Outdoor thermal perception and heatwave adaptation effects in summer - A case study of a humid subtropical city in China

Heatwaves occur more frequently during the summer owing to global warming, which causes excessive heat stress and thermal discomfort. Heat stress increases overheating risk and impacts people's health and outdoor activities. Assessing outdoor thermal risk and clarifying human thermal responses under outdoor high-temperature conditions are of particular importance. However, the effect of thermal adaptation on people's thermal perception during heatwave conditions requires exploration. This paper aims to provide a comprehensive analysis of human outdoor thermal perception under non-heatwave and heatwave conditions to obtain adaptation based outdoor thermal benchmarks to estimate the threshold for thermal discomfort and heat stress. Longitudinal and cross-sectional questionnaire surveys are carried out during the summer in public squares in Chongqing. The results showed that thermal perceptions undergo a dynamic change process in summer, which is closely related to an individual's past thermal experience. In comparison with thermal benchmarks under non-heatwave conditions, the neutral, comfortable, and 80% acceptable range of UTCI under heatwave conditions shifted to a higher temperature. For the heatwave period, the neutral UTCI range was from 21.5 degrees C to 27.9 degrees C. The modified UTCI ranges for heat stress classifications were obtained, including the 80% acceptable temperature range from 21.4 degrees C to 30.1 degrees C. The contributions of this study are in the method of determining outdoor thermal benchmarks in heatwave conditions and clarifying local people's thermal demands. These findings can provide more refined guidance for heat stress assessment and enrich the possibilities for urban design and urban resilience responses to heatwave conditions.