At its height, the ancient Indus Valley Civilization stood among the world’s most sophisticated early societies. Its cities featured well-planned grid layouts, multi-storey brick homes, advanced drainage systems with flushing toilets, and thriving marketplaces. The people cultivated wheat, barley, and cotton, traded gold and precious stones, and produced intricate figurines and toys. Water from rivers powered agriculture and commerce across the region, now part of present-day Pakistan and northwest India.
Yet despite its remarkable achievements, this advanced civilization faded away quietly — without evidence of war, invasions, or political collapse. For decades, the disappearance of its major urban centers, including Harappa, has remained one of archaeology’s greatest mysteries.
Now, scientists believe they may finally have the answer.
A new international study published on November 27, 2025, in Communications Earth & Environment suggests that a series of prolonged and intensifying droughts played the central role in the civilization’s decline. Using paleoclimate data and advanced computer models, researchers reconstructed climate conditions between 3000 and 1000 B.C. and uncovered clear evidence of repeated long-term water shortages.
Lead author Hiren Solanki of the Indian Institute of Technology Gandhinagar explained that the collapse was not caused by a single disaster. Instead, four major droughts, each lasting more than 85 years, gradually weakened the society over centuries.
One of the most severe droughts peaked around 1733 B.C., persisted for roughly 164 years, reduced annual rainfall by about 13%, and impacted nearly the entire region. Overall, researchers found temperatures rose by about 0.5°C while rainfall declined between 10% and 20%.
Co-author Balaji Rajagopalan of the University of Colorado Boulder said drought alone would not have destroyed the civilization. However, when combined with food shortages, weakened governance, and shrinking trade routes, repeated water stress slowly pushed the population toward dispersal.
Hydrological modeling revealed that lakes and shallow water bodies shrank, river flows dropped, and soils dried out. This severely disrupted agriculture and long-distance trade, both of which depended heavily on river transport. With waterways no longer reliably navigable, commercial networks began to fail.
Despite these pressures, the Harappans showed remarkable resilience. They adapted by shifting crops, diversifying trade, and relocating settlements closer to more dependable water sources. Over nearly 2,000 years, communities gradually migrated from tributary areas to locations nearer the Indus River itself.
The researchers traced these climate shifts to changes in the tropical Pacific Ocean. Early in the civilization’s rise, strong monsoon activity — likely linked to La Niña-like conditions — brought abundant rainfall. As ocean temperatures warmed in later centuries, monsoons weakened and prolonged drought set in.
Geoscientist Liviu Giosan of the Woods Hole Oceanographic Institution, who was not involved in the study, called the research a major breakthrough. By combining cave mineral data, lake records, and climate simulations, the team provided the most comprehensive picture yet of how water shortages shaped the fate of the civilization.
The findings also carry an important warning for today’s world. Parts of India and Pakistan are once again experiencing rising temperatures and shifting rainfall patterns. Researchers caution that prolonged climate stress can gradually destabilize even the most advanced societies if long-term water resilience is not planned.
