Researchers found that these extended droughts began approximately 4,200 years ago and continued for over two centuries.
Groundbreaking research led by Cambridge University has brought to light the existence of a series of severe and prolonged droughts, preserved within an ancient stalagmite in the Himalayas, that likely played a critical role in reshaping the Bronze Age Indus Civilization.
The Start of a Dry Spell and the Indus Civilization’s Shift
Researchers found that these extended droughts began approximately 4,200 years ago and continued for over two centuries. This period of aridity aligns with the reorganization of the urban Indus Civilization, which spanned present-day Pakistan and India. The investigation identified three significant droughts during this time frame, each lasting between 25 and 90 years. Prof. Cameron Petrie, a study co-author from Cambridge’s Department of Archaeology, highlighted the progressive transformation of Indus inhabitants’ environmental conditions.
Decoding Rainfall History Through Stalagmite Analysis
To chart historical rainfall patterns, the research team analyzed the growth layers within a stalagmite collected from a cave near Pithoragarh, India. By measuring a range of environmental tracers, they generated a reconstruction of relative rainfall at seasonal resolution. Additionally, high-precision Uranium-series dating was utilized to determine the age and duration of these droughts. Lead author Alena Giesche and the team found evidence of below-average rainfall during both summer and winter seasons, which Prof. Petrie believes is crucial for understanding the impact of climate change on human populations.
New Insights into Drought Duration and Seasonality
These findings bolster existing evidence connecting the decline of Indus megacities to climate change. However, until now, information on the droughts’ duration and seasonality remained a mystery. The additional details offer valuable insight into cultural memory and how people adapted in response to environmental change, according to Giesche.
Indus Megacities: Adapting to a Changing Environment
During the 200-year period of environmental transformation, ancient inhabitants adjusted to the new conditions by depopulating larger urban sites in favor of smaller rural settlements. Concurrently, they shifted agricultural practices towards drought-tolerant summer crops and transitioned to a more self-reliant lifestyle. Prof. David Hodell, a study co-author from Cambridge’s Department of Earth Sciences, pointed out that the improving quality of paleoclimate records allows for more accurate comparisons of climatic and archaeological data.
Looking Ahead: Expanding Climate Reconstructions
The research team plans to expand their climate reconstructions to the western parts of the Indus River Region, where winter rainfall takes on greater importance compared to the Indian Summer Monsoon. However, political instability in Afghanistan and Pakistan could present obstacles for further research in the near future.
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