Response of soil erosion to land use change driven by Grain for Green Project in a typical watershed of the Loess Plateau

Loess Plateau seriously suffers from severe soil erosion. The large-scale Grain for Green Project (GFGP) has been implemented since 1999. This study aims to analyze the impact of land use change driven by the GFGP on soil erosion in this area. Taking the Qingshuihe watershed (a typical watershed on the Loess Plateau) as the study area, four stages were divided into the project implementation from 2000 to 2020, according to the different main measures. The change in soil erosion intensity was estimated by applying the RUSLE (revised universal soil loss equation) model. An effect degree (ED) algorithm was proposed by using scenario simulation method. A systematic analysis was implemented on the degree of impact of land use change on soil erosion. The land use change was divided into two forms of land use conversion and modification. The impact of rainfall change was excluded from the impact process of land use change on soil erosion. The results indicated that: 1) The average erosion moduli of this watershed were 36.21, 41.02, 24.93, 23.72 and 8.24 t/(hm²·a) in 2000, 2005, 2011, 2014 and 2020, respectively, indicating a significant decline trend in erosion intensity. The average EDs of the impacts of only land use change and only rainfall change on soil erosion for the four stages were 75.23% and 24.77%, respectively, indicating that land use change was the dominant factor on soil erosion. 2) The change of erosion intensity was directly influenced by the change of land use categories and the different measures in the regions of each land use type during conversion. By contrast, the implemented measures only directly dominated the change of erosion intensity in the regions of each land use type during modification. The average initial erosion modulus for the four stages in the modification regions of this watershed was 43.47% higher than that of conversion regions, indicating that the overall difficulty in the comprehensive soil erosion management of modification regions was greater than that of conversion regions. The average decrease of erosion modulus for the four stages in the conversion regions of this watershed was 50.80% higher than that of modification regions. By contrast, the reduction of erosion amount over the four stages in the modification regions accounted for 71.16% of the total reduction of the watershed. It inferred that the land use conversion played an important role in the decrease of erosion intensity only in the implementation regions, whereas, the land use modification posed an essential effect to reduce the erosion amount in the whole watershed, due to the larger implementation area. 3) The total variation in the grassland erosion amount over the four stages accounted for 70.51% of this watershed's total variation in the erosion amount. The variation of erosion amount in the modification regions accounted for 67.41% of the grassland's total variation. Therefore, the grassland change, particularly its modification, posed the greatest impact on soil erosion in this watershed. An attempt was made to analyze the degree and process of the impact of land use change on soil erosion. The research result can provide the scientific basis for the achievement consolidation and the high-quality development of the GFGP on the Loess Plateau.