Applying Probability Determination to Refine Landslide-triggering Rainfall Thresholds Using an Empirical “Antecedent Daily Rainfall Model”

Abstract

Rainfall-triggered landslides constitute a serious hazard and an important geomorphic process in many parts of the world. Attempts have been made at various scales in a number of countries to investigate triggering conditions in order to identify patterns in behaviour and, ultimately, to define or calculate landslide-triggering rainfall thresholds. This study was carried out in three landslide-prone regions in the North Island of New Zealand. Regional landslide-triggering rainfall thresholds were calculated using an empirical ''Antecedent Daily Rainfall Model.'' In this model, first introduced by CROZIER and EYLES (1980), triggering rainfall conditions are represented by a combination of rainfall occurring in a period before the event (antecedent rainfall) and rainfall on the day of the event. A physically-based decay coefficient is derived for each region from the recessional behaviour of storm hydrographs and is used to produce an index for antecedent rainfall. Statistical techniques are employed to obtain the thresholds which best separate the rainfall conditions associated with landslide occurrence from those of non-occurrence or a given probability of occurrence. The resultant regional models are able to represent the probability of occurrence of landsliding events on the basis of rainfall conditions. The calculated thresholds show regional differences in susceptibility of a given landscape to landslide-triggering rainfall. These differences relate to both the landslide database and the difference of existing physical conditions between the regions.

Rainfall intensity–duration conditions for mass movements in Taiwan

“…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.…”

“…Although antecedent rainfall was calculated over a period of 168 h, even earlier rainfall might have played a key role in triggering the G1 mass movements. Indeed, the definition of antecedent rainfall is a difficult task (Crozier 1999;Glade et al 2000;Dahal and Hasegawa 2008), and future research is needed to refine this definition and further investigate the effect of topographical and geological factors in triggering mass movements.…”

“…Several studies have also found that peak rainfall intensity and the initiation of mass movements are often concurrent (Aleotti 2004;Chien-Yuan et al 2005;Guzzetti et al 2007Guzzetti et al , 2008Dahal and Hasegawa 2008;Saito et al 2010aSaito et al , 2010b. Although antecedent rainfall also plays an important role in the initiation of mass movement (Kim et al 1992;Glade 1997;Crozier 1999;Glade et al 2000;Guzzetti et al 2007Guzzetti et al , 2008Dahal and Hasegawa 2008), intensity-duration (I-D) thresholds and/or the peak rainfall intensity are often used to predict mass movements and warn the appropriate authorities of potential mass movement hazards (Onodera et al 1974;Keefer et al 1987;Aleotti 2004;Hong et al 2005;Cannon et al 2008;Coe et al 2008;Dahal and Hasegawa 2008;Guzzetti et al 2008).…”

Towards Establishing Climatic Thresholds for Slope Instability: Use of a Physically-based Combined Soil Hydrology-slope Stability Model

“…There is now a large body of field evidence from the hill country of New Zealand regarding the distribution of shallow failures caused by high-magnitude rainstorms in recent years, in a variety of regoliths forming on different bedrock substrates (CROZIER and PILLANS, 1991;CROZIER et al, 1980;PRESTON, 1996;GLADE, 1997GLADE, , 1998GLADE, , 2000GLADE and CROZIER, 1996;GLADE et al, 2000). Detailed accounts of the storm properties that produce shallow landslides are also available.…”

“…The sites provide significant contrasts in regolith hydrology, and are from areas for which considerable effort has been expended in deriving empirical climatic thresholds for landslide initiation (GLADE, 1997(GLADE, , 1998(GLADE, , 2000GLADE et al, 2000). The same sites also enable preliminary validation to be attempted, as a check for robust model performance under appropriate conditions for these climatically-triggered shallow slope failures.…”