New Delhi, May 22 -- Over half of Indian districts (57%), home to 76% of the population and contributing to a combined GDP of Rs 280 lakh crore (almost 85% of India's GDP at current prices) are currently at high to very high heat risk, an analysis by the Council on Energy, Environment and Water has revealed. Around 417 out of 734 districts fall under high and very high heat risk (151 are high risk, 266 are very high risk), while 201 are at moderate risk and 116 are low to very low risk, the analysis found. The ten states/UTs with the highest heat risk are: Delhi, Maharashtra, Goa, Kerala, Gujarat, Rajasthan, Tamil Nadu, Andhra Pradesh, Madhya Pradesh, and Uttar Pradesh. The analysis claims that over the last 40 years (1981-2022), heat extremes in India have increased linearly. This led to severe heatwave episodes in 2013, 2016, 2019, 2022, and 2024. In the last decade, the number of very warm nights has risen faster than that of very hot days. "We found that even in the traditionally cooler Himalayan regions - where heat thresholds are lower than in the plains and coasts - (the number of) both very hot days and very warm nights have increased. For example, in the union territories of Jammu & Kashmir and Ladakh, the number of very hot days and very warm nights has risen by over 15 days and nights each summer. This could severely impact fragile mountain ecosystem," the analysis said. In the last decade, North India, particularly the Indo-Gangetic Plains experienced the highest summer relative humidity increase, exacerbating heat stress. Increasing relative humidity is especially pronounced across the agriculturally important Indo-Gangetic Plain, where farm workers spend long hours outdoors. Cities such as Delhi, Chandigarh, Jaipur, and Lucknow are also experiencing a 6- 9% rise in relative humidity, the report said. While coastal areas typically have 60-70% relative humidity, this used to be around 30-40% in North India during the baseline period. Over the past decade, this has increased to 40-50% according to the analysis. When combined with high temperature, high humidity significantly worsens heat stress on the human body, especially during the peak summer months of May and June. When the body temperature exceeds 37 degrees Celsius, sweating helps cool it down; however, high humidity slows this process, making it harder for the body to release heat. This can increase the occurrence of several heat-related illnesses at a faster rate. "Extreme heat broke all records in 2024, which was recognised globally as the hottest year since records began. Asia, which accounted for 45%of global heat-related deaths between 2000 and 2019, and India, where over a billion people face heatwaves annually, remain among the most affected regions. In 2024, India experienced its longest recorded heatwave since 2010," the analysis said. Many states experienced daytime temperatures of over 40 degrees C for an entire month, leading to more than 44,000 cases of heatstroke, as per studies referred to by the report. Extreme heat is already having a multifaceted impact on day-to-day life, straining public health systems, pushing power demand to record highs, damaging crops, depleting water resources, and reducing the productivity of humans, livestock, and agriculture. Due to heat stress, India could lose the equivalent of 35 million full-time jobs and experience a 4.5% reduction in GDP by 2030, the CEEW analysis said. The heat risk index (HRI) for 734 districts is based on the Intergovernmental Panel on Climate Change (IPCC) AR5 framework, which defines "risk as a combination of hazard, exposure, and vulnerability." "To assess heat risk, we have considered indices related to hazard, exposure and vulnerability. For example, under hazards we have considered the increase in hot days and warm nights; under exposure we have considered indices that show use things that are exposed to extreme temperatures including people, building density and infrastructure and under vulnerability we have considered the population that is most vulnerable including people above 65 years age or under 6 years; percentage of labour, literacy rate, population with electricity access etc. Then we have done geospatial mapping of this information to rank districts at highest risk," said Vishwas Chitale, Senior Programme Lead, CEEW. "There is no doubt that the frequency, severity and length of heat episodes are increasing over India. The projections are very worrying and should be considered for future," said M Rajeevan, former secretary, ministry of earth sciences during the release of the analysis. HT reported on April 16 that the widely accepted wet-bulb temperature survival threshold of 35degC is being questioned after recent physiological studies suggest the limit may actually be closer to 31degC. Wet-bulb temperature combines heat and humidity measurements to indicate how effectively the human body can cool itself through sweating when outdoors....