Indus Valley in Leh, near Ladakh in India. Picture of KenniOMG / Vikipedia
Climate change was almost certainly one of the key factors that forced Harapans people to separate from the flood of the Indus River, a new study by Voodoo Hole Oceanographic Institution (VHOI) researchers said.
Civilization of the Indus Valley has been successful over 4,000 years ago on the plains of the Indus River in India and Pakistan.
It is believed that civilization has covered an area of more than one million square kilometers, from the Arab Sea to Ganga, over what is now Pakistan, northwestern India, and even to eastern Afghanistan. This splendid but not well-known urban culture included parts of Mesopotamia and Egypt.
Scope of civilization in the valley of Indus, 2600-1900. I would picture Sue McIntosh over Wikipedia
Harappa culture was named after Harappi – one of the largest cities of Indus civilization on the River Ravi. The inhabitants of this culture lived near the river and used fertile plains to realize their lives. However, this advanced culture slowly disappeared between 3,900 and 3,000 years ago.
The a new study by researchers at VHOI claims that they have found evidence that Harappan culture residents left their cities until 1800 before the new era and moved to smaller villages at the foot of the Himalayas.
The migration began about 2500 BC before the drastic changes in time patterns over the Indus Valley made agriculture more and more difficult throughout the region. With changes in the climate, the summer monsoon rains over the Indus valley gradually dried up. However, winter rains have become more regular at the foot, feeding small currents there.
Although winter rain at the base brought less water compared to the summer monsoon floods in the Indus valley, they were at least "reliable," says Liviu Giosan, a geologist at VHOI.
The team was hard to find evidence in soil samples to change seasonal precipitation. Instead, they analyzed samples of sediments collected from the bottom of the ocean at different locations in the Arabian Sea. They examined foraminifer shells (or "forams") – a single-cell plankton – in sediments to figure out who they had made in the winter and which during the summer.
After that, the researchers examined ancient genetic material (paleo-DNA) preserved in sediments. The analysis revealed that the end of the Harappa civilization was weakened by the summer of the monsoon, and the winter monsoon became stronger, forcing people to migrate from large cities to smaller villages.
However, the researchers are not sure if this migration happened quickly or it took hundreds of years to complete.
"We can not say that they have disappeared completely because of the climate – at the same time, the Indo-Ancient culture comes with the tools of iron age, horse and car, but it is very likely that the winter monsoon played a role," Giosan says.
The findings of the study were published in the journal Climate past.