Combination of Rainfall Thresholds and Susceptibility Maps for Dynamic Landslide Hazard Assessment at Regional Scale

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.

Rainfall Induced Landslide Studies in Indian Himalayan Region: A Critical Review

“…At present, landslide hazard studies are also quite limited: examples exist that encompass temporal probability of occurrence (by means of rainfall thresholds) or spatial probability of occurrence (by landslide susceptibility maps). A spatiotemporal hazard assessment would be desirable and, to obtain it the future, two options could be explored: the application of distributed physically-based models (which, in turn, require the acquisition of many input parameters with high spatial density-see, e.g., Tofani et al [111]) or the adoption of simpler approaches based on the dynamic combination of rainfall thresholds and susceptibility maps [112].…”

Temporal Probability Assessment and Its Use in Landslide Susceptibility Mapping for Eastern Bhutan

“…Bui et al [6] performed a comparison between a bivariate approach (statistical index) and a multivariate approach (logistic regression) for Vietnam, and found equal forecasting capability. However, one of the main issues with the use of a quantitative approach is the assignment of weights to the landslide-affecting factors [56][57][58]. The use of GIS has been proven to be a powerful tool with which to validate the significance of factors, and it has been used for multi-criterion decision analysis [49,59].…”

Developing a Dynamic Web-GIS Based Landslide Early Warning System for the Chittagong Metropolitan Area, Bangladesh

“…Zoning ID 1 2 3 4 Let us assume again, the rainfall pattern analysis has identified three rainfall rates (R1 = low rainfall, R2 = medium rainfall, and R3 = high rainfall). Next, a purposely-built landslide hazard matrix [54] is proposed ( Figure 3) that assumes-the higher the susceptibility, the lower the rainfall level that could trigger landslides [23,55]. The hazard matrix corresponds between different rainfall rates and susceptibility classes, and produces two levels of qualitative hazard classes (i.e., no-warning state, and warning state).…”