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Based on Normalized Difference Vegetation Index (NDVI) and Standardized Precipitation Evapotranspiration Index (SPEI), we investigated vegetation response to different timescales drought across different vegetation types and homogeneous clusters in China, by annual maximum Pearson correlation (R max) and the corresponding timescales of drought. Results showed that: (1) 8 subregions with homogeneous climate-vegetation conditions were identified using Fuzzy C-Means algorithm; (2) SPEI and NDVI's annual R max were in significantly positive correlation in most regions of China, indicating that vegetation biomass were influenced mainly by the spatiotemporal characteristics of the water availability. The southeastern 3 Yangtze River basin and the lower Pearl River basin are dominated by abundant precipitation, and vegetation is not sensitive to droughts in these regions. The northeastern Heilongjiang province, the Changbai Mountains and western Sichuan province are characterized by weak NDVI versus SPEI relations, indicating a relatively small effect of drought on vegetation ; (3) The effects of annual average water balance, annual average annual precipitation, annual average effective accumulative temperature, and annual average daily sunshine hours on the NDVI versus SPEI correlation show that the annual average water balance is the key factor behind the change of vegetation vigor. It can therefore be concluded that the change of water availability is the key factor behind the change of vegetation activity and biomass. Regional precipitation or water balance was significantly related to the correlation between SPEI and NDVI. Vegetation in the regions with longer sunshine hours is more sensitive to droughts. In general, the sensitivity of grassland to droughts is the largest, followed by the sensitivity of shrubs and forests to droughts.

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This study investigated vegetation response to climate change exhibited by temperature, soil moisture, and solar radiation at Northern Hemisphere (NH) scale during the growing season and seasonal periods by analyzing satellite observations of vegetation activity and climatic data for a period of 1982-2013. Generally, About 75.8% of NH was dominated by increasing NDVI3g during growing season in 1982-2013, and 50.7% significantly increase. Autumn NDVI3g is the main cause, with 77.7% increase (45.0% significantly increase). The increasing tendency of greenness was stalled and even shifted to vegetation browning after 1994-1997 specifically in Central Europe, Northern North America, and Central Siberia. NDVI3g increase during the growing season shifts from 0.017 year-1 to 0.006 year-1 , which mainly due to decreased spring NDVI3g and slowdown of summer NDVI3g increase. Specifically, three time intervals were identified with relatively peak

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