This paper uses a comprehensive risk assessment method to investigate the population risk of debris flows in Southwest China. The methodology integrates models from hazard, vulnerability literature and some empirical equations. The main steps include debris-flow disaster-hazard zoning, estimation of the frequency of the disaster, factor identification of population vulnerability, and calculation of the fragility rate. The results demonstrate that the most hazardous regions in Southwest China are primarily observed in the mountains around the Sichuan Basin, the border area between Sichuan and Yunnan Provinces, the eastern and southern regions of Yunnan Province, and the eastern area of Guizhou Province. The extremely high vulnerability zones are characterized by a fragility rate of 3.89 persons per 10,000 people. The comprehensive risk gradually increases from the southeast of the study area to the central region, reaching its highest value (more than 100 persons/year) on the Jiangyou-Zhaotong-Baoshan Line and decreasing thereafter to its lowest in the northwestern region. Extremely large-scale disasters are the major factor of casualties. Appropriate risk management and mitigation solutions should be comprehensively determined based on the combination of debris-hazard levels and fragility rates in the hazardous regions. © 2018 by the authors.
