A street-scale simulation model for the cooling performance of urban greenery: Evidence from a high-density city

How much can greenery cool a city remains inconclusive in literature, especially in a high-density city where plants interact with anthropogenic heat from surrounding buildings and traffic. A novel simulation model, the Urban Greenery and Built Environment, was developed to assess the time-varying interactions between plants and anthropogenic heat at street scale. The model has been evaluated using field studies in two parks in Hong Kong. A reasonably good agreement was observed between measured and predicted temperature and humidity. Sensitivity studies were then conducted to compare the cooling performances of greenery in five scenarios under various coverage ratio and climates. By covering 40% of site with greenery, a practical limit, the expected air temperature and UTCI reductions were 0.3 degrees C, lower than previous estimates due to limited sunlight and groundlevel surfaces for planting; the cooling benefits of greenery were predicted to be higher in dry climates and lower in humid ones. In a high-density city, plants converted sensible heat into latent gains at a slower rate than the anthropogenic exhaust heat. Alternative strategies, such as breeze enhancement, water-spray and management of anthropogenic heat discharges were predicted to further help to cool the city by 3.1 degrees C, 6.8 degrees C, and 1.8 degrees C, respectively.