers to identify three droughts, one in the early 13th century, one in the mid to late 18th century, and an extended drought between the 14th and 15th centuries at Angkor.
Support for a lengthy drought in the region was earlier identified in a dendrochronological study reported in 2010. That study (Buckley et al.) investigated tree ring data from the rare cypress Fokienia hodginsii, covering the years from 1250-2008. That record revealed a weakened monsoon season from the mid to late 14th century and a shorter but more severe drought in the early 15th, coupled with intensive monsoons.
Evidence from the soil cores reported by Day et al. indicates that in 14th and 15th centuries, decreased sediment, increased turbidity and lower water levels were present in Angkor's reservoirs, compared to the periods before and after.
Attempts to remedy the drought are in evidence at the East Baray, where a massive exit canal was first reduced, then closed off entirely during the late 1300s. The ruling class Angkorians moved their capital to Phnom Penh and switched their main activities from inland crop growing to maritime trade: but in the end, the interrelated geopolitical and economic factors made Angkor vulnerable to severe drought and weakened their ability to adapt to climate change.
Sources
This glossary entry is a part of the About.com guide to Angkor Civilization, and the Dictionary of Archaeology.
Buckley BM, Anchukaitis KJ, Penny D, Fletcher R, Cook ER, Sano M, Nam LC, Wichienkeeo A, Minh TT, and Hong TM. 2010. Climate as a contributing factor in the demise of Angkor, Cambodia. Proceedings of the National Academy of Sciences 107(15):6748-6752.
Day MB, Hodell DA, Brenner M, Chapman HJ, Curtis JH, Kenney WF, Kolata AL, and Peterson LC. 2012. Paleoenvironmental history of the West Baray, Angkor (Cambodia). Proceedings of the National Academy of Sciences Early Edition.
Stone R. 2006. The end of Angkor. Science 311:1364-1368.
