White Roofs, Keep It Cool: A Promising Solution To Urban Heat Challenges

White or reflective paint is more effective at cooling cities than solar panels or greenery on roofs, scientists say, offering potential relief during extremely hot summer days. Two separate studies examined the impact of ‘cool roofing’ and discovered that white or reflective coatings could lower outdoor city temperatures by up to 2 degrees Celsius.

Research on Cooling Methods in London

Scientists at University College London used a model of Greater London to test various cooling methods during its hottest days in 2018, a summer marked by record-breaking heat. The findings, published on Thursday in the journal Geophysical Research Letters, indicated that widespread adoption of cool roofs could reduce surrounding temperatures by 1.2C to 2C. In contrast, other methods, such as planting vegetation at street level or installing solar panels, provided a much smaller cooling effect, averaging about 0.3C across London.

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Expert Insights on Cool Roofing

“We comprehensively tested multiple methods that cities like London could use to adapt to and mitigate warming temperatures, and found that cool roofs were the best way to keep temperatures down during extremely hot summer days,” said the study’s lead author, Oscar Brousse from UCL. “Other methods had various important side benefits, but none were able to reduce outdoor urban heat to nearly the same level.” Scientists also discovered that air conditioning, which moves heat from inside buildings to the outside, could increase temperatures in densely populated central London by up to 1 degree Celsius. “By reflecting rather than absorbing heat, cool roofs have the dual benefit of not only cooling the outside urban environment but the inside of buildings as well,” the report said.

Global Implementation of Cool Roofing

A separate study published in March examined the real-world impact of painting not just roofs, but also roads and exterior walls white in an industrial district of Singapore. Researchers found that this approach reduced overall temperatures by up to 2 degrees Celsius in the afternoon, making it feel 1.5 degrees cooler for pedestrians in tropical climates. Lighter surfaces reflect heat rather than absorbing it, a phenomenon known as albedo.

High albedo surfaces include snow, ice, and light-coloured urban materials. In contrast, asphalt has low albedo, absorbing more energy and heat, similar to oceans and forests. Other studies have shown that white plastic roofing materials can reflect 80 percent of the sunlight that hits them. Cool roofing has already been implemented in various locations, including Greece, which is susceptible to scorching summer temperatures, and parts of India, where heatwaves can be extreme.

Challenges and Future Considerations

However, experiments with painting roads and sidewalks white have been less well-received. In cities that tested this approach in the United States and France, some residents complained about glare and dirt on the surfaces.

Cities act as ‘heat islands,’ experiencing higher temperatures than their surrounding areas due to the absorption of solar energy by buildings and roads. As the global population continues to shift towards urban areas and heatwaves become longer and more intense due to climate change, finding adaptive solutions will become a top priority for urban planners.

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