Deadly Heat Is Baking Cities. Here’s How to Cool Them Down

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if you ever Moved from country to city and temperatures rise dramatically, you’ve felt the urban heat island effect. The streets and buildings of a metropolis absorb the energy of the sun during the day and gradually release it at night. The built environment essentially bakes itself, and temperatures can rise by up to 20 degrees Fahrenheit compared to the surrounding country, benefiting from swaths of trees that “sweat”, release water vapor and cool the air. We do.

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As global temperatures continue to climb, scientists, governments and activists are scrambling for ways to combat the heat island effect. According to World Health OrganizationBetween 2000 and 2016, the number of people exposed to heat waves increased by 125 million. More Americans die from extreme heat any other natural calamity, 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 world Bank. It would be a totally scorched man. Vivek Shandas, a climate adaptation scientist at Portland State University, says, “I really see cities as a canary in coal mine status, where you have a small harbinger of what the rest of the planet might experience. ” The heat island effect has been studied in more than 50 US cities.

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Shandas’ research has shown that even within cities, one neighborhood can be 15 degrees hotter than another, and this disparity reflects income inequalities. A major predictor of a neighborhood’s warmth is how much green space it has. The richer parts of a city have more greenery, and the poorer parts are more solid; They are highly developed, and full of big box stores, freeways and industrial facilities that soak up the sun’s radiation. A concrete landscape is so good at capturing heat, in fact, it will stay warm all night long. When the sun rises, a poor neighborhood is already warmer than a wealthy neighborhood.

Scientists are just beginning to study whether they can reduce the temperature of city structures by deploying “cool” roofs, walls and sidewalks — which are lighter in color and bounce sunlight away. Light surfaces reflect more sunlight than dark surfaces. (Think about how you feel when wearing black instead of white on a sunny day. This albedo effect is also part of the reason the Arctic is warming so rapidly.) But the thermodynamics are straightforward, while cold The deployment turns of surfaces can be strangely complicated.

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Take the problem of cooling roofs, says George Ban-Weiss, an environmental engineer who studies cool infrastructure at the University of Southern California. In theory, it’s easy to paint the large, flat tops of commercial buildings white or light gray. Residential homeowners can opt for lighter tiles—regular old clay, in fact, reflects sunlight well. These modifications will cool the structure as well as the air coming from the roof, meaning occupants won’t need to run air conditioning as often. If a building can support the extra weight, owners can also create a roof garden filled with plants, which will 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, it could have an unintended regional side effect in some areas. In a coastal metropolis such as Los Angeles, urban heat is usually the opposite of ocean coolness, a difference that drives a reliable sea breeze. As land and sea temperatures get closer to each other, the wind may subside. “So that means less clean air is coming into the city, which will increase pollutant concentrations higher,” Ban-Weiss says, as well as the loss of air that keeps people cool.

A cold wall follows the same principle, just with a vertical surface. But it can also have an unintended consequence: Sunlight reflecting off a wall can shine on pedestrians, heating them instead of the building. And engineers like Ban-Weiss are hitting the same snag in their experiments with cold pavements, slathered with a reflective coating. It actually lowers the temperature of the road surface – but it also bounces some of that energy back onto pedestrians.

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“It’s like a tug-of-war,” Ban-Weiss says. “You’ve got a decrease in air temperature that makes people more comfortable. But then you’ve got an increase in this absorbed solar radiation from pedestrians that will make them less comfortable. And so the question is, which one wins. Is the person less comfortable or more comfortable with cold pavement? And the answer is not yet clear.” At least during the day—at night, reflection isn’t an issue.

Initial projects are starting to provide some data. In September, Phoenix officials announced the results of the first year of the city’s Cool Pavement pilot program, in which sections of roads were treated with a reflective coating. Researchers at Arizona State University took temperature readings four times a day and compared treated roads to non-treated roads. They found that the treated sidewalk was an average of 10.5 to 12 degrees Fahrenheit cooler in the afternoon. The surface temperature at sunrise was 2.4 °C colder, suggesting that the coating reduced some of the heat carried from day to day.

But reflectance — or the amount of light that can reflect back on pedestrians — also increased, which the scientists measured with a light-detection instrument called a spectroradiometer. “This may be a necessary trade-off, because if we want to reduce surface temperatures by using a reflective surface, it may not matter,” says Jennifer Vanos, a climate and health scientist at Arizona State University who conducted the study. Would have.” “However, do people walk in the middle of the street? It’s expected not to happen.”

pavement treatment in phoenix

Courtesy of City of Phoenix

There’s another seemingly ingenious solution that cities can deploy anywhere that isn’t in the way of a car: Plant more living things. Done right, a green space produces many benefits: It cools the neighborhood and beautifies it, while also acting as a sponge to absorb flood waters. It provides shade for people to shelter during a heat wave, plus it is good for mental health. Creating space creates jobs, as does maintaining it. And lower temperatures reduce demand for air conditioning, which is a major source of emissions, as well as heat, because of all the hot air that makes machines work. Elizabeth Sauvin, codedirector of Climate Interactive, a nonprofit that focuses on the intersection of climate change and inequality, calls it “multiple solutions.”

But planting greenery can also have an unintended consequence – this is known as green gentrification. Urban investment attracts the attention of speculators, who begin to buy housing in low-income neighborhoods, increasing rents. “Then the investment in neighborhoods was to help migrate people to places that are heat islands or other types of climate risk areas,” says Savin.

Savin says local residents should be involved in the plan to increase green spaces as soon as possible. “It cannot be a tacit approach. It has to add up to forethought about affordable housing or community-owned land trusts. And it needs to happen well before the first shovels of the project,” she says.

Shandas points out that it is still too new to think about heat reduction in urban planning, even as temperatures climb. “There is not a single municipality in the country that I know of that requires consideration of rising temperatures in their design guidelines or regulations,” Shandas says. “Right now developers are building lot-edge-to-lot-edge in cities across the country, and they are leaving no room on the lot for a small garden box, let alone any mature large tree. Give.”

And since the science of urban heat is still young, it’s not always clear which strategy is best to follow. For example: Which trees do best in which climate? Has the heat island effect already become so bad in some places that they can no longer support certain species? And how much coolness can trees really produce? “We don’t have a really good way of understanding the relationship between how well a specific type of heat-correcting design works in terms of temperature levels,” Shandas says. For example, it’s summer in the northwest. “

The city of the future could be more reflective of both And Greener, with both strategies being used in concert to reduce the heat island effect. But in terms of cooling effect, Ban-Weiss says, it’s hard to beat flora when it comes to the many benefits at once that they provide. “If you’re going to choose a technology, I would always go with green space,” he says. “It solves a lot of different problems.”


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