Planting trees not only cools down urban centers, they can reduce crime

SALT LAKE CITY — Salt Lake City officials are looking at ways to cool down what is known as the “Urban Heat Island” effect, UHI. The effect happens when cities are much warmer than surrounding suburban and rural areas because of the concrete and steel.

A report from The Environmental Protection Agency stated even a couple of degrees of extreme heat can affect people’s health negatively. One or two degrees can increase breathing problems, heatstroke and heat exhaustion. 

Trees can lower the surrounding ambient temperature by two degrees, or more if there is a breeze. They could keep Salt Lake City from having another ‘hottest summer ever recorded.’

Laura Bandara, Salt Lake City’s Urban Designer, said that’s one reason for the push to plant 1000 trees a year in the city. Especially in areas that don’t have very many, like the west side of Salt Lake City.

Trees can reduce crime and improve health

“Shade trees lower the temperature on sidewalks and have the added benefit of not have to repave asphalt as often,”  Bandara said. “The trick is to get the right type of tree in the right areas.”

Another benefit is that trees add a sense of community and lowers aggression. Bandara stated, “Studies show neighborhoods with trees have reduced crime.”

Bandara also cited research from Vibrant City Labs which shows hospital patients who look out a window onto trees and grass are discharged much earlier than patients who don’t see any vegetation at all.

All of this is part of the “Urban Forest Action Plan” the city put together. Bandara said the Salt Lake City council will be voting on it soon.

Diane Pataki, a professor of the School of Biological Sciences at the University of Utah said, “There’s a lot of different impacts of trees on climate, but the most direct one is just intercepting sunlight.”

Trees aren’t the only thing that will cool a city down

Another option several other cities are using is green roofs; Where gardens and trees are planted on top of roofs to help reduce the sun’s rays heating a dark surface. But that can cause problems in Utah.

“In the deep soil, green roofs have to be irrigated frequently because the soil is very shallow and if people want to use green roofs in this kind of environment, they just have to be aware that they’re going to require water,” Pataki said.

Bandara concurred and said tree roots at street level can find groundwater, so they don’t require as much human intervention. “Our climate is so dry, trees and grass will need much more water on a rooftop where the soil isn’t as deep,” she said. 

However, city officials are looking into another way to help cool down the “Urban Heat Island” effect. They include white membranes on rooftops and reducing the amount of asphalt.

Residents can help cool down their surroundings

City officials are asking residents not to remove trees from the parking strips. Bandera said, “Well-meaning people are pulling up all vegetation thinking they are saving water. But in reality, they are adding to the heating, especially if they replace grass with rocks.”

“Xeriscaping, using the appropriate water-wise plants, is not the same as Zero-scaping where people pull out all the vegetation,” Bandera said.

Other strategies Salt Lake City is pursuing to reduce Urban Heat Island impacts:

• The new airport redevelopment program chose to construct a 5 level parking garage in an effort to reduce surface parking and mitigate UHI impacts. They also use white membranes on rooftops.
• Public Utilities has investigated the impact of synthetic turf on UHI and have found it to have negative impacts on a variety of urban environmental concerns. As a result, we strongly discourage the use of synthetic turfgrass and prohibit it in park strips.
• Street redesign projects include some strategies to reduce the amount of asphalt, including roadway narrowing.
• Engineering is testing cool pavement coatings.
• We also have an option for redevelopment to meet stormwater management and drainage requirements by providing a site design that reduces the number of impervious surfaces.
• The RDA is looking at incentivizing green roofs.

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