A simulation study on the effects of tree height variations on the façade temperature of enclosed courtyard in North China

Abstract Trees play an important role in improving the microclimate and mitigating the urban heat island (UHI) effect. This paper focuses on the microclimate of an enclosed courtyard in North China and conducts three phases of simulations with an ENVI-met model to investigate the effect of tree height variations on facade temperatures. The results reveal the following. (1) Cooling is the main effect during the day. The maximum temperature decrease is 1.17 °C for every 1-m increase in height within 20 m. The length of time when the temperature decreases reaches 50% or more of the maximum decrease value is approximately 5–8 h (2) There is a weak warming effect at night. The maximum temperature increase is approximately 0.07 °C for every 1-m increase in height within 20 m, which appears approximately 3 h before sunrise in the south. (3) The contribution to the cooling effect of increasing the tree height is the strongest when the height ranges from approximately 8 m–12 m and is minor below approximately 6 m. (4) Cooling is mainly caused by two effects: shading and wind blocking. When the height of a tree is close to that of the building, at noon or 12:00, the two effects can cause maximum temperature drops of 1.87 °C and 0.52 °C, respectively, with a ratio of 3.6:1. These results reveal optimization strategies of existing vegetation in urban built-up areas, which presents more advantages and practicality to control the aggravation of the UHI effect.