According to a recent study, severe and long-lasting river droughts, lasting over 85 years each, impacted the Indus basin from 4,400 to 3,400 years ago. This finding may provide insights into the gradual decline of this ancient civilization and underscores how environmental factors can influence historical societies.
An artist’s reconstruction of the gates and drainage channels of the ancient city of Harappa. Image credit: Chris Sloan.
The Indus Valley Civilization, one of the earliest urban cultures, thrived between 5,000 and 3,500 years ago along the Indus River and its tributaries in present-day Pakistan and northwestern India.
During its zenith, around 4,500 to 3,900 years ago, the civilization was noted for its advanced urban centers and sophisticated systems for managing water resources.
Despite this, the reasons behind the protracted decline following its peak remain largely elusive.
“The Indus River played a crucial role in the growth of the ancient Indus Valley civilization by offering a consistent water source for agriculture, trade, and communication,” stated Dr. Bimal Mishra from the Indian Institute of Technology Gandhinagar and his colleagues.
“Civilizations prospered near the Indus River and its tributaries approximately 5,000 years ago and evolved over time.”
“The mature Harappan phase (4,500 to 3,900 years ago) was marked by meticulously planned cities, advanced water management techniques, and an intricate writing system.”
“However, post 3,900 years ago, the Harappan civilization began to deteriorate and eventually fell into decline.”
“The causes for this decline are still under discussion. Potential factors encompass shifts in river dynamics influenced by climate change, ocean retreat, drought, flooding, and alterations in social and political structures.”
“Understanding ancient hydroclimatic events and their impact on societies provides vital insights into the susceptibility of complex societies to environmental pressures.”
For this research, the authors simulated climate patterns in the Indus Valley from 5,000 to 3,000 years ago.
They integrated these findings with various indirect climate indicators, including the geochemistry of stalactites and stalagmites from two caves in India and water level data from five lakes in northwestern India.
The results indicated that temperatures rose by approximately 0.5 degrees Celsius during this time, while average annual precipitation in the region decreased by 10% to 20%.
They were able to identify four significant drought periods lasting over 85 years between 4,450 and 3,400 years ago, impacting 65% to 91% of the Indus Valley area.
“These droughts affected the selection of settlement locations in the Indus Valley Civilization,” the researchers noted.
“From 5,000 to 4,500 years ago, settlements were primarily situated in regions with abundant rainfall.”
“However, after 4,500 years ago, they shifted closer to the Indus River as drought conditions began to limit water availability.”
“The last identified drought, lasting 113 years from 3,531 to 3,418 years ago, corresponds with archaeological evidence of significant urbanization in the Indus Valley Civilization.”
“Instead of collapsing abruptly due to sudden climate changes, the Indus civilization likely faced a gradual decline, with extended drought being a key factor,” concluded the researchers.
Their study was published on November 27 in the journal Communication Earth and Environment.
_____
H. Solanki et al. 2025. River drought forcing Harappan metamorphosis. Communication Earth and Environment 6,926; doi: 10.1038/s43247-025-02901-1
Source: www.sci.news
