ANALYZING RETURN PERIOD OF NUMBER OF FLOODED RIVERS BY TYPHOON HAGIBIS AND ITS FUTURE CHANGE

Abstract

 Typhoon Hagibis caused serious damage to large area of Japan. This study estimated the future changes in frequency of flood peak discharge and multi-basin flooding probability by the typhoon using bias-corrected d4PDF and a rainfall-runoff model constructed for all the class-A rivers in northeastern Japan (Tohoku, Kanto, and Koshinetsu regions). As the result, the return period of the peak discharges for the two rivers was estimated at 535 and 123 years in the past experiment, and at 32 to 100 years and 16 to 58 years in the 4-degree rise experiment, respectively. Frequencies of multi-basin flooding, defined as annual maximum flood discharge exceeding the river channel’s capacity in the same year, was estimated over all the rivers targeted. Return period of 6 basins (same as Typhoon Hagibis) was 400 years in the past experiment, whereas 20 to 30 years in the 4-degree rise experiment. A typhoon causing flooding in the largest number (13) of rivers in the 4-degree rise experiment showed a similar path with Typhoon Hagibis but more heavy rainfall on shore.