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New Study Proves Trees Are Crucial In Keeping Cities Cool

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It's important to see the forest for the trees, most especially in keeping cities and towns cool, a new study revealed.

Researchers from the University of Wisconsin-Madison found that the right amount of tree cover in an area can lower summertime temperatures by at least 10 degrees Fahrenheit.

This magnificent cooling effect can be noticed from neighborhood to neighborhood, even on a scale of a city block, the study said.

"Keeping temperatures more comfortable on hot summer days can make a big difference for those of us who live and work there," said Monica Turner, one of the coauthors of the study.

Turner said cities are warmer than the countryside, but the new study, which is published in the journal Proceedings of the National Academy of Sciences, proves that temperatures vary just as much in cities.

How Trees Help Keep Cities Cooler

Heat waves in summer are driven more intense by climate change, and experts are working side-by-side to prepare for this extreme condition.

Turner explained that surfaces such as sidewalks, buildings, and roads often absorb heat from the sun at day and then release heat at night.

When there are trees, however, not only does shade surface from the rays of the sun, they also transpire and release water into the air through the leaves, which keeps temperatures cooler.

To get the maximum cooling effect, researchers said tree cover must be more than 40 percent. This means a single city block would need to be nearly half-way covered by trees and plants.

What's The Heat Island Effect?

Carly Ziter, the lead author of the study, said research similar to theirs often focus on a phenomenon called "urban heat island" effect, in which satellites are used to take ground surface temperature readings.

Ziter said the current study differs from previous ones as it looks at temperatures on a finer scale. She said the "heat island" effect could even be a "heat archipelago," which means that smaller islands of heat are interspersed in a city with cooler areas of shade.

What Ziter and her colleagues did instead of using satellites was use one sensor and a bicycle. They did this because deploying air temperature sensors across the city was far more expensive.

In 2016, Ziter biked around Madison city with a small weather station. She strolled around the city in 10 different transects multiple times at different parts of the day. Her sensor helped her mark her location and record air temperatures as she rode, which resulted in real-time data every 5 meters.

Ziter biked around 400 to 500 meters in the duration of the city and she collected enough data to show just how instrumental trees are in keeping cities cool.

Plant Trees, Plan It Well

It will not be enough to just plant trees, Ziter said. It will be important to think about how these trees are planted and where these trees are being planted.

Ziter said city planners should focus on areas that are near the 40 percent threshold by planting trees there. She said it should be in places where people are active and not just in parks.

Additionally, Ziter said areas with lower tree canopy cover should not be abandoned either, because those communities tend to have people with lower income and marginalized people.

The point is that urban landscaping and development is important in making neighborhoods more livable, she said.

"The trees we plant now or the areas we pave now are going to be determining the temperatures of our cities in the next century," added Ziter.

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