Author(s): K. Hashimoto; H. Yajima; T. Hosokawa
Linked Author(s): Hiroshi Yajima
Keywords: PMP; WRF model; Moisture flux; Typhoon; Front
Abstract: Adaptation to minimize the damage of excessive flooding is important in Japanese river planning. Probable Maximum Precipitation (PMP) is one approach used to estimate peak flood levels. In order to apply PMP to Japanese rivers, we focus on an upper river basin, where the topography is steep and heavy rainfalls are caused by a typhoon and/or a front can last for one to three days. This study was conducted to examine the effects of atmospheric conditions on heavy rainfalls. In order to evaluate temporal and areal distributions of a heavy rainfall, the Weather Research and Forecasting model (WRF) was applied to the Tone River basin. The results are summarized as follows: 1) An increase in relative humidity in the atmosphere affects not only total rainfall, but also its temporal variation. In particular, it advances the time of peak rainfall. Moreover, it generated another peak of the rainfall before the original main peak. 2) Moisture fluxes demonstrate high correlation with the total rainfall calculated from both grid point value (GPV) data by meso-scale objective analysis, and WRF model calculations over the upper river basin. 3) Atmospheric stability parameters, such as equivalent potential temperature, affect rainfall by increasing the efficiency of converting vapor into rainfall. Conclusions are as follows: (1) Moisture flux is a suitable parameter for estimating PMP in the case of typhoons, and affects rainfall distribution, which will cause an initial loss of rainfall and increase maximum discharge. (2) The effect of atmospheric conditions on heavy rainfall differs depending on rainfall type of typhoon and/or front.
Year: 2014