Cool-roof effects on thermal and wind environments during heat waves: A case modeling study in Seoul, South Korea

Abstract

This study examines cool-roof effects on thermal and wind environments in Seoul, South Korea during the 2018 heat wave through Weather Research and Forecasting (WRF) model simulations. Two 37-day simulations, one with cool roofs that have a higher albedo and the other with conventional roofs, are conducted. In the daytime, cool roofs decrease the 2-m temperature, 10-m wind speed, surface sensible and latent heat fluxes, and planetary boundary layer height but increase the 2-m water vapor mixing ratio. The daytime maximum decreases are 1.0 °C in 2-m temperature and 0.5 m s−1 in 10-m wind speed. The cool roof-induced reduction of near-surface temperature tends to decrease with increasing heat wave intensity. The decrease in near-surface temperature weakens convergence of near-surface wind, indicating the weakening of daytime urban breeze. Also, the decrease in near-surface temperature, thus decreased land-sea air temperature difference, leads to the weakening of sea breeze. Interestingly, there are occasions on which the cool-roof case produces higher near-surface temperature at late afternoon times in a region of Seoul than the conventional-roof case. This can occur when the cooling caused by the sea breeze in the conventional-roof case is dominant over the cooling due to cool roofs in the cool-roof case.