This study aimed to evaluate the impact of climate change on flood damage and the effects of mitigation measures and combinations of multiple adaptation measures in reducing flood damage. The inundation depth was calculated using a two-dimensional unsteady flow model. The flood damage cost was estimated from the unit evaluation value set for each land use and prefectures and the calculated inundation depth distribution. To estimate the flood damage in the near future and the late twenty-first century, five global climate models were used. These models provided daily precipitation, and the change of the extreme precipitation was calculated. In addition to the assessment of the impacts of climate change, certain adaptation measures (land-use control, piloti building, and improvement of flood control level) were discussed, and their effects on flood damage cost reduction were evaluated. In the case of the representative concentration pathway (RCP) 8.5 scenario, the damage cost in the late twenty-first century will increase to 57% of that in the late twentieth century. However, if mitigation measures were to be undertaken according to RCP2.6 standards, the increase of the flood damage cost will stop, and the increase of the flood damage cost will be 28% of that in the late twentieth century. By implementing adaptation measures in combination rather than individually, it is possible to keep the damage cost in the future period even below that in the late twentieth century. By implementing both mitigation and adaptation measures, it is possible to reduce the flood damage cost in the late twenty-first century to 69% of that in the late twentieth century.

这项研究旨在评估气候变化对洪灾的影响以及减灾措施和多种适应措施的组合在减少洪灾损失中的作用。使用二维非定常流动模型计算淹没深度。根据针对每个土地用途和地区设置的单位评估值以及计算出的淹没深度分布，估算洪水破坏成本。为了估算不久的将来和二十一世纪末的洪水灾害，使用了五种全球气候模型。这些模型提供了每日降水，并计算了极端降水的变化。除了评估气候变化的影响外，还讨论了某些适应措施（土地使用控制，试点建设和提高防洪水平），评估了它们对减少洪水破坏成本的影响。在有代表性的集中途径（RCP）8.5的情况下，二十一世纪末的破坏成本将增加到二十世纪末的破坏成本的57％。但是，如果按照RCP2.6标准采取缓解措施，洪水破坏成本的增长将停止，洪水破坏成本的增长将是20世纪后期的28％。通过组合而不是单独实施适应措施，有可能使未来的损失成本甚至低于二十世纪末的损失成本。通过同时采取缓解和适应措施，可以将二十一世纪末的洪灾损失降低到二十世纪末的百分之六十九。