Global Warming and Drought: The Factors Behind the Indus Civilization’s Collapse

A changing climate and intense droughts significantly impacted the Indus Valley Civilization, a remarkable urban society that thrived approximately 4,000 years ago in present-day Pakistan and India.

This civilization established settlements along the Indus River and its tributaries, extending their reach beyond other prominent ancient cultures like those in Egypt and Mesopotamia. Known as the Harappan civilization, they constructed various cities, with Harappa being a notable hub housing around 35,000 residents.

While their writing system remains largely undeciphered, the Harappans excelled in water management, featuring extensive cisterns and a complex sewage system made of terracotta pipes and brick channels. Unfortunately, these advancements could not endure the prolonged hot and arid conditions over millennia.

“There were four significant droughts between the pre-Harappan and late Harappan periods,” says Vimal Mishra, a researcher at the Indian Institute of Technology Gandhinagar. “This led to ongoing migrations to regions with more reliable water sources.”

Prior studies indicated that a global drought 4,200 years ago weakened monsoon rains in the Indus Valley, contributing to the civilizations’ downfall. However, Mishra and his colleagues posit that the decline was a more gradual process.

Using three climate models, the researchers estimated rainfall patterns in the area, validating their conclusions with data from stalactites, stalagmites, and lake sediments.

The findings revealed that from 4,400 to 3,400 years ago, the Indus Valley Civilization experienced four prolonged droughts, each lasting at least 85 years, accompanied by a temperature increase of about 0.5°C.

Additional modeling suggested a drop in the Indus River’s water levels. It is believed that the Harappans honored the river and relied on its annual floods for irrigation of crops such as wheat and barley, congregating around waterways. Continued droughts ultimately forced them to abandon their cities and resettle in the foothills of the Himalayas and the Ganges plains.

Research indicates that warming and drying trends may have been initiated by natural climate cycles such as El Niño and the Atlantic Multidecadal Oscillation, along with feedback mechanisms including vegetation loss and dust pollution.

This study stands out for its innovative integration of modeling and proxy measurements; however, it advocates for future research to consider evapotranspiration (the transfer of water from land to the atmosphere), particularly significant in hot climates. According to Sebastian Breitenbach from Northumbria University, UK, the current pace of climate change outstrips that of the Harappans, necessitating that policymakers explore adaptive strategies, including improved water storage systems and groundwater conservation.

“These studies serve as a cautionary tale,” Breitenbach remarks, “providing insights into potential future scenarios.”

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