Abstract: By utilizing data of precipitation,topography and geomorphology,population,geological disasters and digital elevation mode (DEM),Jizhou district,located in the north of Tianjin,was taken as the research area in this paper to conduct study on assessment of the hazardous degree of debris flow disasters in Tianjin.More specifically,the research area was divided into the grids using the approach of non-structural irregular design,and then the weights of the debris flow risk factors including the direct and indirect amount of rainfall,flow velocity,topography and geomorphology,population density,frequency of occurrence of debris flow were determined,and the debris flow risk degree model (DFRDM) of Tianjin was established based on the analytic hierarchy process method(AHP).This model was used to evaluate the hazardous degree of the debris flow disasters for the eleven strong rainstorm processes over Jizhou district during 2011-2018.The results show that the rainfall process on July 20,2016 with the largest rainfall amount and concentration has the highest risk of debris flow,and the risk for stable rainfall process on August 12-14,2018 is the lowest.Furthermore,the debris flow occurring over "Shuang'an" Village on July 22,2012 and the small landslides on July 24,2018 over Jizhou district,are both captured by the DFRDM model,indicating that this model has a good assessment ability for debris flow and can be applied to real-time operation and service.Moreover,the generalized extreme value distribution function was used to calculate the 1-hour and 12-hour amount of precipitation in different reoccurrence periods of Jizhou district,and the DFRDM was then used to estimate the debris flow risks for different levels of precipitation,which can provide useful reference for the relevant decision-making departments.

Key words: Debris flow, Analytic hierarchy process (AHP), Risk degrees, Recurrence periods, Disaster assessment