Scientists have for the first time identified what drives India’s most dangerous form of heat during the monsoon season, and shown that the risk can be forecast up to four weeks in advance, according to a study by scientists at University of Reading, University of Leeds and Indian Institute of Tropical Meteorology in the UK and India.The research published in Climate Dynamics found that a single large-scale monsoon pattern can raise the likelihood of a moist heatwave in northern India by 125 per cent above normal.Moist heatwaves are deadlier than dry heat because the body’s primary cooling mechanism, the evaporation of sweat, slows or fails entirely. It strains the cardiovascular system and heatstroke can follow within hours.The study maps out a clear geography of risk. During active monsoon phases, the densely populated Indo-Gangetic Plains of northern India, home to millions of people, face sharply elevated danger, as sudden surges of monsoon moisture push humidity to physiologically harmful levels even as rainfall continues nearby.The populations most at risk are farm workers in Uttar Pradesh and Bihar, construction labourers in Delhi and Mumbai, the elderly without air conditioning, and the urban poor in areas where concrete retains heat through the night. A four-week warning window, researchers say, could allow hospitals to adjust staffing, city authorities to open cooling centres, schools to alter hours, and power utilities to prepare for increased grid demand.Researchers analysed 84 years of atmospheric data (from 1940 to 2023).Dr Akshay Deoras, who led the study, says the gap between how seriously India takes dry heat versus moist heat is itself a danger.“Our research shows for the first time that the monsoon is the key driver of where and when this deadly risk develops. Because we can forecast these monsoon patterns weeks ahead, this creates real opportunities to prepare and protect people. Advance warnings could allow hospitals to increase staffing before moist heat-related admissions rise, enable city authorities to open cooling centres and adjust school hours, and help power grid operators manage infrastructure strain,” Dr Deoras added.