Do children face greater outdoor heat risks? A comparative study of pedestrian-scale vertical thermal environment on different urban land covers

Accurate measurement and assessment of pedestrian-scale thermal environments on different urban land covers (ULCs) is crucial for reducing outdoor heat risks and facilitating targeted improvements in urban thermal environments. However, most studies on the impact of ULCs on outdoor thermal comfort (OTC) focus on a single standard height of 1.5 m, ignoring differences and variations of the thermal environment in the vertical direction. Therefore, it is urgent to conduct pedestrian-scale vertical thermal environment observations, so as to evaluate the difference of heat risk among people at different heights, especially whether children with lower height face greater heat risks on different ULCs. Based on this, 5 typical ULCs were selected in this study, and the changes and differences of ULCs in the pedestrian-scale vertical thermal environment (surface temperature (Ts) and microclimate between 0.3 m and 1.5 m) were investigated and analyzed using the fixed vertical measurement method. The results showed that the dense forest provided the best improvement to the vertical thermal environment during the day, while the lawn and the sparse forest performed best at night. In terms of OTC, children generally faced greater outdoor heat risks than adults, and under certain ULCs, the heat risk for children was greater when squatting compared to standing, particularly on the impervious pavement and the synthetic rubber. Therefore, children's OTC should be given particular attention. Moreover, measurements at 1.5 m may overestimate or underestimate the adults' actual heat risks, so taking measurements at an accurate height is essential for evaluating OTC.