In view of the difference in the monotonicity for risk factors and the nonlinear relationship between the primary risk factors and secondary risk factors in the evaluation of debris flow risk

a new method to evaluate the correlation between the primary risk factors and secondary risk factors by using scatter diagrams and Spearman rank correlation is proposed. In the method

the scatter diagrams are used to analyze the relationship between the primary risk factors and the secondary risk factors

and on this basis

a preliminary screening of the secondary risk factors can be made. Spearman coefficients of rank correlations are used to further screen the secondary risk factors and identify their weights. With the new method

a new formula of debris flow risk is established by using the basic data of 37 debris flow gullies in Yunnan province. Finally

the new formula is taken to calculate the debris flow risk of 12 debris flow gullies in Dongchuan city. The results verify that the source conditions and dynamic conditions are significant to the potential risk of debris flows

so as to justify the rationality of this method.