Vegetation phenology and its response to climate change in the Yellow RiverBasin from 2001 to 2020

     Vegetation phenology is widely recognized as a comprehensive indicator of global climate change. Studying the spatiotemporal characteristics and trends of regional vegetation phenology can improve our understanding of the stability and dynamic changes of the ecosystem. Based on the 16day, 250m resolution MODIS NDVI data from 2001 to 2020, this study used the S-G filtering method and the relative threshold method to extract vegetation phenology parameters in the Yellow River Basin. Combined with the ERA5-LAND hourly climate reanalysis dataset and CHIRPS daily precipitation dataset provided by GEE platform, using trend analysis and partial correlation analysis methods, we explored the spatial distribution characteristics and change trends of vegetation phenology in different vegetation zones under global climate change.We also analyzed its response to climate factors.The results show that: (1) the climate in the Yellow River Basin presented a warm and humid development trend from 2001 to 2020, with an annually average temperature increase of 0.15℃/10a (P>0.05) and an annual precipitation increase of 24mm/10a (P<0.05). (2) The warm temperate deciduous broad-leaved forest region in the Yellow River Basin had the earliest start of the growing season and middle time of the season, while the typical grassland subzone in the southern temperate zone and the desert grassland subzone in the southern temperate zone had the latest start of the growing season and middle time of the season. The end of the growing season in the temperate shrub-grass semi-desert zone was the latest, and the length of growing season in the alpine vegetation region on the Qinghai-Tibet Plateau was the shortest. (3) Within the whole basin, 69.3% and 66.4% of the area showed an advance trend (P<0.05) for start of the growing season and middle time of the season, respectively, 50.9% of the area showed a delay trend (P<0.05) for end of the growing season, and 66.1% of the area showed an extension trend (P<0.05) for length of growing season. (4) There were differences in climate impacts on phenology parameters among different vegetation zones. Temperature had a greater impact on phenology parameters in typical grassland subzone in northern temperate zone, alpine grassland zone, and alpine meadow zone, while precipitation and solar radiation factors had a greater impact on phenology parameters in typical grassland subzone in southern temperate zone, temperate shrub-grass semi-desert zone, desert grassland subzone in southern temperate zone and mid-subtropical evergreen broad-leaved forest zone.