Climate change key to collapse of ancient Indus civilization

Climate change was a key ingredient in the collapse of the ancient Harappan civilization almost 4,000 years ago, a new study suggests.

The Harrapans once occupied morethan one million square kilometres of the plains of theIndus River in what is now a vast desert region that includes parts of Pakistan, northwest India and eastern Afghanistan.

Thecivilization extendedfrom the Arabian Sea to the Ganges River and was the largest of the early urbansocieties along with those of Egypt and Mesopotamia.

An international, interdisciplinary team of geologists, archeologists, mathematicians and geomorphologists collected samples from the area once occupied by the little-known civilization over a period of five years andreconstructed the landscape and topography of the area.

"Once we had this new information on the geological history, we could re-examine what we know about settlements, what crops people were planting and when, and how both agriculture and settlement patterns changed," co-author Dorian Fuller, an archaeologist with University College London, said in anews release.

The researchers' analysis suggested that climate change that weakened monsoon rains and tamed the tributaries of the Indus Riverand reduced run-off from the Himalayan mountains enabled the Harappans to practice agriculture on the river banks.

But when monsoon rains began to decline, the rivers and regular flooding the civilization relied on tomaintain a strong agriculture dried up, and they were forced to move east toward the Ganges River basin and were no longer able to sustain large cities.

The findingswere published last month in the journalProceedings of the National Academy of Sciences.

Listento the lead author of the study, geologist Liviu Giosan of the Woods Hole Oceanographic Institution, discuss theresearch withBob McDonald of CBC'sQuirks & Quarks.