Flood Hazard-Based Evacuation Curve Using Mobile Spatial Statistics

This study proposes a method to quantitatively assess evacuation demographics during regional floods using Mobile Spatial Statistics (MSS). The study areas are Koriyama City, which was affected by Typhoon Hagibis in 2019, and Yamagata City, which experienced torrential rains in July 2020 in the early phase of COVID-19 pandemic. Both events led to high river water levels and flooding. MSS provided by the Japanese mobile service provider NTT Docomo was used to explore the dynamics of the population. The demographics of evacuees according to the changes in river water levels were presented by gender and age range. Our results show differences in evacuation dynamics between the two regions. For instance, in Koriyama, younger people were more likely to evacuate faster, whereas, in Yamagata, older people’s movement was quicker than in other age groups. The average relative evacuation ratios were 2.2 times higher for females in their 20s in Koriyama and 2.5 times higher for females in their 30s in Yamagata at the evacuation peak. Gender differences indicate that women were more likely to evacuate than men. The effect of the COVID-19 pandemic on the evacuation dynamics was not clear, while the expected severity of flooding made a longer stay in Koriyama. MSS provides a robust reflection of evacuation dynamics in the local context and will offer a better policy for decision making in each municipal government.