Abstract: We obtained Normalized Difference Vegetation Index (NDVI) data from National Oceanic and Atmospheric Administration (NOAA) and calculated net primary production (NPP) using the CASA (Carnegie-Ames-Stanford Approach) model from 1982 to 2011. Overall, vegetation coverage and NPP increased during the growing season in the past 30 years, which indicated that vegetation became better on the Plateau. The carbon sink function enhanced on the Qinghai-Tibetan Plateau. The increment of carbon sink on the whole Qinghai-Tibetan Plateau was equivalent to approximately 10% of that in China. Climate change was the
primary driving factor for vegetation change on the Plateau. Various ecological projects (e.g. grazing forbidden) also showed obvious ecological effects. However, there were some regions where vegetation became worse. These regions were mainly centered on the Northern Tibetan Plateau, the Brahmaputra River and its two Tributaries and partial district of Three-River Headwaters Region where ecosystems were more fragile and altitude was higher. Especially, there were worse grassland degeneration in alpine steppe and desert on the western of the Northern Tibetan Plateau, which were attributed to the combined effect of climate change (i.e., warming and drying) and human activities (e.g. overgrazing). Therefore, we should strengthen the construction of long-term monitoring systems and platforms for ecosystem changes and implementation of ecological compensation and projects.

Key words: Qinghai-Tibetan Plateau, ecosystem, carbon balance, climate change