The Rainfall Effect Analysis of Landslide Occurrence on Mount Slopes of Wilis

Water is a significant factor in the occurrence of landslides when rainwater absorbs into the impermeable layer of soil and causes the soil to experience weathering; thus, that the soil is not strong enough to withstand the water load. Therefore, rainfall, as well as a land slope that affects the acceleration of runoff, becomes an important indicator that affects the potential for landslides. In this research, the effect of rainfall intensity on landslide was analyzed based on monthly data collected from 81 rain gauge stations. This idea was an effort to support research related to landslides mapping on the steep area. Thus, the analysis of potential landslides that vary according to rainfall changes monthly was obtained. La Nina phenomenon in 2016 causes the intensity of rainfall in the dry season to be quite high. However, the intensity values continued to show a significant change between dry and rainy seasons. The area of low landslide hazard changed significantly for low rainfall intensity (July 2016) and high intensity in April 2017. The total area of landslide hazard in April 2017 was 1.09 and 0.82 times more massive than in August 2016 for high and moderate potential hazards, respectively. Based on the characteristic of rainfall that change frequently and water as the primary trigger of the landslide, in determining the potential for landslides, rainfall factors need to be considered more detailed.