Determination and analysis of the relationship between microclimate elements and greening structures in the city streets of Shanghai: taking Xuhui District and Yangpu District as examples

  Objective  This paper aims to explain the corresponding relationship between the microclimate elements and street greening layout, guide adaptability design of urban street green space.

  Method  Based on field survey, the correlation between microclimate factors and street greening layout was elaborated, and the influence of several factors as solar radiation, air temperature and wind speed on vertical structure of street greening was explored in this study.

  Result  (1) The relationship between street shade coverage and microclimatic factors: the higher the shade coverage was, the better the reduction efficiency of solar radiation was. The effect was most pronounced when coverage reached more than 90 percent, and the rule characteristics of its cooling effect were more obvious. However, the excessive shade coverage made the street space closed, resulting in a reduced cooling effect. The efficiency of wind speed reduction was more than 21% higher than that of 50%−70% for the street greening with a green coverage rate of more than 90%. (2) Relationship between street greening cladding structure and microclimatic elements: in the multi-layer vertical structure, the more complex the structure is, the greater the greening amount will be, and the higher the solar radiation reduction efficiency will be. Its overall average reduction efficiency of solar radiation was 88.78%. The average daily cooling efficiency of the layered vertical structure was 8.69%. In the natural cycle of one day, the weakening efficiency of the wind speed was the best, followed by that of the tree-shrub-grass, the tree-shrub next, tree-grass third, shrub-grass was the last. The average daily wind speed reduction efficiency of the laminated structure was about 77.61%. (3) Relationship between vertical green ratio and microclimatic elements: the ratio of total green content of trees and shrubs was positively correlated with the solar radiation reduction efficiency. The higher the proportion of trees and shrubs were, the higher the average cooling efficiency was. During the natural cycle of a day, the more the ratio of trees and shrubs to grass close to 1∶1, the better the weakening effect on wind speed was.

  Conclusion  Based on the relationship between the layout of street greening and microclimate elements, the technical countermeasures for improving the comfort of microclimate by regulating the composition of street greening were proposed: (1) to build comfortable street summer microclimate, green shade coverage rate was appropriately maintained 70%−90% . (2) Shade and ventilation should be increased through a moderate greening cladding structure, but it should be avoided to be too complicated to affect the normal ventilation. (3) According to the scientific proportion of vertical green quantity, taking into account the requirements of green shade coverage in summer and temperature increase in winter, we should plant deciduous trees and keep trees and shrubs accounting for more than 50% of the street greening.