黄土高原典型流域土壤侵蚀对退耕还林土地利用变化的响应

黄土高原土壤侵蚀严重，为此中国从1999年起实施了大规模的退耕还林工程。为了分析退耕还林土地利用变化对土壤侵蚀的影响，该研究以黄土高原清水河流域为研究区域，将2000—2020年流域退耕还林工程的实施依据主要措施的不同划分为4个阶段，应用RUSLE（revised universal soil loss equation）模型分析土壤侵蚀强度的变化特征，采用情景模拟方法提出一个区分土地利用变化和降雨变化对土壤侵蚀影响程度的算法，判别土地利用变化对土壤侵蚀的影响程度，将土地利用变化分解为土地利用转换和改造2种形式，在剔除降雨变化影响的基础上分析土地利用变化对土壤侵蚀的影响过程。结果表明：1）2000、2005、2011、2014和2020年流域平均侵蚀模数分别为36.21、41.02、24.93、23.72和8.24 t/(hm²·a)，土壤侵蚀强度明显下降；土地利用变化和降雨变化对土壤侵蚀的阶段平均影响程度分别为75.23%和24.77%，土地利用变化在流域土壤侵蚀的变化中起了主导作用。2）流域土地利用转换区侵蚀强度的变化直接受转换过程中地类类别变更及所实施主要相关措施差异的影响，改造区侵蚀强度的变化直接受改造过程中所实施主要相关措施的影响。剔除降雨变化的影响后：改造区的阶段平均起始侵蚀模数较转换区高43.47%，其水土流失综合治理的难度总体上大于转换区；转换区侵蚀模数的阶段平均下降量较改造区高50.80%，改造区侵蚀量的阶段合计减少量占流域阶段合计减少量的71.16%，土地利用转换在降低其实施地区土壤侵蚀强度方面发挥了重要作用，而土地利用改造因实施面积较大在减少流域土壤侵蚀总量方面发挥了重要作用。3）剔除降雨变化的影响后，草地侵蚀量的阶段合计变化量占流域阶段合计变化量的70.51%，且草地阶段合计变化量中改造区占67.41%，其变化特别是其改造对流域土壤侵蚀的影响最大。该研究在分析土地利用变化对土壤侵蚀的影响程度和过程方面作了一些尝试，研究结果可为黄土高原退耕还林成果巩固及高质量发展有效措施的制定提供科学依据。

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 in recent years. 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.