The Latest Change in the Qinghai-Tibetan Plateau Vegetation Index and Its Relationship with Climate Factors

Based on the remote sensing data of GIMMS(Global Inventory Modeling and Mapping Studies) NDVI (Normalized Difference Vegetation Index) and MODIS (Moderate-resolution Imaging Spectroradiometer) NDVI, as well as data collected at six meteorological stations in the Qinghai-Tibetan Plateau, the authors discussed the spatio-temporal variation of the vegetation in the Qinghai-Tibetan Plateau and its influencing factors using statistical and calculation methods. The results show some obvious differences in the spatial distribution of annual mean Qinghai-Tibetan Plateau vegetation NDVI from 1982 to 2013; the NDVI over all decreased from southeast to northwest. In addition, temporal variations of the vegetation index in different areas were not exactly the same. Using EOF (Empirical Orthogonal Function) analysis, the authors analyzed the regular changing patterns of vegetation coverage over five subregions, which were divided based on NDVI during the growing season from June to September. The results indicate that the largest decrease in NDVI over the Qinghai-Tibetan Plateau occurred in the area of Gar-Lake Bangong Gully and the northern Qiangtang Plateau, while increases in NDVI over the Qinghai-Tibetan Plateau was found in the eastern Qilian Mountain. In order to explore the factors affecting the decline of NDVI in different subregions, two representative stations were selected in subregions Ⅱ, Ⅳ, and Ⅴ of the Qinghai-Tibet Plateau, where the NDVI showed a declining trend. The authors also discussed the relationship between NDVI and total precipitation, average temperature, mean maximum temperature, and percentage of sunshine duration at each station. Preliminary results show that in subregion Ⅱ of the Qinghai-Tibet Plateau, the sunshine duration was double that in other subregions while precipitation was relatively low, resulting in vegetation degradation. The vegetation degradation in subregion Ⅳ was attributed to limited precipitation, high temperature, and strong sunshine. In subregion Ⅴ, precipitation was sufficient but sunshine was weak, which also caused the vegetation degradation. The above results lay a profound foundation for the mechanism study of vegetation degradation in the Qinghai-Tibetan Plateau and its feedback to the atmosphere.