On the performance of human thermal stress models in the outdoors against observations

Urban overheating significantly impacts human well-being, requiring outdoor thermal comfort assessments. This research aims to assess the performance of models to calculate mean skin temperature in outdoor environments against measurements. The study compares a Lumped Human Energy Budget (LHEB) model, which is a simplified representation of the human body thermal state developed in an Urban Canopy Model (UCM), and the more sophisticated thermoregulation model JOS-3. Skin temperatures computed with the LHEB one-node model were significantly higher than observed values (RMSE: 1.71 – 2.76 °C). This variation, however, cannot be attributed to differences between simulated and monitored environmental data. It probably results from simplifications assumed in the human energy balance, such as disregarding dynamic thermoregulation processes, which considerably impact outdoor human comfort. The JOS-3 model, more advanced in terms of heat exchange and thermoregulation processes, performed better (RMSE: 0.21 – 1.62 °C, considering sessions when sensors were stabilized). Since all JOS-3 meteorological inputs can be provided by a UCM, the model can be directly integrated into UCMs for investigating the effects of urban overheating and mitigation strategies on human thermal stress. Therefore, it can serve as the human thermal comfort module for UCMs. The collected dataset is the first to combine measurements of the biophysical energy model outputs and the required UCM inputs, and to evaluate the reliability of the LHEB and the JOS-3 models outdoors, contributing to improve thermal stress modeling in inter-building urban contexts, which is an important approach for designing effective human-centric heat reduction measures and improving cities’ livability.