Increasing gross primary productivity despite vegetation browning over the Tibetan Plateau during 1998−2015

Vegetation dynamics across the Tibetan Plateau (TP) are increasingly influenced by climate warming, warranting further investigation. This study integrates multiple data sources, focusing on Normalized Difference Vegetation Index (NDVI) and gross primary productivity (GPP), to analyze their long-term trends during TP’s growing season. We find a noteworthy shift from greening (increased NDVI) to pronounced browning (decreased NDVI) in the third generation NDVI dataset generated by the Global Inventory Modeling and Mapping Studies (GIMMS3g NDVI), evident from 1998 (1982–1998: 0.0006 yr^-1, p < 0.1; 1998–2015: −0.0008 yr^-1, p < 0.05). This browning trend is corroborated by Moderate-Resolution Imaging Spectroradiometer (MODIS) NDVI (−0.0005 yr^-1, p < 0.05) during 2000–2015. In contrast, all GPP products consistently increase during 1982–2015. Browning and increasing GPP trends decouple in the eastern and southern TP, coinciding with terrestrial water storage (TWS) shifting from increasing to decreasing, and rising trends in solar radiation (SR), vapor pressure deficit (VPD), and temperature post-1998. Analysis highlights increasing SR (VPD) dominance and decreased TWS sub-dominance in GIMMS3g (MODIS) NDVI browning. TRENDYv6 multiple model experiments emphasize climate’s primary role, followed by CO₂ fertilization, in increasing GPP trends. Furthermore, temperature exerts the most significant promoting effect on GPP enhancement, outweighing adverse effects of soil and atmospheric dryness. Additionally, we reconcile browning and increased GPP by attributing it to environment-induced increased light-use efficiency and highlight subtle plant carbon allocation strategies. This study provides valuable insights into the intricate relationship between changing climate and vegetation dynamics over the TP.