## 4 Conclusions  
We analyzed the spatial and temporal NDVI variation and the influence of climatic drivers from 1982 to 2011 in China via methods of regression and statistical tests. The key conclusions are as follows:  
(1) At a national scale, the growing season NDVI significantly increased by 0.0007 year\({}^{-1}\) on average from 1982 to 2011, though the trend abruptly changed at 1994, slowing down from 0.0008 year\({}^{-1}\) to 0.0003 year\({}^{-1}\), which was mainly contributed by the stalled spring NDVI trend. NDVI trends showed great seasonal and regional heterogeneity. It increased rapidly in spring and autumn while no significant trend was observed in summer. In 76.5% of the research area, the growing season NDVI increased while in grassland of northeast Inner Mongolia, decreased trends were observed, mainly caused by decreased precipitation.  
(2) The growing season NDVI was significantly and positively correlated to temperature and precipitation, while temperature contributed more to NDVI than precipitation at a national scale. Regionally, the growing season NDVI was dominated by rising temperature in most forested area in southern China and dominated by precipitation in most grassland in northern China, where water supply is limited. For example, NDVI in northern Xinjiang increased with more precipitation while that in northeast Inner Mongolia decreased due to less precipitation. During spring and autumn, NDVI was dominated by temperature in most research areas, and slightly dominated by precipitation in parts of grassland in northern China during summer. Hence rising temperature in spring and autumn prompted NDVI in southern China while falling precipitation in summer limited the vegetation growth in parts of northern China such as northeast Inner Mongolia.  
(3) 16.64% of the research areas, mainly grassland covered northern China, have undergone slowed down NDVI trends corresponding with slowed down temperature increment since mid 1990s and dropped precipitation since around 2000. While in 14.61% of the research area, mainly forests in southern and central China, growing season NDVI has speeded up together with temperature since mid 1990s. Seasonally, spring and autumn NDVI in southern China has accelerated together with temperature since mid 1990s while summer NDVI in parts of northern China has slowed down due to dropped precipitation since around 2000.  
(4) The reasons leading to similar long term NDVI trends can be various and regional specific. NDVI in northeast Inner Mongolia decreased sharply since around 2000 due to falling precipitation. NDVI in Loess Plateau increased at extremely high rates, which has benefited from accelerated temperature and afforestation. In addition, NDVI in Central China also increased quickly with temperature while fluctuated widely under the effects of drought.  
The results of this study illustrate an overall increasing trend of vegetation growth and the spatial pattern of dominant climatic drivers, which would help to better estimate and predict evapotranspiration and carbon processes. However, the interannual variation of vegetation growth cannot be fully explained by changes in climatic drivers, and further studies on the relationships and feedbacks between vegetation growth and carbon and nitrogen cycles are needed. Furthermore, the different spatial patterns highlight the necessity for more in-situ observations. Abrupt change points of vegetation growth indicate the non-linear response of vegetation growth to climate change, which increased the complexity and highlights the importance of further study on the mechanism of ecosystem processes corresponding to climate change.  
This research was supported by the National Natural Science Foundation of China (Project Nos. 51139002 and 51209117), the Basic Research Fund Program of State Key Laboratory of Hydroscience and Engineering (Grant No. 2014-KY-04), and the Tsinghua University Initiative Scientific Research Program (Project No. 20131089284).