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Urban Heat Islands

Keep it Cool

By Maris Lawyer (Posted April 6, 2020)

Urban heat islands are areas within a city where there is a significant and sustained rise in temperature. A variety of factors can lead to the creation of these isolated, island-like pockets of heat — like elevated levels of automobile exhaust and a lack of air flow caused by the large buildings that shield the city interior from breezes.

However, the primary cause of urban heat islands is a concentration of inorganic building materials such as asphalt and concrete that absorb and retain heat (Önder, 2014). According to a 2019 U.S. Environmental Protection Agency report, urban heat islands have increased city temperatures by 5 to 20 degrees Fahrenheit when compared to temperatures in nearby rural communities.

This growing issue of increased city temperatures will continue to aggravate the climate change crisis. However, there is a simple, inexpensive way to help alleviate urban heat islands that don’t involve demolishing skyscrapers. By bringing more plant life into our urban spaces, we can greatly reduce the temperature increases in city centers — and even improve energy efficiency in our own homes.

For businesses and urban living spaces in the city, one of the most effective ways to counteract urban heat islands is to create rooftop gardens. The National Research Council of Canada reports that an urban rooftop can get as hot as 158 degrees Fahrenheit on a hot day; however, an identical roof featuring a roof garden can maintain a temperature of 77 degrees under the same conditions.

Beyond the staggering benefits of temperature regulation, rooftop gardens also do wonders for stormwater management. Rather than a deluge of rainwater runoff during storms, rooftop garden plants drink up the excess rainwater. In addition, plants are continuously helping to produce more oxygen and reduce CO2 in the atmosphere.

In 2017 the “Gardener’s World” TV show reported on an interesting study from the University of Sheffield. The study noted that relatively small shrubs and flowers planted close to a house can regulate in-home temperatures effectively enough to reduce energy bills by up to 30 percent. In the summer, larger shrubs and trees planted close to a house can keep temperatures up to 15 degrees cooler than if the house were fully exposed to the sun.

Plants accomplish this by not only reflecting heat (rather than absorbing it), their foliage also helps to trap moisture levels, which in turn cools the air and any materials around the plant. Likewise, in winter, those same plants help buffer wind chill around the house, helping the home to retain heat more effectively. Plants also have the added benefit of beautifying your yard, while strategic landscaping can add property value.

When it comes to climate change, it might feel like there’s nothing you can do to help, the good news is that every little bit counts. If you choose the right plant and location, it takes little effort to dramatically reduce the damage, and it will have the added benefit of reducing your utility bill.

As spring begins to flourish, plan some rewarding gardening projects for your own home and encourage local city-centric businesses to explore opportunities for rooftop gardens on their properties.