2025-10-16 北海道大学
研究対象流域（ピンク色の実線で囲われた範囲）の地震直後の空中写真。もともと森林に覆われていたが、地震による斜面崩壊で37％の森林が破壊された。W地点に堰を設置し、流域からの流出量Rを観測。S地点で降雨量Pを観測。
＜関連情報＞
- https://www.hokudai.ac.jp/news/2025/10/post-2090.html
- https://www.hokudai.ac.jp/news/pdf/251016_pr.pdf
- https://onlinelibrary.wiley.com/doi/10.1002/hyp.70293
大規模地震により高密度に発生した斜面崩壊は丘陵地の森林に覆われた流域の蒸発散量を減少させた Dense Landslides Triggered by a Large Earthquake Reduced Evapotranspiration in a Hilly, Forested Catchment
Shin’ya Katsura, Takashi Koi
Hydrological Processes Published: 08 October 2025
DOI:https://doi.org/10.1002/hyp.70293
ABSTRACT
Although many studies have investigated the effects of forest cover reduction, typically resulting from logging, on evapotranspiration or runoff in forested catchments, few have addressed the impact of landslides. In this study, we evaluated the effect of forest cover reduction caused by dense landslides on evapotranspiration in a hilly catchment that was originally entirely forested. The landslides, triggered by the 2018 Hokkaido Eastern Iburi Earthquake, led to the loss of 37% of the forest cover. Evapotranspiration, calculated using the short-term water budget method approximately 3 and 4 years after the earthquake, was 27% (15%–38% considering uncertainty) and 19% (5%–32%) lower than the evapotranspiration without the impact of landslides, as estimated using a forest evapotranspiration model based on the heat balance calculation developed in Japan. These reductions are comparable to those reported from logging activities. Furthermore, a comparison with a nearby site affected by windthrow suggested that landslides may exert a more severe impact on evapotranspiration, likely due to the reduction of both the forest canopy and the understory. Land managers should be aware that a reduction in evapotranspiration leads to increased runoff, which has the potential to heighten the risk of flooding and increase streamwater turbidity downstream.
