Response of the End of the Growing Season to ExtremeClimatic Events in the Semi-Arid Grassland of Inner Mongolia

Climate change impacts on vegetation phenology, especially under extreme climate events, remain inadequately understood. Based on the Fraction of Photosynthetically Active Radiation (FPAR) from MODIS, this study extracted and investigated the end of the growing season (EOS) dynamics in semi-arid grassland of Inner Mongolia from 2003 to 2020. The relationship between the EOS and extreme climate events was examined, and the coincidence rate (CR) between these events and EOS standardized anomaly (EOSSA) was quantified. The results showed that the EOS exhibited a significant delaying trend (1.48 days/year, p < 0.05) after 2011, with its spatial distribution patterns strongly correlated with climatic gradients. Compound dry–warm events exhibited the widest spatial extent and highest frequency among all compound extreme climate events (CECEs). The impact of extreme climate events on EOSSA varied depending on climatic background. Extreme dry delayed EOSSA in colder regions but advanced it in warmer regions. CECEs exerted a stronger regulatory effect on EOSSA. Compound dry–warm events showed high CR with EOSSA (CR > 0.4), which was higher under low temperature gradients but decreased under high gradients. The result enhances our understanding of how semi-arid grassland respond to extreme climate events, aiding the improvement of phenology models.