M. Melillo (1), S. Peruccacci (1), M.T. Brunetti (1,2), S.L. Gariano (1,2), F. Guzzetti (1), 2014, An algorithm for the objective definition of rainfall events and its application in forecasting rainfall-induced landslides, GIT - Geology and Information Technology Convegno Nazionale del Gruppo di Geologia Informatica, 2014,
URL: http://www.cnr.it/prodotto/i/299075

Objective criteria for the identification of rainfall events are lacking or ambiguous, particularly when dealing with the forecast of rainfall-induced landslides. The definition of rainfall conditions that have resulted in past landslides remains somewhat subjective. To overcome this problem, we propose an algorithm for the objective and reproducible reconstruction of rainfall events and of rainfall conditions responsible for failures. The algorithm calculates the duration (D in h) and the cumulated event rainfall (E in mm) of rainfall events and of rainfall conditions that have resulted in past landslides. The algorithm is implemented in a code written in R language (http://www.r-project.org). The algorithm analyses continue rainfall series performing three actions_ (i) it removes isolated events with negligible amount of rainfall from the input data series; (ii) it aggregates rainfall measurements in order to obtain a sequence of distinct rainfall events; (iii) it identifies one or more rainfall conditions responsible for the observed slope failures. The algorithm is independent from the geographical context since it uses a set of parameters to account for different physical settings and climatic conditions. We tested the algorithm in Sicily, southern Italy, using geo-localized rainfall and landslide information between January 2002 and December 2012. Using data from 59 rain gauges, the algorithm reconstructed 13,537 rainfall events, corresponding to a mean of 23 rainfall events per year. Next, using information on 163 documented landslides we reconstructed 343 rainfall conditions as possible triggers of the observed landslides. The algorithm may contribute to reducing the current subjectivity both in the manual reconstruction of rainfall events and in the definition of the rainfall triggering landslides. The objective definition of rainfall conditions responsible for failures is necessary to define reliable rainfall thresholds for the forecasting of landslides. We consider that the objective identification of rainfall events performed by the algorithm could be useful for other hydrological, hydraulic or geomorphological purposes.

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