Combined control of multiple extreme climate stressors on autumn vegetation phenology on the Tibetan Plateau under past and future climate change

Existing research on autumn vegetation phenology is limited to phenological responses to gradual climate change. Considerably less attention has been paid to extreme climate events, resulting in a substantial gap in our understanding of the climatic response mechanism of vegetation autumn phenology. Therefore, in the present study, we used Moderate Resolution Imaging Spectroradiometer (MODIS) observations to explore the responses of autumn phenology to extreme climate events (e.g., frost, heat, wetness, and drought) across the Tibetan Plateau (TP) from 2000 to 2018. We found that preseason drought and high heat stress generally induced early vegetation dormancy onset date (DOD) in most regions of the TP, whereas moderate heat and rainfall delayed the DOD in the agriculture and steppe ecoregions. Overall, cold and heat stress markedly affected the DOD in most ecoregions, whereas water stress (wetness and drought) mainly influenced the DOD in the meadow and steppe ecoregions. Modeling based on partial least squares regression (PLS), which considered these extreme climate events, predicted an earlier DOD (1.9-3.1 days earlier for RCP4.5 and 12.2-14.3 days earlier for RCP8.5) at the end of this century than traditional projections. Our findings demonstrate the combined influence of multiple extreme climate stress events on autumn vegetation phenology on the TP and highlight the need to integrate extreme climate events into future vegetation phenology models.