Long drought cycles reshaped settlement choices in the Indus region. These climate stresses likely contributed to its slow collapse.
A series of severe droughts, each extending for more than 85 years, was likely a major contributor to the gradual decline of the Indus Valley Civilization, according to research published in Communications Earth & Environment.
These results offer new insight into why this influential ancient society — a contemporary of ancient Egypt located near the present-day India-Pakistan border — weakened over time and demonstrate how environmental pressures can shape the course of early civilizations.
Background on the Indus Valley Civilization
The Indus Valley Civilization (IVC) was among the world’s earliest urban cultures, flourishing between 5,000 and 3,500 years ago along the Indus River system in what is now Pakistan and northwest India. At its height, between 4,500 and 3,900 years ago, the society featured well-planned cities and advanced water management. Despite this sophistication, the factors behind the civilization’s slow decline have remained uncertain.
Vimal Mishra and his team reconstructed climate patterns across the IVC region from 5,000 to 3,000 years ago. Their analysis combined climate simulations with evidence from several indirect records of past environmental conditions, including the geochemical signatures of stalactites and stalagmites in two Indian caves and water level data from five lakes in northwest India.
Their findings point to a regional temperature rise of about 0.5 degrees Celsius and a drop in annual rainfall of between 10% and 20%. They also identified four extended droughts occurring between 4,450 and 3,400 years ago, each lasting more than 85 years and affecting between 65% and 91% of the region occupied by the IVC.
Settlement shifts linked to prolonged water shortages
The authors suggest that these droughts influenced settlement location choice in the IVC. Between 5,000 and 4,500 years ago, they report that settlements were concentrated in areas with more rainfall. However, from 4,500 years ago onwards, settlements shifted closer to the Indus River, probably as the droughts started to affect water availability. The final 113-year-long drought that they identify, between 3,531 and 3,418 years ago, coincides with archaeological evidence of major deurbanization in the IVC. The authors conclude that the IVC likely did not collapse suddenly as a result of any one climate event, but instead declined slowly, with the prolonged droughts a major contributory factor.
Reference: “River drought forcing of the Harappan metamorphosis” by Hiren Solanki, Vikrant Jain, Kaustubh Thirumalai, Balaji Rajagopalan and Vimal Mishra, 27 November 2025, Communications Earth & Environment.
DOI: 10.1038/s43247-025-02901-1
The work was primarily supported by the funding from the Department of Science and Technology, Government of India. K.T. acknowledges support from NSF P2C2 Award 2103077.
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