A simplified assessment of how tree allocation, wind environment, and shading affect human comfort

• Onsite measurements and microclimate simulations of tree planting were conducted.
• Lower wind speeds and higher temperatures were found on the downstream side.
• A thermal environment cannot be improved without proper wind corridor design.
• A simplified human comfort assessment methodology is proposed for tree allocation.

Urban areas encounter a common problem called the heat island effect. Public-space plantings and parks have become a crucial countermeasure for decreasing urban temperatures. In this study, field measurements were carried out in a subtropical park in the summer to investigate the effect of plantings on microclimate and the thermal environment of pedestrian areas. It was found that obstructions affected the wind field; although cold air enters parks, an overcrowding of plants resulted in temperature rises in downstream areas. Shading is a key to thermal comfort in both tropical and subtropical regions, and its effect is augmented by ventilation. Trees that are planted without proper planning can decrease wind movement, which in turn has a detrimental effect on thermal comfort, especially downwind. Wind corridors through urban parks can promote both shading and ventilation, improving thermal comfort, and should thus be considered when designing the layout and trimming of plantings. Data from both fixed- and mobile-type measurements were used to validate the feasibility of a computational fluid dynamics simulation model. It was observed that wind speed and shading are the two main variables that influence the human comfort index, based on which a simpler human comfort assessment was proposed to replace the conventional index, standard effective temperature (SET*). The proposed method can be used as a guideline for landscape architects when designing planting locations.