BSIP pollen study from Deoria Tal links weak monsoon to the shrinking of the Harappan Civilisation
A Birbal Sahni Institute of Palaeosciences study of pollen in a Deoria Tal sediment core (Garhwal Himalaya) links a weak Indian Summer Monsoon between ~5100 and 4000 years BP to the shrinking of the Harappan Civilisation, DST said on 29 July 2026.
Summary
Scientists of the Birbal Sahni Institute of Palaeosciences (BSIP), an autonomous institute of the Department of Science and Technology, led by Dr Mohammad Firoze Quamar, studied a well-dated sediment core (10 AMS radiocarbon dates) from Deoria Tal in the Garhwal Himalaya. The pollen record shows an abrupt rise in the oak/pine ratio around 4250 cal yr BP, matching the globally known '4.2 ka event' of abrupt dry climate. The study suggests a weak Indian Summer Monsoon between about 5100 and 4000 cal yr BP shrank the Harappan (Indus Valley) Civilisation, and people along the Indus and Ghaggar-Hakra rivers migrated to the eastern Ganga plains.
Key facts
- Institute
- Birbal Sahni Institute of Palaeosciences (BSIP), DST
- Site
- Deoria Tal, Garhwal Himalaya
- Proxy
- Pollen and spores; 10 AMS radiocarbon dates
- Key signal
- Abrupt rise in oak/pine ratio ~4250 cal yr BP (the '4.2 ka event')
- Finding
- Weak monsoon ~5100–4000 cal yr BP; Harappans migrated to eastern Ganga plains
- Lead scientist
- Dr Mohammad Firoze Quamar
Practice MCQs 2 questions
The BSIP pollen study released in July 2026 that linked a weak monsoon to the shrinking of the Harappan Civilisation was based on a sediment core from which lake?
Show answer
Correct answer: B — Deoria Tal
BSIP studied a well-dated sediment core from Deoria Tal in the Garhwal Himalaya.
Consider the following statements about the BSIP Deoria Tal study: 1. It found an abrupt rise in the oak/pine ratio around 4250 cal yr BP, matching the '4.2 ka event'. 2. It suggests Harappan people migrated westward towards the Indus delta. 3. Pollen and spores were used as tools to reconstruct past vegetation and climate. Which of the statements given above are correct?
Show answer
Correct answer: C — 1 and 3 only
The study reports the oak/pine jump near 4250 cal yr BP and uses pollen and spores as proxies. It says people along the Indus and Ghaggar-Hakra migrated to the eastern Ganga plains, not westward.