Earlier Spring Onset Induced by Increased Autumn Precipitation Dominates Advance in Peak of Season on the Tibetan Plateau

ABSTRACT Vegetation phenology is a response to a finely tuned interplay between different climatic constraints and is thus a critical indicator of vegetation –climate interaction. The rapidly changing climate on the Tibetan Plateau (TP) alters the start of the growing season (SOS), but little is known regarding the following timing and dynamics of the peak of the season (POS) vegetation phenology. In the present study, we used the 2000–2018 Moderate Resolution Imaging Spectroradiometer (MODIS) derived normalized difference vegetation index (NDVI) for land surface phenology (LSP) tracking and analyzed the SOS and POS over time and against climatic changes in the alpine grassland on the TP. We found non‐significant advancing trends in SOS and POS from 2000 to 2018, while spatial heterogeneity existed with a delayed trend of SOS in the steppe area of the western TP. This widespread yet weak delaying SOS in steppe areas was mainly due to the decline in autumn precipitation of the previous year despite the increase in spring temperature, given the negative correlations between SOS and autumn precipitation. In addition, precipitation and SOS were the most important factors leading to changes in spatial variations of SOS and POS, respectively. These findings suggest that high water availability accumulated in the previous autumn may hasten spring phenology. This advancing trend in spring timing could lead to an earlier peak of the season in alpine grasslands. Water availability and phenological carryover effect regulate the interannual and spatial variations of the spring–summer phenology of the Tibetan Plateau. However, spatial heterogeneity of LSP changes is likely to amplify further with consideration of response variability in different vegetation types.