New investigations reveal that prolonged and severe arid conditions, each extending beyond 85 years, impacted the Indus river basin approximately 4,400 to 3,400 years ago. These findings could illuminate the gradual disintegration of this ancient civilization and underscore the profound influence of environmental shifts on the development of past societies.
An artist’s reconstruction of the gateway and drain at the ancient city of Harappa. Image credit: Chris Sloan.
Emerging as one of history’s earliest urban cultures, the Indus Valley Civilization flourished between 5,000 and 3,500 years ago, its expanse centered around the Indus River and its contributing waterways in what is now Pakistan and northwestern India.
At its zenith, coinciding with the period between 4,500 and 3,900 years ago, its society was distinguished by well-developed metropolises and sophisticated water management infrastructure.
Nevertheless, the precise factors contributing to the civilization’s extended decline following this developmental peak remain an area of ongoing scholarly inquiry.
“The Indus River served as the linchpin for the evolution of the ancient Indus Valley Civilization, furnishing a dependable supply of water crucial for sustenance, commerce, and transit,” stated Dr. Vimal Mishra of the Indian Institute of Technology Gandhinagar and his research associates.
“This civilization thrived in the vicinity of the Indus River and its tributaries approximately five millennia ago, undergoing continuous transformation over time.”
“During the advanced Harappan era (spanning 4,500 to 3,900 years ago), the Indus Valley Civilization was characterized by meticulously planned urban centers, advanced hydrological systems, and an intricate script.”
“Subsequently, after 3,900 years ago, the Harappan Civilization embarked on a trajectory of decline, ultimately leading to its dissolution.”
“The drivers of this societal regression are still subject to considerable debate. Proposed hypotheses encompass climatic fluctuations, receding coastlines, arid spells, significant inundation, and alterations in riverine patterns, all potentially interacting with concurrent sociopolitical transformations.”
“Gaining a comprehensive understanding of historical hydroclimatic phenomena and their ramifications for ancient societies offers invaluable perspectives on the susceptibility of intricate civilizations to environmental pressures.”
For the purposes of this investigation, the research team generated climate simulations for the Indus Valley region covering the period from 5,000 to 3,000 years ago.
These simulated outcomes were then integrated with data derived from multiple proxy indicators of past climatic conditions. These included geochemical analyses of stalactites and stalagmites recovered from two cave systems in India, alongside historical records of water levels from five distinct lakes in northwestern India.
Through this integrated approach, the researchers identified a moderate temperature escalation of approximately 0.5 degrees Celsius during the study period, accompanied by a reduction in average annual precipitation across the region ranging from 10% to 20%.
Furthermore, the study successfully delineated four prolonged periods of drought between 4,450 and 3,400 years ago. Each of these arid phases persisted for over 85 years and exerted an influence over a significant portion of the Indus Valley, affecting between 65% and 91% of the region.
“These extended periods of aridity demonstrably influenced the geographical choices for settlement within the Indus Valley Civilization,” the investigators reported.
“From 5,000 to 4,500 years ago, human settlements were predominantly situated in areas that received more substantial rainfall.”
“However, commencing around 4,500 years ago, there was a discernible migration of settlements towards the Indus River, likely in response to the diminishing water availability caused by the onset of these droughts.”
“The final drought identified by the researchers, which lasted for 113 years and occurred between 3,531 and 3,418 years ago, corresponds chronologically with substantial archaeological evidence pointing to a significant depopulation and abandonment of urban centers within the Indus Valley Civilization.”
“It is improbable that the Indus Valley Civilization experienced a sudden collapse triggered by a single climatic event; rather, its decline was likely a gradual process, with these protracted droughts serving as a significant contributing factor,” the researchers concluded.
Their research article was officially published on November 27 in the esteemed journal Communications Earth & Environment.
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H. Solanki et al. 2025. River drought forcing of the Harappan metamorphosis. Commun Earth Environ 6, 926; doi: 10.1038/s43247-025-02901-1
