Shifts in the peak vegetation growth over Tibetan Plateau

Understanding the seasonality of vegetation growth is important for maintaining sustainable development of grassland livestock systems over the Tibetan Plateau (TP). In this study, we investigate the shifts of the date of peak vegetation growth and its climatic controls for the alpine grasslands over the TP during 2001–2020. The date of peak vegetation growth over the TP advanced by 0.81 days decade^-1 during 2001–2020. This spring-ward shift mainly occurs in the semi-humid eastern TP, where the peak growth date tracks the advancing peak precipitation, and shifts towards the timing of peak temperature. Through analyzing the synchrony of peak vegetation growth and climatic peaks, we showed that 26% of the semi-humid eastern plateau is shifting from thermal-constrained ecosystem towards water-constrained ecosystem. The advancing peak growth over the eastern TP could significantly stimulate GPP, but this positive effect is weakened from 3.02 gCm^-2 year^-1 day^-1 during 2000s to 1.25 gCm^-2 year^-1 day^-1 during 2010s. Our results highlighted the importance of water availability in vegetation growth over the TP, and indicated that the TP grassland is moving towards a tipping point of transition from thermal-constrained to water-constrained ecosystem under a rapid warming climate.