Lithological terrain-based rainfall thresholds for possible initiation of shallow landslides in South Korea

Landslides are frequently occurring natural disasters in South Korea, mostly during the rainy season (June to September) due to typhoons and extreme rainfall. Rainfall must be analyzed for its role as a primary trigger of landslides. This study investigates the relationships between rainfall, shallow landslide likelihood, and lithological control in South Korea. We analyzed data from 263 landslides between 1999 and 2020 collected by the National Disaster Management Research Institute, local autonomous entities, and newspapers. The quantile regression method was used to calculate the intensity-duration (I-D) and cumulative rainfall-duration (C-D) thresholds for different levels of exceedance probability. A four-warning level scheme was proposed. These thresholds were then classified based on rock type, since rock type can also affect the likelihood of landslides. Data from recent landslides (occurring between 2018 and 2020) were used to validate the accuracy of the thresholds using receiver operating characteristic curves. The findings of this study indicate that sedimentary rock terrains are more susceptible to rainfall-triggered landslides than other rock types. In addition, more rainfall is required to trigger landslides in metamorphic rock terrains. The area under the curve calculated from the validation data was over 0.8, indicating that the proposed thresholds can accurately predict the occurrence of landslides in different rock types. Hence, this study proposed four warning levels based on rainfall thresholds, which aim to improve the accuracy of early warning systems and reduce the risk of landslides in South Korea.

Automated summary

This study investigates the relationships between rainfall, shallow landslide likelihood, and lithological control in South Korea, and proposes a four-level warning system to predict and reduce the risk of landslides.