Abstract:

[Objective] Previous studies in China on slope erosion characteristics under rainfall patterns have primarily focused on the loess region of Northwest China and red soil region of South China. Research on the purple soil region remains limited. Purple soil is the dominant cultivated soil in the Three Gorges Reservoir Region. Following the reservoir’s construction, substantial cultivated land was submerged, compelling local residents to reclaim more steep slopes for cultivation. This has exacerbated soil erosion issues in this region. Considering both rainfall patterns and land characteristics, this study conducted a comparative analysis of runoff and sediment reduction effects under different soil and water conservation (SWC) measures on purple soil slopes in the reservoir area. Understanding the response characteristics of runoff and sediment yield on purple soil slopes to SWC measures under different rainfall patterns could provide theoretical basis for evaluating the effectiveness of SWC measures in purple soil regions. [Methods] Using runoff and sediment yield data from 37 rainfall events across 10 runoff plots under different SWC measures in purple soil regions, rainfall patterns were classified using K-means clustering based on four indicators: average intensity (I_ave), maximum 30-minute intensity (I₃₀), duration (T), and erosivity (R_r). [Results] The results showed that the 37 rainfall events were classified into five patterns: Type I (low erosivity, long intensity, long duration), Type II (medium-low erosivity, medium-low intensity, medium-long duration), Type III (medium erosivity, medium intensity, medium duration), Type IV (medium-high erosivity, medium-high intensity, medium-short duration), and Type V (strong erosivity, high intensity, short duration).. Among these, Type III rainfall was identified as the primary rainfall pattern causing slope soil erosion, with runoff and sediment yields being 1.2-6.4 times and 2.7-19.4 times higher than the other four types. Narrow-terrace cultivation and platform planting exhibited optimal runoff reduction effects under light (Types I-II) and heavy (Types IV-V) rainfall patterns, respectively. [Conclusion] This was primarily because terraces effectively intercepted runoff sediment from low-intensity, small-volume rainfall, whereas under high-volume and high-intensity rainfall, terraces tended to become saturated, and platform fields were more effective in intercepting runoff sediment. Furthermore, the grass strips in forested areas demonstrated optimal runoff reduction effect under Type I rainfall pattern, primarily because the vegetation effectively slowed runoff velocity, enhanced infiltration, and facilitated sediment deposition. These findings provide a basis for further clarifying the relationship between rainfall and runoff sediment in purple soil regions.

Key words: purple soil, rainfall pattern, runoff and sediment yield, soil and water conservation measures, runoff plot