Changes in phenological events and long-term seasonality in response to climate change and the ecological restoration in China's Loess Plateau

Phenology is highly responsive to environmental changes, particularly in ecologically vulnerable regions that have undergone significant anthropogenic management and rapid climate change. While previous research has mainly focused on interannual variations of specific phenological events such as the start (SOS), peak (POS), and end (EOS) of growing season, little attention has been given to abrupt shifts in long-term phenological seasonality resulting from land management. In this study, we utilized full temporal details of Moderate Resolution Imaging Spectroradiometer-derived normalized difference vegetation index to investigate how phenological metrics and seasonality have changed within the Loess Plateau. Our results indicated an earlier initial phase (SOS-POS) and a prolonged POS-EOS phenophase. Earlier spring onset was dominated by increasing water availability from the previous autumn, and earlier SOS led to an earlier POS but no significant carryover effect on EOS. In addition, spring onset of grassland was sensitive to precipitation while forest community was strongly influenced by temperature. We also reported significant changes in phenological seasonality across the plateau, and this shift in long-term seasonality was mainly controlled by growing season precipitation. Moreover, land use/land cover change also played a role with increasing importance after the abrupt change in seasonality. In sum, our findings highlight the importance of water availability in shaping phenological patterns across this semiarid plateau and illuminate shifts in phenological seasonality that are indispensable to a comprehensive understanding of phenology dynamics.