Spatial Scale Effects on Erosive Runoff and Sediment Flow Behavior on Loessial Slopes: An Erosive Energy Basis

ABSTRACT Runoff erosion response associated with sediment transport as influenced by erosive energy variability is a highly scale‐dependent process. Identifying the spatial scale effect on erosive runoff energy is important to understand the spatial pattern of sediment flow behavior across various sites. This issue was resolved by establishing thresholds for erosive runoff based on frequency analysis, which considered four selected threshold parameters: runoff duration ( T ), stream power ( ω ), stream energy factor (SE), and area‐specific sediment yield (SSY). Based on these thresholds, 77 erosive events were identified and separated from nonerosive events for further analysis of energy–sediment relationships. The threshold for T was roughly constant at hillslopes but rapidly increased at the entire slope. Thresholds for ω and SE exhibited positive linear relationships with the plot area, whereas the threshold for SSY showed a general increasing trend along the downslope direction. The R 2 values of erosive energy–sediment relationships at inter‐ and intra‐event time scales were generally higher for erosive events than for nonerosive events. The sediment delivery capacity ( C d ) for erosive runoff ranged from 0.075 to 0.115 kg·m·J −1 . It demonstrated an initial increase followed by a subsequent decrease from the upper hillslope to the entire slope. Conversely, C d for nonerosive runoff increased with the rise in plot area, and it ranged from 0.053 to 0.083 kg·m·J −1 . The sediment‐increasing capacity ( C i ) for erosive runoff ranged from 0.43 to 4.47 kg·m −2 ·W −1 , whereas C i for nonerosive runoff varied from 3.39 to 17.6 kg·m −2 ·W −1 . The sediment reduction benefit by regulation unit stream energy factor varied from 5% at the entire slope to 65% at the upper hillslope. Therefore, anti‐erosion measures should be implemented at the upper hillslope to prevent nonerosive runoff from becoming erosive runoff.