Guwahati: Long before weather stations or satellites existed, Meghalaya’s caves were quietly recording the rhythms of the Indian monsoon. Today, scientists are decoding these underground archives, revealing insights that are both remarkable and relevant to the present.
A recent study in the Journal of Geophysical Research: Atmospheres reconstructed monsoon behaviour over Northeast India from 722 to 1250 CE. Researchers analysed a stalagmite collected from Krem Bylliat Cave in the Jaintia Hills.
The study was led by Professor Anil Gupta of IIT Kharagpur, along with his students Yachna Verma and Priyantan Gupta. They collaborated with Dr Naveen Gandhi of IITM Pune, Professor Hai Cheng of the Chinese Academy, and Dr Som Dutt of the Wadia Institute of Himalayan Geology. The effort combined Indian and international expertise.
Krem Bylliat sits near Kseh village at 732 metres above sea level. The cave stretches nearly four kilometres underground. Formed within limestone rocks deposited millions of years ago, it still holds fossils of ancient marine organisms.
The cave lies on the Meghalaya Plateau, which shapes the Indian monsoon. Moisture-laden winds from the Bay of Bengal rise over the plateau, triggering intense rainfall. Areas near Kseh village receive some of the heaviest rainfall in the world.
This combination of extreme rainfall and limestone geology makes Krem Bylliat a natural laboratory for studying past climate. Speleothems, such as stalagmites, preserve chemical records of ancient rainfall, allowing scientists to reconstruct monsoon history with precision.
For this study, researchers collected a 26.5 cm-long stalagmite from a chamber one kilometre inside the cave. The chamber’s high humidity preserved uninterrupted growth layers over centuries.
Stalagmites grow slowly as mineral-rich water drips from the ceiling, forming layers that record rainfall conditions. By analysing these layers, scientists can track monsoon fluctuations almost year by year.
“Meghalaya receives over 80 percent of its rainfall from the Indian Summer Monsoon,” said Professor Gupta. “The stalagmites allow us to study monsoon variability from sub-decadal to centennial timescales.”
The findings show sharp monsoon fluctuations during the medieval period. From 722 to 850 CE, rainfall was relatively strong. From 850 to 890 CE, the region faced a severe dry phase, one of the most pronounced droughts of that era.
Around 1140 CE, the monsoon stabilised, maintaining relatively steady rainfall for over a century. Researchers say this pattern resembles today’s “normal” monsoon regime.
Scientists suggest that solar activity and ocean–atmosphere systems, such as El Niño and La Niña, drove these long-term shifts. When these forces aligned in certain ways, the monsoon weakened or strengthened, even in Meghalaya.
Understanding past monsoon behaviour helps put modern climate change into perspective. While today’s warming is mainly human-driven, natural variability has always shaped rainfall. Past droughts would have affected agriculture, water supply, and settlements.
As climate change increases extreme rainfall events and prolonged dry spells, these ancient records are more valuable than ever. Hidden beneath forests and limestone hills, Meghalaya’s caves silently preserve the region’s climate history and guide us in understanding future trends.