| It is described that frequency of heavy precipitation events will increase in 21st century in the IPCC 4th report published in 2007. Increase of frequency of heavy precipitation will obviously lead to the increase of flood disasters and measures to adapt future flood disasters have to be considered as soon as possible. Nevertheless intensity of hourly or daily rainfall in specific watershed is required to analyze flood magnitude and make strategies for flood prevention, rainfall analysis in specific watersheds has not been done quantitatively in such short temporal resolution in both IPCC 4th report and other references. In this study, the rainfall data simulated by the atmospheric general circulation model (AGCM) developed by Meteorological Research Institute (MRI) in Japan was used to analyze the change of frequency and intensity of heavy rainfall in Yoshino River Basin in Japan and Bagmati River Basin in Nepal. The period for analysis is 1979-1999 (21 years) for present climate condition and 2075-2099 (21 years) for future climate condition. At first, simulated daily rainfall in present climate condition and observed rainfall in both river basins were compared and it is found that the simulated rainfall of AGCM underestimates against observation and some bias correction method is needed. The ratio of daily rainfall intensity between AGCM rainfall and observation in present climate condition was estimated and the future rainfall was estimated by multiplying the ratio to AGCM rainfall in future climate condition. According to the correction method, the maximum daily rainfall is estimated as 382.0 mm/day in future climate condition in Yoshino River Basin. It is 66.9 % higher than the daily maximum observed rainfall, 228.4 mm/day, in present climate condition. The number of days in which daily rainfall intensity exceeds 50 mm/day and 100 mm/day will change from 158 and 51 in present climate condition to 169 and 59 in future climate condition. In the case of Bagmati River Basin, the maximum daily rainfall in future climate condition is estimated 157.3 mm/day. It is 2.6 % smaller than the daily maximum observed rainfall, 161.5 mm/day in present climate condition. The number of days in which daily rainfall intensity exceeds 50 mm/day and 100 mm/day will change from 70 and 6 in present climate condition to 107 and 4 in future climate condition. |
