*2.1. Study Area*

Yunnan Province is located at the low latitude plateau of southwest China, with an area of 390,000 km2, accounting for 4.1% of China's total area [18]. The terrain in Yunnan Province is very complex, coupled with the low economic level of remote mountain areas, resulting in the lack of early disaster data. For example, the main terrains are mountains (84%), plateaus and hills (10%), and basins and valleys (6%). The altitude is high in the northwest and low in the southeast, descending stepwise from north to south in this region, and the average altitude is 1980 m, and 87.21% of the land is located in middle-latitude areas (1000–3500 m). The area with a slope below 25◦ accounts for 56.46% of the national total area. Besides, Yunnan Province is characterized by the most widely distributed karst topography, accounting for 28.9% of the province's area; this results in low water retention and frequent flood disasters. Yunnan is rich in water resources, but unevenly distributed in time and space, where more than 70% of the water resources are concentrated in remote mountainous areas. The total population is 47.1 million in 2014, accounting for 3.5% of the national total population. Yunnan has a typical monsoon climate, mainly dominated by the east Asian monsoon and southwest monsoon, and 90% of the precipitation is concentrated from May to October, especially in the flood season (June to August). For example, long-term studies have shown that the critical rainfall is 35–200 mm in northwest Yunnan, 50–200 mm in southwest Yunnan, and 100–300 mm in eastern Yunnan [19]. The above reasons led to frequent flash flood disasters, which has caused extremely serious disasters. For example, 72 people died from flash floods in Yunnan Province in 2014, accounting for 22.2% of the

national total deaths from flash floods. All the preliminary works have promoted the development of flash flood prevention in Yunnan Province [20], but further exploration is still needed, and therefore Yunnan Province was selected as the study area in this study. Figure 1 shows the map of the topography and flash flood disaster distribution in Yunnan Province.

**Figure 1.** Topographical map and locations of flash flood disasters in Yunnan Province (2011–2018).
