Preferential flow reduces overland flow on slopes: insights from a field experiment on the Chinese Loess Plateau

Abstract

Preferential flow, a critical component of soil infiltration processes, plays a pivotal role in eco-hydrological dynamics. Large-scale vegetation restoration on the Chinese Loess Plateau has altered the underlying surface conditions, which in turn influences the preferential flow. However, the influence of preferential flow on slope runoff, under different vegetation restoration types and ages, remains unclear. In this study, artificial rainfall experiments, high-frequency soil moisture monitoring, and the surface covering method were used to investigate the occurrence, contribution, and influencing factors of different preferential flow patterns (non-sequential response type and high wetting-front velocity type) under varying vegetation restoration conditions. Furthermore, it elucidates the underlying mechanisms by which preferential flow influences slope runoff. The results indicate that vegetation restoration significantly increased preferential flow occurrence, which was positively correlated with revegetation age. The occurrence of preferential flow ranged from 18.9% to 40.0%, contributing 59.6% to 78.7% of the total infiltration. In revegetated land, the cumulative infiltration, initial infiltration rate, and stable infiltration rate of both matrix flow and preferential flow were significantly higher than those in cropland (P < 0.05). Soil structure and root characteristics were identified as the primary factors influencing preferential flow occurrence. Vegetation restoration increased preferential flow occurrence, shortened the response time between soil layers, and increased infiltration rates, reducing slope runoff. These findings provide important insights into the soil hydrological processes associated with vegetation restoration on the Loess Plateau and in other arid and semi-arid regions.