## 5 Conclusions  
Several diversion irrigation projects are undergoing in China recently. Although these projects have been economically beneficial, they have resulted in loess geological disasters. Retrogressive landslides occurred in the South Jingyang Platform over the past few decades due to the continuous use of diversion irrigation. This study aimed to reveal the evolution and failure mechanisms of retrogressive loess landslides. The conclusions drawn are as follows:  
1. In the past 20 years, a total of 76 landslides have occurred. The landslides in the study area can be categorized into three types: flowslides, slides, and falls. Flowslides typically have a deeper slip surface, usually located below the groundwater level. Generally, they are larger in scale, with a longer sliding distance and greater fluidity. Slides occur in homogeneous massive clay deposits, usually following flowslides. The slip surface is relatively shallow, usually located above the groundwater level, with a smaller scale. Falls mainly occur on steep cliffs formed after flowslides or slides.
2. The clustering of these landslides was obvious, constantly occurring at one location and extending to both sides to form landslide groups. As the loess is water sensitive, the strength of the accumulated deposits is significantly reduced due to their high water contents. Subsequent landslides are associated with loess mudflow. This caused the platform to undergo retrograde evolution and lateral spread, decreasing its area as well as the farmland area.
3. Several joints, cracks, and caves were distributed in the study area, which provided irrigation channels for groundwater recharge. Due to the water sensitivity of loess, the loess structure will change considerably when in contact with water. Thus, in the long-term irrigation process, loess joints may mutually develop into loess cracks or caves, which cause loess structure destruction during infiltration. Moreover, the expansion of these channels will increase the infiltration of water, thereby increasing the groundwater level of the slope and the water content of the soil and decreasing the slope stability, which promotes the occurrence of retrogressive landslides.
4. The future frequency of retrogressive landslides is projected to decline, attributable to stabilized groundwater levels following irrigation practice reforms. The adoption of efficient methods (e.g., drip irrigation) has diminished groundwater fluctuation amplitudes, thereby reducing flowslide incidence. While slide-type and fall-type land slides may persist--particularly in historically active zones--their overall frequency is anticipated to remain subdued. This trend is expected to enhance slope stability and further mitigate landslide risks in the long term.  
Conceptualization, P.M., T.D. and Z.H.; methodology, P.M. and T.D.; software, Z.H. and Y.X.; formal analysis, T.D., Z.H. and P.M.; investigation, P.M., T.D., Z.H., Y.X., Q.M., Y.N. and K.L.; resources, P.M.; data curation, T.D. and Z.H.; writing--original draft preparation, T.D., Z.H., and P.M.; writing--review and editing, T.D., Z.H., Q.M. and P.M.; visualization, Z.H. and T.D.; supervision, P.M.; funding acquisition P.M. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the National Key Research and Development Program of China (2023 YFC3008401), the National Natural Science Foundation of China (42477175), the Key Research and Development Program of Shaanxi (2024 SF-YBXM-539) and Fundamental Research Funds for the Central Universities, CHD (300102263401, 300102264908, 300102264903, and 300102264911).  
Not applicable.  
The raw data supporting the conclusions of this article will be made available by the authors on request.  
The authors declare no conflicts of interest.