A new study has revealed that heat risk in Indian cities is increasingly driven not only by daytime heatwaves but also by rising night-time heatwaves and compound heatwaves. Compound heatwaves occur when an intense daytime heatwave is followed by persistently high temperatures during the night.
Importantly, the findings highlight a critical gap in India’s Heat Action Plans (HAPs) and urban climate policies, which largely focus on daytime heatwaves while overlooking night-time heat stress. HAPs are designed to function as early warning systems and preparedness strategies for extreme heat events.
Study Highlights Rising Night-Time Temperatures
Speaking to PTI, Kashif Imdad, co-author of the study and Associate Professor of Geography at Pandit Prithi Nath (PPN) PG College, Kanpur, emphasised that policymakers have yet to fully recognise night-time heat as a major threat.
“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,” he said.
Notably, the study’s findings reinforce observations from several earlier research efforts indicating that night-time temperatures in India and globally are steadily increasing.
Evidence from Previous Climate Studies
For example, a 2025 study by the Council on Energy, Environment and Water (CEEW) found that between 2012 and 2022, the number of very warm nights increased faster than very warm days across India.
Furthermore, the analysis revealed that over 70 percent of districts experienced five or more additional very warm nights per summer season (March to June) during this decade.
Health Risks Linked to Hot Nights
These trends are particularly concerning from a public health perspective. When night-time temperatures remain high, the human body struggles to cool down after exposure to intense daytime heat.
Consequently, prolonged heat exposure can significantly increase the risk of heat-related illnesses, including heat stroke, while also aggravating non-communicable diseases such as diabetes and hypertension.
Research on Heatwave Patterns Across Smart Cities
The latest research, titled “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.
As reported by The Hindu Business Line, the study was conducted by Kashif Imdad, Anubha Yadav (PhD scholar at PPN PG College), Archana Chaudhary (researcher at Vikramajit Singh Sanatan Dharma College, Kanpur), and Rayees Ahmed from the Indian Institute of Science (IISc), Bengaluru.
To assess heatwave trends, the researchers developed a Diurnal Persistence Index and analysed 100 Indian smart cities between 2001 and 2024. The study examined the occurrence of daytime, night-time, and compound heatwaves across different geographical regions.
Regional Patterns of Heatwaves in India
The researchers categorised cities into plains, plateau regions, coastal areas, and hill regions to better understand regional variations.
According to Imdad:
- Indo-Gangetic plain cities are experiencing a mixed pattern, where daytime heatwaves are declining while night-time and compound heatwaves are increasing.
- Southern peninsular cities continue to experience dominant daytime heatwaves.
- Coastal and hill cities, on the other hand, are witnessing a higher frequency of night-time heatwaves.
Cities Experiencing the Most Severe Heatwaves
The study also identified cities experiencing the highest frequency and intensity of heatwaves between 2001 and 2024.
- Srinagar recorded the highest frequency of daytime and compound heatwaves among the 100 smart cities analysed.
- Dahod in Gujarat experienced the most intense compound heatwaves.
- Varanasi recorded the most intense night-time heatwaves.
- Imphal experienced the most intense daytime heatwaves.
Urban Planning Solutions to Reduce Night-Time Heat
To address rising night-time temperatures, the researchers emphasised the need to revise Heat Action Plans and urban climate policies. Specifically, authorities should prioritise strategies that reduce night-time heat retention and improve urban cooling.
Key measures suggested in the study include:
- Installing cool roofs
- Improving natural ventilation and ventilation corridors
- Expanding urban greenery and tree cover
These interventions can significantly reduce heat accumulation in densely built urban environments.
Public Health Measures for Extreme Heat
In addition to urban design solutions, the study recommends strengthening public health responses to heat stress. Authorities should consider introducing:
- Hot night warning systems
- Night-time cooling shelters
- Reliable electricity supply for cooling systems
- Risk communication focusing on cumulative heat exposure rather than daytime heat alone
Such measures can help protect vulnerable populations from prolonged heat exposure.
Need for Location-Specific Cooling Strategies
However, Imdad cautioned that heat mitigation strategies must be adapted to local climatic conditions.
For instance, cool roof technology works well in regions where temperatures remain high throughout the year, such as South India or parts of Gujarat. However, the same approach may not be suitable in cities with extreme seasonal temperature variations.
“In places like Lucknow, temperatures may reach 47°C in summer but drop to minus one degree Celsius in winter. If roofs are permanently designed to remain cool, people might benefit during summer but face severe cold during winter,” he explained.
Therefore, he suggested removable cooling solutions for such regions. For example, temporary cool roofs using plants, seeds, or green mats commonly used in nurseries can be installed during summer and removed during winter.
By adopting climate-sensitive urban planning and targeted public health strategies, Indian cities can better prepare for the growing threat of night-time and compound heatwaves in the coming decades.