As cities across the United States brace for potentially record-breaking summer heat, a new study from the UK offers a simple yet effective solution to cool urban environments: painting roofs white.
Research reveals white roofs as a superior urban cooling solution, reducing temperatures by up to 2 degrees Celsius and outperforming green roofs and solar panels in mitigating heat island effects.Photo by Simone Hutsch on Unsplash
Experts Issue Heat Warnings
Forecasters are now warning that high temperatures may persist well beyond the July 4 holiday weekend.
According to the National Weather Service, "Extremely dangerous and record-breaking heatwave to impact much of the West through this weekend," stressing how deadly this early-July heatwave could be.
Excessive heat warnings are in place for much of California, as well as parts of Nevada, Oregon, Washington, and Arizona.
While temperatures are expected to rise further in the coming years due to climate change, certain methods could be implemented to cool cities and protect people from heat-related illnesses.
White Roofs as Top Cooling Solution
The research, published in Geophysical Research Letters, tells us that painting roofs white or covering them with a reflective coating could be more effective at cooling cities than other methods such as green roofs, street-level vegetation, or solar panels.
Dr. Oscar Brousse, lead author of the study and a researcher at UCL's Bartlett School Environment, Energy & Resources, said in a press release, "..cool roofs were the best way to keep temperatures down during extremely hot summer days."
Using a three-dimensional urban climate model of Greater London, the researchers tested the thermal effects of different urban heat management systems during the two hottest days of the summer of 2018, the warmest on record.
They found that if cool roofs were widely adopted, they could reduce outdoor temperatures across the city by about 1.2 degrees Celsius on average and up to 2 degrees Celsius in some areas.
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Other Cooling Methods
This reduction significantly outperformed other systems like extensive street-level vegetation or solar panels, which provided a smaller net cooling effect of about 0.3 degrees Celsius on average.
This approach could mitigate the effects of heat islands, which are urban areas experiencing higher temperatures due to the concentration of buildings, roads, and other structures that absorb and re-emit the sun's heat.
Green roofs, while beneficial for water drainage and providing wildlife habitats, showed a negligible net cooling effect on the city overall.
Interestingly, the study noted that green roofs could lower urban temperatures by an average of 0.5 degrees Celsius during the warmest times of the day.
However, this benefit was offset overnight as the thermal mass from the roofs retained daytime heat and released it at night, increasing nighttime temperatures by a similar amount.
By reflecting rather than absorbing heat, cool roofs not only cool the outside urban environment but also the inside of buildings, offering a dual benefit.
