Social change in late Holocene mainland SE Asia: A response to gradual climate change or a critical climatic event?

The prehistoric archaeology of the Mun River floodplain, northeast Thailand, provides evidence for a long, rich settlement in a now marginal and resource-poor landscape. The valley was settled for over two millennia during the Neolithic, Bronze and Iron Ages. Large settlements with encircling channels, conventionally regarded as defensive sites, are now considered to represent effective water management systems. The environment is currently seasonally arid, saline, sparsely populated and resource-poor. However, from the 4th to 2nd millennia before present, the region supported large communities, apparently in relative comfort. The geoarchaeological study of these sites and their landscape seeks reasons for this difference, and identifies past hydrological and climatic conditions as critical controls on social potential. The demise of this successful society may be explained by a collapse of what must have been a rich supporting environmental system; this in turn was probably driven by several possible environmental processes. While a regionally-significant climatic shift may have provided a critical threshold change around 1400 BP, it seems more likely that the Iron Age society had adapted gradually to long-term environmental (climatic) change, until the engineering solutions to declining water supply and supply reliability that maintained social sustainability were unable to moderate the effects of environmental change.