New reasons found for collapse of Indus Valley civilisation

New reasons found for collapse of Indus Valley civilisation

While previous research blamed a series of sudden but severe droughts behind the fall of one of the world's first modern civilisations, a new study by Indian, Chinese and US scientists unearthed fresh evidences on continued decline in monsoon rainfall for nearly 500 years, forcing the Indus Valley citizens to move eastwards in search of greener pastures.

"Our crude estimate is the decline in rainfall could be anywhere between 25-30%. This is significant considering the fact that even a 10% decline in monsoon rainfall can trigger a drought in India now," Ashish Sinha, one of the team members and a scientist at the California State University told DH. There are two schools of thought on the disappearance of the Indus Valley civilisation from an area encompassing Pakistan and north-west India.

Some of the previous research put the blame on a singular event a sudden and severe drought that lasted for any time between 20 and 100 years. Many other scholars, on the other hand, argue in favour of a gradual decline of monsoon rainfall, as found by the new study.

The new research stands out in comparison to many its predecessors in terms of data quality. Nearly accurate monsoon data for the previous 5,700 years help scientists reconstruct an accurate chronology of the rise and fall of the Indus Valley civilisation.

"The error margin is just 10-15 years unlike the previous studies where the margin of error was in hundreds of years," said the first author of the study, Gayatri Kathayat, from the Xi'an Jiaotong University in China.

The study appeared in the December 13 issue of the journal Science Advance.

The samples, an isotope of oxygen, were collected from the stalagmites inside Sahiya cave, located 120 km from Dehradun. They represent the rain records for the past 6,000 years.

The detailed record disclosed a trend in drier conditions that began nearly 4,100 years ago, but spanned multiple centuries (between 3850 and 3300 years BC) and perhaps contributed to the de-urbanisation of Indus Valley civilisation, they say.

The singular event around 4200 years ago had impacted the Old Kingdom of Egypt and the Akkadian empire in Mesopotamia more.

The impact of weather events was not limited to the old world civilisations.

The same records also suggest the Guge Kingdom in western Tibet collapsed around 1620 AD following two decades of dramatic downturns in Indian monsoon and Northern Hemisphere temperature.

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