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This study calculated the long-term average landslide erosion rate in the Kaoping River watershed in southern Taiwan and investigated the relative importance of extreme rainfall events on landslide erosion. The method followed three steps: first, calculating landslide volumes for 10 rainfall events from a multi-temporal, event-based landslide inventory; second, estimating the frequency of landslide-generating rainfall by using hydrologic frequency analyses; and third, combining the two sets of data to estimate the average landslide erosion rate. Results of the study showed that the average landslide erosion rate is 2.65–5.17 mm yr − 1 , corresponding well to rates reported in other studies using other methods. The study also found that extreme-intensive rainfall events play a more important role on landslide erosion than frequent-moderate rainfall events. Extreme rainfall (maximum 24-h rainfall > 600 mm) contributes 64–79% of the average landslide erosion rate. Moreover, the natural variation of landslide erosion magnitudes is extremely large and can cause significant uncertainty in estimating the landslide erosion rate from total landslide volume. This study found ± 1.2 mm yr − 1 of uncertainty based on simulation results involving a hypothetical 100-year landslide inventory. In summary, this study demonstrates the importance of extreme rainfall events on landslide erosion, and the method proposed in this study is capable of calculating a reliable estimate of average landslide erosion rate in areas with insufficient landslide records. [ABSTRACT FROM AUTHOR]

Abstract: A coupled model has been developed to simulate, at watershed level, landslides and debris flows induced by a severe typhoon (tropical cyclone) in Taiwan. The model comprises a landslide susceptibility model to predict landslide occurrence, an empirical model to select debris-flow initiation points, and a debris flow model to simulate the transport and deposit of failed materials from the identified source areas. In raster format with a 10m spatial resolution, the model output includes unstable cells, debris-flow initiation cells, debris-flow velocities, runout paths, and deposition zones. The model was first tested and calibrated in a small area, where the damage by landslides had been investigated and recorded. It was then applied to a watershed, and the simulation results were validated by comparing them with a landslide/debris-flow inventory map prepared from satellite images using a multiple change detection technique. Model test and validation results confirm the usefulness of the model in predicting the number and size of affected areas (landslides and runouts combined), runout path, and volume of runout deposits. It is a common practice in Taiwan to separate landslide and debris-flow inventories and to study debris flows only in select drainage basins. This study suggests that landslide and debris flow should be modeled as a sequential process for efficient watershed management. [Copyright &y& Elsevier]

Abstract: In the western North Pacific, including Taiwan, typhoons (tropical cyclones) and rainfall rates are predicted to intensify as a result of climate change. Because typhoons are the major triggers of shallow landslides in Taiwan, landslide activity is expected to increase as global warming continues. To assess the worst scenario of landslide occurrence in a mountainous watershed till the end of the century, this study developed a method to select a global climate model (GCM) from 21 available GCMs and correct its monthly precipitation data, before downscaling annual maximum (24-h) rainfall from the corrected GCM data as input to the factor-of-safety model for landslide prediction. Average annual maximum rainfall is expected to increase from 322mm in 1960–2008 to 371mm in 2010–2099. Average total unstable area is expected to increase from 1135ha in 1960–2008 to 1280ha in 2010–2099, a 12% increase. As a first attempt to assess landslide activity due to global warming, this study is useful as a reference for watershed management in Taiwan. The results must be evaluated in light of uncertainties caused by the correction and downscaling of GCM data and the input parameters to the slope stability model. [Copyright &y& Elsevier]

Abstract: Many shallow landslides are triggered by heavy rainfall. Previous studies of landslide modeling have been hampered by the scarcity of rain gauges to adequately depict the spatial variability of rainfall conditions triggering landslides. This study simulates the efficiency of the critical rainfall model for landslide prediction in a mountainous watershed with inputs of different rainfall estimates associated with a typhoon (tropical cyclone) event. Doppler radar data at a spatial resolution of 1 km and measurements from six gauging stations provide the sources for rainfall estimates. Inverse distance weighted, splines, and kriging are the interpolation methods for gauged rainfall estimates. A comparison of the simulation outputs shows that the model using radar rainfall estimates has a better performance than those using gauged rainfall estimates in predicting both landslides and stable areas. In light of the results, this paper also discusses the validity of the critical rainfall model for landslides in relation to its rainfall input and steady-state hydrological assumption. [Copyright &y& Elsevier]

Abstract: Landslides can be caused by storms and earthquakes. Most logistic regression models proposed in recent years have been targeted at rainfall-induced landslides. In areas such as Taiwan, where landslides can be triggered by typhoons (tropical cyclones) and earthquakes, a rainfall-induced model is insufficient because it provides only a partial explanation of landslide occurrence and overlooks the potential effect of earthquakes on typhoon-triggered landslides. This study used landslides triggered by a major earthquake and a typhoon prior to the earthquake to develop an earthquake-induced model and a typhoon-induced model. The models were then validated by using landslides triggered by three typhoons after the earthquake. According to the results, typhoon-triggered landslides tended to be near stream channels and earthquake-triggered landslides were more likely to be near ridge lines. Moreover, a major earthquake could still affect the locations of typhoon-triggered landslides 6 years after the earthquake. This study therefore demonstrates that an earthquake-induced model both sheds light on the environmental factors for triggering landslides, and augments a rainfall-induced model in its predictive capability in areas such as Taiwan. [Copyright &y& Elsevier]