Dhaka worst-affected in the world by urban heat: Study
Nearly 25% of global population exposed to deadly heat, it says
Dhaka is the worst-affected city in the world by deadly urban heat, according to a study published by The Guardian yesterday.
Between 1983 and 2016, during which time the city's population rose dramatically, Bangladesh's capital experienced an increase of 575 million person-days (the cumulative population exposed to cumulative heat in a given year for a particular place) of extreme heat, the study said.
Other cities that underwent rapid population growth include Shanghai and Guangzhou in China, Yangon in Myanmar, Bangkok in Thailand and Dubai in the United Arab Emirates, the Guardian quoted the study as saying.
According to the study, exposure to deadly urban heat has tripled since the 1980s, and now affects nearly a quarter of the world's population.
Scientists put the worrying trend down to the combination of rising temperatures and growing numbers of people living in urban areas, and warned of its potentially fatal impact.
In recent decades, hundreds of millions of people have moved from rural areas to cities, which are now home to more than half the world's population. Amid surfaces such as concrete and asphalt -- which trap and concentrate heat -- and little vegetation, temperatures are generally higher in urban areas.
"This has broad effects," said Cascade Tuholske, the lead author of the study published in the journal PNAS and a postdoctoral researcher at Columbia University's Earth Institute.
"It increases morbidity and mortality. It impacts people's ability to work, and results in lower economic output. It exacerbates pre-existing health conditions."
The study used infrared satellite imagery and maximum daily heat and humidity readings from more than 13,000 cities from 1983 to 2016 to determine the number of people exposed to days in a year that exceeded 30C (86F) on the wet-bulb globe temperature scale (which takes into account the multiplier effect of high humidity) in an area. They matched the findings with the cities' populations over the same period.
The study found that the number of person-days soared from 40 billion a year in 1983 to 119 billion in 2016, representing a threefold increase. In 2016, 1.7 billion people were subjected to extreme heat on multiple days.