Abstract: Understanding the influences of climate change and anthropogenic activities on vegetation is of great significance for restoring vegetation and maintaining ecological balance. The time-lag impact of climate changes on vegetation is usually overlooked, which would underestimate the impacts of climate change on vegetation changes. We analyzed the spatiotemporal variations of vegetation on the Loess Plateau from 2000 to 2019, explored the time-lagged response of vegetation to climate change, proposed a modified residual analysis method considering the climate time-lag effect, and revealed the impacts of climate change and human activities on vegetation. The results showed that the Normalized Difference Vegetation Index (NDVI) of the vegetation on the Loess Plateau increased significantly from 2000 to 2019, with an annual growth rate of 0.048·10 a^-1. Spatially, the NDVI of vegetation in most areas of the Loess Plateau was increasing, with the increases in 76.6% of the area being statistically significant. Temperature had an obvious time-lag effect on the changes of NDVI, with the optimal lag time being 1 month, while precipitation had no lag effect. The time-lag effect of vegetation was the same for different land use types, but the correlation varied. The contributions of climate change and human activities to the changes of NDVI were 0.01·10 a^-1  and 0.03·10 a^-1, respectively. Their combined effect was the main reason for the changes of NDVI on the Loess Plateau in the past nearly 20 years, accounting for 58.3% of the area. The independent effect of human activities is greater than that of climate change.

Key words: vegetation change, time-lag effect, residual analysis, Loess Plateau