Simulation and Attribution of the Start of the Growing Season in Qinghai-Tibet Plateau Grasslands

The Qinghai-Tibetan Plateau (QTP), recognized as one of the world's most ecologically sensitive regions, exhibits particularly pronounced responses of alpine grasslands to climate change. In this study, we extracted the Start of Season (SOS) for QTP grasslands from 1982 to 2014 using NDVI data and developed a coupled cumulative temperature-accumulated soil moisture model to simulate future SOS trends under different climate scenarios. The model demonstrates strong performance in capturing SOS temporal patterns, with mean absolute errors (MAE) below 8 days across most study regions. Our analysis revealed that temperature serves as the dominant control factor for grassland SOS initiation during the 1982 ~ 2014 period, while the influence of soil moisture shows a gradual increasing trend. Under both SSP2-4.5 and SSP5-8.5 scenarios, SOS exhibits an overall advancing trend with notable spatial heterogeneity, showing greater advancement under the SSP5-8.5 scenario. Temperature consistently exerts an advancing influence on SOS across both scenarios, whereas soil moisture demonstrated opposing effects. These findings provide valuable insights into the complex interactions between climatic factors in alpine grassland ecosystems, offering important implications for predicting ecosystem responses to climate change and developing adaptation strategies.