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Volume 18, issue 9 | Copyright
Nat. Hazards Earth Syst. Sci., 18, 2367-2386, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 13 Sep 2018

Research article | 13 Sep 2018

Rainfall events with shallow landslides in the Entella catchment, Liguria, northern Italy

Anna Roccati1, Francesco Faccini2, Fabio Luino1, Laura Turconi1, and Fausto Guzzetti3 Anna Roccati et al.
  • 1Istituto di Ricerca per la Protezione Idrogeologica, Consiglio Nazionale delle Ricerche, Turin branch office, Strada delle Cacce 73, 10135 Torino, Italy
  • 2Dipartimento di Scienze della Terra, dell'Ambiente e della Vita, Università di Genova, Corso Europa 26, 16132 Genova, Italy
  • 3Istituto di Ricerca per la Protezione Idrogeologica, Consiglio Nazionale delle Ricerche, Head office, Via Madonna Alta 126, 06128 Perugia, Italy

Abstract. In recent decades, the Entella River basin, in the Liguria Apennines, northern Italy, was hit by numerous intense rainfall events that triggered shallow landslides and earth flows, causing casualties and extensive damage. We analyzed landslide information obtained from different sources and rainfall data recorded in the period 2002–2016 by rain gauges scattered throughout the catchment, to identify the event rainfall duration, D (in h), and rainfall intensity, I (in mmh−1), that presumably caused the landslide events. Rainfall-induced landslides affected the whole catchment area, but were most frequent and abundant in the central part, where the three most severe events hit on 23–24 November 2002, 21–22 October 2013 and 10–11 November 2014. Examining the timing and location of the slope failures, we found that the rainfall-induced landslides occurred primarily at the same time or within 6h from the maximum peak rainfall intensity, and at or near the geographical location where the rainfall intensity was largest. Failures involved mainly forested and natural surfaces, and secondarily cultivated and terraced slopes, with different levels of maintenance. Man-made structures frequently characterize the landslide source areas. Adopting a frequentist approach, we define the event rainfall intensity–event duration (ID) threshold for the possible initiation of shallow landslides and hyper-concentrated flows in the Entella River basin. The threshold is lower than most of the curves proposed in the literature for similar mountain catchments, local areas and single regions in Italy. The result suggests a high susceptibility to rainfall-induced shallow landslides of the Entella catchment due to its high-relief topography, geological and geomorphological settings, meteorological and rainfall conditions, and human interference. Analysis of the antecedent rainfall conditions for different periods, from 3 to 15 days, revealed that the antecedent rainfall did not play a significant role in the initiation of landslides in the Entella catchment. We expect that our findings will be useful in regional to local landslides early warning systems, and for land planning aimed at reducing landslide risk in the study area.

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Short summary
Natural instability processes are very common. Almost every year, landslides, mud flows and debris flows in the Alpine and Apennine areas and flooding in the Po flood plain cause severe damage to structures and infrastructure and often claim human lives. Geology researchers collect thousands of rain data and process them to try the most precise prediction about the triggering of superficial landslides in order to mitigate the risk and safeguard human goods and lives.
Natural instability processes are very common. Almost every year, landslides, mud flows and...