Hydrometeorological thresholds for landslide initiation and forest operation shutdowns on the north coast of British Columbia

Abstract

Debris flows and debris avalanches are the most widespread and hazardous types of landslides on the British Columbia north coast. Triggered by heavy rain, they pose risks to forestry workers in sparsely developed regions. The scarcity of long-term quality rain gauges and the lack of weather radar information create significant challenge in predicting the timing of landslides, which could be used to warn and, when necessary, evacuate forestry personnel. Traditional methods to relate rainfall antecedents and rainfall intensity to known landslide dates have proven to be unsatisfactory in this study due to extreme spatial variability of rainfall, enhanced by the orographic effect and the scarcity of rain gauges in a very large area. This has led to an integration of meteorological variables in a landslide advisory system that classifies three types of approaching storms by the 850-mbar wind speed and direction, the occurrence of subtropical moisture flow, and the existence of a warm layer characterized by high thickness values of the 500-to 1,000-mbar pressure levels. The storm classification was combined with a 4-week antecedent rainfall and the 24-h rainfall measured near or in the watershed where logging operations are taking place. This system, once implemented, is thought to reduce loss of life, injury, and economic losses associated with forestry works in the study area.

Rainfall intensity–duration conditions for mass movements in Taiwan

“…Some previous studies have used 1 week of antecedent rainfall for analyzing the antecedent soil moisture and found that it is an important factor for triggering landslides (Crosta 1998;Jakob 2006). Therefore, we also examined rainfall totals for 168 h (1 week) before the beginning of rainfall events that triggered mass movement events.…”

“…This indicates that G2 is composed primarily of landslides, with release mechanisms directly related to hillslope hydrology. Soil moisture content is directly related to landslide occurrence (Terlien 1998;Wu and Chen 2009), and high antecedent rainfall elevates moisture content (Glade 1997;Crosta 1998;Crozier 1999;Glade et al 2000;Jakob 2006). Therefore, abundant antecedent rainfall combined with high-intensity rainfall can easily trigger landslides, especially around the time of peak rainfall.…”

A debris-flow alarm system for the Alpine Illgraben catchment: design and performance

“…Many systems have been developed for densely populated mountainous areas throughout the world. Recent examples are available from Canada (Jakob et al 2006), Italy (Bacchini and Zannoni 2003), Taiwan (Chang 2003;Chen et al 2005;Kung et al 2008), China (Brand et al 1984;Zhang 1993), and Japan (Hirano 1997;Itakura et al 1997;Tanabashi 1998).…”

Risk-based analysis of monitoring time intervals for landslide prevention

“…20 Different numbers of days have been considered and examined by researchers to find the most suitable correlation with landslide initiation (Aleotti, 2004;Polemio and Sdao, 1999;Zêzere et al, 2005). Of the issue, the researchers have proposed different numbers of days, however, only with local validity, which means that suggested rainfall thresholds are applicable to the respective study cases, and it also depends on the landside type (Jakob et al, 2006;Martelloni et al, 2012). Therefore, we referred to the domestic research results in that characteristics of local geology, soil and vegetation, as well as precipitation 25 patterns are different from the areas of other studies.…”

“…Despite the limitation on the accumulated landslide inventory data over the study region, the frequency of landslide occurrence was estimated by establishing a rainfall threshold. The selection of the rainfall threshold has been examined and proposed by various methodologies (Crozier, 2005;Guzzetti et al, 2007;Zêzere et 25 al., 2005;Frattini et al, 2009;Crosta and Frattini, 2003;Aleotti, 2004;Polemio and Sdao, 1999;Caine, 1980), and it has been shown that proposed rainfall thresholds are applicable to the respective study cases depending on the landside type with local validity (Jakob et al, 2006;Martelloni et al, 2012), so the criteria of cumulative precipitation and daily rainfall intensity for rainfall threshold setting were determined by referring to the local research results.…”