## 2 Study Area and Materials
### Landslide Inventory  
A landslide map is based on important information to determine the quantitative zoning of landslide susceptibility, hazards, and risk [34; 35]. In this study, a visual interpretation of digital aerial photographs with a high resolution of 50 cm was used for accurate landslide mapping. Although visual  
\begin{table}
\begin{tabular}{c c c c c c} \hline
**Category** & **Factors** & **Data Type** & **Scale** & **Source** \\ \hline \multirow{8}{*}{DEM} & \multicolumn{4}{c}{Slope} & \multirow{8}{*}{\begin{tabular}{c} Slope \\ Aspect \\ Plan curvature \\ Convexity \\ Mid-slope position (MSP) \\ Terrain ruggedness index (TRI) \\ Topographic position index (TPI) \\ Landforms \\ Slope length (SL) \\ Stream power index (SPI) \\ Topographic wetness index (TWI) \\ \end{tabular} } & \multirow{4}{*}{Grid} & \multirow{4}{*}{1:5000} & \multirow{4}{*}{\begin{tabular}{c} National Geographic \\ Information Institute \\ (NGII) in Korea \\ \end{tabular} } \\  & \multicolumn{4}{c}{} \\  & \multicolumn{4}{c}{} \\ \multirow{2}{*}{\begin{tabular}{c} Hydrologic \\ factors \\ \end{tabular} } & \multicolumn{4}{c}{Slope length (SL)} \\  & \multicolumn{4}{c}{} \\ \multirow{2}{*}{\begin{tabular}{c} Hydrologic \\ Stream power index (SPI) \\ Topographic wetness index (TWI) \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} Land-use \\ Material \\ Agricultural Science \\ (NAAS) in Korea \\ \end{tabular} } \\  & \multicolumn{4}{c}{} \\ \multirow{2}{*}{Soil map} & \multicolumn{4}{c}{} \\  & \multicolumn{4}{c}{} \\  & \multicolumn{4}{c}{} \\ \multirow{2}{*}{Forest map} & \multicolumn{4}{c}{} \\ \multirow{2}{*}{\
\begin{tabular}{c} Timber density \\ Timber diameter \\ \end{tabular} } & \multirow{2}{*}{Polygon} & \multirow{2}{*}{1:5000} & \multirow{2}{*}{
\begin{tabular}{c} Korea Forest Research \\ Institute (KFRI) \\ \end{tabular} } \\  & \multicolumn{4}{c}{} \\ \end{tabular}
\end{table}
Table 1: Data layer related to the landslide of the study area.  
Figure 2: Hourly precipitation characteristics in the past led to landslide events in the study area.  
interpretation is a classical method [34], it is very useful in detecting accurate landslide locations and scars using high resolution photographs, as landslide scars are similar to tombs and their surrounding area in the study area.  
These types of photographs without ground control points (GCPs) can be freely obtained at portal sites such as DAUM [36] and Skymap [37] (\"Skymap\") in Korea [38]. The eighteen photos (taken before and after the landslide events) were selected from each region of landslide occurrences and five GCPs were applied to each photo from digital topographic features using ArcMap 10.2. Three out of the 82 landslides detected from the visual interpretation of the photos are shown in Figure 3. The photos taken before and after landslide occurrences are shown in Figure 3a-c, respectively. Figure 3c,d shows the blue plastic-covered area to prevent soil flow after landslides, and Figure 3d was taken by field survey. Most of the intensive rainfall-triggered debris flows were approximately 10-70 m in length, 3-20 m in width range, and less than one m in depth.