Evaluation on the performance of tree view factor in a high-density subtropical city: A case study in Hong Kong

Outdoor thermal comfort is a primary concern when designing urban environments suitable for pedestrian activities. In previous research, urban greenery had been considered as an effective strategy to mitigate the deterioration of the street-level thermal environment. Tree view factor (TVF), a parameter that can estimate the amount of tree cover visible in the overlying hemisphere, was applied in recent thermal environment assessment studies. However, a detailed understanding of TVF's suitability and application in a subtropical high-rise compact metropolis with diversified land uses is still lacking. To fill the knowledge gap, this study used Hong Kong as a study case and conducted ENVI-met simulations to analyse the human thermal comfort at two levels of TVF sites and two weather conditions. Results showed that high TVF (Htvf) sites had a pronounced reduction in mean radiant temperature (TMRT) of at least 15 & DEG;C after 12:00 under both typical and extreme weather scenarios. A lower mean physiological equivalent temperature (PET) of below 30 & DEG;C and 35 & DEG;C remained in the daytime of typical and extreme weather scenarios, respectively. It was also found that low TVF sites inside parks received more solar radiation, while Htvf sites inside parks exhibited a more substantial cooling potential than that inside street canyons. Htvf sites could maintain better pedestrian thermal comfort due to the shading effect. This study also proved that TVF is more suitable than green coverage ratio (GCR) in urban thermal environment assessments and urban green infrastructure design to create a thermally comfortable high-rise and high-density metropolis.