The Indus Valley civilization was wiped out 4,350 years ago by a 900-year-long drought, scientists at the Indian Institute of Technology in Kharagpur (IIT-Kgp) have found. Evidence gathered during their study also put to rest the widely accepted theory that the said drought lasted for only about 200 years.

The study will be published in the prestigious Quaternary International Journal by Elsevier this month.

Researchers from the geology and geophysics department have been studying the monsoon’s variability for the past 5,000 years and have found that the rains played truant in the northwest Himalayas for 900 long years, drying up the source of water that fed the rivers along which the civilization thrived. This eventually drove the otherwise hardy inhabitants towards the east and south, where rain conditions were better.

The IIT-Kgp team mapped a 5,000-year monsoon variability in the Tso Moriri Lake in Leh-Ladakh – which too was fed by the same glacial source – and identified periods that had continuous spells of good monsoon as well as phases when it was weak or nil.

“The study revealed that from 2,350 BC (4,350 years ago) till 1,450 BC, the monsoon had a major weakening effect over the zone where the civilization flourished. A drought-like situation developed, forcing residents to abandon their settlements in search of greener pastures,” said Anil Kumar Gupta, the lead researcher and a senior faculty of geology at the institute.

These displaced people gradually migrated towards the Ganga-Yamuna valley towards eastern and central UP; Bihar and Bengal in the east; MP, south of Vindhyachal and south Gujarat in the south, Gupta added.