Research Highlight

Simultaneous day-night heatwaves increasing in India

doi:10.1038/nindia.2018.158 Published online 4 December 2018

Researchers from the Indian Institute of Technology Gandhinagar have found that concurrent hot day and hot night (CHDHN) heat waves are increasing in western, north-eastern and southern parts of India. They warn that a 2°C increase in the Earth’s temperature could increase such CHDHN incidents by six times in India 1.

Health risks due to increased day temperatures can be attenuated by cooler night temperatures. However, simultaneous high day and night temperatures have a significant impact on morbidities and mortality related to heat. 

Between 1998 and 2016, heatwaves caused more than 2000 deaths in India.

Mapping India's one-day and three-day CHDHN events between 1951 and 2016, the scientists found that every year after 1984, the three-day events increased in western, north-eastern and southern parts. The Indo Gangetic plain, however, showed a decrease. They suggest that leaf transpiration in this heavily irrigated plain may be responsible for the cooling effect.

The researchers used  Representative Concentration Pathways (RCP) to describe the possible trajectories of carbon dioxide (CO2) emissions, with RCP 2.6 being the best-case scenario (global emissions decline to zero by 2080), and RCP 8.5 the worst-case (emissions continuing to peak through the early and middle 21st century).

Simulating the RCP 8.5 scenario, they say, that the three-day CHDHN events could increase 12 times by the end of the 21st century. Also, both one- and three-day CHDHN events could increase sixfold in India if global warming increased by 2°C.


1. Mukherjee, S & Mishra, V. A sixfold rise in concurrent day and night-time heatwaves in India under 2 °C warming. Scientific Reports (2018) doi: 10.1038/s41598-018-35348-w