Abstract
This paper first reports the current situation of the IDF (Intensity-Duration -Frequency) equations used in all the local prefectural governments in Japan, based on the authors' questionnaire responded from all the forty-seven prefectures in summer 2004. The responses to the questionnaire showed that the traditional methods for IDF equations are still widely used, regardless of the recent remarkable developments of data processing including computer technologies, frequency analysis methods and accumulation of systematic meteorological and hydrological data. Based on the results of the questionnaire and rainfall data provided by a number of prefectures, this paper also discusses how to select probability distribution functions and IDF equations from their candidate ones.
