A human thermal climatology of subtropical Sydney

Using a physiologically relevant thermal comfort index (OUTT*), an analysis of the week-by-week human thermal climate of Sydney was carried out for three levels of metabolic activity. The OUTT* index is an outdoor version of the widely used indoor comfort index called the standard effective temperature (SET*) incorporating air and mean radiant temperatures, relative humidity, air velocity, clothing insulation and activity level. The 'outdoor comfort zone' for Sydney in terms of OUTT* was found from earlier subjective field studies to be in the range 23.8-28.5°C. The analysis indicated that the mid-summer period (weeks 43 through to 12 in the Southern Hemisphere) was most suitable for sedentary outdoor activities (e.g. watching spectator sport), whereas the mid-winter period was more suitable for light activities such as walking. Sydney's winter was found to be a very suitable season for tourism in many respects because of (a) low rainfall months, like August, and (b) the ability to undertake light activities while remaining within the outdoor comfort zone. For high metabolic activities during the day, for example the mass participation Sydney City-to-Surf fun run, it was found that the threshold limit value for increased risk of heat stress (as defined by ISO 7243, 1989) is exceeded up to 50% of the time during the summer (weeks 50 through to 9 at 3 p.m.) at the 90th percentile probability level. The methods and results of this study should be relevant to end-users such as architects, engineers, outdoor-event planners and the tourism industry in general.