The deadly heat is baking the city.This is the way to cool them

If you ever Driving from the countryside into the city and marveling at the sharp rise in temperature, you have already felt the urban heat island effect. The streets and buildings of the metropolis absorb solar energy during the day and release it gradually at night.Built environment Basically bake it yourself, The temperature can be 20 degrees Fahrenheit higher than in neighboring countries, thanks to the large tracts of trees “sweating”, releasing water vapor and cooling the air.

With the rapid rise in global temperature, scientists, governments and activists are scrambling to find ways to deal with the heat island effect.according to World Health OrganizationBetween 2000 and 2016, the number of people exposed to heat waves increased by 125 million.The extreme heat caused more than Any other natural disaster, And it is especially dangerous for people with congenital diseases, such as asthma.

By 2050, seven out of ten people will live in cities, World Bank. That would be a lot of stuffy people. Vivek Shandas, a climate adaptation scientist at Portland State University, said: “I really think of cities as canaries in the case of coal mines, where you have a little foreboding of what the rest of the planet might be going through.” Researched the United States. Heat island effect in more than 50 cities.

Shanda’s research shows that even within a city, one block may be 15 degrees higher than another block, and this difference reflects income inequality. A major predictor of the heat of a block is how much green space it has.The richer part of the city tends to have more greenery, while the poorer part tends to have more greenery More specific; They are very developed, with hypermarkets, highways and industrial facilities that absorb solar radiation everywhere. Concrete landscape is very good at insulation, in fact, it will stay warm throughout the night. When the sun rises, the poor neighborhoods are already hotter than the rich neighborhoods.

Scientists have only just begun to study whether they can reduce the temperature of urban structures by deploying “cool” roofs, walls, and sidewalks. These roofs, walls, and sidewalks are light-colored to reflect sunlight. Brighter surfaces reflect more solar radiation than dark surfaces. (Think of how it feels to wear black instead of white on a sunny day. This albedo effect is also in the Arctic Heating up so fast.) However, although the thermodynamics are simple, the deployment of cold surfaces is extremely complicated.

George Ban-Weiss, an environmental engineer who studies cooling infrastructure at the University of Southern California, said the problem of cooling roofs is an example. In theory, it is simple to paint the large, flat top of a commercial building in white or light gray. Residential owners can choose lighter tiles-in fact, ordinary old clay can reflect sunlight well. These renovations will cool the air from the roof and the structure itself, which means that the occupants do not need to run the air conditioning frequently. If the building can bear the extra weight, the owner can even build a roof garden full of plants to cool the entire area by releasing water vapor.

However, although these changes will make the lives of people in each reconstructed building more tolerable, if enough owners follow suit, it may have unexpected regional side effects in some areas. In a coastal metropolis like Los Angeles, the warmth of the city is usually in sharp contrast with the cold of the ocean, and this difference promotes a reliable sea breeze. As the temperature of land and sea get closer, the wind may decrease. “This means less clean air entering the city, which tends to increase the concentration of pollutants,” Ban-Weiss said, plus the loss of the breeze that keeps people cool.

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