street trees

How to make cities cooler

March 26, 2024 By EarthWise Leave a Comment

In cities, the air, surface, and soil temperatures are almost always warmer than in rural areas. This is known as the urban heat island effect. Urban heat islands occur when cities replace natural land cover with dense concentrations of pavement, buildings, and other surfaces that absorb and retain heat.

Urban planners around the world have been researching ways to reduce the effects of heat in cities. For example, trees, green roofs, and vegetation can help reduce urban heat island effects by shading building surfaces, deflecting radiation from the sun, and releasing moisture into the atmosphere.

A new study led by researchers from the University of Surrey in the U.K. has analyzed how well various green spaces and waterways are able to cool down cities. The study, which was recently published in the journal The Innovation, found that wetlands, parks, and even botanical gardens are among the best ways to keep cities cool.

In fact, the researchers found that botanical gardens can cool city air by a whopping 9°F during heatwaves on average. Wetlands can cool city air by 8.5°F on average, followed by rain gardens at 8.1°F, green walls at 7.4°F, street trees at 6.8°F, city farms at 6.3°F, city parks at 5.8°F, and reservoirs and playgrounds at 5.2°F.

The researchers also found that cities can unlock even greater benefits by connecting green spaces into green corridors. Greening projects can also help remove carbon emissions and prevent flooding.

The research team hopes its findings will help urban planners design more resilient cities.

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Wetlands, parks and even botanical gardens among the best ways to cool cities during heatwaves

Photo, posted April 25, 2022, courtesy of Catherine Poh Huay Tan via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio

Street Trees And Depression | Earth Wise

February 25, 2021 By EarthWise Leave a Comment

**According to a study published in the journal Jama Network Open last fall, the COVID-19 pandemic has tripled the rate of depression in U.S. adults in all demographic groups.**

Previous studies have demonstrated that greenspaces in urban areas can have a positive effect on those people experiencing mental ill health. But most of those studies used self-reporting measures, which makes it difficult to compare results and draw conclusions.

As a result, an interdisciplinary research team from three research organizations in Germany tried to improve upon the work by involving an objective indicator: prescriptions of antidepressants. To figure out whether greenspaces – in this case street trees – could positively influence mental health, the researchers focused on how the number of street trees and their proximity to homes correlated to the number of prescribed antidepressants.

After analyzing data from nearly 10,000 people living in Leipzig, Germany, and combining the findings with data on city street trees, researchers were able to identify an association between antidepressant prescriptions and the number of street trees. The results were controlled for other factors known to be associated with depression, such as employment, gender, age, and body weight.

Having more trees within 100 meters of the home was associated with a reduced risk of being prescribed antidepressants. The association was especially strong for groups of people deprived of street trees.

Street trees in urban cities can not only serve as a nature-based solution for good mental health, but they can also contribute to climate change mitigation and biodiversity conservation.

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Street trees close to the home may reduce the risk of depression

Photo, posted August 17, 2011, courtesy of Aleksandr Zykov via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio.

Cooling Down Urban Heat Islands

November 6, 2019 By EarthWise Leave a Comment

Researchers have known about and studied the urban heat island effect for quite some time. Since large cities began to emerge in the 19th century, it has been understood that various aspects of the urban environment lead to warmer temperatures than the surrounding countryside.

Researchers led by a group at Portland State University in Oregon have been utilizing a new way of studying the urban heat island effect. They have used citizen science volunteers in 24 cities around the world to map temperatures in the cities at ground level in great detail using mobile sensors attached to slow-moving vehicles. Previous studies have used data from satellite or stationary sensors. They have learned that the urban heat island effect is more complicated, more varied, and subtler than the earlier data indicated.

They found that there are six things that affect urban heat. Three are living — the volume of the tree canopy, the height of the tree canopy, and the ground level vegetation. Three are human-built — the volume of buildings, the difference in building heights, and the coloring of the buildings.

Buildings can have both negative and positive effects. Tall buildings that cast shade actually lower relative afternoon temperatures, while densely packed shorter buildings, like the big-box stores in suburban areas, lead to hotter afternoon temperatures. The studies show that increasing the difference in building heights in an area creates more air circulation, which has a cooling effect.

The study also showed that urban heat is a social justice issue. Lower-income neighborhoods largely barren of trees have considerably higher temperatures than more affluent, tree-shaded areas.

Such detailed research can be used to guide decisions in urban planning with regard to trees, building heights, and the color and type of surfaces in our urban spaces.

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Can We Turn Down the Temperature on Urban Heat Islands?

Photo, posted July 21, 2009, courtesy of Daniel Dionne via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio.

The Value Of Street Trees

July 13, 2016 By WAMC WEB

Why should you care whether there are trees on your street or on the streets nearby? Besides the obvious fact that they make streets more attractive, street trees provide a number of real benefits both for residents and for the environment.

Planning Cooler Cities

October 28, 2015 By EarthWise

Anyone who has walked the streets of New York City or Washington, D.C. on a stifling summer day can attest to the fact that cities feel hotter. It’s not a matter of perception.

Street Trees Are Good For Us

September 11, 2015 By EarthWise

Want to feel younger? Live on a street with more trees. That’s the finding of University of Chicago researchers who studied the impact of street trees on the real and perceived health of residents of Toronto, Canada.