Impact of national-scale changes in forest cover on floods and rainfall-induced sediment-related disasters in Japan

Changes in forest cover influence floods and sediment-related disasters. In Japan, forest cover has changed substantially at the national scale, and floods and rainfall-induced sediment-related disasters have subsequently decreased. In this study, we determined the quantitative impact of national-scale changes in forest cover on floods and rainfall-induced sediment-related disasters. The growing stock of forests and the flooded area were obtained from the Forestry Agency and the Ministry of Land, Infrastructure, Transport and Tourism, and were used as indices to examine the relationship between forest cover and floods and rainfall-induced sediment-related disasters. The flooded area decreased exponentially until the growing stock of forests reached 3.13 billion m³ (124.5 m³/ha), but was not reduced more as the growing stock further increased. Our findings agree with a previous study that investigated the growing stock of forest needed to prevent landslides. The two indices used in this study were suitable because they have corresponded with forest cover, floods, and rainfall-induced sediment-related disasters since the 1960s. The results of this study can be a guide to determining the volume of logging without increasing floods or sediment-related disasters.