Indian cities’ heat action plans must focus on high night-time temperatures, study says

New Delhi, A new analysis has found that heat risk in Indian cities is increasingly being shaped not only by daytime heatwaves but also by night-time heatwaves and compound heatwaves, which occur when a daytime heatwave is followed by a night-time heatwave.

This is significant because current Heat Action Plans and urban climate policies mainly focus on daytime heatwaves, according to the study. A H serves as an early warning system and preparedness plan for extreme heat events.

In an interview with PTI, Kashif Imdad, a co-author of the study and associate professor of geography at Kanpur’s Pandit Prithi Nath PG College, said, “Most state and district plans, including the Uttar Pradesh State Plan, focus almost entirely on daytime heatwaves. We have not identified night-time and compound heatwaves as a problem yet.”

The findings align with what several other studies have been observing in India and around the world for years: night-time temperatures are steadily increasing.

For instance, a 2025 study by the Council on Energy, Environment and Water revealed that between 2012 and 2022, the number of very warm nights increased faster than very warm days.

Over 70 per cent of districts witnessed five or more additional very warm nights per summer during this period, according to the CEEW analysis.

These developments are concerning, as higher temperatures during the night make it difficult for the body to cool down after intense daytime heat, which can lead to a rise in health risks such as heat stroke and worsening of non-communicable diseases like diabetes and hypertension.

The latest study, ‘Night-time and compound heatwaves as emerging climate risks in India’s smart cities’, was published in the journal Physics and Chemistry of the Earth on March 12.

The analysis was conducted by Imdad, Anubha Yadav, a PhD scholar at PPN PG college, Archana Chaudhary, a researcher at Kanpur’s Vikramajit Singh Sanatan Dharma College, and Rayees Ahmed, a researcher at Bengaluru’s Indian Institute of Science.

For their study, the researchers developed a diurnal persistence index to analyse 100 Indian smart cities and find where daytime, night-time, and compound heatwaves existed for the period between 2001 and 2024.

“We categorised Indian smart cities into plain, plateau, coastal, and hill areas. In the Indo-Gangetic plain cities, there is a mixed regime , but compound and night-time heatwaves are rising. In southern Peninsular India, daytime heatwaves dominate. In coastal and hill cities, night-time heatwaves dominate,” Imdad stated.

Notably, between 2001 and 2024, Srinagar experienced the highest frequency of daytime and compound heatwaves among the 100 smart cities.

While Gujarat’s Dahod saw the most intense compound heatwaves, Varanasi experienced the most intense night-time heatwaves, and Imphal the most intense daytime heatwaves.

To tackle rising night-time temperatures, authorities need to develop Hs and urban climate policies that prioritise interventions which directly reduce night-time heat retention and enhance night-time cooling.

These measures may include implementing cool roofs, improving natural ventilation and ventilation corridors, and expanding urban greenery.

The study said, “Public health responses should explicitly incorporate hot night warnings, the provision of night-time cooling shelters, reliable electricity supply for cooling and risk communication focused on cumulative heat exposure rather than daytime extremes alone.”

However, Imdad cautioned that these interventions should be tailored to specific local conditions.

“For example, cool roof technology is suitable for cities where temperatures stay high year-round, like in South India or parts of Gujarat. In places like Lucknow, temperatures soar to 47 degrees Celsius in summer but drop to minus one degree Celsius in winter. If you paint the roof to be cold, you might save people in summer, but they could die from the cold in winter, especially vulnerable populations in huts,” he said.

Therefore, in Lucknow, for example, one needs to install removable cool roofs, such as plants, seeds, or green mats used in nurseries, which can be removed in winter.

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