Variation in the frequency and characteristics of landslides in response to changes in forest cover and rainfall in Japan over the last century: A literature review

Rainfall-induced shallow landslides are a common geohazard in mountainous areas, often causing human and economic losses. The frequency and characteristics of these landslides are affected by changes in both triggering and inherent factors. This study reviewed the long-term trends in landslide occurrence in Japan over the past century, emphasizing the role of changes in forest cover and rainfall. Documents written in Japanese (i.e., journal articles by professional organizations in Japan, disaster reports, books, policy documents, and government statistics) and research published in English were collected and synthesized to describe changes in forest cover, rainfall, and landslides. The review revealed that Japan has experienced a reduction in landslide frequency and damage as forest cover has matured at a national scale. In contrast, recent climate change has altered rainfall patterns, leading to extreme rainfall events. These changes have highlighted the negative impacts of forest maturity, such as landslides with sliding surfaces extending deeper than the root system of mature forests and an increase in landslides containing large volumes of woody debris. We also compared these Japanese cases with previous studies to identify their features and future research directions. This study provides the international community with a historical perspective on landslide trends in Japan in response to shifts in forest cover and rainfall. The results will contribute to future research and improved practices for management of landslide risk and forest resource management adapted to climate change.