*4.4. E*ff*ect of Antecedent SWI*

The antecedent SWI values for one month until the beginnings of rainfall events were calculated for comparison with the rainfall conditions for triggering LSLs. Based on the approaches proposed by Chen, et al. [27] for separating landslides into three categories by two values of antecedent SWI, 14.7 mm (the average value) and 29.4 mm (twofold the average value), Table 3 displays the values of the 98th percentiles of average intensity, cumulative event rainfall, and duration for these three categories. Figure 11 shows that the rainfall conditions for triggering LSLs gradually descend with increases in antecedent SWI. With increases in antecedent SWI, the decline in rainfall intensity and cumulative rainfall for triggering LSLs is more evident than that for SSLs. This finding reveals the significant effect of water content before a rainfall event on the occurrence of an LSL. Figure 11 also shows that when antecedent SWI is less than 29.4 mm, the 98th percentiles of rainfall intensity and cumulative rainfall for triggering LSLs are higher than those for SSLs. The 98th percentile of duration for LSLs exceeds 100 h, even though it is shorter than that for SSLs. When antecedent SWI is higher than 29.4 mm, the decrease in the duration for triggering LSLs is smaller than that for SSLs. This finding indicates that long-duration rainfall can be considered as one of the main conditions for triggering LSLs.

**Figure 11.** Variations of (**a**) average rainfall intensity, (**b**) duration, and (**c**) cumulative rainfall for triggering LSLs during 2001–2016 with the antecedent SWI. Red lines represent the 98th percentile of rainfall parameters for triggering LSLs in different categories of antecedent SWI. Dashed lines represent the 98th percentile of rainfall parameters for triggering SSLs in different categories of antecedent SWI reported by Chen, et al. [27].


**Table 3.** The 98th percentile of duration, cumulative amount, average intensity of rainfall triggering LSLs in different categories of antecedent SWI.
