Analysis of erosive rainfall distribution and sediment yield on long-term field monitoring sloping bare land of red soil

Red soil region in southern China is one of the regions where soil erosion and flood disasters are serious, and the erosive rainfall is the direct driving force. The distribution of erosive rainfall and its erosion characteristics are the basis for understanding the law of soil erosion, and can also provide a theoretical basis for comprehensive control of soil and water conservation. At present, most of the relevant research data series are collected relatively in short time frames and the conclusions from those studies need further verifications. At the same time, there is a lack of research on soil erodibility characteristics under erosive rainfall. In this study, data of rainfall and sediment of 565 individual erosive rainfalls from 2001 to 2016 in experimental plots on bare slopes of red soil in north part of Jiangxi Province were collected, and then the distribution characteristics of erosive rainfall and its erosivity were analyzed from the intensity and frequency of rainfall and their impacts on soil erosion. On this basis, the influence of rainfall pattern on erosion and sediment yield was analyzed. The results showed that the average annual erosive rainfall in the study area was 1 246.2 mm, accounting for 87.82% of the total annual average rainfall, mainly distributed in the rainfall amount greater than 25 mm and the rain intensity less than 5 mm/h. The durations of rainfall erosion events with erosion intensity less than 100 t/km2 accounted for 76.81% of the total rainfall times, while the total amount of erosion sediment accounted for only 7.28% of the total amount of sediment. Rainfall erosion duration with erosion intensity greater than 500 t/km2 accounted for only 6.36% of the total times, but the erosion sediment amount accounted for 60.96% of the total amount of sediment, which indicated that the distribution of sediment yield under rainfall erosion was extremely uneven. The amount of soil erosion mainly occurred in the slope land under 25-100 mm rainfall, and the number of soil erosion occurred under this rainfall accounted for 46.37% of the total number of rain events, resulting in 71.67% of the total amount of soil erosion. Among them, erosion intensity greater than 1 000 t/km2 was concentrated in 25-50 mm grade rainfall. High rainfall intensity greater than 20 mm/h had a low proportion of soil erosion, resulted in both occurrence frequency and in the total amount of soil erosion, but the probability of strong erosion caused by such event was high. Soil erosion of bare slopes in red soil was mainly affected by both rainfall intensity and rainfall. The rainfall of 25-50 mm and the average rainfall intensity of 5-10 mm/h resulted in the largest amount of soil erosion. Medium rainfall intensity and heavy rainfall or moderate rainfall and large rainfall intensity were the rainfall patterns that caused severe erosion. The rainfall amount of 100 mm and the rainfall intensity of 20 mm/h can be used as the reference value of rainfall standard for soil erosion prevention in red soil bare sloping land. The results will provide a useful reference for further revealing the law of soil erosion on red soil sloping land and constructing erosion prediction model.