Abstract
We propose a methodology to couple rainfall thresholds and susceptibility maps for dynamic landslide hazard assessment at regional scale. Both inputs are combined in a purposely-built hazard matrix to get a spatially and temporally variable definition of landslide hazard: while statistical rainfall thresholds are used to accomplish a temporal forecasting with very coarse spatial resolution, landslide susceptibility maps provide static spatial information about the probability of landslide occurrence at fine spatial resolution. The test site is the Northern part of Tuscany (Italy), where a recent landslide susceptibility map and a set of recently updated rainfall thresholds are available. These products were modified and updated to meet the requirements of the proposed procedure: the susceptibility map was reclassified and the threshold set was expanded defining additional thresholds. The hazard matrix combines three susceptibility classes (S1, low susceptibility; S2 medium susceptibility; S3 high susceptibility) and three rainfall rate classes (R1, R2, R3), defining five hazard classes, from H0 (null hazard) to H4 (high hazard). A key passage of the procedure is the appropriate calibration and validation of the matrix, letting the hazard classes have a precise meaning in terms of expected consequences and hazard management. The employ of the proposed procedure in a regional warning system brings two main advantages: (i) it is possible to better hypothesize when and where landslide are expected and with which hazard degree, thus fostering a more effective hazard and risk management (e.g. setting priorities of intervention); (ii) the spatial resolution of the regional scale warning system is markedly refined because from time to time the areas where landslides are expected represent only a fraction of the alert zone.
Highlights
Since landslides are continuously responsible of damages and casualties worldwide, landslide hazard assessment is a cogent research topic, aiming to determine the spatial and temporal probability of occurrence of landslides (Fell et al, 2008; Corominas et al, 2013)
It is worth to notice that the hazard assessment procedure that we propose in this work is related only to these types of landslides involving mainly soil material, while we do not take into account rock falls and topples
We propose a dynamic landslide hazard assessment procedure based on the combination of rainfall thresholds and susceptibility maps
Summary
Since landslides are continuously responsible of damages and casualties worldwide, landslide hazard assessment is a cogent research topic, aiming to determine the spatial and temporal probability of occurrence of landslides (Fell et al, 2008; Corominas et al, 2013).Spatial occurrence is called susceptibility. Since landslides are continuously responsible of damages and casualties worldwide, landslide hazard assessment is a cogent research topic, aiming to determine the spatial and temporal probability of occurrence of landslides (Fell et al, 2008; Corominas et al, 2013). A landslide susceptibility map subdivides the terrain into zones with differing likelihoods that landslides of a certain type may occur (Fell et al, 2008). A large part of the quantitative methods to produce landslide susceptibility maps relies on regression. The approaches followed to determine the temporal occurrence of landslides are: heuristic methods (judgmental approaches) (Lee et al, 2000; Wong, 2005), physically based methods (Montgomery and Dietrich, 1994; Pack et al, 1998; Iverson, 2000; Crosta and Frattini, 2003; Baum et al, 2005; Godt et al, 2008; Mercogliano et al, 2013; Rossi et al, 2013; Tofani et al, 2017) and empirical/statistical rainfall thresholds (Guzzetti et al, 2008; Segoni et al, 2018; and references therein)
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