Outdoor thermal comfort assessments and variations in Neutral Temperature(s) across demographics profiles in the Humid Tropical City of Singapore

Neutral Temperature (NT) is an Outdoor Thermal Comfort (OTC) threshold that provides a valuable benchmark for urban planners to design and enhance outdoor space usability. NT can be determined by comparing respondents' Temperature Sensation Votes (MTSV) with thermal index outputs of empirical (bio)climatic conditions. It corresponds to the thermal conditions (°C) when MTSV equals "0," indicating neither hot nor cold, but neutral thermal perception. 

Using a dataset of over 5,000 matched microclimate perception surveys and measured microclimate data, this study examines NT variations across Singapore's demographic profiles, including age, sex, heat acclimation by lifestyle (e.g., exercise frequency, indoor/outdoor exposure, air-conditioning use), and acclimatisation by residency (e.g., duration of stay >6 months). Results show a smaller increase but greater spread in MTSV when Wet Bulb Globe Temperature (WBGT), Physiological Equivalent Temperature (PET), and Modified PET (mPET) exceed 28.86±0.015°C, 33.00±0.038°C, and 32.00±0.025°C, respectively, suggesting a non-linear relationship between climatic conditions and temperature perception. The scattering of MTSV could be attributable to contradictory causes – better tolerance of, if not ambivalence towards ‘hotter’ conditions; or inhibited thermoregulation leading and thus inability to perceive ‘hotter’ conditions.  

The study also examines variations in OTC across six distinct urban study sites. Findings indicate that highly shaded and green spaces correspond to narrower WBGT, PET, and mPET ranges, while more open, urban areas exhibit greater thermal variation. These insights highlight the complex interactions between urban design, microclimate, and human thermal perception, informing strategies for enhancing outdoor comfort in tropical cities.