Assessment Of Soil Erosion And Spatial-temporal Change Based On CSLE In Beiluo River Basin

The Loess Plateau is one of the most serious areas of soil erosion in China and even in the world.After more than 60 years of management,the ecological environment of the Loess Plateau has been greatly improved,and the degree of vegetation cover has significantly increased,which has effectively inhibited the development of soil erosion.The Beiluo River basin(26905 km~2),develops from northwest to southeast,spans the main vegetation,soil,climate and terrain typology of the Loess Plateau and is well represented.In this study,the Beiluo River basin was selected as the research area,Based on the analysis of climate and land use/cover change in recent 50 years in this region,combined with engineering measures and operation status,Chinese Soil Loss Equation(CSLE)was used to evaluate and estimate the amount of soil erosion in different periods of the basin in 1971 to 2019.And the temporal and spatial characteristics of soil erosion were also analyzed.The main conclusions are as follows:(1)The annual average rainfall erosivity of the Beiluo River basin was 1552.28MJ?mm/(hm~2?h?a),and the spatial distribution increased from northwest to southeast,with the minimum value of 994.70 MJ?mm/(hm~2?h?a)and the maximum value of 2051.06MJ?mm/(hm~2?h?a).From 1961 to 2018,rainfall erosivity showed an insignificant increasing trend with a tendency rate of 19.147 MJ?mm/(hm~2?h?10a).In terms of time period,it went down from 1980 to 2000 and went up significantly after 2000.The annual distribution of rainfall erosivity in this basin was obviously unimodal.rainfall erosivity was concentrated in May to September,accounting for 90.8%of the annual rainfall erosivity.The average rainfall erosivity reached the maximum in July,which was481.03 MJ?mm/(hm~2?h),accounting for 30.81%of the annual rainfall erosivity.The seasonal distribution of rainfall erosivity was obvious,following the rule of summer>autumn>spring>winter.(2)The soil types in Beiluo river basin were mainly loessal soil,followed by cinnamon soil,grey cinnamon soil and new alluvial soil.The range of K value was 0-0.0174t·hm~2·h/(hm~2·MJ·mm),with an average of 0.0129 t·hm~2·h/(hm~2·MJ·mm).The LS value of the basin decreased from northwest to southeast,ranging from0-22.478,with an average of 8.313.Under the great influence of land-use change,the value of biological measure factor(B)in the upper reaches of the river basin decreased obviously in five periods;the B value of the gully area of the plateau showed a significant decrease trend;and it was relatively stable in the forestland of earth-rock mountain and terrace plain area.Based on the image data,human-computer interactive interpretation and reasonable deduction,a series of river basin level terraces(engineering measure factor E)was obtained,with an accuracy of 79.5%.The horizontal terraces in the basin were mainly distributed in the upstream hilly and gully area,middle and lower reaches of gully area,and terrace plain area.From 1980 to 2019,the distribution of T value(tillage measure factor)in hilly and gully region and gully region changed significantly,while that in the forestland of earth-rock mountain and terrace plain area did not.(3)Comparing the soil erosion modulus estimated by CSLE with the sediment transport modulus of the corresponding hydrological station in the basin,the spatial distribution kept a good consistency,and the trend change of time series also maintained a certain correlation.The linear fitting accuracy R~2was 0.7147.From 1971 to 2019,the total soil erosion in the basin showed a significant downward trend.The proportion of erosion area(above the level of light erosion intensity)in the five periods was 41.26%,42.49%,30.98%,18.47%and 15.01%respectively.After 2000,the decrease increased.There were obvious regional differences in the change of soil erosion area in the basin from 1971 to 2019,with the most intense change in the hilly and gully areas,obvious change in the gully areas,stable change in the forestland of earth-rock mountain areas,and weak change in the terrace plain areas.The largest decline was in Zhidan County(79.4%)and Wuqi County(76.3%)in the upstream hilly and gully region,and the smaller drop was in Huachi County(50.0%)and Huanglong County(39.7%)in the forestland of earth-rock mountain areas.The average erosion modulus in different time periods showed the characteristics of cultivated land>grassland>forest land.Compared with the period from 1971 to 1980,the soil erosion modulus of cultivated land from 2001 to 2019 decreased by 21%,and that of forest land and grassland decreased by 62%and 74%respectively.Spatially,the average erosion modulus of cultivated land and grassland decreased from northwest to southeast,and the erosion modulus of forest land in the middle and lower reaches was at the micro erosion level for many years.