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Cool roofs could have saved lives during London's hottest summer

As many as 249 lives could have been saved in London during the 2018 record-setting hot summer had the city widely adopted cool roofs, estimates a new study by researchers at UCL and the University of Exeter.

The paper, published in Nature Cities, analyzed the cooling effect that roofs painted white or other reflective colors would have on London's ambient temperature between June and August 2018, the city's hottest summer. From June through August, the average temperature around London was 19.2 degrees C, about 1.6 degrees warmer than average for that time of year.

Urban environments tend to absorb a lot of heat and are usually a few degrees warmer than the surrounding region, an effect known as the "urban heat island." Painting roofs white or reflective colors would absorb less radiant energy from the sun than traditional dark roofs, effectively cooling the city.

The researchers found that had cool, light-colored roofs been widely installed throughout London, it could have cooled the city by about 0.8 degrees C on average, preventing the heat-related deaths of an estimated 249 people—equating to around 32% of the 786 heat-related deaths during that period.

In the same paper, the researchers also found that had rooftop photovoltaic solar panels been similarly widely adopted, they would also have cooled the city by about 0.3 degrees C. This would have prevented the deaths of an estimated 96 people across the city, or 12% of the heat-related deaths during that summer.