France Media Agency07 Oct 2021 12:56:13 IST
Rapid population growth and global warming are increasing exposure to extreme heat in cities, worsening health problems and making travel to urban areas less beneficial for the world’s poor, according to a study released Monday.
The increase affects nearly a quarter of the world’s population, according to the report published in the “Proceedings of the National Academy of Sciences. “
Over the past decades, hundreds of millions of people have moved from rural areas to cities where temperatures are typically higher due to surfaces such as asphalt that trap heat and lack of vegetation.
Scientists studied the maximum daily heat and humidity in more than 13,000 cities from 1983 to 2016.
Using the so-called “wet globe temperature” scale, a measure that takes heat and humidity into account, they defined extreme heat as 30 degrees Celsius (86 degrees Fahrenheit).
The researchers then compared the weather data with city population statistics over the same 33-year period.
They calculated the number of extremely hot days in a given year by the city’s population that year to come up with a definition called person-days.
The authors found that the number of person-days of exposure of city dwellers increased from 40 billion per year in 1983 to 119 billion in 2016.
Columbia University’s Earth Institute Tuholske Waterfall, lead author of the study, said the increase “increases morbidity and mortality.”
“It impacts the ability of people to work and leads to lower economic output. It worsens pre-existing health problems,” he said in a statement.
Population growth accounted for two-thirds of peak exposure, with actual warming temperatures contributing a third, though proportions vary from city to city, they wrote.
The capital of Bangladesh, Dhaka, was the worst affected city, with an increase of 575 million person-days of extreme heat during the study period.
Much of this was due to the fact that its population has grown from around four million in 1983 to around 22 million today.
Shanghai, Guangzhou, Yangon, Dubai, Hanoi and Khartoum as well as various cities in Pakistan, India and the Arabian Peninsula are other major cities showing similar trends.
Major cities that saw about half of their exposure caused by global warming were Baghdad, Cairo, Kuwait, Lagos, Kolkata and Mumbai.
The authors said the patterns they found in Africa and South Asia “could critically limit the ability of the urban poor to realize the economic gains associated with urbanization.”
They added that “sufficient investments, humanitarian intervention and government support” would be needed to counter the negative impact.
In the United States, around 40 large cities have seen their exposure grow “rapidly”, mainly in the Gulf Coast states of Texas, Louisiana, Mississippi, Alabama and Florida.
The study was conducted by researchers from Columbia in New York, the University of Minnesota Twin Cities, the University of Arizona at Tuscon, and the University of California at Santa Barbara.