**2. Study Area**

Taiwan is located at the convergent plate boundary where the Philippine Sea plate subducts below the Eurasian plate at a velocity of 80 mm/year; hence, it experiences a high orogenic uplift rate (5–7 mm/year) and frequent earthquakes [30]. This high orogenic uplift rate is responsible for an active mountain belt with many summits higher than 3000 m above sea level (a.s.l.) [31]. Almost 48% of the mountain range in Taiwan is higher than 1000 m a.s.l., and the montane slopes are frequently steeper than 45◦ and have thin (<1 m) regolith cover [32,33]. The mountains in Taiwan have a steep slope and significant relief, and the rock formations are highly fractured and fragile. These geological settings are unfavorable to slope stability. Taiwan is also situated in the East Asian monsoon belt and in the region of subtropical climates, so Taiwan has a humid and warm climate. The annual rainfall is 2500 mm, and on average, 3–5 typhoon strikes occur yearly [34,35]. Torrential precipitation during the summer seasons often triggers geological hazards. In short, the geological and topographic conditions make Taiwan a high-risk region for slope failure (Figure 1).

**Figure 1.** Distribution of rain gauges around Taiwan and geological map.
