Frequency of debris flows and their relation with precipitation: A case study in the Central Alps, Italy

This paper reports the variation in rainfall characteristics associated with debris flows in the Chenyulan watershed, central Taiwan, between 1963 and 2009. The maximum hourly rainfall I_m, the maximum 24 h rainfall R_d, and the rainfall index RI (defined as the product R_dI_m) were analysed for each rainfall event that triggered a debris flow within the watershed. The corresponding number of debris flows initiated by each rainfall event (N) was also investigated via image analysis and/or field investigation. The relationship between N and RI was analysed. Higher RI of a rainfall event would trigger a larger number of debris flows. This paper also discusses the effects of the Chi-Chi earthquake (CCE) on this relationship and on debris flow initiation. The results showed that the critical RI for debris flow initiation had significant variations and was significantly lower in the years immediately following the CCE of 1999, but appeared to revert to the pre-earthquake condition about five years later. Under the same extreme rainfall event of RI = 365 cm² h⁻¹, the value of N in the CCE-affected period could be six times larger than that in the non-CCE-affected periods

Section: Introductionmentioning

confidence: 99%

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

Chen

Jan

Huang

2013

“…This technique has successfully been applied to the spatio-temporal analysis of debris-flow activity (Bollschweiler et al, 2007;Pelfini and Santilli, 2008;Šilhán and Pánek, 2010;Stoffel, 2010), snow avalanches (Butler and Sawyer, 2008;Casteller et al, 2008), landslides (Fantucci and Sorriso-Valvo, 1999;Stefanini, 2004;Lopez-Saez et al, 2012a, b;Šilhán et al, 2013) and gully erosion (Corona et al, 2011;Stoffel et al, 2012). The great advantage of dendrogeomorphic methods is that they allow rapid acquisition of data, which is otherwise accessible only by means of long-term field monitoring.…”

Section: Introductionmentioning

confidence: 99%

Implications of spatial distribution of rockfall reconstructed by dendrogeomorphological methods

Šilhán

Pánek

Hrádecký

2013

Rockfall is a dangerous geomorphological process. The prediction of potentially threatened areas requires thorough reconstruction of spatial rockfall activity. Dendrogeomorphic methods allow precise determination of both temporal and spatial occurrences of rockfall without the necessity of long-term monitoring. At the case-study site of Taraktash, located among southern slopes of the Crimean Mountains, 114 Crimean pine trees (Pinus nigra ssp. pallasiana) were sampled on a talus slope located under a 150 m high rockwall. Based on their age, the trees were divided into two distinct groups (young and old trees). Considerable disturbance in the age structure of the trees on the talus was probably caused by a series of strong earthquakes. Major differences were identified in the ability of young and old trees to record a rockfall event. We found that in the first decades of their growth, the ability of the studied P. nigra to record rockfall events gradually increased. The trees showed the highest sensitivity at the age of 80 to 90 yr; after that age their sensitivity gradually decreases. Two indicators were selected for the spatial reconstruction of rockfall events (the number of rockfall events per tree and recurrence interval). The highest activity was identified on the talus using selected indicators

“…As a consequence, the frequency of rainfall-related phenomena, such as floods, landslides and debris flows, is changing all over the world (Eybergen and Imeson, 1989;Haeberli et al, 1990;Rickenmann and Zimmermann, 1993;Evans and Clague, 1994;Blijenberg, 1998;Van Steijn, 1996Gärtner et al, 2003;Jomelli et al, 2007Jomelli et al, , 2009Pelfini and Santilli, 2008), with potentially huge economic and social implications. However, the influence of global climate change on the increase in intense rainfall events in the Mediterranean area is still not completely understood (Bodini and Cossu, 2010).…”

Section: Introductionmentioning

confidence: 99%

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

Floris

D’Alpaos

Genevois

et al. 2010

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.