## 4 Results and Discussion
### Temporal Performance Analysis
In particular, SEM-LEWS successfully discriminated two rainfall conditions that triggered landslides from the five remaining rainfall conditions, by further raising the warning level to higher than \"Watch.\" For the remaining five rainfall conditions that did not trigger landslides, the warning level was raised to \"Attention\" for relatively low continuous rainfall as considerably high levels of 20-day antecedent rainfall caused the threshold of \(I_{ERL}\) to be exceeded. In the case of a weak continuous rainfall event with a high antecedent rainfall amount, we suggest a precautionary \"Attention\" level to be reasonable, as it offers time to prepare for possible slope instability and post-rain slope failure induced by increased soil moisture conditions. In Figure 14, the progression of continuous rainfall and the corresponding warning levels that led to Landslide occurrence 2 (a debris-flow type event) in Figure 13a are depicted over a specific time scale. Under the condition of great antecedent rainfall amounts, the warning level increased from \"Attention\" to the highest level of \"Emergency\" in response to the continuous rainfall amount increasing from approximately 140 to 200 mm in an hour. Considering that, as shown in Figure 14, the debris flow event was reported after the rainfall became tenuous, it is speculated that the debris flow actually initiated several minutes to a few hours before it was reported. Before further discussing results from the temporal performance analysis, the term \"warning event\" should be defined as follows: an event in which a series of warning levels are initiated and then reduced to \"Null.\" During the 1224-day period corresponding to the duration of the rainy seasons over the eight years, a total of 55 days had warning events (4.5%). This indicates that approximately seven days with warning levels can be expected annually when the system is operational. Another important temporal characteristic of early warnings is lead-time. [PERSON] and [PERSON] [42] defined lead-time as \"a time interval between the moment when the occurrence of a landslide event is reasonably certain (i.e., initiation of each warning level), and the moment of its actual occurrence.\" Table 5 shows the mean lead-time for each warning level in the study region over the eight-year period. We suggest that the deduced mean lead times are reasonable, considering that these values are similar to the preliminary applicability test results of the SEM-LEWS model in which six historical landslide events were sampled and analyzed ([PERSON] et al., 2019). During the eight-year study period, SEM-LEWS generated a total of 30 warning events. Among the events, five were cases that involved high warning levels (\"Alert\" or \"Emergency\"), and landslides occurred in four of those five cases (Figure 13a,c,d). The remaining case  
Figure 13: Progression of changes in rainfall and corresponding warning levels in the specific case study region during the rainy season of **(a)** 2009; **(b)** 2010; **(c)** 2011; **(d)** 2012; **(e)** 2013; **(f)** 2014; **(g)** 2015 and **(h)** 2016.  
that falsely warned with high warning levels is shown in Figure 13f. Here, the \"Emergency\" level was reached, but no landslides occurred. Therefore, from our results, landslide probabilities during a warning event and during a high-level warning event were 13% (4/30) and 80% (4/5), respectively. By analyzing rainfall and landslide data over the eight-year study period, we suggest the importance of certain rainfall boundaries, i.e., critical amounts of rainfall that trigger landslides in the study region. With a continuous rainfall of approximately 220 mm as a criterion, no landslides were recorded in areas with smaller continuous rainfall amounts, while the occurrence of larger continuous rainfall amounts resulted in landslides. Furthermore, the two largest landslides (landslides 1 and 2, Figure 13a) could be distinguished from other landslides by having continuous rainfall amounts of more than 310 mm.