Fragility curve between flood index and human damage

In recent years, unprecedented heavy rains occurred frequently in Japan, resulting in significant human and building damage associated with huge river flooding. To alleviate this damage, it is crucial to clarify the relationship between human damage and flood situations. The present study aims to develop a fragility curve or flood human damage function for the relationship between human damage and flood situations by conducting field surveys and numerical simulations for flooding. We collected and analyzed human damage data due to recent flood disaster in Japan. We also summarized three indices for the flood inundation situation such as inundation depth, rising speed of water level, and their multiplication value from the numerical simulations for flooding. The results indicated that a significant human fragility curve was obtained for the elderly aged over 65 years based on the above three indices. Inundation depth and the multiplication value showed a statistically significant relationship for human damage in the people under 65 years, suggesting that the risk assessment of the elderly and young people should not be evaluated in the same way. The correlation coefficient of the relationship with inundation depth was largest among three indices. At the confluence of tributaries where a rapid rise in water level occurs, the rate of water-level rise should also be taken into account.