FUTURE CHANGE ANALYSIS OF EXTREME FLOODS USING LARGE ENSEMBLE CLIMATE SIMULATION DATA

d4PDFから得た降水量データを用い，極値降水量の確率分布の将来変化を分析するとともに，降雨流出モデルを介して推定した極値流量の確率分布の将来変化を分析した．また，再現期間1000年相当の流量規模を調べ，それらをもたらす降水要因を考察した．対象流域は荒川流域，庄内川流域，淀川流域である．以下の結果を得た．1) 観測値とd4PDF過去実験から得られる年最大24時間降水量の頻度分布は非超過確率0.95以下ではよく対応した．2) 4度上昇実験の200年確率年最大24時間降水量は，過去実験のそれの1.3～1.4倍，年最大時間流量では1.5～1.7倍となった．3) 4度上昇実験の200年確率年最大降水量と過去実験の900年確率年最大降水量とがほぼ同じ値となった．4) 既往大洪水をもたらした降水要因とd4PDFで再現・予測される大洪水の降水要因はよく適合した．Future changes of probability distributions of extreme rainfall and flood are analyzed using “Database for Policy Decision-Making for Future Climate Change, d4PDF” having 60-years climate simulations with 50 ensemble members for the historical experiment and 90 members for the future experiment. The magnitude of a largest-class flood equivalent to a 1000-years flood is also analyzed. The study basins are the Ara River basin (2940km²), the Shonai River basin (1010km²), and the Yodo River basin (8240km²) in Japan. The results show that 1) the frequency distributions of annual maximum 24-hours rainfall for d4PDF of the historical experiment match with the ones for observed data in the range of the non-exceedance probability less than 0.95; 2) the 200-years annual maximum 24-hours rainfall for the d4PDF of the future experiment is 1.3 to 1.4 times larger than the one of the historical experiment and 1.5 to 1.7 times larger for the annual maximum river discharge; 3) the 200-years annual maximum 24 hours rainfall for the d4PDF of the future experiment is equivalent to the one of 900 years of the historical experiment; and 4) the rainfall patterns that cause largest-class floods simulated by d4PDF well match with the one of large historic floods for the three basins