A series of severe droughts over several decades led to the end of the Indus Valley Civilization, one of the world’s oldest civilizations, a new study has found.
The Indus Valley Civilization (also known as the Harappan civilization) flourished between 5,000 and 3,500 years ago in the region that straddles the modern-day border between India and Pakistan. Its people built cities with advanced water management systems, such as Harappa and Mohenjo-daro. They also created a script that has not been deciphered by modern scholars and traveled to Mesopotamia, where they traded.
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“Successive droughts that lasted more than 85 years were likely an important factor in the final collapse of the Indus Valley Civilization,” the scientific team said in a statement. As these droughts worsened, the researchers found, populations within societies moved to areas where sufficient water sources still existed.
Eventually, cities across the region fell. A century-long drought that began about 3,500 years ago “coincided with widespread deurbanization and the cultural abandonment of major cities.” [cities]” the team wrote on paper.
climate simulation
For their analysis, the team used three different publicly available global climate simulations. This is a complex computer simulation that uses vast amounts of data to determine how the climate has changed over thousands of years. They used these to study how rainfall and temperature changed between 5,000 and 3,000 years ago in the region where the Indus Valley Civilization once flourished. All three simulations showed the presence of drought.
“Precipitation has consistently decreased from 5,000 to 3,000 years.” [ago] “Through all our simulations, we ensure that features such as centuries-long droughts, weaker monsoons, and changes in winter rainfall are real, persistent signals and not artifacts of a single model,” study lead author Hiren Solanki, a doctoral student at the Indian Institute of Technology Gandhinagar, told Live Science in an email.
The researchers incorporated rainfall and temperature data into hydrological models to reveal how rivers, streams, and other bodies of water in the region have changed over time. They compared this with archaeological data showing where settlements existed and found that over time they tended to migrate to stay near water.
To double-check their results, the researchers looked at previous studies that analyzed how fast stalagmites and stalactites grow in caves in the region. These structures grow more slowly when rainfall is low, providing indirect evidence of drought. As an additional way to determine how precipitation patterns have changed, the research team also looked at previous studies showing how lake sediments in the region have changed over time.
By comparing the simulation data with cave and lake sediment data, they were able to confirm that the simulation data was fairly accurate.
Nick Scroxton, a hydrology, paleoclimate and paleoenvironmental researcher at University College Dublin who was not involved in the study, praised the work.
“The Indus River is clearly important to the Harappans, and modeling the river’s flow can help us understand how changes in rainfall patterns have influenced changes in both urban settlement and agricultural practices,” Scroxton told Live Science via email.
Liviu Giosan, a geoscientist at Woods Hole Oceanographic Institution in Massachusetts who was not involved in the study, also spoke positively about the paper, praising the “sophisticated modeling” done by the team. “This result is an important step forward in studying the role of hydroclimate in the evolution of ancient civilizations,” Giosan told Live Science via email.
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