Are more reflective roofs associated with cooler neighborhood air?

Details

Researchers investigated how neighborhood-scale land use and land cover (LULC) properties relate to observed air temperatures in Central Los Angeles and the San Fernando Valley (SFV), two regions within Los Angeles County. They focused on albedo, or reflectivity, and tree fraction.

High-spatial-density meteorological observations came from 76 personal weather stations. For each hour of July 2015, the researchers used robust regression to relate observed air temperatures to the spatial mean of each LULC parameter within a 500 m radius neighborhood around each station.

In the neighborhoods studied, higher roof albedo was associated with lower air temperatures, with the strongest sensitivities in the afternoon. At 14:00–15:00 local daylight time, air temperatures were lower by 0.31 °C in SFV and 0.49 °C in Central Los Angeles per 1 MW increase in daily average solar power reflected from roofs per neighborhood. Per 0.10 increase in neighborhood average albedo, daily average air temperatures were lower by 0.25 °C and 1.84 °C.

During the day, roof albedo effects on air temperature appeared to exceed those of tree fraction in the two regions. At night, higher tree fraction was associated with lower air temperatures.