Eighty Years of Data Collected for the Determination of Rainfall Threshold Triggering Shallow Landslides and Mud-Debris Flows in the Alps

Fabio Luino,Marcella Biddoccu,Chiara Giorgia Cirio,Jerome De Graff,Laura Turconi,Francesco Faccini,Anna Roccati

doi:10.3390/w12010133

Abstract

Identifying the minimum rainfall thresholds necessary for landslides triggering is essential to landslide risk assessment. The Italian Alps have always been affected by shallow landslides and mud-debris flows, which caused considerable damage to property and, sometimes, casualties. We analysed information provided from different sources carrying on the most thorough research conducted for this alpine area. Thousands of documents and reports of rainfall values recorded over 80 years by rain gauges distributed in Sondrio and Brescia Provinces define the mean annual precipitation (MAP)-normalized intensity–duration thresholds for the initiation of shallow landslides and mud-debris flows. The established curves are generally lower compared to those proposed in literature for similar mountain areas in Italy and worldwide. Furthermore, we found that landslides occurred primarily at the same time or within 3 h from the maximum peak of rainfall intensity in summer events and in a period from 0 to 5 h or later in spring-autumn events. The paper provides a further contribution to the knowledge framework on the rainfall conditions required for the initiation of surficial landslides and mud-debris flows and their expected timing of occurrence. This knowledge is crucial to develop better warning strategies to mitigate geo-hydrological risk and reduce the socio-economic damage.

Highlights

According to the European Environment Agency (EEA) report on the impacts of natural hazards in Europe [1], almost 70 major landslides were recorded over the period 1998–2009 in different mountain areas, mainly in the Alps, the Scandinavian Peninsula, and the southern Europe
To define the rainfall conditions that may have triggered shallow landslides and mud-debris flows in the study area, we adopted a methodology structured in the following stages: (i) bibliographic research of historical information of rainfall-induced landslides occurred in the last century in the Lombardy Region, with particular reference to mud-debris flows and shallow landslides, in order to compile a regional georeferenced database of instability phenomena correlated to rainfall events primarily for the Sondrio and Brescia Provinces, (ii) research, analysis, and validation of pluviometrical data, (iii) definition of thresholds for the possible initiation of mud-debris flows and shallow landslides in the Rhaetian Alps and Lombard Prealps, and (iv) comparison to other curves proposed in literature for similar geographical regions
We identified 661 individual mud-debris flows and shallow landslides triggered by rainfall events in the Sondrio and Brescia Provinces

Summary

Introduction

According to the European Environment Agency (EEA) report on the impacts of natural hazards in Europe [1], almost 70 major landslides were recorded over the period 1998–2009 in different mountain areas, mainly in the Alps, the Scandinavian Peninsula, and the southern Europe These events claimed a total of 312 lives and caused economic losses and extensive damage to buildings and infrastructures. Every year, several shallow landslides and mud-debris flows triggered by intense rainfalls occurred in many areas in the Italian Alps and similar mountain regions worldwide [1,2,3,4,5,6,7,8,9,10,11,12,13,14] In these countries, they represent one of the most significant cause of death, damage, and destruction to property.

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