Indus Valley Civilisation died a slow death - Scientists reveal what really led to its fall

The Indus Valley Civilisation flourished in the northwestern regions of South Asia, comprising portions of India and Pakistan, 3,500 to 5,000 years ago. Harappa and Mohenjo-Daro were its main cities, and it was known for its advanced urban planning, the street layouts and drainage system. However, it declined suddenly, and archaeologists have never been able to conclusively find the reason. A new study, published Thursday (November 27) in the journal Communications Earth & Environment, states that decades-long droughts likely spelt doom for the Indus Valley Civilisation. "Successive major droughts, each lasting longer than 85 years, were likely a key factor in the eventual fall of the Indus Valley Civilisation," the team stated.

As the water started drying up, the population shifted to regions where water sources were still present and accessible. This led to a gradual decline in the number of people who inhabited the Indus Valley, ultimately leading to its demise. The researchers point to one particular drought that extended for 100 years, 3,500 years ago, coinciding with "widespread deurbanization and cultural abandonment of major [cities]."

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Global simulations show rivers dried up, rainfall patterns changed

The researchers relied on three different global climate simulations to understand how the climate has changed over thousands of years. They analysed how rainfall and temperature witnessed shifts between 3,500 and 5,000 years ago. They also determined how rivers, streams and other bodies of water in the region changed over time, and that settlements consistently moved to stay close to water sources. Surprisingly, they found droughts slammed the region in all three simulations.

"The consistent decline in rainfall from 5000 to 3000 years ago in all three simulations shows that multi-century droughts, monsoon weakening, or winter rainfall shifts are real, persistent signals and not artefacts of a single model," Hiren Solanki, a doctoral student at the Indian Institute of Technology at Gandhinagar, and lead author of the study, said. To be fully sure of their results, the team also looked at previous studies to gauge the growth speed of stalagmites and stalactites in caves, since less precipitation means slower growth. They also looked at sedimentary deposits in lakes. These studies matched their research and strengthened the new research on the fall of the Indus Valley Civilisation.