Thermal benefits of Chinese Banyan in subtropical Hong Kong

Abstract

Urban trees are known to reduce air temperature and improve thermal comfort by intercepting solar radiation and prompting evapotranspiration. However, few studies have used Universal Thermal Climate Index (UTCI) to evaluate the thermal benefits of a tree. Therefore, this study aims to quantify the thermal benefits under the canopy of a large Chinese Banyan (Ficus microcarpa) in the summer of Hong Kong. Air temperature, relative humidity, wind speed, black globe temperature and global solar radiation were monitored simultaneously under the tree and at a nearby control site. The average daytime UTCI were 1.4 ℃ (cloudy day) and 3.9 ℃ (sunny day) lower under the tree. The tree canopy effectively reduced solar radiation by 85 % on the sunny day. A maximum cooling of 12.3 ℃ was recorded on the same day around noon. No reduction in wind speed and nocturnal warming were observed at night at the treed site.