Climate Change Responsible For Indus Decline

Brett Smith for

New research has shed a light on an ancient Asian civilization and given a glimpse into what the future might hold for the region.

Climate change is now thought to be responsible for the decline of the Indus civilization, an empire that stretched over more than a million square kilometers. One of the first great urban cultures that also included Egypt and Mesopotamia, its people lived primarily along rivers from the Arabian Sea to the Ganges, over what is now Pakistan, northwest India and eastern Afghanistan.

The study, published this week in the Proceedings of the National Academy of Sciences, involved geologists and archeologists from the U.S., U.K., Pakistan, India, and Romania. Using topographic data and satellite photos, the researchers created and analyzed digital maps of landforms constructed by the Indus and neighboring rivers, which were then surveyed in the field by drilling, coring, and even manually-dug trenches. The samples that researchers collected from 2003 to 2008 were used to determine the sediments’ makeup, age and origins; whether brought in and shaped by rivers or wind.

“We reconstructed the dynamic landscape of the plain where the Indus civilization developed 5200 years ago, built its cities, and slowly disintegrated between 3900 and 3000 years ago,” said Liviu Giosan, a geologist with Woods Hole Oceanographic Institution and lead author of the study. “Until now, speculations abounded about the links between this mysterious ancient culture and its life-giving mighty rivers.”

Archeological evidence shows that the Harappans, who were named after one of their largest cities, had developed a highly complex society that included a sophisticated urban culture, intricate trade trades, and a currently-undeciphered writing system.

“They had cities ordered into grids, with exquisite plumbing, which was not encountered again until the Romans,” Giosan told LiveScience. “They seem to have been a more democratic society than Mesopotamia and Egypt – no large structures were built for important personalities like kings or pharaohs.”

Giosan and his team found that at one point, the monsoon-drenched rivers were prone to devastating floods. Over time, these monsoons weakened, enabling agriculture and civilization to flourish along riverbanks for nearly 2,000 years. River settlers slowly became dependant on seasonal river floods to fuel their agricultural surpluses.

However, over time, these monsoon-based rivers, which held too little water, dried up, making them unfavorable for civilization. Eventually, over the course of centuries, Harappans fled along an escape route to the east toward the Ganges basin, where monsoon rains remained reliable, the study suggested.

“The Harappans were an enterprising people taking advantage of a window of opportunity – a kind of “Goldilocks civilization,” Giosan said.

This climate change-based evidence not only provide a window into the ancient past, it gives an indication of what current weather patterns might mean for this swath of Asia.

“If we take the devastating floods that caused the largest humanitarian disaster in Pakistan’s history as a sign of increased monsoon activity, than this doesn’t bode well for the region,” Giosan told LiveScience. “The region has the largest irrigation scheme in the world, and all those dams and channels would become obsolete in the face of the large floods an increased monsoon would bring.”