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

1. 目的：世界上的城市地区在规模和高度上都在继续增长，由于建筑和道路路面使用的混凝土和沥青的低导热性和高热容量在城市中积累热量，街道峡谷内空气团和热量的封闭，以及绿色和水生区域（湖泊，池塘和沿海地区）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，将大涡模拟（LES）概念扩展到包括植物叶片和树枝的影响。为了评估植被对城市气候减缓的影响，建立了一个将土壤-植物-空气三个领域作为一个整体的LES模型。结果：(1)利用新建立的LES模型模拟了植物层内和植物层上的湍流流动。(2)植物层与气流交界面处产生较大的涡旋，对植物层间的热和质量交换有重要作用。(3)模拟故宫周边热环境。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在缓解城市气候方面具有相当大的作用。(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.