## 4 Results and Discussion
### Temporal Performance Analysis  
In this section, the results of a temporal performance analysis of SEM-LEWS are described using historical rainfall and landslide data from Busan for the eight years from 2009 to 2016. For a temporal performance analysis, the scale of study area should be constrained to the point where causative factors of landslides, such as rainfall and geo-properties, are nearly homogeneous. Therefore, in this study, we selected a specific region (Figure 12) that has near-uniform meteorological and hydrogeological characteristics. In terms of meteorological characteristics, spatially uniform rainfall input data was generated for each of the 17 Thiessen districts that partition the entire Busan territory. In terms of hydrogeological characteristics, a part of IC zone 4 that overlaps with the Daeyeon Thiessen district was selected to reduce the spatial variability of hydrogeological characteristics. This was possible as IC zone boundaries demarcate areas with specific unsaturated soil characteristics so that slopes within each IC zone have near-homogeneous rainfall infiltration and subsurface water flow characteristics. In a physically based modelling study to define \(CR_{Critical}\) thresholds of shallow landslides, [PERSON] [41] reported that, in Busan, infiltration characteristics related to unsaturated soil parameters play a bigger role in reducing slope stability than other geotechnical characteristics such as cohesion, friction angle, and slope angle. Therefore, it can be inferred that the selected region would exhibit near-uniform spatial changes regarding landslide hazard, and thus the same warning levels over the same time scales. Using historical rainfall data obtained from the Daeyeon rainfall observatory, the changes in warning levels over time were investigated for the specific region where the highest number of historical landslides were recorded within the Busan area. During the eight-year period, on four dates, landslides were recorded in this specific region (hereafter referred to as study region). The distribution of the recorded historical landslide data is shown in Figure 12. On each of the four dates, only one landslide record contained occurrence time information as follows: 09:23 on 7 July 2009, 10:40 on 16 July 2009, 10:20 on 27 July 2011, and 04:00 on 15 July 2012. The remainder of the historical landslides was assumed to have occurred concurrently. Figure 11: Prediction results of historical landslide data in each of the eight infiltration characteristic (IC) zones in Busan. Figure 13 shows the changes in rainfall and corresponding warning levels in the study region during the rainy season (June to October) across the eight-year time period. Although small, the initiation time of a particular warning level was spatially variable within the study region. Therefore, we defined the initiation time as the time when a particular warning level starts to constitute the largest area within the study region compared to other warning levels. In the case of the highest \"Emergency\" level, however, the study region was considered to enter the phase of this level if the number of \"Emergency\" cells exceeded half the maximum number of cells that could be assigned this warning level within the study region. Figure 12: Map of the study region used for temporal performance analysis including the distribution of historical landslides recorded on four different dates. Figure 13: _Cont._  
During the rainy season of 2009 (Figure 13a), the landslide early warning model characterized seven rainfall conditions among various combinations of continuous rainfall and 20-day antecedent rainfall by generating warnings.