Urban form affects the cool island effect of urban greenery via building shadows

Abstract

Many studies have revealed that the cool island effects of urban greenery (GCIE) were largely depended on vegetation characteristics, while few studies have examined whether and how the GCIE can be influenced by surrounding urban contexts. This study analyzed the impacts of background urban form on the GCIE via multi-scenario simulations with the ENVI-met model. Two street orientations in conjunction with three building heights, two building spatial layouts, and two greening settings generated a total of 24 scenarios for the microclimatic simulation. The results indicated that urban greenery displays a greater cooling intensity in the daytime than in the nighttime. Urban form can noticeably influence the building shadow area, thereby affecting the shading effect and daytime GCIE. For every percentage increase in building shadow area, the GCIE decreases by 0.92 °C. Of the three factors, the street orientation exerts the greatest impact on the GCIE, followed by the building height and the spatial layout. Among the 12 simulated scenarios, the building group with the E-W orientation, 3-story height, and linear layout has the highest cooling potential by the urban greenery, while that with the N–S orientation, 18-story height, and scattered layout has the lowest. This research indicates an intense thermal interaction between buildings and urban greenery. The results may contribute to a better understanding of the formation mechanism of the GCIE, and can inform climate-adaptive urban design with respect to the spatial configuration of buildings and green space.