Background The Pisha sandstone area represents one of the most severely eroded regions on the Loess Plateau. However, current research on the characteristics of soil erosion evolution in this area remains insufficient, failing to meet the demands of high-quality soil and water conservation development. Check dams, while intercepting and storing sediment, preserve valuable information related to erosion and sediment yield. This makes them highly effective for reflecting the evolutionary characteristics of soil erosion at the watershed scale. Furthermore, research on soil erosion inversion serves as an effective approach for evaluating the benefits of soil and water conservation measures.

Methods Therefore, this study selected the small check dam in Lujiagou within the Huangfuchuan watershed of the Pisha sandstone region as the research subject. By examining the correspondence between sediment deposition data from the check dam and rainfall erosivity from 2007 to 2022, this research elucidated the characteristics of soil erosion evolution in the watershed.

Results 1) Based on the relationship between annual cumulative rainfall erosivity and annual cumulative sediment deposition from 2007 to 2022, the study period was divided into three distinct phases: Phase I (2007–2012), Phase II (2013–2017), and Phase III (2018–2022). The total erosion modulus for these phases was calculated at 25 652.45, 6 071.32, and 26 492.85 t/km², respectively. Correspondingly, the average annual erosion modulus for each phase was 5130.49, 1214.26 and 5298.57 t/km². Analysis revealws a clear increasing trend in rainfall erosivity across the sequential phases within this small watershed. This observed intensification in rainfall erosivity was primarily attributable to rainfall events exceeding 35 mm. The contribution of these heavy rainfall events to the total increase in rainfall erosivity was particularly significant, accounting for 149.87% and 105.60% of the total increase in the respective transitional periods between phases. 2) Both the soil erosion modulus and the erosion modulus per unit rainfall erosivity exhibited a trend of initial decrease followed by an increase across the three phases. Specifically, the erosion modulus per unit rainfall erosivity in phases II and phases III was lower than that in phases I, with reductions of 804.27 and 410.03 t·h/(MJ·mm), respectively.

Conclusions The capacity of vegetation to control soil erosion exhibits a threshold effect. When the rainfall erosivity of heavy rain and above events increased from 23.27 MJ·mm/(hm²·h) in Phase II to 32.64 MJ·mm/(hm²·h) in Phase III, the erosion modulus per unit rainfall erosivity rose from 178.20 t·h/(MJ·mm) to 572.45 t·h/(MJ·mm). The findings of this study can provide a scientific reference for evaluating the benefits of soil and water conservation measures in the Pisha sandstone region.