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

1.目标：世界上的城市地区在规模和高度上持续增长，这是由于用于建筑物和道路路面的混凝土和沥青的低导热性和高热容、街道峡谷内的空气质量和热量的封闭以及绿色和水生区域的减少而在城市中积累热量（湖泊、池塘和海岸带），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，大涡模拟（LES）概念的湍流数值模拟已经扩展到包括植物的叶子和树枝的影响。为了评价植被对城市气候的减缓作用，建立了一个将土壤-植物-大气三个圈层作为统一体的大涡模拟模型.结果：（1）用新发展的大涡模式模拟了植物层内和植物层上的湍流流动。(2)在植物层与气流的交界面处产生大涡，对植物层间的热质交换有重要作用。(3)模拟了皇家宫殿周围的热环境。该地区周围的高速公路是热羽流的来源，而该地区的绿色区域及其周围的池塘在缓解城市气候方面具有相当大的作用。(4)与没有路边树木的情况相比，路边一排树木可以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.