To protect an entire city’s residents from heat during summer, simply painting every rooftop white or opting for a reflective coating could help reduce outdoor temperatures across a city by 1.2 degrees Celsius, according to a new study published in Geophysical Research Letters. Additionally, widespread installation of solar panels on rooftops could bring down temperatures by 0.5 degrees Celsius.
Lead author of the study, Oscar Brousse at the UCL Bartlett School Environment, Energy & Resources, said in a press release: “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. Other methods had various important side benefits, but none were able to reduce outdoor urban heat to nearly the same level.”
Because most cities are concrete jungles where natural land is mostly covered with pavements, buildings, and other asphalt/concrete surfaces that absorb and retain heat, a common phenomenon known as “urban heat islands” takes place. This makes urban areas significantly warmer than rural areas and every summer, urban heat islands make city dwellers far more vulnerable to suffering from heat exhaustion and heat stroke.
“Commonly proposed urban passive cooling strategies, which should be considered as measures that directly lower the temperatures, include increased urban vegetation, roofs incorporating vegetation (known as green roofs), or the deployment of highly reflective roofs that can 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 at city-scale, they can also reduce the outdoor air temperature and associated heat-related mortality.”
The study reported that green roofs did not contribute to city-wide cooling in any way when compared to cool roofs and rooftop solar panels.
“While rooftop solar photovoltaic (PV) panels are primarily considered as a source of electrical power, they can also be considered as a passive-active strategy for impacting outdoor and indoor air temperature by increasing the roofs’ albedo (the fraction of light that any surface reflects) and by transforming incoming solar radiation into electrical power that can be used to run the AC system,” the authors explained. “City scale impacts of any intervention are reduced when applied to a smaller area or fewer buildings. For cool roofs, we find that although major impacts are found when applied over low-rise residential areas of London, already applying them over central mid-rises of the city could reduce the temperature in surrounding residential areas.”
In 2023, the United Kingdom reported 2,295 deaths that could be attributed to heatwaves during the English summer. Heatwaves are known as one of the most fatal extreme weather events globally. The summer of 2023 was the hottest in human history, according to climate scientists. Studies have associated heat waves with higher levels of air pollution. Being exposed to heat for prolonged periods can make people far more prone to cardiovascular-related mortality, chronic kidney disease, and even respiratory distress.