Analysis of meteorological parameters triggering rainfall-induced landslide: a review of 70 years in Valtellina

Abstract

Abstract. This paper presents an extended reanalysis of the rainfall-induced geo-hydrological events that have occurred in the last 70 years in the alpine area of the Lombardy region, Italy. The work is focused on the description of the major meteorological triggering factors that have caused diffuse episodes of shallow landslides and debris flow. The aim of this reanalysis was to try to evaluate their magnitude quantitatively. The triggering factors were studied following two approaches. The first one started from the conventional analysis of the rainfall intensity (I) and duration (D) considering local rain gauge data and applying the I–D threshold methodology integrated with an estimation of the events' return period. We then extended this analysis and proposed a new index for the magnitude assessment (magnitude index, MI) based on frequency–magnitude theory. The MI was defined considering both the return period and the spatial extent of each rainfall episode. The second approach is based on a regional-scale analysis of meteorological triggers. In particular, the strength of the extratropical cyclone (EC) structure associated with the precipitation events was assessed through the sea level pressure tendency (SLPT) meteorological index. The latter has been estimated from the Norwegian cyclone model (NCM) theory. Both indexes have shown an agreement in ranking the event's magnitude (R2=0.88), giving a similar interpretation of the severity that was also found to be in accordance with the information reported in historical databases. This back analysis of 70 years in Valtellina identifies the MI and the SLPT as good magnitude indicators of the event, confirming that a strong cause–effect relationship exists among the EC intensity and the local rainfall recorded on the ground. In respect of the conventional I–D threshold methodology, which is limited to a binary estimate of the likelihood of landslide occurrence, the evaluation of the MI and the SLPT indexes allows quantifying the magnitude of a rainfall episode capable of generating severe geo-hydrological hazards.

Orographic Precipitation Extremes: An Application of LUME (Linear Upslope Model Extension) over the Alps and Apennines in Italy

“…Flash floods, shallow landslides, and debris flows represent critical hydrogeological hazards that can occur across mountainous areas [1][2][3][4][5][6][7]. They constitute a serious threat to infrastructures, cities, and populations since they can evolve rapidly and can affect entire catchments, causing extensive injuries and loss of lives [1,6,8,9].…”

“…Flash floods, shallow landslides, and debris flows represent critical hydrogeological hazards that can occur across mountainous areas [1][2][3][4][5][6][7]. They constitute a serious threat to infrastructures, cities, and populations since they can evolve rapidly and can affect entire catchments, causing extensive injuries and loss of lives [1,6,8,9]. From an emergency management viewpoint, it is extremely important to try to predict or anticipate the possible triggering of those threats to reduce the associated risk to the population [10][11][12].…”

“…From an emergency management viewpoint, it is extremely important to try to predict or anticipate the possible triggering of those threats to reduce the associated risk to the population [10][11][12]. One of the main strategies to forecast these hydrogeological hazards involves the study of triggering rainfall [1,3,4,[13][14][15]. In fact, these severe hydrometeorological events are generally associated with episodes of intense or extreme precipitation [1].…”

“…One of the main strategies to forecast these hydrogeological hazards involves the study of triggering rainfall [1,3,4,[13][14][15]. In fact, these severe hydrometeorological events are generally associated with episodes of intense or extreme precipitation [1].…”

“…Extreme precipitation is defined as rainfall where large amounts of rain pour onto the surface in a short amount of time [16][17][18]. At midlatitudes, extreme precipitations can be triggered by atmospheric convection (thunderstorms), explosive cyclones, and atmospheric rivers [1,17,[19][20][21][22][23][24][25]. Here, the orographic effect may cause rainfall intensification [20,21,26], acting as a precursor of convective storm formation, as reported by [21,27].…”