It has long been known that installing white roofs helps reduce heat buildup in cities. But new research indicates that making surfaces more light-reflecting can have a significant impact on lowering extreme temperatures…

The systematic replacement of dark surfaces with white could lower heat wave maximum temperatures by 2 degrees Celsius or more. And with climate change and continued urbanization set to intensify “urban heat islands,” the case for such aggressive local geoengineering to maintain our cool grows.

The meteorological phenomenon of the urban heat island has been well known since giant cities began to emerge in the 19^th century. The materials that comprise most city buildings and roads reflect much less solar radiation – and absorb more – than the vegetation they have replaced. They radiate some of that energy in the form of heat into the surrounding air.

The darker the surface, the more the heating. Fresh asphalt reflects only 4 percent of sunlight compared to as much as 25 percent for natural grassland and up to 90 percent for a white surface such as fresh snow.

Most of the roughly 2 percent of the earth’s land surface covered in urban development suffers from some level of urban heating.

In 2016, San Francisco became the first American city to make green roofs compulsory on some new buildings. [The new law, going into effect in January, will require between 15 to 30 percent of roof space on most new construction projects to incorporate solar, green roofs, or a blend of both.]

Solar panels “cool daytime temperatures in a way similar to increasing albedo via white roofs,” according to a study by scientists at the University of New South Wales. The research, published in the journal Scientific Reports last year, found that in a city like Sydney, Australia, a city-wide array of solar panels could reduce summer maximum temperatures by up to 1 degree C.

Source: https://e360.yale.edu/features/urban-heat-can-white-roofs-help-cool-the-worlds-warming-cities