A landmark paleoclimate study published in the journal Nature has reframed our understanding of the decline of the Indus Valley Civilisation (IVC), one of the world's earliest and largest urban civilisations. The research identifies not a single catastrophic drought but a series of "centuries-long recurring mega-droughts" as the primary driver of IVC's gradual collapse.

Key findings: The study identifies four major drought episodes between approximately 2425 BCE and 1400 BCE — spanning over a millennium. These mega-droughts were caused by warming of the tropical Pacific Ocean (similar to an extended El Niño-like pattern), which disrupted atmospheric circulation and weakened the Indian Summer Monsoon (ISM). Reduced monsoon rainfall over the IVC's agricultural heartland — stretching from modern Pakistan through northwestern India — progressively undermined the civilisation's food production and urban water management systems.

The IVC, which flourished approximately 2600–1900 BCE, encompassed over 1,500 known sites across present-day Pakistan, India, and Afghanistan. Major cities included Mohenjo-daro, Harappa, Dholavira (Gujarat, a UNESCO World Heritage Site), and critically for Rajasthan — Kalibangan.

Kalibangan (in Hanumangarh district, Rajasthan) is one of the most archaeologically significant IVC sites in India. It has yielded evidence of the world's earliest ploughed field, fire altars, and sophisticated urban planning. The new research suggests that Kalibangan and similar Rajasthan IVC settlements would have been among the first to feel the impact of weakening monsoons given their position on the eastern/desert fringe of the civilisation.

This research has significant implications for climate science: it demonstrates that even ancient pre-industrial warming of the Pacific can trigger civilisation-scale collapse through monsoon disruption — a warning relevant to modern anthropogenic climate change.