- Meteorological Society of Japan
- 気象集誌. 第2輯 (ISSN:00261165)
- vol.38, no.1, pp.27-46, 1960-12-26 (Released:2007-10-19)
According to official observation, the maximum rainfall recorded in Japan is 55.9mm in 10 minutes, 87.9mm in 30 minutes, 157.0mm in 1 hour, 415.3mm in 6 hours, 844.5mm in 10 hours, 1, 109mm in 24 hours, 3, 462mm in 1 month and 10, 21.6mm in 1 year, Comparing these amounts with the world records reported by Jennings (1950), it is noticed that maximum rainfall in Japan is comparable only to world figures in the 1∼0 to 24 hour duration. This is thought to be because polar fronts or tropical cyclones in Japan and adjacent areas are stronger in that time period, while convectional rain, such as thunderstorms of short duration, or continuous rain, such as orographic rainfall under monsoonal conditions, are weaker than in another parts of the world. In addition, distribution maps of observed maximum rainfall within 10 minutes, 1 hour, 6 hours and 24 hours were drawn, and the distribution patterns were considered in connection with their causes.The constants, k and n, for an experimental equation of the depth-duration curve, R=ktn, where t is time (in minutes) and R, rainfall amount (in mm), were then calculated. As for the rainfall amount, R, the mean values obtained from the 1 st to the 5 th ranking in the official records of the Japan Meteorological Agency from 1941 to 1950, as observed every 10, 20 and 30 minutes and every 1, 3, 6, 18, 24, and 36 hours for each of the 109 stations in Japan, were used. Separating the time periods into those between 10 minutes and 1 hour and those between 6 and 36 hours, it was shown that the k and n values exhibited a wide range according to geographical regions and the above-mentioned time periods. These facts are shown in the accompanying figures and tables.Finally, the constants, b, k, and n, for an experimental equation for the intensityduration curve, i=k/(t+b)n, where t is time (in minutes) and i, the rainfall intensity (in mm per minute) were obtained by calculating the intensity values by the same method as is described above for the mean rainfall values. The distribution of b, k, and n values revealed marked localization as is shown in the figures attached. The values decrease with distance from the sea coast in central Japan, and are generally smaller on mountain tops than at the bottoms.