## 2 Materials and Methods
### Preliminary Analysis of the Relationship between Extreme Rainfall Trends and Geological Hazards  
The geomorphology of the Jinshajiang River Basin is cut by the Hengduan Mountains, with high mountains and deep valleys, and the terrain is severe. The structure in the area is complex, mainly based on a series of north-south upsurge and oblique thrust faults, and there are many north-south compound folds and fold groups with strong tectonic movements. The strata in the area are completely exposed, and the strata are almost distributed from all ages. The valley area is mainly composed of the metamorphic rock series of the Pre-Devonian, mainly composed of various schists, quartz sandwiched marble and metamorphic basic igneous rocks; Carboniferous sedimentary and igneous rocks of Permian, Triassic and Jurassic; dispersive distribution of Tertiary and Quaternary rock layers.  
The Jinshajiang River Basin has a strong physical and geological effect and impacts the development of collapses and landslides. The main stream section of the river has formed a large-scale bank collapse stream or gully five times in the past 100 years, and the branch gully has been the source of more collapses. The distribution law of geological hazards  
Figure 4: Statistical chart of the months in which mudslides and landslides occurred: (**a**) frequency of mudslides by month; (**b**) frequency of landslides by month.  
Figure 5: Correlation analysis of landslides with monthly cumulative rainfall.  
is the comprehensive embodiment of its control and influence factors and its formation mechanism. The distribution of geological hazards in the study area is strictly affected by the combined action of geological environment conditions, climatic factors, and human engineering economic activities, and has obvious regularity, which is generally manifested in the concentrated distribution of strips along the water system and fault structures.  
The main induced factors of landslides in the area are natural. According to the geological investigation, the formation of a landslide caused by rainfall is mainly reflected in two aspects: first, continuous heavy rainfall makes the slope body saturated and reduces physical and mechanical properties; second, the erosion of the slope foot ditch caused by rainfall.  
As geological hazards are mainly closely related to rainfall, the relationship between extreme rainfall trends and geological hazard distribution in the study area was mapped based on the climatic analysis of extreme rainfall time series in the Jinshajiang River Basin. As shown in Figure 6, the high probability of extreme rainfall in the study area is mainly concentrated in two places: The left bank area of the Jinshajiang River in Leibo County; The areas on both sides of the Jinshajiang River valley in Ningnan County-Qiaojia County. By superimposing the hazard point data, it can be found that the areas with high extreme rainfall trends have a high density of geohazard development and are concentrated, while the areas with low extreme rainfall trends have relatively less geohazard development and are scattered.  
Figure 6: Map of extreme rainfall trends in relation to the distribution of geological hazards.