Famed Ancient Civilization May Have Been Toppled Slowly

The Indus Valley Civilization, one of the world's oldest, was a thriving society in what is now Pakistan and northwest India for some 2,000 years. Then it was gone—without signs of war or conquest. A new study in Communications Earth & Environment offers fresh insight into what may have happened. The Washington Post reports scientists used paleoclimate data and computer simulations to reconstruct the region's climate between 3000 and 1000 BC and identified four prolonged droughts—each persisting for at least 85 years and impacting 65% to 91% of the region, per a press release. Rather than being felled by a single disaster, the researchers argue it was this "repeated, long, and intensifying" cycle of droughts that weakened the civilization over centuries.

As the Post explains, the researchers focused on the city of Harappa, one of the biggest in the valley. The Harappan's settlements had been positioned near water sourses including tributaries and the Indus River itself. Monsoon conditions made the region far wetter than typical until about 2475 BC, at which point the first drought hit. "The Harappans switched crops, diversified their trade [as river conditions may have prevented the regular movement of boats and barges], and relocated settlements to make them more resilient to climate change," says lead author Hiren Solanki.

Despite these efforts, declining water and food supplies eventually helped pushed the society toward dispersion and collapse, the researchers suspect. Liviu Giosan, a geoscientist at Woods Hole Oceanographic Institution who was not involved in the study, calls the research "a significant step ahead in studying hydroclimate's role in the evolution of ancient civilizations. It is remarkable that they survived so long under repeated climate crises. A lesson for us? Prolonged climatic stress weakens society and could lead to collapse if not prepared." LiveScience mentions one other mystery that persists: The civilization's people developed a written script that has yet to be deciphered.