Quantifying Landslide Damage Characteristics and Influencing Factors Across Mountain Forest Watershed Types Using Random Forest and SHAP

Landslide damage in mountain forest watersheds may vary not only with local slope conditions but also with hydrological and geomorphological connectivity within watersheds. This study quantitatively analyzed differences in landslide damage characteristics and influencing factors among forest watershed types to support watershed-based landslide damage mitigation. We extracted 1809 landslide damage polygons that overlapped mountain forest watersheds in the Chungcheong region of the Republic of Korea during 2022–2024 and classified them into catchment, slope, and independent zones. Damage area, perimeter, width, length, and elongation ratio were compared among watershed types. Area, perimeter, width, and length were largest in catchment zones and smallest in independent zones. Random forest models were developed and evaluated using repeated stratified 5-fold cross-validation with 13 topographic, soil, forest, geological, and watershed morphometric factors, and SHAP analysis was applied to interpret factor contributions. Watershed area was identified as a common important factor across all watershed types. However, secondary key factors differed by type: relief, DBH class, and slope length were relatively important in catchment zones; slope gradient, DBH class, and relief in slope zones; and relief and slope gradient in independent zones. These findings indicate that landslide damage characteristics and landslide-influencing factors vary by forest watershed type and can support differentiated forest disaster management and landslide mitigation strategies.