A series of four prolonged droughts, each spanning 80 to 160 years within a period of about 1,000 years, severely impacted the Indus Valley (Harappan) Civilization and likely contributed to its eventual decline, according to new research published in Nature. The study, conducted by researchers from IIT Gandhinagar, the University of Arizona, and the University of Colorado Boulder, analysed paleoclimate data from 17 key Harappan sites. Using a Variable Infiltration Capacity (VIC) hydrological model, the team reconstructed ancient river flows by simulating climatic conditions from 4,000 to 5,000 years before present. This allowed them to identify shifts and anomalies in major river systems, including the Indus, offering fresh insight into the environmental stresses faced by the civilization.
The findings are presented in the research paper titled “River drought forcing of the Harappan metamorphosis.” The study was carried out by Hiren Solanki, Vikrant Jain, and Vimal Mishra of IIT Gandhinagar; Kaustubh Thirumalai of the University of Arizona, USA; and Balaji Rajagopalan of the University of Colorado Boulder, USA. It has been published in the latest issue of Communications Earth and Environment, a journal under the Nature portfolio.
Along with major Harappan sites such as Harappa, Mohenjo Daro, Kalibangan, Kot Diji, and Ganeriwala, the study also considered Gujarat-based sites such as Dholavira, Lothal, and Surkotada, among others, while understanding the climatic conditions and water availability. The researchers divided the periods of very low rainfall and water flow at major sites based on simulation into four droughts (D). The earliest one (D1) is recorded from 4445 to 4358 years BP, lasting about 88 years, followed by D2 from 4122 to 4021 BP for 101 years, D3 from 3826 to 3663 BP for 164 years, and the last D4 from 3531 to 3418 BP for 114 years. In all, in a span of about 1,027 years corresponding with the Late Harappan period, 467 years experienced droughts, according to researchers. The simulated climate data and calculations for river discharge in the IVC indicated reduced streamflow that is crucial for irrigation, drinking water, and floodplain agriculture, according to the study.
Archaeologists have noted that climate change played a major role in the decline of the Harappan civilization, as major towns such as Dholavira and Lothal were abandoned, giving way to smaller settlements. Extensive research and excavations in regions like Gujarat over the decades support this observation. Even today, sites such as Dholavira display large water reservoirs, highlighting the civilization’s reliance on water management. The present study indicates a long-term rise in temperatures and a reduction in rainfall. Experts analyzed speleothems—mineral deposits formed in caves by dripping water—in Uttarakhand and other locations to compare with simulated climate data.
Experts note that the Pre-Harappan period is marked by high rainfall and widespread freshwater, allowing settlements to thrive. During the Mature Harappan period, urbanization shifted towards the Indus River, and regions like Saurashtra and Upper Indus remained relatively stable despite droughts. In the Late Harappan period, prolonged droughts began to affect populations, prompting changes in agriculture—such as a shift to drought-tolerant millets—and migration towards areas that still had water.
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