## 4 Results and Discussion
### Results of the Landslide Susceptibility Mapping  
Figures 4 and 5 showed the different space layers of conditioning factors and the landslide susceptibility map constructed by the VR model and RIRA method, respectively. In Figure 4, higher susceptibility values were in the layers with the convex slope and concave slope, as well as the distance of less than 50 m to the river, the distance of less than 50 m to the road, the slope of 25-35\({}^{\circ}\), and the slope higher than 35\({}^{\circ}\); the values were all more than 10. Among the nine related factors examined in the study, elevation, distance to river, lithology, and rainfall are hard to change, and the other factors, slope, profile curve, distance to road, land-use, and NDVI, can be modified to reduce the landslide  
susceptibility. Slope gradients can be reduced by converting slope land into terraces [21]. In terms of profile curve and distance to road, human activity and road construction should be carried out in a planned way. Especially, a preliminary reconnaissance survey should be implemented on the topography and geology of the area. In terms of land use, many landslides were observed on the bareland. Thus, the reduction of ground exposure may reduce landslide susceptibility. For the NDVI, it can be seen that soil bioengineering is not omnipotent and did not apply to all situations, e.g., deep-seated, rock, or extremely steep slopes [52]. Therefore, the comprehensive effect of the conditioning factors should be considered in the process of prevention and control of landslides. In the study area, reconstruction of the eco-environment had already been conducted since 1997. In the past decade, grasses or shrubs are the main types of plantings on the top of hills or upper part of hill slopes, while trees were mainly selected in the hilly slope with a moderate gradient, and most of the slope of cropland was converted to woodland or grassland [53]. Nevertheless, a quantitative assessment of the effectiveness of those comprehensive measures in inhabiting landslides is still lacking. Figure 4: Susceptibility value of spatial layers influencing landslide occurrence in the study area: (**a**) profile curvature, (**b**) distance to river, (**c**) distance to road, (**d**) rainfall, (**e**) elevation, (**f**) slope, (**g**) NDVI, (**h**) lithology, and (**i**) land use. As shown in Figure 5c, a very low susceptibility zone occupies 6.90 km\({}^{2}\). Similarly, low, medium, high, and very high susceptibility zones occupy 12.81, 12.83, 9.42, and 5.87 km\({}^{2}\), respectively. As depicted in Figure 5a, the susceptibility levels decreased with distance from rivers and road. Very high susceptibility was in the region with a larger relief and along the river and road, which was also in line with the site investigation. In the whole province, landslides were mostly distributed on both sides of the roads and rivers. For example, collapses often take place on both sides of the Yan and the Fenchuan Rivers, especially along the roads and railways, [51]. This is due to the fact that Yan'an City and urban population centers are located in major river valleys and that intensive human engineering activities are often responsible for many landslides and related serious damages [51]. Therefore, in the road construction and other engineering works on the Loess Plateau, the engineers and researchers should be committed to the prevention and control of loess landslides [48], and, also, the road and the river located in the gullies. As a result, the down-cutting of channels during rainstorms, as well as the high content of soil moisture adjacent to a channel, make it more prone to landslides [21]. Moreover, in the regional susceptibility assessment of the Baota district, the specific area was extended along the Nanchuan River, and its tributaries to Shitouguoul village got a high susceptibility [28].