Hisashi KASUGA

Estimation of Spatial Distribution of Probabilistic Rainfall Using Fair's Equation

Minjiao LU

In this study, rainfall data with different duration is used to make comparison. Fairfs equation is utilized to calculate probabilistic rainfall intensity. Then, the spatial distributions of probabilistic rainfall with different durations are estimated. In addition, three methods are to estimate the parameters of Fairfs equation and the one giving smallest RMSE(root mean square error) is selected to estimate spatial distributions of 100-year probabilistic rainfall all over the Japanese islands. Here, the spatial distributions of 100-year 1-hour, 2-hour, 4-hour, 6-hour, 8-hour, 12-hour, 24-hour and 48-hour rainfall is estimated. From these distributions, you can speculate that large rainfall events with duration longer than 24 hours, most likely due to typhoons, mostly occur in wide area in Kyushyuu, Sikoku and Izu peninsula. On the other hand, the rainfall events with shorter duration, due to fronts and thunderstorms, occur at very limited areas located in Kantou region, Hokuriku region. Considering the existence of large number of small and mid-sized rivers, rainfall events with short duration should be considered in river planning in Japan.