2025-09-24 東京大学生産技術研究所
将来の100年確率洪水流量の変化率。気候予測データの複数のシナリオを統合して、気温が1.5度、2度、3度、4度上昇した場合の流量変化率をより精密に求めた。
※100年確率洪水流量の変化率：100年に一度の確率で発生する河川流量が現在を基準として将来どの程度大きくなるかの比率を示す。青色は100年確率洪水流量が大きくなる地域を示す。
＜関連情報＞
複数のSSP-RCPシナリオ間の類似性に焦点を当てることで将来気候下における洪水予測の不確実性を低減 Reduction of the uncertainty of flood projection under a future climate by focusing on similarities among multiple SSP-RCP scenarios
Y. Kimura,Y. Hirabayashi & D. Yamazaki
Scientific Reports Published:22 September 2025
DOI:https://doi.org/10.1038/s41598-025-16327-4
Abstract
Climate projections contain the uncertainty due to the internal variability of the climate system, including its chaotic nature. While the uncertainty due to the internal variability can be theoretically mitigated by executing large ensemble simulations with perturbed initial conditions, only a limited number of large-ensemble experiments are available in CMIP6 future scenario dataset. Here we propose a method that increases the effective ensemble sampling size in evaluations of future projection by integrating multiple SSP-RCPs for a period corresponding to a specific increase in temperature from the preindustrial level (i.e., X°C warming). The success of the method was assessed by investigating whether the uncertainty due to small number of ensemble members could be reasonably reduced. First, we confirmed that the spatial distributions of the future flood magnitude change were similar under a 2 °C warming in all SSP-RCP scenarios. Additionally, the uncertainty due to the different SSP-RCPs (5–10%) was smaller than the differences between different warming levels such as between 2 and 3 °C (around 20–50%), suggesting differences among SSP-RCPs as to future flood discharge change are relatively small. These results suggested that integrating SSP-RCPs to increase the effective ensemble size was a reasonable approach, reducing unbiased variance among GCMs in about 70% of land grid points comparing to the result using SSP5-RCP8.5 alone.
