The Increased Effect of Spring Leaf Unfolding on Autumn Senescence in the Northern and Southern Hemispheres

Vegetation phenology, the timing of periodic events in vegetation development, is an essential indicator for detecting climate-vegetation dynamics. Although the importance of vegetation growth carryover (VGC) on phenology has been recognized in the Northern Hemisphere (NH), it is unclear how VGC and climatic factors contribute to phenology and how these contributions evolve at a global scale. Utilizing two sets of satellite NDVI data (1982-2022) and PEP725 ground observations (1963-2015), we explored the impacts of climate change and VGC on start-of-season (SOS) and end-of-season (EOS) across the Northern and Southern Hemispheres during the past five decades. Here we show that, globally, advanced SOS was driven primarily by increasing temperature and radiation, while delayed EOS was attributed to rising temperature and the carryover effect of spring vegetation growth (VGC_SOS). VGC_SOS was the dominant driver of EOS in the SH, whereas temperature played a larger role in the NH. Over the past four decades, the contribution of VGC_SOS on EOS has increased significantly on a global scale. However, the SH experienced pronounced "warming and drying" trends, which weakened the relative contribution of VGC_SOS on EOS compared to climate-driven delays. These findings improve our understanding of vegetation dynamics and offer valuable insights for predicting vegetation growth and carbon sequestration under future global warming scenarios.