October 4 (WNN) — A study published Monday by the Proceedings of the National Academy of Sciences found that the number of days city residents around the world are exposed to extreme heat and humidity has tripled since the 1980s.
The increasing number of days with extreme heat and humidity in urban areas now affects nearly a quarter of the global population and is a combined result of both rising temperatures and urban population growth, the researchers said.
The data shows that the number of person-days – or population multiplied by days – in which city residents were exposed to extreme heat and humidity increased from 40 billion per year in 1983 to 119 billion in 2016.
According to the researchers, as of 2016, 1.7 billion people were being subjected to these conditions on several days per year.
“Extreme heat and increased humidity have wide-ranging effects,” study co-author Cascade Tuholske said in a press release.
Among other concerns, “it affects people’s ability to work, and results in lower economic output”. [and] It exacerbates pre-existing health conditions,” said Tuholske, a postdoctoral researcher at Columbia University’s Earth Institute in New York City.
According to researchers, over the past 40 years, hundreds of millions of people have moved from rural areas to cities, which now house more than half of the world’s population.
Temperatures in these urban areas are generally higher than in rural areas because of sparse vegetation and abundant concrete, asphalt and other surfaces that trap and concentrate heat, he said.
A study focused on cities in the United States published in July found that the effects of extreme heat conditions are felt more in poorer areas.
For this study, Tuholske and colleagues combined infrared satellite imagery and readings from thousands of ground instruments to determine maximum daily heat and humidity readings in 13,115 cities from 1983 to 2016.
He defined extreme heat as 86 degrees Fahrenheit on the so-called “wet-bulb globe temperature” scale, a measurement that takes into account the effects of high humidity on the human body.
This weight-bulb temperature equates to about 106 degrees Fahrenheit on the “real experience” heat index, at which point even most healthy people find it difficult to work outside for long periods of time, and the unhealthy can get very sick or even die. .
The researchers matched the weather data with the population data of the cities over the same time period.
The data suggest that the increase in urban population accounted for two-thirds of the exposure spike, while actual climate warming contributed a third.
The most affected city in terms of person-days was Dhaka, the rapidly growing capital of Bangladesh, which saw an increase of 575 million person-days of extreme heat in the study period.
Its ballooning population alone — from 4 million in 1983 to 22 million today — caused an 80% increase in extreme heat and humidity for the people living there, the researchers said.
According to the researchers, other cities with a similar population-heavy trend include Shanghai and Guangzhou in China, as well as Dubai, Hanoi and Khartoum, Sudan.
The cities that saw nearly half or more exposure to extreme heat and humidity due to the warm climate alone were Baghdad, Cairo, Kolkata and Mumbai, the researchers said.
Seventeen percent of the cities studied added extreme heat days throughout the month over the 34-year study period, which includes nearly 40 large cities in Texas and the Gulf Coast of the United States.
The data shows that cities such as Houston, Dallas-Fort Worth, San Antonio and Austin, as well as Pensacola, Fla., have different combinations due to both rising populations and rising heat.
However, in Las Vegas, as well as Savannah, Ga and Charleston, SC, this has been primarily due to population growth, while in Baton Rouge, LA and Gulfport, Miss., the primary culprit was warming temperatures.
Because the period covered by the study included data as far back as 2016, it did not include the series of record heat waves that hit much of the United States and Canada this summer.
Still, the study “could serve as a starting point to identify ways to address local heat issues,” such as planting trees, said Christina Dahl, a climate researcher at the Union of Concerned Scientists.
“This study shows that it will take a considerable, conscientious investment to ensure that cities remain livable in the face of warmer climates.”