城市不同下垫面的能量平衡及温度差异模拟

城市能量平衡是研究城市热岛效应的物理基础。利用北京市教学植物园2010年的实测数据,设置不同类型下垫面(植被覆盖类型:林地、草地和不透水层覆盖类型:道路、房屋),利用局地尺度城市气象参数化方案模拟并分析了相同气象条件和净辐射通量输入下,不同类型下垫面的显热、潜热通量及蒸散降温效应的差异。结果显示:(1)不同类型下垫面的各能量支出项有明显差异,植被覆盖区域和不透水层覆盖区域的波文比年均值分别为0.28和4.60,且在植被生长季差异较大;(2)城市扩展过程中道路、房屋替换林地、草地的过程,也是显热增加而潜热减少的过程。植被层向不透水层转换的过程中,显热通量年均增加32.74W/m²,潜热通量减少38.87W/m²,储热通量增加7.95W/m²;(3)理论上,植被蒸散的年降温效应使单位面积植被覆盖区域的气温比不透水层区域可低2.63℃。

Modeling urban energy balance and temperature differences of different underlying surfaces

Urban energy balance is a physical basis of studying urban heat island effect.Underlying surfaces have a significant effect on urban thermal budget.In this study,different types of underlying surface,namely vegetation cover types(forest and grassland),impervious overlay types(roads and houses),and meteorological data measured in Beijing teaching botanical garden in 2010,were used to study urban energy balance and temperature differences of different underlying surfaces with a local-scale urban meteorological parameterization scheme(LUMPS).The results showed that: 1) urban underlying surfaces had a large impact on energy expenditures.Therein,the annual average Bowen ratio of vegetation cover regions was 0.28,while that of impervious layer regions reached 4.60.Moreover,the differences of energy expenditure mainly appeared in the vegetation growing season;2) the common process of urban sprawl was that grassland or forest were replaced by houses and roads.This process was accompanied by the significant changes of energy expenditures,namely the process of sensible heat increased and latent heat decreased.For example,in the process of conversion of vegetation surface to impervious surface,the sensible heat flux increased by 32.74 W/m2,the latent heat flux decreased by 38.87 W/m2,and the surface heat flux increased by 7.95 W/m2;3) corresponding to the differences of latent heat and temperature,the results displayed that the vegetation cover regions had lower temperture than impervious cover regions due to their different specific heat capacity and energy assignment.And only the cooling effect of evapotranspiration could make the air temperature of vegetation cover regions 2.63℃ lower than impervious cover regions in theory.