Abstract: The aim of this research is to investigate the spatiotemporal changes in vegetation phenology and their response to climate change in the Western Sichuan Plateau from 2001 to 2020 and provide insights for the study of vegetation phenology changes in the plateau. Based on MODIS NDVI data, vegetation zoning data, digital elevation data, and meteorological data, we extracted the SOS (start of the growing season), EOS (end of the growing season), and LOS (length of growing season) of vegetation by using the Savitzky-Golay filter and dynamic threshold method. We then explored the relationship between vegetation phenology and climatic factors, such as monthly mean temperature and precipitation. Results indicate that 1) the SOS, EOS, and LOS of vegetation in the Western Sichuan Plateau were mainly concentrated in the 90^th to 130^th days, 260^th to 290^th days, and 130-190 d, respectively. As altitude increased, the SOS trended towards an advance, while EOS trended towards a delay, and LOS trended towards an extension. 2) Specifically, 60.56% of the vegetation area exhibited an advanced SOS trend, 51.21% a delayed EOS, and 60.75% a prolonged LOS, of which 7.19% showing a significant prolonged LOS trend. 3) The SOS of vegetation was negatively correlated with mean temperature from February to April, displaying significant spatio-temporal differences. Additionally, a significant positive correlation was found between EOS and average temperature in October, and precipitation in November. Moreover, average temperature in June and precipitation in August had a significant positive effect on LOS. Overall, the phenology of vegetation in the Western Sichuan Plateau displayed distinct distribution rules in different vegetation divisions.

Key words: vegetation phenology, Western Sichuan Plateau, temperature, precipitation, dynamic threshold method