Outdoor thermal environments and activities in open space: An experiment study in humid subtropical climates

The outdoor thermal environment correlates with occupant behaviors in open spaces. The appropriate range of thermal environment that is conducive to outdoor activities, however, remains inadequately defined. Existing studies fail to characterize the behavioral responses to thermal environments in important dimensions including activity types, age or gender. We conducted field studies on six open spaces in Wuhan, China, a city with humid subtropical climate and ideal for this research. Data based on field observations, questionnaires, and measurement were collected under a variety of weather conditions over 4 years. We renovated a playground by adding shading shelters and vegetation cover to reduce summertime heat stress. On-site thermal environment were assessed using the Universal Thermal Climate Index (UTCI). Findings are as following: the outdoor thermal environment is a strong predictor of mean attendance over a period of time, but not spontaneous occupancy at a specific time or space; the Optimum Thermal Environment (OTE), defined as the range in which an open space is well-attended (attendance above 90% of peak value), is more consistent than the self-reported Thermal Acceptable Range (TAR) in this study. Behavioral responses to thermal environment differ by gender, age, and types of activities. The experiment confirmed the causality between outdoor thermal environment and activities: the renovated playground attracted 80% more occupants in summer; people stayed longer, reported less heat stress, and interacted with each other more often. Results remained significant after controlling for weather, air quality, daily and weekly routines. Findings had implications for the design of open spaces.