Unified Hydrological Study on Climate Mitigation Effects in Soil-Plant-Atmosphere

1.目的：由于用于建筑和道路路面的混凝土和沥青的低导热系数和高热容在城市中积累热量，街道峡谷内的空气质量和热量被包围，以及绿色和水上区域(湖泊、池塘和海岸地带)的减少，城市正在成为所谓的热岛。为了计算植物冠层内的湍流气流，扩展了大涡模拟的概念，将植物树叶和树枝的影响包括在内。为了评估植被对城市气候缓解的影响，将土壤-植物-空气三个圈作为一个统一的整体，建立了LES模型。结果：(1)用新开发的大涡模拟模型模拟了植物层内及以上的湍流流动。(2)植物层与气流交界处产生大涡，对两层间的热量和质量交换有显著的促进作用。(3)模拟了皇宫周围的热环境。该地区周围的高速公路是热羽流的来源，而该地区的绿地和周围的池塘对缓解城市气候有相当大的作用。(4)与没有行道树的情况相比，行道树可使街道峡谷内的温度降低10度。

1. AIMS: Urban areas in the world are continuing to grow in size and height, Owing to the accumulation of heat in the urban by the low conductivity of heat and high heat capacity of concrete and asphalt used for buildings and road pavement, enclosure of air mass and heat within street canyon and also by the reduction of green and aquatic areas (lake, ponds and coastal zone), cities are becoming the so-called "heat islands".To compute the turbulent air flow within plant canopies, the LES (Large Eddy Simulation) concept to model numerically the turbulent flow has been extended to include the effect of leaves and branches of plant. In order to estimate the effects of vegetation on the urban climate mitigation, an LES model has been developed taking the three spheres of soil-plant-air as a united entity.2. RESULT: (1) Turblent flows within and above plant layer are simulated by the newly developed LES model. (2) Large eddies are produced at the interface between plant layer and air flow, which contribute significantly to the exchanges of heat and mass between the layers. (3) The thermal environment around the Royal Palace is simulated. Highway roads around the area act as a source of thermal plumes, while the green area of the place and ponds around it has a considerable effect in mitigating the urban climate. (4) Row of roadside trees has the effect to reduce the temperature within street canyon as much as 10 degrees compared with the situation without them.