Characteristics of Spatial and Temporal Vegetation Succession in the Yellow River Basin and Its Impact on Runoff

Vegetation is an important part of the ecosystem and all play an important role in the hydrological cycle. This study uses MODIS NDVI data from the Yellow River Basin (YRB) for the last two decades, together with corresponding meteorological and hydrological data for the same period. Spatial and temporal trends in vegetation succession within the YRB were analysed using a variety of methods including Theil-Sen median trend analysis, Mann-Kendall test, partial correlation, geographic detector and Hurst index. Furthermore, attribution analyses were performed, along with a quantitative assessment of the influence on runoff through the application of the Budyko–Fu equation. The results indicate that: (1) the vegetation cover of the YRB exhibited a significant overall increasing trend from 2001 to 2021, characterized by a multi-year average NDVI value of 0.574 and an average growth rate of 0.0047/a. (2) Precipitation and NDVI exhibited a strong positive correlation, whereas air temperature and the evapotranspiration factor demonstrated a negative correlation. The contributions of human activities and climate change to vegetation changes in the YRB were quantified at 57.8% and 42.2%, respectively. (3) Future projections indicate a declining trend in NDVI within the YRB. (4) Runoff in the basin increased from 2001 to 2012, then decreased from 2013 to 2017, and subsequently increased again after 2018, revealing an overall upward trend. (5) The impact of changes in vegetation cover on runoff variations ranged from 7.6% to 18.1%. This study offers a valuable reference for ecosystem protection and sustainable development in the YRB.