Frequency Distribution of Intense Rainfall in the Wards of Tokyo and Its Relationship with the Spatial Structure of Building Heights

Abstract

This study presents the minute spatial structure of both the frequency of intense rainfall （data from the 1991 to 2002, except 1993, were used） and recent trends （15-25 years until 2002） in the special wards of the Tokyo Metropolis in summer （June to September） , on the basis of hourly rainfall data from a dense rain-gauge network. As this is the first step in elucidating the relationship between the distribution of the frequency of intense rainfall and that of surface roughness in metropolitan Tokyo, the averaged number of building stories within a certain area, which is referred to as the smoothed building height （SBH） , was assumed to be an alternative parameter when deciding surface roughness. The distribution of the ascending rate of SBH （hereafter, the ascending rate of SBH is referred to as ARS） for wind direction was calculated by varying the averaging area for SBH, in order to compare it to the distribution of intense rainfall frequency. The results are summarized as follows. The high-frequency areas of intense rainfall appear in the western to northern parts of the