Abstract
To estimate the effects of rainfall and spatiotemporal fluctuation of artificial forest stand age on probability of shallow landslide occurrence, distributed shallow landslide model that incorporated the effect of stand age on soil strength parameter was applied to artificial forest of Hinoki Cypress stand (area: 3.1km2) of Utsunomiya University forest at Funyu during 33 years between 1979 and 2011. In this area, the heavy rainfall in late of August 1998 caused shallow landslides mainly in the 20 years stand age area. After consecutive rainfall data during 33 yeas were divided into 2303 individual rainfall events bounded by periods (>24 h) of no rainfall, 33 heavy rainfall events ranked in the top 33 of event rainfall amount were chosen as model input rainfall events. As the calculation start condition of this model, antecedent rainfall index induced from probabilistic analysis of 33 heavy rainfall events is applied, because of this model is calculated under the wet condition. Although the spatial landslide prediction rate is not high, the calculation results shows that the highest probability of shallow landslide occurrence is late of August 1998, and the highest probability of shallow landslide occurrence in spatial stand age distribution is that of 1981.
