Research On The Temporal And Spatial Changes Of Soil Erosion In The Loess Plateau And Its Main Controlling Factors In The Past 40 Years

The Loess Plateau was one of the most serious soil erosion areas in China and even in the world.In the past few decades,China has invested a lot of manpower,material and financial resources to carry out long-term and systematic control of soil erosion in the Loess Plateau.It has successively implemented major ecological construction projects such as comprehensive management of small watersheds and returning farmland to forests(grass).The soil erosion of the Loess Plateau has been initially controlled,and the amount of sediment entering the Yellow River is significantly reduced.In the past few decades,scholars have conducted a large number of studies on soil erosion,soil and water conservation measures,sediment transport,land use,and vegetation cover change in the Loess Plateau.However,the temporal and spatial variation of soil erosion rate under long time series,the change of main controlling factors of soil erosion,and the application of advanced technology methods such as big data and machine learning in the field of soil erosion research still need to be further explored and studied.On the basis of the existing research results,this research is based on the theory and technical methods of CSLE model,sampling survey,machine learning and Google Earth Engine(Google Earth Engine,GEE)to obtain high-resolution soil erosion factors and sampling survey units.On this basis,two methods of map algebra and spatial prediction are used to complete soil erosion mapping.The temporal and spatial changes of soil erosion rate in the Loess Plateau in the past 40 years and the changes of main controlling factors of soil erosion before and after returning farmland to forest(grass)are systematically analyzed.Clarified the impact of land use and vegetation coverage changes on soil erosion,in order to implement the Yellow River Basin ecological protection and high governance development strategy,provide scientific support for the high-quality development of soil and water conservation in the new era.The main conclusions of the research are as follows:(1)The soil erosion environment of the Loess Plateau is characterized by strong soil erodibility,steep surface slope,and low vegetation coverage,which are the main inducing factors of soil erosion.Since 2000,with the large-scale implementation of the project of returning farmland to forest(grass),the return of farmland on steep slopes,the gradual restoration of forest and grass vegetation,and the continuous effect of project measures are the main factors of weak soil erosion.(2)Both the map algebra method and the spatial prediction method can complete the soil erosion mapping on the Loess Plateau.Both mapping results can reflect the macroscopic pattern of soil erosion in the Loess Plateau,that is,soil erosion above slight levels is concentrated in the Loess Hilly and Gully areas and Loess Yuan area of the Loess Plateau.The average soil erosion rates calculated by map algebra and spatial prediction methods are 640.0 t/(km2·a)and 522.41 t/(km2·a),respectively,and the two values are relatively close.Spatial prediction methods can better reflect the local differences outside the sampling points,and the prediction results are closer to the sediment observation data,it can be used as the preferred method for regional soil erosion mapping.(3)The soil erosion rate of the Loess Plateau in 1980,1990,2000,2010,and 2017 was2207.571,1725.131,981.18,727.79,and 640.00 t/(km2·a),showing a gradual decreasing trend.The soil erosion rate in the Loess Hilly and Gully area and Loess Yuan area showed a significant decreasing trend.The average soil erosion rate of the five phases were4015.15?3182.71?1828.95?1256.62?1031.89 t/(km2·a)in Loess Hilly and Gully area,and6013.25?4695.13?2106.06?1454.59?1547.67 t/(km2?a)in Loess Yuan area,which were about twice to triple the average of the whole area.Before 2000,rainfall erosivity(R)was the main controlling factor of soil erosion.After2000,the influence of vegetation and biological practice factor(B)on the rate of soil erosion increased.In the wind-sand area of the Loess Plateau,which is dominated by low-cover grassland,soil erosion is significantly affected by rainfall erosivity(R).The main controlling factors of soil erosion in the Loess Hilly and Gully area have undergone a significant change around 2000,from the joint influence of slope length and steepness factors(LS)and vegetation and biological practice factor(B)to the joint influence of rainfall erosivity(R),gully factor(g)and vegetation and biological practice factor(B).(4)Before 2000,the Loess Plateau was dominated by cropland and grassland,which accounted for 69.7% of the area.After 2000,the area of forest in the Loess Plateau increased,showing the characteristics of the compound land use structure cropland,forest,and grassland.The average soil erosion rate under different land use types showed the characteristics of cropland>grassland>forest land.From 1980 to 2017,the soil erosion of cropland converted to forest land decreased the most,with a change rate of-74.84t/(km2·a),followed by cropland to grassland and grassland to forest land.The soil erosion rate is-51.88 t/(km2·a)and-49.05 t/(km2·a),respectively.The vegetation coverage of the Loess Plateau has been increasing,from 28.56% in1975~1982 to 61.85% in 2017.As the vegetation coverage increases,soil erosion gradually decreases.The reduction rate of soil erosion from low coverage,medium-low coverage to higher coverage is greater,and the rate of change is between-46.44 and-18.24 t/(km2·a).This type of land use is shifting forward and the shift of low-cover vegetation to higher levels all occurred in Loess Hilly and Gully areas and Loess Yuan area.