Quantify the effect of antecedent effective precipitation on rainfall intensity-duration threshold of debris flow

α and β are the two key parameters of the rainfall intensity-duration (ID) threshold curve for debris flow; the antecedent effective precipitation (AEP) poses influence on the ID threshold curve through changing α and β. It is critical to explore the correlations of α ~ AEP and β ~ AEP in order to quantify the influence of antecedent precipitation on ID threshold. However, the quantitative relationship between the AEP and the two parameters is still undetermined. In this study, a hydrological process–based numerical model that can derive the ID threshold curve is adopted to address this issue. Jiangjia Gully (JJG) in Dongchuan District of Yunnan Province, China, was chosen as the study area. The analysis results show that a higher AEP can provide favorable hydrological conditions for runoff generation and solid material resource recharge in JJG, but it do not always mean that the ID threshold condition for triggering debris flow is decreased. As for JJG, only after AEP > 40 mm, the AEP and ID threshold condition for triggering debris flow will be completely negatively correlated; when 15 mm ≤ AEP ≤ 40 mm, the solid material supply is rapidly increased by the AEP, a stronger hydrodynamic condition is required to transform them into debris flow meaning that the ID threshold condition for triggering debris flow is enhanced in JJG, and this positive correlation between them persists until the two ID threshold curves intersect in the I-D coordinate system. AEP will significantly change the position of the threshold curve in the I-D coordinate system, and the change law of the position of the ID threshold curve can be described by the functions of α ~ AEP and β ~ AEP. Due to the two functions, the ID threshold curve can regularly move in the I-D coordinate system rather than a conventional threshold curve stay the same regardless of AEP variation; it is beneficial to improve the prediction capacity of the ID threshold.