Deadly heat burns cities. Here’s how to cool them

If you ever are taken out of the country in the city and you were amazed at the drastic rise in temperature, you felt the effect of the city’s heat island. The streets and buildings of a metropolis absorb solar energy during the day and gradually release it at night. The built environment essentially burns and temperatures can rise up to 20 degrees Fahrenheit higher than the surrounding side, which takes advantage of parts of the trees that “sweat”, releasing water vapor and cooling the air.

As global temperatures rise rapidly, scientists, governments and activists are fighting for ways to counteract the heat island effect. According to the World Health Organization, the number of people exposed to heat waves jumped by 125 million between 2000 and 2016. Extreme heat kills more Americans than any other natural disaster and is especially dangerous for people with pre-existing conditions such as asthma.

By 2050, seven out of 10 people will live in cities, says the World Bank. These will be very inflatable people. “I really see cities as something like a canary in a coal mine situation, where you have little forerunner of what the rest of the planet could go through,” said Portland State University climate adaptation scientist Vivek Shandas, who studied the effect. on the heat island in over 50 American cities.

Shandas research shows that even in cities, one neighborhood can be 15 degrees hotter than another, and this discrepancy affects income inequality. The main predictor of the heat of the neighborhood is how many green areas there are. The richer parts of the city tend to have more greenery, and the poorer parts have more concrete; they are highly developed and full of large shops, highways and industrial facilities that absorb solar radiation. The concrete landscape is actually so good that it retains heat that it will stay warm all night. When the sun rises, a slum is already hotter than a slum.

Scientists are just beginning to study whether they can lower the temperature of urban structures by installing “cool” roofs, walls and flooring – ones that are bright and reflect sunlight. Lighter surfaces reflect more solar radiation than dark surfaces. (Think about how you feel while wearing black instead of white on a sunny day. This albedo effect is also part of the reason the Arctic is warming so fast.) But while thermodynamics are clear, unfolding cool surfaces turns out to be strangely complicated.

Take the problem of roof cooling, says environmental engineer George Ban-Weiss, who studies cool infrastructure at the University of Southern California. In theory, it is easy to paint the large, flat tops of commercial buildings in white or light gray. Homeowners could opt for lighter tiles – regular old clay actually reflects sunlight quite well. These modifications would cool the air coming out of the roof, as well as the structure itself, which means that passengers will not have to turn on the air conditioner as often. If a building can withstand the extra weight, homeowners could even create a roof garden full of plants to cool the entire area by releasing water vapor.

But while these changes would make life more bearable for people in any modified building if enough owners followed suit, in some areas it could have unforeseen regional side effects. In a coastal metropolis like Los Angeles, urban warmth usually contrasts with the coldness of the ocean, a differential that drives a reliable sea breeze. As land and sea temperatures approach each other, there may be less of this wind. “This means that less clean air enters the city, which would lead to higher concentrations of pollutants,” says Ban-Weiss, plus the loss of the breeze, which in itself keeps people cool.