## 4 Results and Discussion
### Analysis of Prediction Statistics of Historical Landslide Data
Among the early warning levels of the grid cells (\(5\times 5\) m) constituting the domain area, the early warning level assigned to the largest number of cells was considered as the representative early warning level of that domain area. In the case of the highest \"Emergency\" level, however, the domain area was represented by this level only if the number of cells classified as \"Emergency\" exceeded half the maximum number of cells that could be assigned this warning level within the domain area. This is because the area to which the \"Emergency\" level can be assigned is limited to debris-flow-prone areas by a geomorphologically fixed threshold (i.e., \(I_{DF}\) = 0.8). Among the 222 historically recorded landslides, 186 (84%) were categorized as slope failures and 36 (16%) as debris flows. In Figure 9, the recorded landslides are grouped into the two landslide types, and sub-grouped according to assigned warning level at the respective time of occurrence. The \"Alert\" and \"Emergency\" levels were interpreted as states in which slopes are saturated to the point of imminent danger of failure, and states in which possible failure masses are likely to mobilize as debris flow, respectively. Therefore, ideal predictions would forecast all 186 slope failures within the \"Alert\" level and all 36 debris flows within the \"Emergency\" warning level. Results from our analyses indicate that 81% (150/186) of slope failures and 86% (31/36) of debris flows were correctly predicted by the \"Alert\" and \"Emergency\" warning levels, respectively. More specifically, there were no cases of slope failures incorrectly predicted as \"Emergency\" or debris flows wrongly predicted by \"Alert\", which shows the ability of the system to discriminate between slope failure and debris flows. The results also indicate that 17% ((12 + 20)/186) of slope failures were incompletely predicted by conservative (or low) warning levels (i.e., \"Attention\" and \"Watch\"). Considering that the interpretation of these two levels involves the possible occurrence of minor failures or erosive soil losses, it can be concluded that the SEM-LEWS succeeded in warning for 98% (182/186) of slope failures. From the perspective of the fundamental purpose of early warning systems, i.e., to enable preparation for or avoidance of future danger, the most significant error of LEWS may be where  
Figure 9: Prediction results of historical landslide data based on the simulation of landslide early warning system applying the sequential evaluation method for the period of 2009–2016. landslides occurred without warning or with insufficient warning information (hereafter, referred to as missed-warning errors). Five debris flows were classified as having missed-warning errors due to warning levels only being raised to \"Watch\" at the time of occurrence. These five events were recorded during lower rainfall events that did not exceed thresholds of \"Alert\" and \"Emergency\" levels. Through indirect field checks and information from primary sources on damage area and recovery costs, the five events were found to be a type of minor erosive soil loss from valley channels and not large-scale debris flows. As for slope failures, four were classified to have occurred without warnings (i.e., \"Null\" level), and 32 occurred at low warning levels (i.e., \"Attention\" and \"Watch\"). Therefore, 36 of 186 slope failures (19%) occurred with lower rainfall than the threshold level for the \"Alert\" warning. We suggest that the relatively large dispersion of prediction results for slope failures, compared to that of debris flows, can be attributed to historical slope failure data that includes artificial as well as natural slopes (see Section 3.2.). As shown in Figure 10, the four slope failures that occurred without warning were found to be minor local failures of artificial slopes such as retaining walls, embankments, or cut slopes.