States in Indo-Gangetic Plain record spike in humid heat days: Study
Although humidity is the highest during early mornings, when combined with high temperature, high humidity significantly worsens heat stress on the human body.
Over half of India’s districts, which are home to 76% of the country’s population and contribute to a combined GDP of ₹280 trillion, are currently at ‘high to very high’ heat risk, an analysis by the Council on Energy, Environment and Water (CEEW) has revealed.
Around 417 out of India’s 734 districts fall under high and very high risk (151 high risk, 266 very high risk), while 201 are moderate and 116 are low to very low risk, the analysis found.
The 10 states/UTs with the highest heat risk include Delhi, Maharashtra, Goa, Kerala, Gujarat, Rajasthan, Tamil Nadu, Andhra Pradesh, Madhya Pradesh, and Uttar Pradesh.
Further, the number of ‘very warm’ nights is rising faster than hot days, particularly in districts with large populations, the study found. For instance, in the last decade, Mumbai saw 15 more very warm nights per summer, Bengaluru (11), Bhopal and Jaipur (7 each), Delhi (6), and Chennai (4).
In the last decade, the Indo-Gangetic Plain experienced the highest relative summer humidity increase, exacerbating heat stress. Increasing relative humidity is especially pronounced in North India, particularly across the agriculturally important Indo-Gangetic Plain, where farm workers spend long hours outdoors. Cities like Delhi, Chandigarh, Jaipur, and Lucknow are also experiencing a 6-9% rise in relative humidity. While coastal areas typically have 60-70% relative humidity, North India used to have around 30-40% during the baseline period (1982 to 2011). Over the past decade, this has increased to 40-50%, the CEEW analysis found.
Although humidity is the highest during early mornings, 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 (or 100°F), 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 report stated.
Many states experienced daytime temperatures of over 40 degrees Celsius for an entire month, leading to more than 44,000 cases of heatstroke. By April 2025, more than 10 states had already experienced severe heatwaves.
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, CEEW said.
CEEW has developed a heat risk index (HRI) for 734 districts in India to assess heat risk at the district scale. The index is based on the Intergovernmental Panel on Climate Change (IPCC) AR5 framework, which defines risk as “a combination of hazard, exposure, and vulnerability”.
In our HRI, we mapped long-term heat trends (1982-2022) using the Indian Monsoon Data Analysis and Assimilation (IMDAA) — a high-resolution climate dataset that breaks down India’s area into 12-km grids.
The team used 12 indices falling under the hazards category to analyse the hazards component when quantifying heat using IMDAA data. These indices capture relative humidity, rainfall, and the frequency, intensity, and duration of day and nighttime heat extremes.
