Application of Universal Thermal Climate Index (UTCI) for microclimatic analysis in urban thermal environments

Abstract

Microclimatic effects were investigated for human thermal sensation on human bioclimatic maps in summer, 2009 using the Universal Thermal Climate Index (UTCI). Study locations were downtown Nanaimo, BC, Canada and Changwon, Republic of Korea. Air temperatures and humidities of several sites were collected at the two locations. Mean radiant temperatures of outdoor study areas in high resolution were simulated with the HURES human-urban radiation exchange simulation model. Wind speeds estimated using the ENVI-met model were corrected using collected wind speed data and adjusted from one to ten meters above the surface via UTCI's wind speed converting formula. Greatest heat stress was around mid-afternoon. Sunny areas had moderate to strong heat stress, 28–38°C UTCI. Shady areas had no thermal stress to moderate heat stress, 20–27°C UTCI. Narrow streets had lower UTCI's than open spaces in both areas. A 1ms−1 reduction in 10m height wind speed (u) increased UTCI by 1°C. In this study, u varied by up to 3.3ms−1. Observed direct beam solar radiation variations changed UTCI by three heat stress levels, diffuse and reflected solar radiation and longwave radiation changed it by 1.5 levels and u altered UTCI by half a level. UTCI is an accepted, easy to determine human thermal index whose results can be mapped as human bioclimatic maps and should be a useful tool for analyzing possible outdoor human thermal effects of urban and landscape planning and design.