River drought forcing of the Harappan metamorphosis

Hydroclimatic variations are among the factors shaping the rise and fall of the Indus Valley Civilization. Yet, constraining the role of water availability across this vast region has remained challenging owing to the scarcity of site-specific paleoclimate records. By integrating high-resolution paleoclimate archives with palaeohydrological reconstructions from transient climate simulations, we identify the likelihood of severe and persistent river droughts, lasting from decades to centuries, that affected the Indus basin between ~4400 and 3400 years before present. Basin-scale streamflow anomalies further indicate that protracted river drought coincided with regional rainfall deficits, together reducing freshwater availability. We contend that reduced water availability, accompanied by substantially drier conditions, may have led to population dispersal from major Harappan centers, while acknowledging that societal transformation was shaped by a complex interplay of climatic, social, and economic pressures.