Evaluating the 3D cooling performances of different vegetation combinations in the urban area

Abstract

Vegetation has been considered as an effective strategy to combat the urban heat island effect. Most researches have focused on evaluating the cooling effect of trees in the urban thermal environment. Little attention has been paid to the cooling effect of the combination of different vegetation elements. Moreover, most studies are focused on the horizontal cooling performance of plants, while fewer studies have investigated the vertical cooling effect of vegetation. Therefore, this study evaluates the 3D (horizontal and vertical) cooling performances of the three vegetation combination scenarios in the urban area using the ENVI-met model. The study indicates that the tree-grass (TG) combination has the best 3D cooling effect, followed by the tree-shrub-grass (TSG) combination, while the shrub-grass (SG) combination has the weakest 3D cooling effect. Among them, the 3D cooling effect of TG and TSG is significantly better than that of SG, while no big differences are noticed between the cooling effects of TG and TSG. Besides, it is economical to plant TSG combinations because fewer trees are needed than planting TG combinations. Therefore, the study recommends the tree-shrub-grass combination rather than TG or SG combination in urban areas to effectively improve the thermal environment. The study also shows that the relationship between increasing tree coverage and the resulting cooling effect is not linear. The results of this study can effectively guide the design of greening strategies in urban areas to improve thermal comfort.

Phases of Urban Development Impact on the Assessment of Thermal Comfort: A Comparative Environmental Study

“…The surface energy balance and the hydrosphere-atmosphere water vapor cycle are both influenced by tree transpiration. It is also the primary cause of the ecological effects of trees, such as cooling and humidification [19]. As mentioned previously, the real temperature at noontime was measured at 52 ºC.…”

A Relationship between Micro-Meteorological and Personal Variables of Outdoor Thermal Comfort: A Case Study in Kitakyushu, Japan

“…It means the higher the Tmrt value, the higher the PET value. According to Tan [15], the Tmrt value is influenced by how much shading is produced from the presence of vegetation or buildings around the measurement location. This shows that the presence of shadows greatly affects the thermal comfort value in the Green Park Kitakyushu.…”

“…Based on this study, shadows can directly affect the 3D cooling effect of the vegetation combination. The larger the shaded area, the better the cooling effect for the same vegetation cover [15]. A study in Sao Paulo found that during autumn, April 2013, the average maximum air temperature difference reached 0.5 • C and in February 2014, during the extreme warm summer, air temperature differences became more significant, and the effect of vegetation was slightly more pronounced showing maximum air temperature differences up to 0.6 • C [14].…”

“…Studies on the impact of shading, the presence of trees, and vegetation on decreasing city temperatures show a positive effect during the day [13,14]. Many evaluations and simulations of the city's temperature cooling performance through vegetation have also been carried out [15][16][17][18]. Tan, Liao, Bedra, and Li [15] evaluated the 3D cooling performances of the three vegetation combination scenarios in the urban area using the ENVI-met model.…”

“…Many evaluations and simulations of the city's temperature cooling performance through vegetation have also been carried out [15][16][17][18]. Tan, Liao, Bedra, and Li [15] evaluated the 3D cooling performances of the three vegetation combination scenarios in the urban area using the ENVI-met model. Based on this study, shadows can directly affect the 3D cooling effect of the vegetation combination.…”