Sato Tadamichi, Katsuki Yoh, Shuin Yasuhiro
Graduate School of Bioresource and Bioenvironmental Sciences, Kyushu University, Fukuoka, Japan.
Faculty of Agriculture, Kyushu University, Fukuoka, Japan.
Sci Rep. 2023 Aug 31;13(1):14258. doi: 10.1038/s41598-023-41539-x.
In this study, we evaluated the influence of forest cover changes on rainfall-induced shallow landslides by comparing two shallow landslides and debris flows that occurred on plantation forests of different ages in Japan: the Kake disaster in 1988 and the Asakura disaster in 2017. At Kake, the trees ranged in age from 10 to 30 years, whereas at Asakura the trees were over 40 years old. The rainfall characteristics that triggered each landslide were estimated using a three-layer tank model, and the results, as well as the volume of driftwood produced by the landslides, were then compared. Both landslides occurred when the first tank storage layer value, corresponding to the temporal variation in groundwater level in the shallow soil layer, exceeded its previous maximum. The return period of this value at the time of the landslides was 3.0-fold higher in the more mature forests of Asakura than in the young forests of Kake. The upper limit of driftwood volume was 30-fold higher in Asakura than in Kake. Our findings indicated that shallow landslides and debris flows become increasingly rare as forests mature; however, the large volume of driftwood produced by landslides in mature forests may cause substantial damage when extreme rainfall events exceed the landslide resistance of those forests. These insights may be applied to effective landslide risk management.
在本研究中，我们通过比较日本不同树龄人工林发生的两次浅层滑坡和泥石流，评估了森林覆盖变化对降雨引发的浅层滑坡的影响：1988年的加计灾害和2017年的朝仓灾害。在加计，树木树龄为10至30年，而在朝仓，树木树龄超过40年。使用三层水箱模型估算引发每次滑坡的降雨特征，然后比较结果以及滑坡产生的浮木量。两次滑坡均发生在对应浅层土壤层地下水位时间变化的第一层水箱蓄水量值超过其先前最大值时。滑坡发生时该值的重现期在朝仓较成熟的森林中比在加计的幼龄森林中高3.0倍。朝仓的浮木量上限比加计高30倍。我们的研究结果表明，随着森林成熟，浅层滑坡和泥石流越来越少见；然而，当极端降雨事件超过成熟森林的抗滑能力时，成熟森林中滑坡产生的大量浮木可能会造成重大破坏。这些见解可应用于有效的滑坡风险管理。
