## 2 Materials and Methods
### Analysis of the Formation Mechanism of Geological Hazards  
The occurrence and development of geological hazards are closely related to rainfall, which is the main precipitating factor for geological hazards in the study area [32]. The average annual rainfall over the past five years in the study area was 960.0 mm, with \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline  & & **rx1 Day** & **rx5 Day** & **r10 mm** & **r20 mm** & **r50 mm** & **cdd** & **cwd** & **r95p** & **r99p** \\ \hline \multirow{4}{*}{Precipitation} & Wudongde & 0.04 & 0.06 & \(-\)0.01 & 0.00 & 0.01 & 0.03 & \(-\)0.02 & 0.68 & 0.03 \\  & Baihetan & 0.22 & 0.21 & \(-\)0.02 & 0.01 & 0.01 & 0.08 & \(-\)0.03 & 0.87 & 0.63 \\  & Xiluodu & 0.04 & 0.14 & 0.02 & 0.02 & 0.01 & 0.06 & \(-\)0.01 & 0.74 & 0.17 \\  & Xiangjiaba & \(-\)0.33 & \(-\)0.38 & \(-\)0.01 & 0.00 & \(-\)0.01 & 0.03 & \(-\)0.02 & \(-\)0.74 & \(-\)0.68 \\ \hline \end{tabular}
\end{table} 
Table 3: Linear trends in extreme precipitation events for typical regions during 1961–2020. (Underlining indicates statistically significant by 95%) (units/10 years). Figure 2: Typical regional extreme precipitation events time series. (Blue: Wudongde; Green: Baihetan; Purple: Xiluodu; Orange; Xiangjiaba). an annual maximum of 1547.8 mm. Precipitation is mostly concentrated in the annual rainy season (May-September), accounting for about 75% of the annual precipitation. Moreover, due to the complex topography of the mountainous area, localized strong rainstorm weather processes are often formed and induce serious geological disasters, such as landslides, cave-ins and mudslides. According to the statistics of the time of year when geological hazards occur or show signs of deformation and damage, of the 3557 geological hazards in the county, 22 occurred or showed signs of deformation and damage in January-April, 3513 in May-September and 22 in October-December. It can be seen that all geological hazards in the study area occur during the rainy season (May to September), accounting for 98.77% of the total number of occurrences. Moreover, the geological hazards tend to be concentrated on the day when local heavy rainfall occurs. 1. Rainfall and mudslides  
The role of rainfall in the formation of mudslides is reflected in two aspects: first, it provides hydrodynamic conditions for the formation of mudslides. Rainfall causes the soil to initiate the formation of mudslides through surface confluence and erosion; second, it becomes one of the important components of mudslide bodies and is an indispensable condition for mudslide outbreaks. According to the results of visits to mudslide disasters in the study area in recent years and a survey, the mudslides in the territory all occur from May to September, and there \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**County Name** & **Collapse** & **Landslide** & **Debris Flow** & **Total** \\ \hline Butuo County & 8 & 34 & 35 & 77 \\ \hline Cuiping District & 4 & 38 & & 42 \\ \hline Dongchuan District & & 20 & 76 & 96 \\ \hline Huidong County & 11 & 300 & 41 & 352 \\ \hline Huli County & 19 & 185 & 32 & 236 \\ \hline Huize County & 12 & 375 & 62 & 449 \\ \hline Jinyang County & 24 & 122 & 50 & 196 \\ \hline Leibo County & 59 & 98 & 44 & 201 \\ \hline Ludian County & 4 & 63 & 15 & 82 \\ \hline Luquan Yi and Miao & 13 & 108 & 20 & 141 \\ Autonomous County & 7 & 279 & 82 & 368 \\ \hline Pingshan County & 34 & 212 & 10 & 256 \\ \hline Qiaojia County & 18 & 35 & 31 & 84 \\ \hline Renhe District & 4 & 40 & 1 & 45 \\ \hline Shuitfu City & 14 & 81 & 24 & 119 \\ \hline Suijiang County & 22 & 98 & 2 & 122 \\ \hline Wuding County & 11 & 60 & 25 & 96 \\ \hline Syrian District & 11 & 45 & & 56 \\ \hline Yongren County & 1 & 101 & 5 & 107 \\ \hline Yongshan County & 1 & 239 & 20 & 260 \\ \hline Yuanmou County & & 52 & 30 & 82 \\ \hline Zhaoyang district & 18 & 58 & 14 & 90 \\ \hline Total & 295 & 2643 & 619 & 3557 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Statistics of geological disaster distribution in the research area.