Influence of blue infrastructure on lawn thermal microclimate in a subtropical green space

Abstract

Thermal modifications by a 1.5 m deep pond on adjacent lawn microclimate on sunny, cloudy, overcast and rainy summer days were investigated in subtropical Hong Kong. Microclimatic parameters at a pondside lawn were monitored and compared to an open lawn and a concrete rooftop (Control), with focus on Universal Thermal Climate Index (UTCI) to investigate thermal comfort. The cooling capability of the studied pond has been ascertained – pondside lawn registered the lowest air temperatures (Ta) in most weather conditions, and mean Ta of sunny daytime at pondside lawn was 0.7 °C cooler than open lawn. Compared to Control, UTCI calculations indicated hotter mean daytime conditions at pondside lawn (−2.3 °C) than open lawn (−3.5 °C) on sunny day. Despite the pond's ability to lower Ta, the lack of pondside tree shading created worse human heat-stress scenarios than open lawn. Cloudy day displayed lower heat-stress levels, but pondside lawn still recorded the highest frequency of strong heat stress (83.6%). To synergistically resolve the thermal-stress problems and transform pond-induced microclimatic cooling into physiological cooling for humans, deeper and more dynamic waterbodies could be incorporated alongside pondside tree shading and natural surfaces in urban park design.