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Urban centres in South Asia were among places most affected by increased exposure to extreme heat and humidity from 1983 to 2016, found a new study. Population boom and global warming were the primary causes behind the change.
Big cities in Bangladesh, India, China, Pakistan, Myanmar and some other countries in South Asia and the Arabian peninsula were the worst-hit, according to the analysis. Most of them are located in lower altitudes.
The health impacts of increased exposure to extreme heat and humidity are exacerbation of existing conditions, rise in chronic illnesses and fatalities, according to the lead author of the report Cascade Tuholske, a postdoctoral researcher at Columbia University’s Earth Institute.
The crisis also lowered economic output by affecting a person’s ability to work, he said.
Dhaka, the capital of Bangladesh, saw the highest increase (575 million) of person-days of extreme heat during the period, according to the report. Person-days was defined in the report as the annual increase in the urban population exposed to extreme heat.
Increasing global urban population exposure to extreme heat
Climate scientists from universities in the United States of America analysed the data for maximum daily heat and humidity in 13,115 cities across the globe. The findings were published in the Proceedings of the National Academy of Sciences journal October 4, 2021.
Around 17 per cent of the cities added an entire month of extreme-heat days over the 34-year study period, the analysts wrote.
The share of population explosion and global warming in the factor behind the exposure increase was different for different cities, the researchers observed. “Sheer urban population growth accounted for two-thirds of the exposure spike, while actual warming contributed a third,” the researchers concluded.
In Dhaka, for instance, population growth accounted for around 80 per cent of the exposure rise. The number of residents in the city rose to 22 million at present from 4 million in 1983, the paper stated. Surge in the number of residents was behind the exposure to deadly heat and hummidity in Delhi as well.
The authors of the paper said:
Over recent decades, hundreds of millions have moved from rural areas to cities, which now hold more than half the world’s population. There, temperatures are generally higher than in the countryside, because of sparse vegetation and abundant concrete, asphalt and other impermeable surfaces that tend to trap and concentrate heat — the so-called urban heat island effect.
In several other cities such as Kolkata and Mumbai in India, Baghdad in Iraq and Cairo in Egypt, rising temperature was a bigger contributing factor, found the study.
Globally, person-days during which urban residents were exposed to extreme heat and humidity tripled in the 34 years, growing to 119 billion in 2016 from 40 billion in 1983, the report showed.
As many as 1.7 billion city-dwellers were found to be subjected to harsh temperatures and humidity levels on multiple days by the end of the study period. A fourth of the global growth in person-days was driven by 25 settlements studied.