Relationship between landslide size and rainfall conditions in Taiwan

This study analyzed the size of 172 rainfall-induced landslides in Taiwan during 2006-2012. Comparing the landslide size with rainfall conditions, this study found that large and deep landslides usually occurred due to long-duration and moderate-intensity rainfall (11.5-31.0 mm/h; 26.5-62.5 h), whereas small and shallow landslides occurred in a wide range of rainfall intensity and duration (8.5-31.0 mm/h; 4.0-62.5 h). This observation is ascribable to the fact that large and deep landslides need a high ground water level caused by a prolonged rainfall. Concerning the area of landslides, their frequency-area distribution correlates well with a power law relation having an exponent of -1.1 +/- 0.07, over the range 6.3 x 10(2) to 3.1 x 10(6) m(2). The slope of the power law relation for the size-frequency distribution of landslides in Taiwan is lower than those for other areas around the world. This indicates that for the same total area or total number of landslides, the proportion of large landslides is higher in Taiwan than in other areas.