The greening of vegetation on the Loess Plateau has resulted in a northward shift of the vegetation greenness line

Vegetation greenness is crucial for assessing vegetation dynamics and evaluating the effectiveness of ecological governance on the Loess Plateau. In this study, we utilized Google Earth Engine (GEE) platform and Landsat image to investigate the spatiotemporal evolution of vegetation greenness and the shift of vegetation greenness lines (VGLs) during the growing season on the Loess Plateau from 1987 to 2020. The driving factors were analyzed using a geographic detector. The results show that the average annual growth rates of NDVI and EVI in the Loess Plateau growing season from 1987 to 2020 were 0.0042/year (P < 0.01) and 0.0023/year (P < 0.01), respectively, with the growth rate after 2000 being three to four times higher. Spatially, significant increases of 78.8% in NDVI and 69.2% in EVI were observed across the entire area of the Loess Plateau. Furthermore, the average VGL based on NDVI and EVI on the Loess Plateau from 1987 to 2020 exhibited a northwestward shift at a rate of 9.79 km/year. This shift resulted in an average movement of 271.83 km over the period. The most significant shifts occurred between 2005 and 2010. Land use and precipitation emerged as the predominant driving factors influencing both the change in vegetation greenness and the shift of the VGLs. Land use and precipitation are the primary factors influencing changes in vegetation greenness and the shift of the VGLs. Land use explains 49.7% of the variation in vegetation greenness, while precipitation accounts for 43%. The combined influence of land use and precipitation explains 68% of the variation in vegetation greenness on the Loess Plateau. Prolonged growing seasons due to climate changes and the "Grain for Green" Project significantly contributed to increased vegetation greenness and northward VGL shifts. Our study offers valuable insights into the spatiotemporal dynamics of vegetation greenness and the shift of VGLs, enhancing our understanding and providing guidance for effective vegetation restoration efforts on the Loess Plateau.