One of the greatest mysteries of India is how and why the flourishing Indus Valley Civilisation disappeared. Now, researchers from IIT Gandhinagar propose that it was a series of extended droughts that forced the people of the region to abandon the urban cities of Harappa, Mohenjo-Daro, Rakhigarhi and Lothal.
The Indus Valley Civilisation (IVC), also called the Sindhu-Saraswati civilisation, flourished between 5,000 and 3,500 years ago in what is now northwest India and Pakistan, and was one of the world's earliest urban societies. So advanced that cities had drainage systems and the metal craft so advanced that beauties like the 'Dancing Girl' were crafted 5,000 years ago.
Renowned for its advanced cities, water management, and trade networks, the IVC's decline has long puzzled archaeologists and historians. Recent research led by Vimal Mishra of IIT Gandhinagar and colleagues provides compelling evidence that successive, severe droughts played a central role in the civilisation's gradual disappearance. An eleven-page research paper in the journal 'Communications Earth and Environment' suggests it was water scarcity that killed the flourishing civilisation.
Climate Change and Water Scarcity
The Indus River was the lifeblood of the civilisation, supporting agriculture, trade, and daily life. However, historical climate records, called paleoclimate records and climate simulations, reveal that the region experienced significant hydro-climatic variability, driven by changes in both the Indian summer and winter monsoons. Using high-resolution climate models and geological proxies (such as cave stalactites and lake sediments), researchers reconstructed rainfall and river flow patterns over thousands of years.
Their findings show a persistent drying trend, with average annual rainfall decreasing by 10-20 per cent and temperatures rising by about 0.5 degrees Celsius during the civilisation's lifespan. Four major droughts, each lasting more than 85 years, were identified between 4,450 and 3,400 years ago. The most severe drought lasted 164 years and affected over 91 per cent of the Indus Valley Civilisation region. These droughts were not isolated events but part of a broader pattern of declining water availability.
Impact on Settlements and Agriculture
Initially, IVC settlements were concentrated in areas with abundant rainfall. As droughts became more frequent and intense, communities shifted closer to the Indus River, seeking reliable water sources. Hydrological simulations show that river flow anomalies coincided with these droughts, leading to water scarcity even along the riverbanks. Evidence of plant remains, called archaeo-botanical evidence, suggests that farmers adapted by switching from wheat and barley to drought-tolerant millets, but these measures could not fully offset the impact of prolonged aridity.
Lake level records and cave data corroborate the climate models, showing declines in water bodies and rainfall during key drought periods. The final, century-long drought (3,531-3,418 years ago) matches archaeological evidence of widespread de-urbanization-large cities were abandoned, and populations dispersed into smaller, rural communities.
The Role of Global Climate Drivers
The current research highlights how global climate phenomena, such as El Nino events and cooling in the North Atlantic, contributed to the weakening of the Indian monsoon. Warmer Pacific and Indian Ocean temperatures reduced the land-sea thermal gradient, suppressing monsoon rainfall. These changes were amplified by shifts in atmospheric circulation, further reducing moisture transport into South Asia.
A Slow Decline, Not a Sudden Collapse
Contrary to earlier theories of abrupt collapse, the evidence points to a slow, complex process of decline. The IVC's disappearance was shaped by a combination of climatic, social, and economic pressures. While prolonged droughts were a major factor, communities also adapted through migration, crop diversification, and trade. The civilisation fragmented into smaller units, marking a transformation rather than a complete disappearance.
Lessons for Today
The story of the Indus Valley Civilisation serves as a cautionary tale about the vulnerability of complex societies to environmental stress. It underscores the importance of water management and climate adaptation, lessons that remain relevant as modern societies face increasing risks from climate change and water scarcity. The saving grace for the current 21st-century Indian Monsoon is that paleo climate researchers feel as the globe warms up due to climate change, more rainfall will be added to the Indian monsoon.
