Diurnal differences in children's outdoor thermal comfort and adaptive behaviors during physical activity in a subtropical region

Against the backdrop of global warming and the intensification of urban heat islands, the thermal health risks faced by children during outdoor physical activities have become increasingly severe. In a subtropical region of China, this study systematically evaluated the characteristics of outdoor heat stress in children under different combinations of solar radiation and metabolic rate, using field monitoring, physiological measurements, and questionnaire surveys. The results revealed significant diurnal differences in the relationship between TSV and the UTCI: the neutral UTCI during the day was 25.7 °C, while it decreased to 22.3 °C at night, with both the thermal comfort peak and the acceptable thermal range shifting to lower values during nighttime. The dominant meteorological and physiological factors influencing thermal sensation varied significantly under different combinations of solar radiation and metabolic rate: under low solar radiation, air temperature and core temperature were the primary determinants of TSV; under high solar radiation, solar radiation became the dominant factor, while the predictive power of skin temperature diminished. Drinking water was the most commonly adopted heat adaptation behavior. During the daytime, under intense solar radiation, children reported a higher preference for active cooling strategies such as seeking shade and using fans, whereas at night, they tended to prefer passive recovery measures, such as prolonged rest. This study established a context-sensitive predictive model for children's TSV and compared diurnal differences in TSV under physical activity, offering scientific support for optimizing outdoor activity planning and heat mitigation strategies. © 2026 Elsevier Ltd