Abstract

The higher temperature of urban areas compared to their surrounding rural areas is called urban heat island (UHI). UHI during summer may harm inhabitants and aggravate cooling energy demand. Increasing urban albedo is proposed to counter the undesirable impacts of UHI. To analyze the effect of albedo enhancement on urban climate, land-atmosphere interactions and various physical processes in the atmosphere and on the land should be modeled. Weather Research and Forecasting (WRF) model, urban canopy model (UCM), building energy model (BEM), and chemical transport model (CHEM) are coupled, to accurately investigate the effect of an increase in the urban albedo. To select appropriate models sensitivity of near surface air temperature and near surface wind velocity to the choice of parameterization is evaluated. Montreal and Toronto, as the two most populated Canadian cities, are selected for evaluation of UCMs and an increase in the urban albedo.
Seasonal performance of the increase in albedo of roofs, walls, and road by 0.45, 0.4, and 0.25, respectively, results in an average decrease of 0.25 °C during summer and a negligible effect during winter (<0.1 °C). The daily building energy savings of HVAC systems in summertime is about 18 Wh/100m2, while, the winter heating penalty is about 2 Wh/100m2. Considering the effect of aerosols and other pollutants, in summertime, the simulated maximum air temperature decreased by about 1 °C, near surface 8-hour average ozone concentration decreased by 0.1 ppbv, and 24-hour average PM2.5 concentration decreased by 2 μg/m3. Simulations show that increasing the urban albedo results in a reduction in summertime air temperature, leading to a lower cooling energy use and an improved outdoor air quality.