Vegetation Change Trends and Turning Points in Northwest China: A BFAST and Human Activity Perspective

Understanding vegetation evolution is crucial for exploring terrestrial ecosystem changes and identifying future challenges. However, the mutation information in the vegetation change trends of Northwest China (NWC) has not been thoroughly investigated..Based on MODIS NDVI data from 2000 to 2022, this study uses the BFAST method to analyze the spatiotemporal variation characteristics of vegetation kNDVI and trend turning points (TPs) in NWC, and combines land use data to explore the impact of human activities on vegetation dynamics. Results show that: (1) The kNDVI in NWC has significant spatial heterogeneity, with high - value areas concentrated in forest - grass regions like the Qinling and Tianshan Mountains, and low - value areas in arid basins and desert zones.(2) In the study area, 36.42% of the region shows a stable increasing trend (mainly in southern Shaanxi and Gansu), while 17.59% experiences negative reversals (from increase to decrease), focusing on the Hexi Corridor and the oases of the Tarim Basin.(3) Over 75% of vegetation trend TPs occurred after 2010, with negative mutations peaking in 2016, linked to urbanization and a warmer, wetter climate.(4) Ecological restoration projects have significantly increased forestland (85.44% of areas with rising kNDVI) and improved farmland trends (71.30% of areas), but grassland degradation persists (only 45.47% of areas improved). (5) The mutation frequency in unstable vegetation areas (e.g., afforested regions) (44.59%) is significantly higher than in stable areas (31.58%), indicating that intense human intervention increases vegetation dynamics complexity. Research shows that ecological restoration projects has improved NWC’s vegetation. Yet, afforestation thresholds in arid areas, grassland overloading, and the combined effects of climate and human activities may limit sustainable development. There’s a need to optimize vegetation restoration strategies and enhance the protection of ecologically vulnerable regions. This study offers a scientific basis for vegetation restoration and adaptive management in arid and semi - arid areas.