Coupling Rainfall Statistical Properties and Topographic Information
to Characterise Susceptibility to Shallow Landsliding in Taiwan
Marco Borga, University of Padova
Paolo Tarolli, University of Padova
Kang-tsung (Karl) Chang, Kainan University
A model for the prediction of shallow landslide initiation processes in hilly-mountainous
terrain (Borga et al., 2002) is coupled with a simple scaling model for the rainfall Intensity
Duration Frequency (IDF) relationship. The hydromechanic model is based on a theory for
coupled shallow subsurface flow and landsliding of the soil mantle previously proposed by
Montgomery and Dietrich (1994). The model uses a 'quasi-dynamic' wetness index to predict
the spatial distribution of soil saturation in response to a rainfall of specified duration. The
rainfall predicted to cause instability in each topographic element is characterised by duration
and frequency of occurrence. The incorporation of a scaling model for the rainfall frequencyduration relationship provides a practical way to include climate information into estimation
of the relative potential for shallow landsliding.
The model is applied in both diagnostic and predictive modes to a small catchment in Taiwan
for which an inventory of shallow landslides is available. In the diagnostic mode, the model is
used with satisfactory results to reproduce the pattern of instability generated by an intense
storm occurred on 2004, which triggered a large percentage of the surveyed landslides. In the
predictive mode, the model is used for hazard assessment and the return time of the critical
rainfall needed to cause instability for each topographic element is determined. Model results
obtained in the predictive mode are evaluated against all the surveyed landslides. The results
suggested a good performance of the generalized quasi-dynamic model in predicting existing
landslides as represented in the considered landslide inventory.
Borga, M., Dalla Fontana, G., Gregoretti, C., Marchi, L., 2002. Assessment of shallow
landsliding by using a physically based model of hillslope stability. Hydrological Processes
16, 2833–2851.
Montgomery DR, Dietrich WE. 1994. A physically based model for topographic control on
shallow landsliding. Water Resources Research 30: 1153–1171.