## 2 Materials
### Landslide Influencing Factors
#### 2.3.1 Topographic Factors  
Altitude is a commonly used factor in landslide susceptibility assessments and plays an important role in landslide occurrence demonstrated by many studies [44; 45; 47; 54]. Environmental conditions (such as vegetation distribution and rainfall) vary with altitude, affecting the occurrence of landslides [30].  
Slope is one of the most direct and important factors affecting slope stability [52]. With changing slope degrees, the stress field in the slope also changes, affecting slope stability [9]. In general, the steeper the slope, the greater the chance of failure [55].  
Aspect refers to the direction a slope faces, which primarily affects environmental conditions such as soil moisture, weathering, and topographic vegetation through rainfall, wind, and solar radiation, thereby indirectly affecting slope stability [53]. Aspect ranges from 0\({}^{\circ}\) to 360\({}^{\circ}\), which can be divided into eight basic directions of North, Northeast, East, Southeast, South, Southwest, West, and Northwest, as well as flat areas.  
Plan curvature and profile curvature are two types of curvature commonly used in landslide susceptibility studies to reflect the geometric characteristics of slopes. The plan curvature affects the convergence and divergence of flow, while the profile curvature  
Figure 2: Landslite influencing factor layers: (**a**) altitude; (**b**) slope; (**c**) aspect; (**d**) plan curvature; (**e**) profile curvature; (**f**) degree of relief; (**g**) topographic wetness index (TWI); (**h**) lithology; (**i**) seismic intensity; (**j**) distance from fault zones; (**k**) stratigraphy; (**l**) distance from main rivers; (**m**) distance from streams; (**n**) annual rainfall; (**o**) normalized difference vegetation index (NDVI); (**p**) land cover; (**q**) soil erosion intensity; (**r**) distance from roads; (**s**) residential kernel density; (**t**) distance from hydropower stations.  
affects the acceleration and deceleration of flow [9; 30; 36; 41; 44]. A positive plan curvature indicates that the slope is sideward convex, while a negative value indicates that the slope is sideward concave, and values around zero represent flat surfaces. On the contrary, positive and negative values of profile curvature indicate upward concave and upward convex respectively [9; 33].  
The degree of relief refers to the difference between the highest altitude and the lowest altitude in a specific area and has a regional correlation with landslide occurrence [51; 52]. The calculation formula is:  
\[R=H_{max}-H_{min} \tag{1}\]  
where \(R\) is the degree of relief of a unit area, \(H_{max}\) is the altitude of the highest point in the area, and \(H_{min}\) is the altitude of the lowest point in the area.  
TWI is a physical indicator of the impact of regional topography on the direction and accumulation of runoff flow. This index helps identify rainfall-runoff patterns, potential areas with increased soil moisture, and waterlogging areas, as well as quantify the control of topography over basic hydrological processes, which is commonly used in landslide susceptibility assessments [36; 44; 52; 53]. In this study, TWI was calculated with the SAGA-GIS ([[http://saga-gis.org](http://saga-gis.org)]([http://saga-gis.org](http://saga-gis.org)), accessed on 11 July 2021) software using the following calculation formula:  
\[TWI=ln(A_{S}/tan\beta) \tag{2}\]  
where \(A_{S}\) is the slope contributing area, and \(\beta\) is the slope gradient.