Photo: (a) Geographical map of India showing the Korba District, Chhattisgarh, CMZ, India (dark black and bold lines). (b) Shuttle Radar Topographic Mission (SRTM) Digital Elevation Model (DEM) of the Korba District (Chhattisgarh), showing the site of investigation (red star).

India may have faced a much stronger monsoon than was previously believed. Scientists have discovered evidence of intense rainfall, forests, and climate change dating back to roughly between 1,060 and 1,725 CE in central India, hidden in the Raja Rani Lake of the Korba district in Chhattisgarh.

Understanding the vegetation dynamics and corresponding hydro-climate variability from the Core Monsoon Zone, wherein the rainfall is essentially controlled by the ISM, which contributes to 89 to 90 per cent of India’s rainfall, could be crucial in understanding the monsoonal variability during the Late Holocene, i.e. Meghalayan Age, particularly as the CMZ is sensitive to ISM fluctuations.

Read in Hindi: झील के नीचे छिपे प्राचीन पराग कणों ने यूं बयां की शक्तिशाली मानसून की कहानी!

Scientists from the Birbal Sahni Institute of Palaeosciences in Lucknow, an autonomous institute of the Department of Science and Technology, have found evidence of unusually strong Indian Summer Monsoon in ancient pollen grains preserved in lake sediments in Raja Rani Lake of Korba district in Chhattisgarh, right in the heart of India’s Core Monsoon Zone.

Researchers extracted a 40-centimetre-long sediment core from Raja Rani Lake. The mud records revealed environmental changes going back about 2,500 years. Within these layers lie microscopic pollen grains shed by plants that once grew around the lake.

By identifying and counting these pollen grains, a science known as palynology, researchers reconstructed past vegetation and, in turn, past climate. Forest-loving plants pointed to warm and humid conditions, while grasses and herbs suggested drier phases.

During the Medieval Climate Anomaly, the pollen record showed a clear dominance of moist and dry tropical deciduous forest species, indicating strong monsoon rainfall and a warm, humid climate in central India. Crucially, the study found no evidence of contrasting dry conditions within the Core Monsoon Zone during this period.

The scientists attributed this strong monsoon to a global warm phase known as the Medieval Climate Anomaly, which occurred between approximately 1,060 and 1,725 CE. The study attributes the enhanced monsoon to a combination of global and regional factors, La Niña–like conditions, which are typically associated with stronger Indian monsoons, northward movement of the Intertropical Convergence Zone, positive temperature anomalies, increased sunspot numbers and high solar activity could be driving the climate change and increased ISM during the MCA.

This understanding of the Indian Summer Monsoon (ISM) and related climate change variability during the Holocene could be of immense interest in order to strengthen our understanding of the present ISM-influenced climatic conditions, as well as of possible future climatic trends and projections.

Moreover, the high-resolution palaeoclimatic records generated in the present study could help develop paleoclimatic models for the simulation of future climatic trends and rainfall patterns and also for a scientifically sound policy planning with a key aspect of societal relevance.