Spatial and Temporal Variations in Spectrum-Derived Vegetation Growth Trend in Qinghai-Tibetan Plateau from 1982 to 2014
WANG Zhi-wei1,2,3, WU Xiao-dong1, YUE Guang-yang1, ZHAO Lin1*, WANG Qian1, NAN Zhuo-tong1, QIN Yu1, WU Tong-hua1, SHI Jian-zong1, ZOU De-fu1，2
1. Cryosphere Research Station on the Qinghai-Tibet Plateau, State Key Laboratory of Cryosheric Sciences, Cold and Arid Regions Environmental and Engineer Research Institute, Chinese Academy of Sciences, Lanzhou 730020, China 2. University of Chinese Academy of Sciences, Beijing 100049, China 3. Guizhou Institute of Prataculture, Guizhou Academy of Agricultural Sciences, Guiyang 550006, China
Abstract：Recently considerable researches have focused on monitoring vegetation changes because of its important role in regulating the terrestrial carbon cycle and the climate system. There were the largest areas with high-altitudes in the Qinghai-Tibet Plateau (QTP), which is often referred to as the third pole of the world. And vegetation in this region is significantly sensitive to the global warming. Meanwhile NDVI dataset was one of the most useful tools to monitor the vegetation activity with high spatial and temporal resolution, which is a normalized transform of the near-infrared radiation (NIR) to red reflectance ratio. Therefore, an extended GIMMS NDVI dataset from 1982—2006 to 1982—2014 was presented using a unary linear regression by MODIS dataset from 2000 to 2014 in QTP. Compared with previous researches, the accuracy of the extended NDVI dataset was improved again with consideration the residuals derived from scale transformation. So the model of extend NDVI dataset could be a new method to integrate different NDVI products. With the extended NDVI dataset, we found that in growing season there was a statistically significant increase (0.000 4 yr-1, r2=0.585 9, p<0.001) in QTP from 1982 to 2014. During the study period, the trends of NDVI were significantly increased in spring (0.000 5 yr-1, r2=0.295 4，p=0.001), summer (0.000 3 yr-1, r2=0.105 3，p=0.065) and autumn respectively (0.000 6 yr-1, r2=0.436 7，p<0.001). Due to the increased vegetation activity in Qinghai-Tibet Plateau from 1982 to 2014, the magnitude of carbon sink was accumulated in this region also at this same period. Then the data of temperature and precipitation was used to explore the reason of vegetation changed. Although the trends of them are both increased, the correlation between NDVI and temperature is higher than precipitation in vegetation growing season, spring, summer and autumn. Furthermore, there is significant spatial heterogeneity of the changing trends for NDVI, temperature and precipitation at Qinghai-Tibet Plateau scale.
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