The deadly heat is baking cities. Here’s how to calm her down


If you ever Driving from the countryside to the city and marveling at the skyrocketing temperature, feel the urban heat island effect. City streets and buildings absorb the sun’s energy during the day and gradually release it at night. Built environment It basically bakes itself, And temperatures can rise up to 20 degrees Fahrenheit higher than the surrounding areas, which benefit from expanses of trees that “sweat”, releasing water vapor and cooling the air.

With global temperatures rising rapidly, scientists, governments and activists are scrambling to find ways to counter the heat island effect. according to World Health Organization, the number of people exposed to heat waves jumped by 125 million between 2000 and 2016. Extreme heat kills more Americans Any other natural disasterIt is especially dangerous for people with pre-existing conditions such as crisis.

By 2050, seven out of 10 people will live in cities, she says world bank. That would be a large number of people suffering from heat. says Vivek Chandas, a Portland State University climate adaptation scientist who has studied the effect of heat islands in more than 50 US cities.

Shandas’ research showed that even within cities, one neighborhood may be 15 degrees hotter than another, and that the variance indicates income inequality. A key factor in predicting a neighborhood’s heat is the amount of green space it has. Richer parts of the city tend to have more green spaces and poorer parts You have more tangible; It has been highly developed and filled with supermarkets, highways and industrial facilities that soak up the sun’s rays. Concrete landscaping is so good at holding up heat, in fact, it will stay warm all night long. When the sun rises, the poor neighborhood is already much hotter than the rich neighborhood.

Scientists are just beginning to study whether they can lower the temperature of city structures by spreading “cool” roofs, walls and sidewalks – those that are light-colored and reflect sunlight away. Lighter surfaces reflect more sunlight than dark surfaces. (Think about how you feel wearing black instead of white on a sunny day. This whiteness effect is also part of the reason why the Arctic warming quickly.) But while thermodynamics is straightforward, the diffusion of cold surfaces turns out to be strangely complex.

Take the problem of rooftop cooling, for example, says environmental engineer George Pan Weiss, who studies Cool Infrastructure at the University of Southern California. In theory, it is easy to paint large, flat surfaces of commercial buildings in white or light gray. Residential homeowners can opt for the lightest tiles – plain old clay, in fact, reflects sunlight well. These modifications will cool the air coming out of the roof, as well as the structure itself, meaning occupants won’t need to run the air conditioner as often. If the building could withstand the extra weight, the owners could create a rooftop garden filled with plants, which would cool the entire area by releasing water vapor.

But while these changes will make life more bearable for the people inside each modified building, if enough owners follow suit, in some areas they may have unintended regional side effects. In a coastal city like Los Angeles, urban warmth usually contrasts with the coolness of the ocean, a difference that drives the reliable sea breeze. As land and sea temperatures approach each other, there may be less of those winds. “This means less clean air flows into the city, which would make pollutant concentrations higher,” as well as a loss of breeze that keeps people cool in and of itself, says Pan Weiss.



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