Response Of Different Vegetation Types And Slopes To Erosive Rainfall In Loess Hilly Gully Areas

As one of the most serious areas of soil erosion in China,rainfall and runoff are the main drivers of soil erosion in the Loess Hills and Gullies region,and vegetation measures are one of the main measures to manage soil erosion in the region.To investigate the soil and water conservation benefits of different vegetation types under different slopes in the Loess Hills and Gullies region,this thesis uses the Contract Gullies sub-watershed soil and water conservation monitoring station of Dalat Banner,located in the Loess Hills and Gullies region,as a test area,to analyse the distribution characteristics of erosive rainfall in the region based on rainfall and runoff plot observation data from the monitoring station from 2018 to 2022,and uses K-mean clustering analysis to The classification was carried out to explore the soil and water conservation benefits of different vegetation types under different rainfall type conditions;meanwhile,the characteristics of rainfall intensity on runoff volume and erosion volume changes of different vegetation types and slopes during typical sub-rainfall were analyzed to explore the suitable vegetation types for soil and water conservation on different slopes,with a view to providing a theoretical basis and scientific guidance for the optimal allocation of soil and water conservation measures on slopes in the loess hilly gully area.The main conclusions are as follows:(1)The inter-annual distribution of rainfall in the Loess Hills and Gullies area is uneven and the seasonal distribution within the year is obvious,with rainfall mostly occurring in June to August,while erosive rainfall is mainly concentrated in July and August,accounting for 70.58% of the total number of erosive rainfall,and the total amount of erosive rainfall is larger,and soil erosion occurs more frequently.(2)Based on the erosive rainfall characteristic values of rainfall volume and I30 rainfall intensity using K-mean clustering analysis drop,the 51 erosive rainfall events in the study area were classified into five rain types,including I rain type(medium rainfall volume and medium rainfall intensity),II rain type(small rainfall volume and small rainfall intensity),III rain type(small rainfall volume and medium rainfall intensity),IV rain type(medium rainfall volume and large rainfall intensity)and V rain type(large rainfall volume and large rainfall intensity),in which the rainfall volume Among them,rainfall type II,which has a low rainfall amount and intensity,occurs most frequently,while rainfall types IV and V,which have a high rainfall amount and intensity,occur less frequently,but produce the greatest amount of soil erosion.(3)Different vegetation types produce flow and sand characteristics of different rain patterns in response to different relationships,but relative to the bare ground have certain flow and sand reduction benefits,in different rain patterns under the conditions of each vegetation flow and sand reduction benefits in order of oil pine > lemon grass > alfalfa >Ben’s needle grass > buckwheat,which,oil pine and lemon grass is the best flow and sand reduction benefits,flow and sand reduction rate always remains above 80%,alfalfa and Ben’s needle grass second,buckwheat plots have the worst flow and sand reduction benefits,flow and sand reduction rate are in less than 30%,and by the rain pattern changes have a greater impact.(4)Under typical rainfall conditions,the runoff and erosion processes of each vegetation type on different slopes show four stages: start,peak,stabilisation and abatement with different rainfall intensities,and the change in runoff and erosion volume is basically the same,with the same vegetation type on different slopes showing the start of runoff and sand production and runoff and erosion volume as 15° slope > 10° slope >5° slope;and different vegetation types on the same slope show bare ground >buckwheat > Ben’s needlegrass > alfalfa > lemongrass > oil pine.(5)Rainfall intensity,runoff volume and erosion volume at different vegetation types and slope conditions all fit each other best under Linear(linear regression model),and there is a significant(p < 0.05)and highly significant(p < 0.01)positive correlation between runoff volume and erosion volume at different rainfall intensities at different time periods.The correlation coefficients between rainfall intensity,runoff volume and erosion volume were found to be progressive,with rainfall intensity directly influencing the change in runoff volume and runoff volume dominating the occurrence of erosion volume,and rainfall and runoff jointly influencing the occurrence of soil erosion.(6)Comprehensive analysis of soil and water conservation benefits of different slopes and different vegetation types,under different slope conditions,the best soil and water conservation benefits were achieved by oil pine and lemon tree shrub plots,followed by herbaceous plants such as alfalfa and Ben’s needle grass,while the worst soil and water conservation effects were achieved by buckwheat crop plots;and through a hierarchical cluster analysis of runoff and erosion of different vegetation types under different slope conditions,the classification results by inter-class distance d < 5,d < 10,and d < 15 were verified.The classification results are basically the same as those of the previous analyses of the soil and water conservation effectiveness of different vegetation types,indicating that the results of this study on the soil and water conservation effectiveness of different slopes and different vegetation types are scientific and reasonable.