Influence of Urban Geometry on Thermal Environment of Urban Street Canyons in Hong Kong

Abstract

Hong Kong is a typical high-density city in a subtropical climate region, and deep street canyons are among the main features of its urban planning. How the urban geometry influences the urban thermal environment in this city has become a hot topic these days. The height-to-width ratio (H/W) and sky view factor (SVF) are commonly used to indicate the outdoor thermal environment performance, while previous studies in Hong Kong rarely analysed the importance bias of these two influencing factors systematically in this context. To fill this research gap, in this paper, we chose four typical sites in Hong Kong as research objects. Firstly, we conducted a field investigation to calculate the main influencing factors of urban street geometry (H/W and SVF) and then used field measurements to collect climatic data, including air temperature, wind speed, and relative humidity, and finally used regression to analyse the correlation between H/W, SVF, and temperature. The results indicate the following: (1) There is a greater correlation between H/W and air temperature than between SVF and air temperature by regression analysis, and H/W is more effective at improving the thermal environment within urban street canyons. (2) After field measurements, it was found that H/W at the measurement sites was 0.60 to 6.02, with an average of 2.13. (3) In the study area, H/W of 2.31–2.48 and 3.35–3.60 had a positive correlation with air temperature, and H/W had a dominant influence on outdoor air temperature, and H/W of 2.09–2.31 and H/W > 3.60 was inversely related to air temperature. The conclusions can provide support for urban planning in Hong Kong.

Keywords

• thermal environment
• urban street canyon
• urban geometry
• height-to-width ratio (H/W)
• sky view factor (SVF)