Determination and energy-sediment relationship analysis of erosive runoff events on the entire slope of the Chinese Loess Plateau

Erosive events are the primary rainfall–runoff patterns responsible for soil erosion on slopes. Understanding the energy–sediment relationship during erosive events is crucial for the control of soil erosion. While previous studies have focused on defining erosive rainfall thresholds, the thresholds for erosive runoff and the associated energy erosion mechanisms remain unclear. This study addressed this gap by investigating a typical agricultural catchment in the hilly loess region of the Chinese Loess Plateau, using data from three entire-slope plots. Two energy parameters (stream energy factor and stream power) were constructed to derive erosive runoff thresholds for the entire slope using frequentist statistics. Based on the energy thresholds, erosive and nonerosive runoff events were separated, and their energy–sediment relationship and sediment flow behavior were examined. Results showed that the threshold for stream power (ω) ranged from 166.7 W·m⁻¹ to 385.0 W·m⁻¹, while the threshold for the stream energy factor (SE) varied between 0.72 and 1.02 W. Area-specific sediment yield (SSY) demonstrated the strongest correlation with SE, predominantly following linear and power function relationships. Average sediment concentration exhibited the best correlation with ω in nonerosive events, adhering to a logarithmic relationship. For similar values of ω (difference ≤ 20 W·m⁻¹), SSY of erosive runoff was 2.07–2.48 times higher than that of nonerosive runoff. Sediment delivery capacity of erosive runoff was 1.03–1.26 times higher than that of nonerosive runoff. Nonerosive runoff showed a greater potential for sediment increment, ranging from 6.05 times to 12.62 times that of erosive runoff. Under the threshold for ω, the sediment reduction benefit from the transition of erosive runoff to nonerosive runoff ranged from 12.3 % to 55.0 %. Thus, implementing soil and water conservation measures to regulate erosive energy and facilitate the transition from erosive to nonerosive runoff is essential for effective soil erosion control on slopes.