A new study in Communications Earth & Environment says that a series of long and severe droughts likely played a major role in the slow disappearance of the Indus Valley Civilisation, one of the world’s earliest urban cultures.
Researchers—including Vimal Mishra of IIT Gandhinagar—studied 2,000 years of rainfall and river-flow patterns across the Indus region. They used climate data from natural sources, along with computer models, to understand how the monsoons took place in the past.
They found four major droughts between about 4,445 and 3,418 years ago. Each drought lasted more than 85 years. One lasted around 164 years and reduced annual rainfall by roughly 13 per cent, affecting most of the civilisation’s core area.
The study also shows a long-term weakening of the monsoon between 5,000 and 3,000 years ago. River flow reduced, and temperatures rose by about half a degree Celsius. According to the authors, these changes damaged the water systems that supported big Indus cities such as Harappa, Mohenjo Daro and Dholavira.
Archaeological findings from these sites also show that people slowly began to move away as water became scarce. Researchers say this was not a sudden collapse, but rather large cities gradually breaking into smaller rural settlements as communities adjusted to worsening drought.
The study notes that climate alone did not decide the civilisation’s fate—social and economic changes also influenced how people responded. Still, the results strengthen the view that repeated droughts reduced agricultural output, weakened trade networks, and made it harder for cities to survive.
This research adds new evidence to a long-running debate about why the Indus Valley Civilisation faded after centuries of stability. By measuring how severe and long these droughts were, the study also provides a clearer picture of how environmental change can reshape complex societies.
The authors also say the findings carry a warning for today.
River basins in South Asia are already facing more climate stress, and long-term drops in rainfall and water flow could create similar pressures for modern populations.