Severe droughts revealed as possible cause of Indus Civilization collapse

Environmental tracers found in ancient stalagmite show a series of prolonged droughts may have changed the way of life for ancient civilization
Abdul-Rahman Oladimeji Bello
Mohenjo-daro, Sindh province, Pakistan.
Indus remains: Mohenjo-daro archaeological site in Sindh province, Pakistan.

CameraCoy / iStock  

Scientists have discovered evidence of a series of severe droughts, locked within an ancient stalagmite from a Himalayan cave, that may have led to the reorganization of the once-flourishing civilization.

The Bronze Age Indus Civilization flourished in present-day Pakistan and India between 3300 BCE and 1300 BCE and is considered one of the three earliest civilizations of the Near East and South Asia, alongside Egypt and Mesopotamia.

The Indus Civilization was known for its impressive cities. However, despite its many achievements, the Indus Civilization eventually declined and collapsed. For a long time, the cause of its downfall remained a mystery, but new research involving Cambridge University sheds light on a possible reason: prolonged droughts.

The study uncovered three prolonged droughts, each lasting between 25 and 90 years, during this arid period. "We find clear evidence that this interval was not a short-term crisis but a progressive transformation of the environmental conditions in which Indus people lived," explained Prof. Cameron Petrie, study co-author from Cambridge's Department of Archaeology.

By analyzing growth layers in the stalagmite and measuring various environmental tracers, the researchers were able to reconstruct historical rainfall patterns.

Severe droughts revealed as possible cause of Indus Civilization collapse
A section of the Dharamjali stalagmite.

"The evidence for drought affecting both cropping seasons is extremely significant for understanding the impact of this period of climate change upon human populations," said Petrie, adding that the third drought would have spanned multiple generations.

This discovery supports existing theories that the decline of the Indus megacities was due to climate change. "But what's been a mystery until now is information on the drought duration and the season they happened in," said lead author Alena Giesche. "That extra detail is really important when we consider cultural memory and how people make adaptations when faced with environmental change."

How the change affected inhabitants

Over a 200-year period, the ancient inhabitants adapted to the changing environment by depopulating larger urban sites and shifting agriculture towards drought-tolerant crops. "Palaeoclimate records are becoming progressively better at refining changes in rainfall on a seasonal and annual basis, which directly affects people's decision making," said study co-author David Hodell from Cambridge's Department. 

However, there is still a huge blind spot in our maps extending across Afghanistan and Pakistan, where the Indian summer monsoon and the Westerlies interact. Unfortunately, the political situation is unlikely to allow for this kind of research in the near future. 

Still, it is exciting to understand the prospects of the research. This groundbreaking study is part of the TwoRains Project, a collaboration between Cambridge and Banaras Hindu University. It was also funded by the European Research Council (ERC). The project findings emphasize the importance of continued research by both paleoclimatologists and archaeologists.

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