## 4 Results and Discussion
### Analysis of Prediction Statistics of Historical Landslide Data
To obtain relevant incident times for the remainder of the historical landslides, the following assumptions were made: (1) historical landslides recorded during a particular rainstorm and distributed within the same IC zone have a negligible difference in occurrence time and thus, can be said to have occurred at the same time; (2) in the case of an IC zone containing more than one landslide with recorded occurrence times, the earliest recorded time can be used as the representative occurrence time of the IC zone for conservative evaluations; (3) in the case of an IC zone in which no landslide occurrence time information is present, the representative landslide occurrence time was postulated by considering that of adjacent IC zones with the same lithological conditions and comparatively analyzing cumulative landslide-triggering rainfall patterns of adjacent IC zones. In terms of assumption (2), our study contained two cases in which multiple landslide-timing records were present within an IC zone on the same date. The time difference between the records was not significantly large for both cases, specifically, 1 h and 1 h 8 min, respectively. [PERSON] [39] concluded that a large number of landslides are triggered near the peaks of severe rainstorms. In the case of a landslide where only the occurrence date and rainfall event are known, [PERSON] et al. [40] considered the time (hour) of the last rainfall measurement of the day on which the landslide occurred as the landslide occurrence time. As such, determining the correct landslide occurrence time remains a limiting factor in landslide research that uses historical data. Table 4 represents the landslide occurrence times and IC zones for landslides that occurred on each of the eight landslide event dates. The representative times with superscript \"P\" are those that were postulated in compliance with assumption (3). In the next step, early warning levels at the respective landslide occurrence times were investigated for each of the 222 historical landslide records using early warning level maps. These maps were generated using an hourly interval, as historical rainfall data from the KMA observatories were also recorded hourly. Therefore, the early warning level maps that correspond to the rounded-down hours of the respective landslide occurrence times were used to determine early warning levels of the historical landslide events. In addition, a polygon circle centered around each historical data point \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**Date of Landslide**} & \multicolumn{8}{c}{**Representative Landslide Occurrence Time (hh:mm)**} \\ \cline{2-9}  & **IC Zone 1** & **IC Zone 2** & **IC Zone 3** & **IC Zone 4** & **IC Zone 5** & **IC Zone 6** & **IC Zone 7** & **IC Zone 8** \\ \hline
7 July 2009 & - & - & - & 09:23 & 12:50 & 09:20 & - & - \\
16 July 2009 & 06:30 P & 07:50 & 10:40 & 7:00 P & 10:00 & 07:30 & - \\
27 July 2011 & - & - & 10:14 & 10:20 & - & - & - & - \\
15 July 2012 & - & 13:00 & 02:30 & 04:00 & 00:10 & - & - & - \\
18 August 2014 & - & - & - & - & 05:25 & - & - & - \\
25 August 2014 & - & - & 15:30 P & 14:22 & 14:30 P & 16:00 P & 16:00 \\
4 July 2016 & - & 03:21 & 08:07 & - & - & - & - & - \\
5 October 2016 & - & - & - & - & - & 10:00 & - & - \\ \hline \hline \end{tabular} \({}^{\text{P}}\) Postulated landslide occurrence time.  
\end{table} 
Table 4: Representative landslide occurrence times per infiltration characteristic (IC) zones in which landslides occurred on the eight landslide event dates. with a 50 m radius was used as the domain area for determining a representative early warning level for each historical landslide. The radius of 50 m was determined in reference to the maximum possible error distance of the 2 nd class spatial precision data points, as the 222 historical landslide records contained either 1 st or 2 nd spatial precision data.