India may have faced a much stronger monsoon about a thousand years ago than what is presently believed, studies conducted on ancient pollen found below a lake in Chhattisgarh have revealed.
The findings could strengthen the understanding of present monsoon-influenced climatic conditions, as well as help discern possible future climatic trends and projections.
“Scientists have found evidence of intense rainfall, forests and climate change roughly between 1060 and 1725 CE (Common Era) in central India, hidden in the Raja Rani Lake of Korba district of Chhattisgarh,” the Ministry of Science and Technology has said.
Scientists from the Birbal Sahni Institute of Palaeosciences extracted a 40-centimeter-long sediment core from the 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 process 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.
A shift in the vegetation from savannah to wooded savannah about 2,000–2,800 years ago was observed, corresponding to a moderately strengthened Indian Summer Monsoon (ISM) rainfall regime. Thereafter, the region experienced a transformation from wooded savannah vegetation to mixed tropical deciduous forests in a warm-humid climate, reflecting a comparatively increased ISM rainfall.
“From 890 to 225 cal yr BP (current era 1060–1725), dense mixed tropical deciduous forests came into being in a warm and relatively more humid climate, indicating intensified ISM rainfall,” the researchers said in their study published in the January issue of Review of Palaeobotany and Palynology’.
“An intense warm-humid climate with intensified ISM rainfall between 1060–1725 likely supported the establishment of dense mixed tropical deciduous forests in the Core Monsoon Zone (CMZ). The initial part of this phase corresponds with the global Medieval Climate Anomaly between 700-1400,” the researchers observed.
The study also noted that agricultural practices and other human activities such as horticulture, arboriculture, and livestock rearing increased during this period owing to the increased ISM rainfall. Understanding the vegetation dynamics and corresponding hydro-climate variability from the CMZ, where the ISM contributes to 89 to 90 per cent of India’s rainfall, could be crucial in understanding the monsoonal variability during the Late Holocene, particularly as the CMZ is sensitive to ISM fluctuations, according to the ministry.
The Holocene is the current geological epoch, beginning around 11,700 years ago after the last major ice age and is characterised by a relatively stable, warm climate, retreat of glaciers and development of human civilizations, agriculture and complex societies.
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 CMZ during this period.
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.
