Kolkata: Scientists and meteorologists have termed the extremely heavy rain that lashed Kolkata from Monday night to Tuesday morning—251.4 mm in less than 24 hours—as rare and unusual, linking it to climate change.
Mahesh Palawat, vice president (Meteorology and Climate Change), Skymet Weather, said a low-pressure area over Odisha and adjoining regions triggered intense convective clouds. “Continuous moisture incursion from the Bay of Bengal kept energising the clouds, making the spell more intense. The static cloud build-up caused extremely heavy rain in a short time. With the Bay warming due to rising temperatures, evaporation has increased, feeding such systems with more moisture. We must prepare for more such extreme events,” he said.
Climate scientist Raghu Murtugudde, Emeritus Professor, University of Maryland and retired IIT-Mumbai professor, said global ocean warming is altering weather in India. “Multiple typhoons brewing in the Pacific—also warming—demand huge amounts of moisture. These systems draw from the North Indian Ocean, disturbing monsoon circulations. Under this influence, weather systems form in the Bay of Bengal. The low-pressure that drenched Kolkata was one such case. Such erratic rainfall is directly tied to abnormal ocean warming,” he said.
Over 90 per cent of global warming is absorbed by oceans. A recent Nature study found oceans have warmed by more than 1.5 degree C since the industrial era, higher than earlier estimates. The Indian Ocean, a climate hotspot, has witnessed the fastest surface warming since the 1950s. This has increased marine heatwaves, which reduce rainfall over central India while intensifying it in the southern peninsula. Marine heatwaves, currently lasting around 20 days annually, are projected to increase to 220–250 days, pushing the tropical Indian Ocean into a near-permanent heatwave state.
The India Meteorological Department (IMD) said the downpour was Kolkata’s heaviest since 1986 and the sixth-highest single-day rainfall in 137 years. Peak intensity was recorded between 3 am and 4 am on September 23, when 98 mm fell in an hour—just short of the 100 mm
cloudburst mark.