Geographical research on the relationship between the occurrence of short-duration heavy rainfall and the spatial structure of surface property in the Tokyo metropolitan area

从气候学和城市形态两个方面分析了东京都夏季短时强降雨的发生与城市地表结构的关系。主要研究结果如下：1.东京市中心西北部和南部的强降雨区域在短时间内有向邻近地区发展的趋势，显示出东京市区强降雨的特征。在东京地区，强降雨发生频率的地方尺度差异明显。强降雨多发区位于东京区的西部和北部。前者和后者的强降水分别对应于偏东风和偏南风。这些地区位于新宿、池袋等高层建筑的背风地带。这说明由于地面粗糙度较大而导致的地面风辐合增强了城市地区的对流活动。介绍了利用数字地面模式(DSM)计算天视因子(SVF)的方法，并对东京城区的SVF进行了计算。由于SVF在某一给定点的空间代表性较弱，需要对SVF进行放大，以探讨城市热岛与SVF之间的关系。由1公里×1公里区域的SVF直方图估计出东京地区典型的SVF。利用DSM计算了东京病区的空气动力学参数，并对水平/垂直风速分布进行了评估。大的上升风出现了新宿-目黑岛、池袋等，上升风区随风向而变化。结果表明，暴雨发生频次的局地差异与高层建筑形成的地表粗糙度密切相关。

In this research, relationships between the occurrence of summertime short-duration heavy rainfall and the urban surface structure in the Tokyo metropolitan area were analyzed in terms of climatology and urban morphology. The results can be summarized as follows :1. The heavy rainfall area in the northern-western and southern area of central Tokyo tends to develop in its neighborhood during a short period, which indicates the characteristic feature of heavy rainfall in the urban area of Tokyo.2. Local-scale differences in the occurrence frequency of heavy rainfall are distinct in the Tokyo ward area. The frequent heavy rainfall areas are found in the western and northern part of the Tokyo ward area. Heavy rainfall in former and latter areas tends to occur corresponding to easterly and southerly wind, respectively. These areas are located in the leeward of high-rise buildings such as Shinjuku and Ikebukuro. It is suggested that convergence of surface wind due to large surface roughness enhances the convective activity in the urban area.3. The calculation method of sky view factor (SVF) by using digital surface model (DSM) was introduced, and the calculation of SVF over the Tokyo ward area was conducted. As the spatial representativeness of SVF at a given point is scarce, scale-up of SVF is required for the discussion on the relationship between urban heat island and SVF. The typical SVFs in the Tokyo ward area are estimated from SVF histogram of 1km×1km areas.4. The aerodynamic parameters in the Tokyo ward area were computed by using DSM, and horizontal/vertical wind velocity distribution was evaluated. Large ascending wind appears Shinjuku-Meguro, Ikebukuro, etc., and the areas of ascending wind vary with wind directions. It is concluded that the local-scale differences in the occurrence frequency of heavy rainfall is strongly related to the surface roughness which high-rise buildings forms.