2022

Author(s): Ko J, Schlaerth H, Bruce A, Sanders K, Ban-Weiss G

Climate change is expected to exacerbate the urban heat island (UHI) effect in cities worldwide, increasing the risk of heat-related morbidity and mortality. Solar reflective 'cool pavement' is one of several mitigation strategies that may counteract the negative effects of the UHI effect. An increase in pavement albedo results in less heat absorption, which results in reduced surface temperatures (T (surface)). Near surface air temperatures (T (air)) could also be reduced if cool pavements are deployed at sufficiently large spatial scales, though this has never been confirmed by field measurements. This field study is the first to conduct controlled measurements of the impacts of neighborhood-scale cool pavement installations. We measured the impacts of cool pavement on albedo, T (surface), and T (air). In addition, pavement albedo was monitored after installation to assess its degradation over time. The field site (similar to 0.64 km(2)) was located in Covina, California; similar to 30 km east of Downtown Los Angeles. We found that an average pavement albedo increase of 0.18 (from 0.08 to 0.26) corresponded to maximum neighborhood averaged T (surface) and T (air) reductions of 5 degrees C and 0.2 degrees C, respectively. Maximum T (surface) reductions were observed in the afternoon, while minimum reductions of 0.9 degrees C were observed in the morning. T (air) reductions were detected at 12:00 local standard time (LST), and from 20:00 LST to 22:59 LST, suggesting that cool pavement decreases T (air) during the daytime as well as in the evening. An average albedo reduction of 30% corresponded to a similar to 1 degrees C reduction in the T (surface) cooling efficacy. Although we present here the first measured T (air) reductions due to cool pavement, we emphasize that the tradeoffs between T (air) reductions and reflected shortwave radiation increases are still unclear and warrant further investigation in order to holistically assess the efficacy of cool pavements, especially with regards to pedestrian thermal comfort.

DOI: https://dx.doi.org/10.1088/1748-9326/ac58a8