Rainfall patterns and critical values associated with landslides in Povoação County (São Miguel Island, Azores): relationships with the North Atlantic Oscillation

Abstract

Abstract:São Miguel Island (Azores) has been affected by hundreds of destructive landslide episodes in the last five centuries, triggered either by earthquakes, volcanic eruptions or rainfall episodes, which were responsible for many deaths and very important economic losses.Among the instability causes, meteorological factors are of primary importance on Povoação County, namely the high recurrence rate of calamitous rainfall triggering landslides. The most recent catastrophic episode took place on the 31st October 1997 when almost 1000 soil slips and debris flows were triggered, and 29 people died in the Ribeira Quente village.The role of rainfall on regional landslide activity was analysed applying cumulative rainfall methods. The method comprises the reconstruction of both absolute and calibrated antecedent rainfalls associated with each major landslide event. The critical rainfall combination (amount-duration) responsible for each landslide event was assessed and a rainfall critical threshold for landslide occurrence was calculated. Rainfall-triggered landslides in the study area are ruled by the function I D 144Ð06 D 0Ð5551 , and they are related both to short duration precipitation events (1-3 days) with high average intensity (between 78 and 144 mm/day) and long-lasting rainfall episodes (1-5 months) with a lower intensity (between 9 and 22 mm/day).The impact of the North Atlantic Oscillation (NAO) on the regional precipitation regime was evaluated. It is shown that the monthly precipitation of São Miguel is largely modulated by the NAO mode presenting a significant negative correlation with the NAO index. This result arises from the NAO control on the travelling latitude of most storm tracks that cross the Northern Atlantic Ocean.

Rainfall thresholds for landslide activity in Portugal: a state of the art

“…Usually failures occur on steep slopes ([30°) and are associated with cohesionless pyroclastic deposits or highly weathered lava basaltic (s.l.) lava flows (Marques 2013). Under these conditions, matric suction plays a crucial role in the shear strength, due to the effect of apparent cohesion, and contributes to maintaining slopes in physical equilibrium (Amaral et al 2009;Amaral 2010).…”

“…1b). The noncohesive materials (mostly pumice fall-out deposits) associated to the central volcanoes and the dominant steep slopes allow the existence of a very prominent landslide activity (Marques 2013).…”

Species Distribution Modeling: Comparison of Fixed and Mixed Effects Models Using INLA

“…The island is characterized by a large variety of volcanic structures, including three active trachytic composite volcanoes with caldera (i.e., Sete Cidades, Fogo and Furnas; [85]). The highest elevation of the island (Pico da Vara, 1103 m) is localized between Povoação and Nordeste.…”

Establishing rainfall frequency contour lines as thresholds for rainfall-induced landslides in Tegucigalpa, Honduras, 1980–2005

“…In a previous threshold study, a total of 19 different antecedent rainfall amounts ranging between 1 and 60 days were chosen and rainfall thresholds having short-term (7 days), medium-term (15 and 30 days) and long-term (60 days) durations were constructed (Garcia-Urquia and Axelsson 2015). The method used was the critical rainfall intensity, which had been applied successfully by Marques et al (2008) and Khan et al (2012) to assess landslide occurrence in Portugal and Bangladesh, respectively. Garcia-Urquia and Axelsson (2015) concluded that the predictive performance of the thresholds decreased with an increase in the threshold duration and therefore the threshold with the best performance in distinguishing between landslide and non-landslide days (hereafter known as LDs and NLDs, respectively) was the 7-day threshold.…”