Abstract
Abstract. The present study is to explore the potential relationship between debris flow and landslides by establishing susceptibility zoning maps (SZMs) separately with the use of random forest (RF). Lhünzê county, located in southeastern Tibet, was selected as the study area. The work was carried out with the following steps: (1) an inventory map consisting of 399 landslides and 49 debris flows was determined; (2) slope units and 11 conditioning factors were prepared for the susceptibility modeling of landslide while watershed units and 12 factors were prepared for debris flow; (3) SZMs were constructed for landslide and debris flow, respectively, with the use of RF; (4) the performance of two models was evaluated by 5-fold cross-validation using receiver operating characteristic (ROC), area under the curve (AUC) and statistical measures; (5) the potential relationship between landslide and debris flow was explored by the superimposition of two zoning maps; (6) the Gini index was applied to determine the major factors and analyze the difference between debris flow and landslides; (7) a combined susceptibility map with two considered hazardous phenomena was obtained. Two used models had demonstrated great predictive capabilities, with an accuracy of 87.33 % and 85.17 % and AUC of 0.902 and 0.892, respectively. Comparing the overlap of different susceptibility classes for two obtained maps, it was concluded that there is no straightforward relationship between the occurrence of debris flow and landslides. Although most landslides can be converted into debris flow, the area prone to debris flow did not promote the occurrence of a landslide. A susceptibility zoning map composed of two or more hazardous phenomena is comprehensive and significant in this regard, which provides a valuable reference for research studies of disaster-chain and engineering applications.
Highlights
Soil slide and debris flow are two kinds of natural phenomena mainly occurring in mountainous areas, which pose considerable threats to people, industries, and the environment directly or indirectly
The predictive accuracy, receiver operating characteristic (ROC) curves and area under the curve (AUC) values of the random forest (RF) models using the training dataset were shown in Table 1 and Fig. 7
Susceptibility assessment models for landslide and debris flow are established through RF, and the performance of the models is excellent in terms of accuracy and goodness of fit
Summary
Soil slide and debris flow are two kinds of natural phenomena mainly occurring in mountainous areas, which pose considerable threats to people, industries, and the environment directly or indirectly. Extensive research has been conducted for the prediction and susceptibility assessment of landslide and debris flow. Most of debris flows are runoff generated (Imaizumi et al, 2006; Theule et al, 2012; Ma et al, 2018). Landslides that occur on a steep slope and become disaggregated as they tumble down can transform into debris flows if they contain sufficient water for saturation (Huang et al, 2019). Debris flow usually occurs on a channel bed for the entrainment into abundant runoff of debris supplied by deep or shallow slides of slopes incised by the channel (Hurlimann et al, 2013; Zhou et al, 2019; Simoni et al, 2020). Landslides may provide sufficient material source for debris flow, and most of the landslides are accom-
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