## 4 Discussion
### Future Evolution of Retrogressive Landslides  
Flowslides primarily occur in saturated soil layers below the groundwater level, driven by fluctuations in the groundwater level. Falls and slides, on the other hand, are primarily related to the loosening of slope structures caused by prior sliding. Remote sensing satellite imagery reveals that landslides occurred annually; however, flowslides predominated prior to 2015, with a marked decline thereafter. After 2015, flowslides have been rare, and since 2016, only falls and slides have occurred. This change is likely related to the alternation of the irrigation mode on the edge of the platform by the local government. The government recently encouraged residents to drill agricultural wells and use drip irrigation, which promoted the effective use of irrigation water. Thus, the infiltration of water flow on the platform was reduced, slowly increasing the groundwater level. Herein, changes in the groundwater level of 22 wells were dynamically monitored along with the data of the three phases from 2014 to 2016. Using Surfer 12, we interpolated and calculated groundwater level distributions (2014-2016), followed by change analysis via ArcGIS 10.6. As shown in Figure 12, from April 2014 to September 2016, the groundwater levels around Zones I, II, and III varied significantly, ranging from 2 to 6 m. However, after the government changed the irrigation modes, the fluctuations in groundwater levels noticeably slowed down. From April 2016 to September 2016, the groundwater levels around Zones I, II, and III remained unchanged, ranging between \(-1\) and \(2\) m. Therefore, in the past five years, only a few landslides have occurred at these locations, possibly due to the gradual increase in the groundwater level resulting from changes in irrigation methods.  
Figure 12: Variation in groundwater levels. (**a**) from April 2014 to September 2016; (**b**) from April 2016 to September 2016.  
Based on these data, we predict that the future development trends of landslides may present the following characteristics: First, the stabilized groundwater level is expected to reduce landslide frequency. With the change in irrigation methods, the amplitude of groundwater fluctuations has decreased, especially after 2016, when the groundwater level has stabilized. This stabilization helps to reduce the frequency of flowslides. Although the overall frequency of landslides may decrease, landslides of the fall and slide types may still continue to occur, especially in old landslide areas, which are more susceptible to the influence of previous landslide activities. Our analysis indicates that, while flowslides have decreased, landslides of the slide and fall types still dominate. In the long term, with the continued rise and stabilization of groundwater levels, the frequency of landslides in the coming years is expected to remain at a lower level, and the stability of the slope will improve, further reducing the risk of landslides. Additionally, we further analyzed the impact of changes in irrigation methods on landslide occurrence trends. The government-promoted drip irrigation and agricultural wells have effectively reduced the infiltration of water, thus slowing the rise of groundwater levels. This change may help suppress the future development of landslides, especially in terms of reducing the frequency of retrogressive landslides.