The recent trend in annual death toll by landslide disasters in Japan

Yoshinori SHINOHARA and Hikaru KOMATSU

In Japan, the number of deaths caused by landslide disasters has consistently decreased for this70years. To maintain this situation, it is important to pay attention to risks for occurring deaths by landslide disasters. Although the trend in the number of landslide disasters would be affected by the trend in precipitation, no studies examined the trend in the number of landslide disasters and deaths to consider the trend in precipitation. This study examined the trend in the number of deaths by landslide disasters to consider the trend in precipitation. We used survey data from 1983 to 2013 in Japan. The number of landslide disasters in each year was significantly correlated to the precipitation amount averaged over northern, eastern, and western Japan between May and October (p<0.05;R=0.78). The relationship in the first16years (1983�|1998) was similar to that in the last15years (1999�|2013). The death toll by landslide disasters was correlated to the number of landslides. The slope in the first period was steeper than that in the second period, indicating a decreasing trend in the ratio of deaths to landslides. We also found a decreasing trend in the number of houses involved in landslide disasters during the analysis period. However, there was no trend in the ratio of deaths to that of completely collapsed houses. Our results suggest that the decrease in the number of houses involved in landslide disasters is the dominant factor in the reduced death toll by landslide disasters.