A rainfall threshold is a function of some rainfall quantities that provides the conditions beyond which the probability of debris-flow occurrence is considered significant. Many uncertainties may affect the thresholds calibration and, consequently, its robustness. This study aims to assess the uncertainty in the estimate of a rainfall threshold for stony debris flow based on the backward dynamical approach, an innovative method to compute the rainfall duration and averaged intensity strictly related to a measured debris flow. The uncertainty analysis is computed by performing two Monte Carlo cascade simulations: (i) to assess the variability in the event characteristics estimate due to the uncertainty in the backward dynamical approach parameters and data and (ii) to quantify the impact of this variability on the threshold calibration. The application of this procedure to a case study highlights that the variability in the event characteristics can be both low and high. Instead, the threshold coefficients have a low dispersion showing good robustness of the threshold estimate. Moreover, the results suggest that some event features are correlated with the variability of the rainfall event duration and intensity. The proposed method is suitable to analyse the uncertainty of other threshold calibration approaches.

中文翻译：

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基于后向动力法的石质泥石流降雨阈值估计不确定度分析

降雨阈值是一些降雨量的函数，提供了泥石流发生概率被认为显着的条件。许多不确定性可能会影响阈值校准，从而影响其稳健性。本研究旨在评估基于后向动力学方法的石质泥石流降雨阈值估计的不确定性，这是一种计算与实测泥石流严格相关的降雨持续时间和平均强度的创新方法。不确定性分析是通过执行两个 Monte Carlo 级联模拟来计算的：(i) 评估由于后向动力学方法参数和数据的不确定性而导致的事件特征估计的可变性，以及 (ii) 量化这种可变性对阈值校准。将此程序应用于案例研究强调了事件特征的可变性可以是低的也可以是高的。取而代之的是，阈值系数具有低分散性，表明阈值估计具有良好的鲁棒性。此外，结果表明一些事件特征与降雨事件持续时间和强度的可变性相关。所提出的方法适用于分析其他阈值校准方法的不确定性。