Study On The Driving Factors And Prediction Of Soil Erosion In Yan’an City

Soil erosion is a natural phenomenon in which the soil is moved by external forces,which not only affects the local agricultural production and food security,but also brings great hidden danger to the lives and properties of laborers in the middle and lower reaches of the Yellow River.Yan’an City is located in the middle reaches of the Yellow River.Due to the constraints of site conditions such as large undulating terrain,loose soil texture and low vegetation coverage,it become a typical area of soil erosion,which is a potential danger to the local ecosystem.Therefore,Yan’an City was selected as the study area,and the temporal and spatial characteristics of soil erosion parameters and intensity from 2000 to 2020 were extracted and analyzed by collecting remote sensing images,DEM,meteorology,soil and land use data,and using the revised general soil erosion loss equation and trend analysis method.On this basis,the driving factors of soil erosion in Yan’an City are analyzed by using the geo-detector model and CA-Markov model,and the development trend and dynamic change characteristics of soil erosion intensity in 2030 are predicted,so as to provide significant decision support and theoretical basis for regional comprehensive harnessing and ecological restoration.The main conclusions are as follows:（1）In the past 20 years,the rainfall erosivity has shown an overall upward trend from north to south,and the rainfall erosivity has similar fluctuation characteristics with the average annual rainfall.The vegetation coverage is decreasing from south to north,showing a fluctuating upward trend.The area of vegetation improvement area（99.04%）is much larger than that of vegetation degradation area（0.54%）,but the future development trend of vegetation is still uncertain in the northern region.The area of landuse type in Yan’an City is mainly changed among grassland,cultivated land and woodland.The area of arable land continues to decrease significantly and the area of woodland and grassland increased continuously,which is closely related to the policy of returning farmland to woodland.The lowest value of soil and water conservation factor is mainly distributed in building land and water area,where soil and water conservation measures are the worst.The range of soil erodibility factor values is 0-0.046（t·h）/（MJ·mm）,which are mainly distributed in loess areas.The average value of slope factor is 5.55°,and the average slope length is 1.4m.The spatial distribution of slope and slope length factor is similar.The highest value is distributed in earth-rock hills and rocky mountains,and the lowest value is distributed in loess plateau.（2）In 2000,2010 and 2020,the average modulus of soil erosion in Yan’an City was4546.77 t·km^-2·a^-1,3212.65 t·km^-2·a^-1and 2305.71 t·km^-2·a^-1,and the decrease trend of soil erosion modulus was obvious in recent 20 years,which decreased by 56.59%.The distribution of soil erosion in the north and south of Yan’an is quite different,and the intensity of soil erosion was higher in the northern loess hilly,but lower in the southern region.From2000 to 2020,the erosion area of the extreme intensity and above was decreasing,and slight erosion area was increasing.With the implementation of the policy of"conversion of farmland to forests",the obvious reduction and change of early erosion mainly concentrated in Ganquan County,Fuxian County,Huanglong County,Huangling County and Luochuan County,and the late change mainly concentrated in Zhidan County,Baota District,Yanchuan County,Yanchang County,Yichuan County and Wuqi County in the northwest.In a word,the effect of soil and water conservation in Yan’an in recent 20 years has been remarkable,and the quality of ecological environment has been improved to some extent.（3）Using geographic detectors to explore the main driving factors of soil erosion,the research shows that vegetation coverage and rainfall are the main factors restricting the spatial pattern of soil erosion.The interaction between vegetation coverage and slope has the strongest effect on soil erosion,and the synergistic effect of vegetation coverage and other factors is higher than that of any single factor.Different classifications of each driving factor also show different effects.When the landuse type is bare land,the vegetation coverage is less than 30%,the slope is more than 25°,the elevation is less than 860m,and the rainfall is less than 400mm,the average soil erosion intensity in the region is the largest,which is regarded as a high risk area of soil erosion.（4）Based on the CA-Markov model,the prediction of soil erosion in 2020 is compared with the actual situation,and it is found that the precision of the Kappa coefficient is 80.74%with high reliability.The change characteristics of soil erosion in Yan’an in 2030 were predicted.The results showed that the percentage of slight erosion area was 56.72%,which was the main erosion type.The minimum area of severe erosion was 278.01km²,which was only 0.76%.In general,the area of soil erosion in Yan’an City in 2030 has decreased significantly,and the soil erosion situation continues to improve,but there are still soil erosion risks of extreme intensity and above in the study area,and the task of preventing and controlling soil erosion in the future is still very arduous.Therefore,it is suggested that the government should raise the public’s awareness of participation,prevent and control soil erosion in accordance with the law,divide the area into northern key monitoring protection areas in light of local conditions,and implement zoning prevention and control of soil erosion in southern protection areas and key areas along the Yellow River.