‘Cool roofs’ can help protect city residents during heat waves

To protect residents of an entire city from the heat during the summer, simply painting every roof white or opting for a reflective coating can help reduce outside temperatures in a city by 1.2 degrees Celsius, according to a new study published in Geophysical research letters. In addition, the large-scale installation of solar panels on roofs could reduce temperatures by 0.5 degrees Celsius.

Lead author of the study, Oscar Brousse from UCL Bartlett School Environment, Energy & Resources, said in a press release: “We extensively tested several methods that cities like London could use to adapt to and improve global warming. to mitigate, and discovered that cool roofs were the best way to keep temperatures down during extremely hot summer days. Other methods had several important side benefits, but none were able to reduce outdoor urban heat to nearly the same level.”

Because most cities are concrete jungles where the natural land is largely covered with sidewalks, buildings, and other asphalt/concrete surfaces that absorb and retain heat, a common phenomenon known as “urban heat islands” occurs. This makes urban areas significantly warmer than rural areas and every summer, urban heat islands make city dwellers much more vulnerable to heat exhaustion and heat stroke.

“Commonly proposed urban passive cooling strategies, which should be viewed as measures that directly reduce temperatures, include increased urban vegetation, roofs that incorporate vegetation (known as green roofs), or the deployment of highly reflective roofs that may be composed of different roofing materials . (e.g. concrete, metal or single-ply membrane), known as cool roofs,” the authors wrote in the study. “Changes to roofs can reduce indoor temperatures 67 or cooling needs in a building. When deployed on a city scale, they can also reduce outdoor air temperatures and associated heat-related mortality.”

The research shows that green roofs do not contribute in any way to cooling in the entire city, compared to cool roofs and solar panels on roofs.

“While rooftop photovoltaic (PV) solar panels are primarily considered a source of electrical energy, they can also be considered a passive-active strategy to influence indoor and outdoor air temperatures by increasing the roof’s albedo ( the portion of light that any surface reflects) and by converting incoming solar radiation into electrical current that can be used to run the AC system,” the authors explain. “The city-scale impact of any intervention is reduced when it is applied to a smaller area or fewer buildings. For cool roofs, we find that while major impacts are seen when applied to low-rise residential areas of London, applying them already to central mid-rise buildings in the city could reduce temperatures in surrounding residential areas.”

In 2023, Britain reported 2,295 deaths attributed to heatwaves during the English summer. Heat waves are known as one of the most fatal extreme weather events in the world. The summer of 2023 was the hottest in human history, according to climate scientists. Studies have linked heat waves to higher levels of air pollution. Long-term exposure to heat can make people much more susceptible to death from cardiovascular disease, chronic kidney disease and even respiratory problems.