The intensity-duration (I-D) threshold is considered an effective indicator for landslides triggered by short-term high-intensity rainfall and long-term low-intensity rainfall. However, previous studies have not considered the influence of antecedent rainfall. Herein, we analyzed hourly rainfall data for 613 shallow landslides that occurred from 1963 to 2018 in South Korea to obtain rainfall thresholds and investigated the effect of antecedent rainfall conditions on threshold variations. The I-D and IMAP-D, which is normalized by dividing I by mean annual precipitation (MAP), thresholds were determined to be I = 10.40D–0.31 and IMAP = 0.006D–0.26 (4 ≤ D (h) ≤ 84), respectively, at the 2nd percentile level through quantile regression analysis. These thresholds were lower than other local thresholds (i.e., excluding global and regional thresholds), suggesting that the southern region of the Korean Peninsula was more susceptible to rainfall-induced landslides. Although the effective length of antecedent rainfall was not presented herein, the I-D threshold of landslide-triggering rainfall was confirmed to be low for the absolute and/or calibrated antecedent rainfalls greater than event cumulative rainfall at 5, 7, 10, and 20 days prior to the event. Such differences in I can be greater at shorter durations; however, these differences gradually decrease as D increases, suggesting that they lose their effect as soil water content increases. The results of the current study can improve the understanding of the effect of antecedent rainfall conditions on landslide occurrence and should be further tested with respect to the hydrologic response of hillslopes by considering regional climate and local site conditions.

中文翻译：

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韩国先行降雨条件及其变化对浅层滑坡触发降雨阈值的影响

强度持续时间（ID）阈值被认为是由短期高强度降雨和长期低强度降雨引发的滑坡的有效指标。然而，以前的研究没有考虑前期降雨的影响。在此，我们分析了韩国 1963 年至 2018 年发生的 613 次浅层滑坡的每小时降雨量数据，以获得降雨阈值，并研究了前期降雨条件对阈值变化的影响。ID 和 IMAP-D，通过将 I 除以年均降水量 (MAP) 进行归一化，阈值确定为 I = 10.40D–0.31 和 IMAP = 0.006D–0.26 (4 ≤ D (h) ≤ 84)，分别在第二个百分位水平通过分位数回归分析。这些阈值低于其他局部阈值（即不包括全球和区域阈值），表明朝鲜半岛南部地区更容易发生降雨引发的山体滑坡。虽然这里没有给出先行降雨的有效长度，但对于大于前 5、7、10 和 20 天的事件累积降雨的绝对和/或校准先行降雨，滑坡触发降雨的 ID 阈值被确认为较低到活动。I 的这种差异在较短的持续时间内可能会更大；然而，这些差异随着 D 的增加而逐渐减小，这表明它们随着土壤含水量的增加而失去作用。