屋顶绿化对城市降温效应的模拟分析——以南京市为例

A Case Study of Simulated Cooling Effect of Roof Greening in Urban Area of Nanjing

利用WRF模式耦合单层城市冠层模式,针对屋顶绿化对城市降温效果进行了模拟,结果表明:(1)南京夏季绿化后的屋顶反照率约为0.15,较水泥及其他反光材料的反照率略小,在白天可造成约0.2℃的升温。(2)绿化后的屋顶热容量明显增加,可使白天气温下降0.33℃;在夜间,可使气温升高0.21℃左右。(3)在植被阻挡作用及土壤层阻挡作用下,屋顶的导热率降低。在白天,净辐射能很难向下层传递,从而转化为感热加热大气,造成气温升高。(4)土壤湿度的改变使更多净辐射能转化为潜热释放。在白天可使温度降低1.23℃;在夜间,平均降温幅度为0.44℃。除此之外,模拟不同季节的统计结果表明,屋顶绿化降温效果在夏季最为明显,最大降幅可达1.22℃,春季0.96℃,秋季0.75℃,冬季只有0.38℃。

In the present study, the WRF model with the incorporation of a Single Layer Urban Canopy Model is used to investigate the cooling effect of roof greening in Nanjing. Sensitivity tests of albedo, heat capacity, thermal conductivity and humidity are conducted for the time period from 28 to 29 July 2013. The simulation results show that： （1） the albedo of roofs is reduced to approximately 0.15 after greening, which is smaller than the albedo values of the roofs built with cement or other reflective materials. This re- sult may lead to the increase of city temperature by 0.2℃ in daytime. （2） The heat capacity of roofs in- creases significantly after greening, leading to the decline of temperature by 0.33℃ in daytime while the temperature at night increases by about 0.21℃. （3） Due to the existence of vegetation and soil layer, the thermal conductivity of roofs is weakened. As a result, the net radiation on roofs is more easily converted to sensible heat rather than being transferred downwards, warming the overlying ambient air. （4） The change of soil humidity enhances the release of latent heat from the net radiation on roofs. Therefore, tem- peratures in daytime and nighttime are reduced by about 1.23℃ and 0.44℃, respectively. In addition, the statistical analysis of the simulation results for different seasons shows that the reduction of temperature by roof greening is the strongest in summer, which can reach 1.22℃. In comparison, the temperature de- creases by about 0.96℃ in spring, 0.75℃ in autumn and only 0.38℃ in winter.