The Indus Valley Civilisation, one of the world’s earliest urban societies, flourished across northwest India and Pakistan with advanced city planning, brick houses, drainage systems and even early flush toilets. For decades, historians believed its mysterious decline was caused by a sudden disaster such as invasion, disease or a major flood.

However, a new international study published in Communications Earth & Environment has revealed a different reality. Using paleoclimate data and advanced computer models, researchers analysed environmental changes between 3000 and 1000 BCE. Their findings show that the civilisation did not fall overnight. Instead, it suffered from centuries-long droughts that slowly dried rivers, weakened agriculture, and degraded soil quality. Harappa-one of the key urban centres-saw gradual depopulation as water sources shrank.

This prolonged climate change forced communities to migrate, reduce urban activity, and eventually abandon major cities. The research marks a major breakthrough, proving that environmental stress, not a single catastrophe, led to the fall of the Indus Valley Civilisation.