Differential cooling effects of landscape parameters in humid-subtropical urban parks

Thermally comfortable urban parks can attract more visitors and promote the delivery of health benefits to citizens. High tree cover (TREE) and low sky view factor (SVF) are known to reduce air temperature and improve thermal comfort. However, the temperature effects of other landscape parameters are less clear, such as building volume ratio (BV), distance from sea (SEA), park area (AREA), pavement cover (PAVEMENT), road cover (ROAD), shrub cover (SHRUB), turf cover (TURF) and water body (WATER). This study aimed to identify landscape parameters that were significantly associated with air temperature in urban parks and estimate their cooling potentials through empirical models. One hundred precision sensors were installed in 14 urban parks in Hong Kong in summer 2018 to collect air temperature data. ROAD, SEA, TREE and SHRUB had the strongest impacts on temperatures. Considering a circular area with a 20-m radius, a 50% decrease in ROAD, 50% increase in TREE and SHRUB could reduce daytime mean air temperature by 0.3, 0.4 and 0.2 degrees C respectively. The same landscape changes would reduce nighttime mean air temperature by viz. 0.3, 0.2 and 0.2 degrees C. Compared to an inner-city park (500 m from sea), the empirical model suggested that daytime and nighttime mean air temperature in a waterfront park (10 m from sea) is expected to be 0.4 and 0.2 degrees C lower respectively. Urban parks should be sufficiently large to buffer the warming effect of roads. Very high tree cover ( > 90%) is recommended for an effective interception of solar radiation.