NDVI Reflection of Alpine Vegetation Changes in the Source Regions of the Yangtze and Yellow Rivers

The spatial distribution and dynamic change of vegetation cover in the source regions of the Yangtze and Yellow rivers of the Tibetan Plateau are anal yzed in recent 20 years based on 8 km resolution multi-temporal NOAA AVHRR-NDVI data from 1982 to 2001. The data are from NASA Pathfinder AVHRR Land datasets. O n the basis of simple correlation analysis of air temperature, precipitation, sh allow ground temperature and NDVI, which is 3×3 pixel at the center of Wudaolia ng, Tuotuohe, Qumalai, Maduo, and Dari meteorological stations, the statistical models of air temperature, precipitation, shallow ground temperature and NDVI ar e constructed in this paper under two conditions-considering ground temperature action and not considering ground temperature effect. The results show that as a whole vegetation cover keeps original conditions basically in recent 20 years, vegetation continues to degrade in local areas of the source regions of the Yang tze and Yellow rivers. Remarkable decrease regions in NDVI are Zhaling Lake and Eling Lake edges, areas to the east and the north of the lakes, the headwater ar ea of Duoqu river in the northern foot of Bayan Har Mountain in the source regio n of the Yellow River, part areas in Geladandong region, some regions along the Qinghai-Xizang Highway between Tuotuohe and Wudaoliang, Qumalai and Zhiduo belts in the source region of the Yangtze River. Decrease range of NDVI is 0% to 20%. Vegetation degraded very severely in the above-mentioned regions. In the source regions of the Yangtze and Yellow rivers annual NDVI changes, namely good or ba d vegetation cover is influenced mainly by temperature, especially near 40 cm gr ound temperature below the earth surface. NDVI is very sensitive to near 40 cm g round temperature change. Permafrost is widely distributed in the source regions of the Yangtze and Yellow rivers. Its freezing-thawing processes are not only a ssociated with ground temperature change, but also affect soil water content. Pe rmafrost degradation will influence directly alpine vegetation growth in the sou rce regions of the Yangtze and Yellow rivers.