Spatiotemporal variation of land use in counties of the upper reaches of the Beiluo River and its impact on runoff and sediment

Objective The purpose of this study was to investigate the favorability of land use changes in identifying the causes of runoff and sediment variations, providing guiding significance for the implementation and improvement of watershed soil and water conservation and ecological protection policies.

Method The research selected the upper reaches of the Beiluo River as the study area and utilized the GEE and PIE-Engine platforms to acquire land use and fraction vegetation cover (FVC) data from 1990 to 2020. Descriptions of land use in various counties in the upper reaches of the Beiluo River were conducted from four aspects: land class transitions, FVC, land use intensity (LUI), and landscape pattern (average patch area, AREA_MN; largest patch index, LPI; landscape shape index, LSI; aggregation index, AI). Additionally, the correlation between land use and runoff-sediment was explored by integrating runoff and sediment data.

Result (1) After 2000, there was a shift from farmland to grassland and forests in the upper reaches of the Beiluo River, with a reduction in area by 79.05%. The transition from “farmland to forest” was concentrated in the southeast of Wuqi County, while “farmland to grassland” was most densely distributed in Dingbian County, Shaanxi Province of northwestern China. (2) From 2000 to 2020, the FVC in the basin increased rapidly, with Wuqi County having an overall higher FVC than Dingbian County. The change in land use intensity in Dingbian County lagged behind that of Wuqi County, but both exhibited a significant decreasing trend from 2010 to 2020. (3) Around 2000, the reduction rates of annual runoff and sediment transport were 46.68% and 81.83%, respectively. Coefficient of sediment inflow from 2000 to 2020 (0.42) was less than that from 1990 to 2000 (0.80). (4) Under the same runoff volume, sediment transport from 2000 to 2020 was much lower than that from 1990 to 2000. FVC showed a significant negative correlation with runoff-sediment, while forest AREA_MN and AI were significantly positively correlated with runoff. Forest LPI, LSI were significantly negatively correlated with runoff, and forest LSI was negatively correlated with sediment transport.

Conclusion The runoff and sediment in the upper reaches of the Beiluo River are closely related to the structural layout of land use. Different counties exhibit significant differences in land cover and land use intensity. Under the driving force of returning farmland to forest (grassland), the overall trend of land in this region contributes to the reduction of runoff sediment. The research results will provide reference for the study of the relationship between watershed land use and runoff sediment on the Loess Plateau.