Decades‑Long Droughts Linked to Collapse of the Indus Valley (Harappan) Civilization

A new study finds that a sequence of severe, multi‑decade droughts played a major role in the decline of the Indus Valley (Harappan) civilization, one of the world's earliest urban societies.

The Indus Valley civilization flourished roughly between 5,000 and 3,500 years ago across territory that now spans the India–Pakistan border. Its people built planned cities such as Harappa and Mohenjo‑Daro, developed a still‑undeciphered script, maintained long‑distance trade with regions including Mesopotamia, and engineered advanced water‑management systems.

Researchers publishing in Communications Earth & Environment report that successive droughts — each lasting more than 85 years — and a particularly long dry spell of about a century beginning around 3,500 years ago coincided with widespread deurbanization and settlement abandonment across the region.

To reach these conclusions the team ran three publicly available global climate simulations covering the period from 5,000 to 3,000 years ago. All three models showed a consistent long‑term decline in rainfall in the Indus region, indicating persistent changes in the monsoon and winter precipitation patterns rather than artifacts of a single model.

'Successive major droughts, each lasting longer than 85 years, were likely a key factor in the eventual fall of the Indus Valley Civilization,' said Hiren Solanki, the study's lead author and a doctoral student at the Indian Institute of Technology Gandhinagar.

The researchers converted the climate outputs into hydrological reconstructions to estimate changes in river and stream flows over time. They compared these reconstructions with archaeological records and found that populations shifted toward remaining reliable water sources as conditions deteriorated, ultimately leading to the collapse of many urban centers.

To validate the model results, the team compared their simulations with independent paleoclimate proxies. Published records of cave stalagmite and stalactite growth — which slows during drier conditions — aligned with the timing of reduced precipitation implied by the models. Lake sediment records provided additional corroboration, strengthening the case that multi‑decadal droughts were a real regional signal.

Independent experts praised the study's approach. Nick Scroxton, a hydrology and paleoclimate researcher at University College Dublin, noted that modeling river flows is critical for understanding how changing rainfall could have driven shifts in urban settlement and agricultural practice. Liviu Giosan, a geoscientist at the Woods Hole Oceanographic Institution, called the team's modeling 'sophisticated' and said the results represent an important advance in understanding how hydroclimate influences the rise and fall of ancient societies.

Implications

The study highlights how long‑duration climate stress — not just sudden catastrophe — can undermine even well‑engineered societies by reducing water availability, shifting agricultural productivity and forcing population movements. While climate was likely not the only factor in the Indus decline, the evidence suggests prolonged drought was a decisive pressure that contributed to widespread societal reorganization.