A warming climate and severe droughts have dealt a mortal blow to the Indus Valley Civilization, a mysterious urban culture that flourished some 4,000 years ago in what is now Pakistan and India.

This culture arose along the Indus River and its tributaries and spread over a larger area than the other great ancient civilizations of Egypt and Mesopotamia. Its representatives built cities and are also known as the Harappan civilization – after the name of the city of Harappa, whose population reached 35,000 people, which was a huge figure at that time.

Advanced civilization

Although the Harappans’ writing has not yet been fully deciphered, it is known that they had advanced technologies in the field of water supply, such as giant storage tanks and sewage systems made of terracotta pipes and brick channels. But even advanced engineering solutions have not withstood the test of a millennium of abnormal heat and drought.

“There were four major droughts from the pre-Harappan to the late Harappan period. The response was continuous migration to where water was available,” says Professor Vimal Mishra of the Indian Institute of Technology, Gandhinagar.

Previous research suggested that monsoon rains in the Indus Valley weakened after a global megadrought 4,200 years ago, which accelerated the demise of civilization. However, Mishra and his colleagues argue that the decline of the Harrapan culture was not a sudden collapse, but a gradual disintegration.

The scientists reconstructed the region’s rainfall patterns using three climate models and compared the data with rainfall estimates based on studies of stalactites, stalagmites and lake sediments. The results of the analysis were published on the pages Communications Earth & Environment.

Four droughts

They showed that between 4,400 and 3,400 years ago, the Indus Valley Civilization was struck by four droughts, each lasting at least 85 years. The temperature during this period increased by approximately 0.5 °C.

Additional modeling has shown that the level of the Indus has dropped. The Harappans, who are believed to have worshiped rivers and used their seasonal floods to irrigate crops such as wheat and barley, began to settle closer to waterways. When the droughts continued, they finally abandoned their cities and migrated to the foothills of the Himalayas and the Ganges River valley.

The authors suggest that warming and droughts may have been triggered by natural climate patterns such as El Niño and the North Atlantic Oscillation, and exacerbated by feedback effects such as loss of vegetation cover and air pollution from dust.

A dire warning

Paleoclimatologist Sebastian Breitenbach of Northumbria University in England praised the study as innovative in its combination of modeling and indirect measurements. However, in the future, in his opinion, it is also necessary to take into accountevapotranspiration– the process of evaporation of moisture from the surface of the earth into the atmosphere, which in such a hot region can be very pronounced.

Given that today’s climate is changing much faster than in Harappan times, decision-makers should consider adaptation measures such as creating water reserves and conserving groundwater, he added.

“Such studies can serve as a dire warning for us. They allow us to look into the future and see what may await us,” concluded Breitenbach.