Susceptibility assessment of debris flow hazards from the perspective of watershed units grounded in the Random Forest (RF) model—a case study in the upper reaches of the Fujiang River

) are primarily concentrated in unstable valley regions in the northwestern part of Maoxian-Beichuan, the eastern part of Songpan County, and the southeastern part of Pingwu County; (3) Among the 144 debris flow hazard sites within the watersheds, 56.94% (82 sites) are located in very high susceptibility areas, and 27.78% (40 sites) are in high susceptibility areas, validating the reliability of the assessment results. This study innovatively employs watershed units as evaluation units, thereby overcoming the limitations of traditional grid and administrative units. It clarifies the spatial pattern and key driving mechanisms of debris flow susceptibility in the upper reaches of the Fujiang River, providing a scientific basis and technical support for precise disaster prevention and control, land-use planning, and ecological protection in mountainous regions of southwest China.