How to define rainfall thresholds automatically

The empirical rainfall thresholds while representing a useful approach used to forecast landslide occurrence in wide areas, are affected by several uncertainties related to the rainfall and the landslide information accuracy, the reconstruction of the rainfall events responsible for the failure, and the method to calculate the thresholds. Definition of the rainfall conditions responsible for landslides is a crucial issue and may contribute to reduce landslide risk but the criteria for identify the rainfall conditions that could initiate slope failures are still lacking or uncertain. Furthermore, expert investigators usually perform the reconstruction of rainfall events manually increasing uncertainty in the use of non-objective procedures. To solve these problems, we developed a tool named CTRL-T (Calculation of Thresholds for Rainfall-induced Landslides-Tool) that automatically and objectively reconstructs rainfall events and the triggering conditions responsible for the failure, and calculates rainfall thresholds at different exceedance probabilities adopting a frequentist approach that allows the objective and reproducible definition of empirical cumulated event rainfall-rainfall duration thresholds and their associated uncertainties.

CTRL-T was implemented using the R open-source software (www.r-project.org).The structure of the tool consists of three distinct blocks The first operates the reconstruction of rainfall events in terms of duration (D, in h) and cumulated event rainfall (E, in mm) using rainfall series and several parameters to account for different seasonal and climatic settings. Rainfall event parameters were calibrated adopting the monthly soil water balance model and evapotranspiration analysis. The second block performs the selection of the rain gauge representative for the landslide, the modeling of the antecedent rainfall, and the reconstruction of single or multiple rainfall conditions (MRC) likely responsible for the failures (associating a probability to each condition). The third block calculates the rainfall thresholds using the multiple rainfall conditions or the condition with the maximum probability (MPRC) for each failure. The rainfall event parameters, rainfall data, rain gauge location, landslide location and landslide occurrence time represent the input data used by CTRL-T.

Further details

Melillo M., Brunetti M. T., Peruccacci S., Gariano S. L., Roccati A., Guzzetti F. (2018). A tool for the automatic calculation of rainfall thresholds for landslide occurrence. Environmental Modelling & Software, 105, 230–243. doi:10.1016/j.envsoft.2018.03.024

https://doi.org/10.5281/zenodo.4533719

https://doi.org/10.5194/hess-25-3267-2021

https://doi.org/10.5194/nhess-20-2307-2020

https://doi.org/10.1007/s10064-018-1415-2

https://doi.org/10.3390/w12051449

About the tool:

“A tool for the automatic calculation of rainfall thresholds for landslide occurrence” M. Melillo, M. T. Brunetti, S. Peruccacci, S. L. Gariano, A. Roccati, F. Guzzetti.
https://doi.org/10.1016/j.envsoft.2018.03.024

On the frequentist method:

“Rainfall thresholds for the possible occurrence of landslides in Italy” M. T. Brunetti, S. Peruccacci, M. Rossi, S. Luciani, D. Valigi, F. Guzzetti.
https://doi.org/10.5194/nhess-10-447-2010
“Lithological and seasonal control on rainfall thresholds for the possible initiation of landslides in central Italy”
S. Peruccacci, M.T. Brunetti, S. Luciani, C. Vennari, F. Guzzetti
https://doi.org/10.1016/j.geomorph.2011.10.005