Climate Change

2.2 bn people in Pakistan’s Indus Valley & India at risk of moist heatwaves, high temperatures: Study

The impacts expand along the Bay of Bengal as well as into Bangladesh and parts of Myanmar in 3°C and 4°C warmer world

By Rohini Krishnamurthy
Published: Tuesday 10 October 2023
Representative photo: iStock__

Some 2.2 billion people living in India and the Indus River Valley may see a dramatic increase in hot hours annually if global temperatures rise 2 degrees Celsius above the preindustrial era, according to a new study.

These regions are also likely to experience the first moist heatwaves if global warming continues, the study published in journal PNAS stated. Moist heatwaves occur when  relative humidity exceeds 66 per cent, according to a study.

“As people get warmer, they sweat, and more blood is pumped to their skin so that they can maintain their core temperatures by losing heat to the environment,” Larry Kenney, professor of physiology and kinesiology (study of human movement), the Marie Underhill Noll Chair in Human Performance at Penn State and co-author of the new study said in a statement.

These adjustments, he added, are no longer sufficient at certain levels of heat and humidity. Subsequently, the body’s core temperature (37°C) rises.

“This is not an immediate threat, but it does require some form of relief. If people do not find a way to cool down within hours, it can lead to heat exhaustion, heat stroke and strain on the cardiovascular system that can lead to heart attacks in vulnerable people,” the expert explained.

When the ambient environment reaches the wet-bulb temperature (Tw) of 35°C, the body can no longer regulate the body temperature via blood flow or sweat evaporation on the skin’s surface. Tw of 35°C is the limit to which humans can adapt or survive.

Previous observations have recorded a Tw of more than 35°C in the Middle East and South Asia on rare occasions, for an hour or two at a time.

Kenney and his team initiated the study to identify regions where warming would lead to heat and humidity levels that exceed human tolerance. They used computer modelling, and the results showed that at 1.5 °C and 2 °C warming, impacts are concentrated across the Indus Valley area in eastern Pakistan and northern India.

The impacts expand along the Bay of Bengal as well as into Bangladesh and parts of Myanmar in 3°C and 4°C warmer worlds.

The annual hot hours for Delhi, Mumbai, Kolkata and Chennai at 2°C are estimated to be 39, 0.2, 31.4 and 0.4, respectively.

At 4°C of warming, the annual hot hours would increase to 556.9, 55.4, 548.5 and 94.2 for Delhi, Mumbai, Kolkata, and Chennai, respectively.

These impacts extend globally as well. In a 4°C warmer world, around 2.7 billion people will experience at least 8 hours across a week of daytime ambient conditions associated with unbearable heat stress.

An additional 1.5 billion will experience a month of such conditions, and 363.7 million will be faced with an entire season of three months of life-altering extreme heat stress, the study highlighted.

For instance, North America experiences the largest proportion of non-humid days of non-compensable heat stress (when sweating cannot compensate for heat) with 23.8 per cent of person-hours at 3 °C and 31.8 per cent at 4 °C.

“The worst heat stress will occur in regions that are not wealthy and that are expected to experience rapid population growth in the coming decades,” Matthew Huber, professor of earth, atmospheric and planetary sciences at Purdue University, said in a statement.

These countries, he explained, generate far fewer greenhouse gas emissions than wealthy nations. “As a result, billions of poor people will suffer, and many could die. But wealthy nations will suffer from this heat as well, and in this interconnected world, everyone can expect to be negatively affected in some way,” he added.

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