## 2 Landslide Early Warning System for Busan: SEM-LEWS
### Development and Structure of SEM-LEWS
\begin{table}
\begin{tabular}{c c} \hline \hline
**Category** & **Specifications** \\ \hline \hline \multicolumn{2}{c}{Areal management scale} & Regional scale (citywide) \\ \hline \hline \multicolumn{2}{c}{Typical landslide type} & Rapid shallow landslide and debris flow induced by heavy rainfall. \\ \hline \hline \multirow{6}{*}{Hazard evaluation method} & Sequential evaluation approach using the following thresholds: \\  & Statistical thresholds: \(I_{\text{ELR}}\), \(I\)-\(D\) curve, and \(I_{\text{LS}}\) \\ \cline{1-1}  & \(\bullet\) & Physically based threshold: \(CR_{\text{Critical}}\) \\ \cline{1-1}  & \(\bullet\) & Geomorphological threshold: \(I_{\text{DF}}\) \\ \cline{1-1}  & \(\bullet\) & Ground-monitoring instruments for validation analysis. \\ \hline \hline \multirow{6}{*}{Input factors} & \(\bullet\) & Four different rainfall characteristics, saturated hydraulic conductivity, and storage capacity required to run the decision-making algorithm for early warning levels. \\  & \(\bullet\) & Topographic, geotechnical, geo-hydraulic, and geomorphological properties used to derive fixed thresholds, including \(I_{\text{LS}}\), \(CR_{\text{Critical}}\), and \(I_{\text{DF}}\) in advance. \\ \hline \hline \multirow{3}{*}{
\begin{tabular}{c} Interest in time for hazard evaluation \\ \end{tabular} } & \(\bullet\) & Current for ”Nowcasting” module \\ \cline{1-1}  & \(\bullet\) & 24 h in advance for ”Foncasting” module \\ \hline \hline \multirow{3}{*}{Warning level resolution} & Temporal (Update frequency) & \(\bullet\) & ”Nowcasting” module: every 10 min \\ \cline{1-1}  & \(\bullet\) & \"Fonccasting\" module: every 6 h \\ \cline{1-1} \cline{2-5}  & \multirow{3}{*}{Spatial} & \(\bullet\) & Specific areal warning map: \(5\times 5\) m grid cell area \\ \cline{1-1}  & & \(\bullet\) & Administrative warning map: primary administrative division area \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Specifications of the landslide early warning system for Busan based on the sequential evaluation method [21]. Figure 2: Structure of the landslide early warning system for Busan based on the sequential evaluation method. analyzed rainfall infiltration modeling results used to derive a physically based threshold (\(CR_{Critical}\)) for the SEM-LEWS. Two landslide early warning level maps with different spatial resolutions were generated as final outputs from the single evaluation cycles of each module as follows: a specific areal warning map and an administrative warning map. The specific areal warning map includes warning level information with a spatial resolution of \(5\times 5\) m that helps identify warning levels related to specific areas and establish localized management plans (Figure 2(a)), while the administrative warning map provides individual warning level information for each primary administrative division area (Figure 2(b)). This allows for the rapid identification of representative warning levels per primary administrative division and thus, assists in the making of efficient and swift decisions in response to potential disasters. The outputs (landslide early warning level maps) are displayed on the GIS-based interface of Smart Big Board, which supports public officials or other decision-makers in charge of disaster management in making timely and appropriate decisions with improved certainty and efficiency. Additionally, other supplemental information on geo-properties, as well as real-time-collected rainfall tracking information relative to the thresholds of \(I_{ERL}\), \(I\)-\(D\)_curve_, and \(CR_{Critical}\), and landslide historical information, among others, can be displayed on the system interface. Figure 2: Two different types of landslide early warning level maps obtained from a landslide early warning system based on the sequential evaluation method including (**a**) a specific areal warning map and (**b**) an administrative warning map.