Scientists have identified prolonged droughts as a key factor in the decline of the ancient Indus Valley Civilization, shedding light on one of archaeology’s greatest mysteries.
At its zenith, the ancient Indus Valley Civilization was one of the most advanced societies in the world. Its cities were characterized by meticulously planned grid layouts, multi-storey brick homes, sophisticated drainage systems complete with flushing toilets, and bustling marketplaces. The inhabitants cultivated crops such as wheat, barley, and cotton, engaged in trade involving gold and precious stones, and created intricate figurines and toys. The civilization thrived on the water supplied by rivers, which fueled both agriculture and commerce across what is now Pakistan and northwest India.
Despite its remarkable achievements, this advanced civilization experienced a quiet decline, leaving behind no evidence of warfare, invasions, or political upheaval. For decades, the reasons behind the disappearance of major urban centers, including Harappa, have puzzled archaeologists and historians alike.
Recent research may finally provide answers. An international study published on November 27, 2025, in the journal Communications Earth & Environment, suggests that a series of prolonged and intensifying droughts played a pivotal role in the civilization’s decline. By utilizing paleoclimate data and advanced computer modeling, researchers reconstructed climate conditions from 3000 to 1000 B.C. and uncovered compelling evidence of repeated long-term water shortages.
Lead author Hiren Solanki from the Indian Institute of Technology Gandhinagar explained that the collapse of the Indus Valley Civilization was not the result of a single catastrophic event. Instead, it was the cumulative effect of four major droughts, each lasting more than 85 years, that gradually eroded the society over centuries.
One of the most severe droughts peaked around 1733 B.C. and persisted for approximately 164 years. This drought reduced annual rainfall by about 13% and affected nearly the entire region. Overall, researchers observed a temperature increase of about 0.5°C, accompanied by a decline in rainfall of between 10% and 20%.
Co-author Balaji Rajagopalan from the University of Colorado Boulder noted that while drought alone would not have led to the civilization’s downfall, it exacerbated existing vulnerabilities. The combination of food shortages, weakened governance, and diminishing trade routes due to repeated water stress ultimately drove the population toward dispersal.
Hydrological modeling revealed significant changes in the landscape: lakes and shallow water bodies shrank, river flows diminished, and soils dried out. These changes severely disrupted agriculture and long-distance trade, both of which relied heavily on river transport. As waterways became less navigable, commercial networks began to collapse.
Despite these challenges, the Harappans demonstrated remarkable resilience. They adapted by altering their agricultural practices, diversifying trade, and relocating settlements closer to more reliable water sources. Over nearly 2,000 years, communities gradually migrated from tributary areas to locations nearer the Indus River itself.
The researchers traced these climatic shifts back to changes in the tropical Pacific Ocean. During the early stages of the civilization’s rise, strong monsoon activity—likely linked to La Niña-like conditions—brought abundant rainfall. However, as ocean temperatures warmed in subsequent centuries, monsoon patterns weakened, leading to prolonged drought conditions.
Geoscientist Liviu Giosan from the Woods Hole Oceanographic Institution, who was not involved in the study, described the research as a significant breakthrough. By integrating cave mineral data, lake records, and climate simulations, the team has provided the most comprehensive understanding to date of how water shortages influenced the fate of the Indus Valley Civilization.
The findings also serve as a cautionary tale for contemporary society. Parts of India and Pakistan are currently experiencing rising temperatures and shifting rainfall patterns. Researchers warn that prolonged climate stress can gradually destabilize even the most advanced societies if long-term water resilience is not effectively planned.
Source: Original article