BSIP Study Reconstructs 4,600 Years of Monsoon History

Scientists of the Birbal Sahni Institute of Palaeosciences (BSIP), an autonomous institute of the Department of Science and Technology, have pieced together 4,600 years of climate and environmental history from a single lake in the Central Ganga Plain. Their work, announced on 16 October 2026, shows how swings in the Indian Summer Monsoon shaped lake water levels, the movement of sediment, plant cover, microbial life and the way the earliest farmers of the region adapted.

Where the record came from

The team worked on Karela Lake, an oxbow lake at Hulas Khera in Mohanlal Ganj near Lucknow, Uttar Pradesh. Sediment at the bottom of such a lake traps a layered record of the Late Holocene. The lake also sits beside the Hulas Khera archaeological site, a Kushan-period settlement, so the natural record and the human record could be read side by side.

How the study was done

• Radiocarbon dating by the accelerator mass spectrometry method to fix the timeline
• Stable isotopes of carbon and nitrogen to track vegetation and organic matter
• Grain-size analysis and end-member modelling to trace how sediment moved
• Palynology, the study of pollen, to reconstruct plant cover

What was found

Researchers Biswajeet Thakur, Anand Rajoriya and Maneesha M, with the radiocarbon dating laboratory team, identified four major environmental phases tied to well-known climate events, among them the 4.2 ka arid event, the Roman Warm Period and the Little Ice Age. Moisture brought by westerly winds during the colder stretch of the Little Ice Age left clear signs of flooding in the region. Monsoon swings also drove shifts between C3 and C4 vegetation and changed the kind of organic matter settling in the lake bed.

Why it matters

The rise and fall of the Indus Valley Civilization has long been linked to monsoon change, but far less was known about how later communities of the Ganga Plain coped. Several migrations are recorded in the region between 4500 and 1000 calibrated years before present, which makes it a natural laboratory for studying climate and human interaction. The study, published in the Journal of Asian Earth Sciences, establishes that small oxbow lakes of the plain are sensitive natural archives, and the long baseline it provides can feed into climate modelling, water security, wetland conservation, disaster risk reduction and land-use planning.