New research suggests that the once mighty and ancient Indus Valley civilization may have ended due to climate change, which caused mass migration as a direct result. This civilization was based around the Indus River Valley around the areas of modern-day northwestern India and Pakistan and contained large metropolitan areas and cities and even the first sewer systems which were invented long before those of ancient Rome.
During its heyday, the civilization of the Indus Valley were firm trading partners with different areas of Mesopotamia, but by 1800 BC this had suddenly stopped, with most of the residents of this ancient culture leaving their cities in droves and choosing instead to migrate to the Himalayan foothills, as Phys.org reports.
Now a new study conducted by the Woods Hole Oceanographic Institution (WHOI) has determined that climate change was the likely culprit behind the mass exodus of the Harappans from their Indus Valley homes. Starting around 2,500 BC, temperatures in the Indus Valley began to change which caused the region to dry up substantially, greatly lessening summer monsoons.
As geologist lead author Liviu Giosan noted, this loss of rain would have made agriculture next to impossible and would have led to the migration away from the Indus River Valley.
“Although fickle summer monsoons made agriculture difficult along the Indus, up in the foothills, moisture and rain would come more regularly. As winter storms from the Mediterranean hit the Himalayas, they created rain on the Pakistan side, and fed little streams there. Compared to the floods from monsoons that the Harappans were used to seeing in the Indus, it would have been relatively little water, but at least it would have been reliable.”
— Phys.org (@physorg_com) November 13, 2018
While discovering direct evidence of this climate change in the Indus Valley through soil samples proved impossible, Giosan and his researchers instead analyzed ocean floor sediments that were found around the coast of Pakistan. After extracting several of these samples from the Arabian Sea and studying the shells of foraminifera, researchers were able to learn which types of plankton did best in both summer and winter. After this, they delved into the paleo-DNA that was hidden within these samples, as Giosan explained.
“The seafloor near the mouth of the Indus is a very low-oxygen environment, so whatever grows and dies in the water is very well preserved in the sediment. You can basically get fragments of DNA of nearly anything that’s lived there.”
After Giosan’s team has completed their DNA analysis, it was determined that during this transitional period of climate change in the Indus River Valley, monsoons during the winter became much more fierce, while those in the summer lessened greatly, which was found to correspond to the time that the Indus Valley civilization would have begun departing from their homes.
“We don’t know whether Harappan caravans moved toward the foothills in a matter of months or this massive migration took place over centuries. What we do know is that when it concluded, their urban way of life ended. We can’t say that they disappeared entirely due to climate—at the same time, the Indo-Aryan culture was arriving in the region with Iron Age tools and horses and carts. But it’s very likely that the winter monsoon played a role.”
As Giosan also noted, “It’s remarkable, and there’s a powerful lesson for today. If you look at Syria and Africa, the migration out of those areas has some roots in climate change. This is just the beginning—sea level rise due to climate change can lead to huge migrations from low lying regions like Bangladesh, or from hurricane-prone regions in the southern U.S. Back then, the Harappans could cope with change by moving, but today, you’ll run into all sorts of borders. Political and social convulsions can then follow.”
The study which suggests that climate changed played a major role in the demise of the Indus Valley civilization has been published in Climate of the Past.