抄録
A three-dimensional numerical model of the atmosphere incorporating basin orography has been used to study the rainfall distribution in a basin at the storm-event level. It was shown that under a certain balance of time and space scale, the rainfall distribution in a basin is mostly dominated by orographical factors—the main effect being that of ground-forced-induced ascending current of the air. The numerical model was used to estimate the regions in a basin where the ascending current of air can occur, for any wind direction. A new concept called Directional-Probability-of-Storm-Event (DiPoSE) has been proposed by the authors. It was shown that severe storms are likely to occur when wind blows from a high DiPoSE direction, compared to that from a low DiPoSE one. The method of determining the wind direction from a DiPoSE analysis for use in the numerical model, has been used to show the severe rainfall regions in 18 river basins in Japan.
