Preprints
https://doi.org/10.5194/nhess-2020-243
https://doi.org/10.5194/nhess-2020-243

  30 Sep 2020

30 Sep 2020

Review status: a revised version of this preprint is currently under review for the journal NHESS.

Uncertainty analysis of the estimation of stony debris flow rainfall threshold: the application to the Backward Dynamical Approach

Marta Martinengo, Daniel Zugliani, and Giorgio Rosatti Marta Martinengo et al.
  • Department of Civil, Environmental and Mechanical Engineering, University of Trento, Trento, Italy

Abstract. Rainfall thresholds, namely rainfall intensity-duration conditions beyond which the probability of debris flow occurrence is considered significant, can be used as a forecasting tool in debris-flow early warning system. Many uncertainties may affect the thresholds calibration and, in turn, the reliability and effectiveness of this tool. The purpose of this study is to assess the uncertainty in the determination of the rainfall threshold for stony debris flow based on the Back Dynamical Approach (BDA) (Rosatti et al., 2019), an innovative method to estimate the rainfall duration and averaged intensity strictly related to measured debris flow. The uncertainty analysis has been computed performing two Monte Carlo cascade simulations: (i) to assess the variability in the estimate of rainfall conditions due to the uncertainty of some of the BDA parameters and (ii) to quantify the impact of this variability on the threshold parameters, obtained by using the frequentist method. Then, the deviation between these analysis outcomes and the values obtained in Rosatti et al. (2019) has been examined. The results highlight that the variability in the rainfall condition estimate is strongly related to the debris flow characteristics and the hyetograph shape. Depending on these features, the spreading of the obtained distributions can take both low and high values. Instead, the threshold parameters are characterised by a low statistical spreading. Finally, the consistency between the outcome of this study and the results obtained in Rosatti et al. (2019) has been proved and the critical issues related to the rainfall condition estimation have been discussed.

Marta Martinengo et al.

 
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Marta Martinengo et al.

Marta Martinengo et al.

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Short summary
Rainfall thresholds are relations between rainfall intensity and duration on which the forecast of the possible occurrence of a debris flow can be based on. To check the robustness of a physical-based stony debris flow rainfall threshold, in this work we developed a procedure to estimate the effects of various sources of error on the determination of the threshold parameters. Results show that these effects are limited and therefore, the threshold is quite reliable.
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