India’s ‘moist heatwaves’ getting worse, says study | India News

PUNE: India’s summer heatwaves — the humid, suffocating kind that have more impact than the dry heat — are becoming not only more frequent, but also more intense through a now-familiar specific atmospheric chain reaction. A January 2026 study by scientists from IMD and Indian Institute of Tropical Meteorology (IITM) Pune, published in the Journal of the Atmospheric Sciences, explains the precise mechanisms behind these “moist heat waves” and the findings have direct implications for early warning, public health and climate preparedness.IITM scientist Rajeev Chattopadhyay told TOI that their earlier study had identified two types of Indian summer heat waves and classified them as dry and wet. “The dry variety, which predominantly scorches the Northwest Plains, does not show an increasing trend. But the humid variety, in which high humidity combined with high temperatures frustrates the body’s cooling system, shows a statistically significant and accelerating trend. The present study provides a hint towards the mechanism that could intensify the humid heat wave in India,” he said.Scientists have traced the trigger to Rossby atmospheric wave patterns that originate off the west coast of Europe. These waves travel through the Europe-Central East-Indian Ocean and come over India as a high-pressure system of high-pressure air, suppressing clouds and baking the surface. “But what makes a bad heat wave worse is the second actor – the anomalous warmth in the southernmost Bay of Bengal. When that warm patch develops its own circulation pattern and the two systems reach northwest India simultaneously, they superimpose and extend each other,” Chatterjee said.The anticyclone strengthens, lasts longer and simultaneously pumps moisture westward into India, creating a deadly combination of heat and moisture. The team verified this using a mathematical atmospheric model run under 129 different test configurations.“The model results showed a clear pattern. When the Bay of Bengal warms as atmospheric waves arrive from Europe, the temperature and ‘feel’ heat index in northwest India increase markedly. We also found that if the atmospheric wave pattern changes slightly, the strong heat stress zone moves towards the east and southeast coastal parts of India,” Chattopadhyay said.Observational data suggested that the moist heat signal in the region has been strengthening in recent decades, he said. “In experiments examining climate conditions, we found that this interaction between atmospheric waves and the warming of the Bay of Bengal works most effectively when the speed of the jet stream operates within the range seen under current conditions. This is important because climate change is expected to affect large-scale atmospheric patterns, including jet stream and wave behavior.“