Using WaTEM/SEDEM to characterize the spatiotemporal trend of the erosion and sediment transportation and the driving factor in a Loess Hilly-gully watershed

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Abstract: Understanding the spatiotemporal changes of sediment yield in watersheds over long time scales and their influencing factors is of great significance for soil and water conservation. Taking the upper Beiluo River Basin(7325 km2)as an example, the WaTEM/SEDEM model was used to analyze the spatiotemporal characteristics of soil erosion and sediment yield in the watershed from 1980 to 2016, as well as the driving factors, providing a scientific theoretical basis for soil and water conservation on the Loess Plateau. The results show that there have been significant changes in land use in the Beiluo River Basin. Compared to 1980, by 2016,the area of forest and grassland in the upper Beiluo River increased by 1188.60 km², a growth of 25.08%, while the area of cultivated land decreased by 1118.64 km², a reduction of 45.86%. In areas where farmland was converted to forest, the sediment yield of the watershed showed a significant decline. The sediment transport in the study area decreased from an average of 50.99 million tons per year in the 1980s to a multi-year average of 9.3434 million tons per year in this century,and the corresponding sediment transport modulus decreased from 6963 tons/(km²·year)to 1275.65 tons/(km²·year). The intensity of soil erosion was mainly characterized by severe and intense erosion before 1980, while after that, it was mainly slight erosion, followed by extremely intense and light erosion, with the smallest proportion of severe, intense, and moderate erosion. The WaTEM/SEDEM model is applicable to this study area, with a Nash coefficient reaching 0.7. Farmland conversion to forest and ecological restoration are the main driving factors for the reduction of erosion and sediment yield in the study area over the past 40 years. The erosion in the Beiluo River Basin from 1980 to 2016 showed an overall weakening trend. The results indicate that the policy of farmland conversion to forest on the Loess Plateau has been remarkably effective, and ecological vegetation construction should continue to be actively carried out.Keywords:Soil erosion; WaTEM/SEDEM model; Driving factors; Loess Plateau

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