Study on the relationship between grassland components and soil erosion and its responses to rainfall scenarios in the loess region

The relationship between vegetation and slope erosion in the Loess Plateau will face challenges of more complex and extreme rainfall scenarios with the climate change. This study selected the grassland slope in the loess hilly area as the experimental subject. Three typical rainfall events in the local area were used to research the relationship between plant canopy, litter and roots and soil erosion, and their response regularity to different rainfall scenarios. Event-Ⅰ had short duration, high intensity and large rainfall amount; event-Ⅱ had moderate duration, intensity, and rainfall amount; and event-Ⅲ had long duration, low intensity and small rainfall amount. The three events represented the three scenarios which classified by the k-means clustering analysis of erosive rainfall events during 2015-2017. At the scale of multi-year rainfall events, the canopy mainly affected the reduction of sediment concentration, which reduced 48.20% of sediment concentration and accounted for 53.03% of the total contribution, and the canopy also contributed about 1/3 of the total reduction of runoff and soil loss; the litter showed the highest effects on runoff reduction, which reduced 28.43% of runoff and accounted for 50.75% of the total contribution, but the relative contribution rate of the litter on soil loss reduction was only 26.41%; and the roots had the highest effects on soil loss reduction, reducing soil loss by 36.33% and contributing 37.95% of the total contribution, which was much higher than its relative contribution rate of runoff reduction（15.58%）. It indicated that the influencing mechanism of grassland plant on soil erosion was controlled by the canopy, litter and roots, where the more complete of components, the higher capacity of reducing runoff and soil loss. The single event analysis showed that with the change of event-Ⅰ, event-Ⅱ to event-Ⅲ, the contribution of canopy to reducing runoff and soil loss were both negative values（from-77.97% to-0.91%）, and the relative contribution gradually decreased; while the contribution of litter and roots to reducing runoff and soil loss reached 12.05%-57.70% and 86.90%-95.51%, and the relative contribution gradually increased. It indicated that the main approaches of different grassland components controlling soil erosion were influenced by rainfall scenarios. The statistical conclusions of rainfall at a long time scale were not necessarily applicable to specific rainfall scenarios. This study compared and a