Recent changes in rainfall characteristics and their influence on thresholds for debris flow triggering in the Dolomitic area of Cortina d'Ampezzo, north-eastern Italian Alps

Abstract

Abstract. In this paper, we examine variations in climate characteristics near the area of Cortina d'Ampezzo (Dolomites, Eastern Italian Alps), with particular reference to the possible implications for debris-flow occurrence. The study area is prone to debris-flow release in response to summer high-intensity short-duration rainfalls and, therefore, it is of the utmost importance to investigate the potential increase in debris-flow triggering rainfall events. The critical rainfall threshold is agreed to be a crucial triggering factor for debris-flows. Data from a monitoring system, placed in a catchment near Cortina (Acquabona), show that debris-flows were triggered by rainfalls with peak rainfall intensities ranging from 4.9 to 17.4 mm/10 min.The analyses of meteorological data, collected from 1921 to 1994 at several stations in the study area, show a negative trend of annual rainfall, a considerable variation in the monthly rainfall distribution, and an increase in the temperature range, possibly related to global climate changes. Moreover, high-intensity and short-duration rainfall events, derived from data collected from 1990 and 2008, show an increase in exceptional rainfall events. The results obtained in a peak-over-threshold framework, applied to the rainfall data measured at the Faloria rain gauge station from 1990 to 2008, clearly show that the interarrival time of over-threshold events computed for different threshold values decreased in the last decade. This suggests that local climatic changes might produce an increase in the frequency of rainfall events, potentially triggering debris flows in the study area.

The impact of rainfall time series with different length in a landslide warning system, in the framework of changing precipitation trends

“…In several zones of the Mediterranean area, the recent climatic trends are leading to shorter and more intense rainfalls (Floris et al 2010). The trends observed in Emilia Romagna for the last 10 years seem coherent with this assumption.…”

“…Concerning landslide rainfall thresholds, some authors pointed out that their validity is limited in time as constant updates are necessary to account for the changing precipitation characteristics (Floris et al 2010;Arnone et al 2013;Rosi et al 2015). Some authors point out that these changing trends have tangible consequences in the definition of statistical rainfall thresholds (Wilson 2000;Floris et al 2010;Quadrelli et al 2001;Martina et al 2010), hence the need of performing periodic updates of the thresholds to have a fully functional operating EWS Rosi et al 2015).…”

Characteristics of rainfall triggering of debris flows in the Chenyulan watershed, Taiwan

“…As a consequence, higher frequencies and larger magnitudes of rainfall-induced landslides and/or debris flows have been reported worldwide (Eybergen and Imeson, 1989;Rickenmann and Zimmermann, 1993;Evans and Clague, 1994;Van Steijn, 1996;Jomelli et al, 2007;Pelfini and Santilli, 2008;Floris et al, 2010). This paper examines the variation in the characteristics of rainfall events triggering debris flows and the effects on the number of debris flows in the Chenyulan watershed, central Taiwan.…”

A two-step framework for over-threshold modelling of environmental extremes

“…Tawn and Vassie (1989) suggested a value of λ T around 5 for extreme sea surge. Floris et al (2010) analyzed λ T in a framework of extreme rainfall analysis.…”