Controlling factors resulting in decreases in landslide fatalities: a case study in Kure City, Japan

Decreasing landslide fatalities is an ongoing global goal. This study identifies factors that decreased the number of landslide fatalities from the 1945 to 1967 events and from the 1967 to 2018 events in Kure City, Japan. The numbers of fatalities (N_F), landslides (N_L), and collapsed houses (N_H) were collected, and changes in N_F and three features of N_F (i.e., N_L, N_H/N_L, and N_F/N_H) were examined for debris flows and steep-slope failures. Many check dams were constructed from 1945 to 1967, and N_H/N_L was smaller in 1967 than in 1945. Consequently, N_F caused by debris flows was considerably smaller in 1967. The forest growing stock increased drastically from 1967 to 2018, and N_L was smaller in 2018 than in 1967. In addition, N_F/N_H was smaller in 2018 than in 1967 because of the decrease in the average number of household members and the increase in the ratio of residential buildings built with non-wooden materials. Consequently, N_F caused by steep-slope failures dropped to zero in 2018. Accordingly, the factors decreasing N_F differed between 1945–1967 and 1967–2018. Although this difference has been observed throughout Japan, the timing of each factor contributing to the reduction in N_F in Kure City differed from that observed for Japan overall. Kure City has experienced more severe landslide events and population reduction than other areas in Japan. Understanding the factors affecting landslide fatalities in Kure City could help in the mitigation of landslide disasters in other regions of Japan and worldwide.