The Spatial-temporal Change Of Vegetation In Source Region Of The Yangtze And Yellow River And Its Response To Climate Change From 1982 To 2013

The terrestrial ecosystem has changed with global warming. The Tibetan Plateau is the region where is sensitive to climate change. The vegetation change not only influences the environment change, but also influences climate system of the northern hemisphere even all over the world. The source region of the Yangtze and Yellow River is located in the eastern and central of Tibetan Plateau. It is the source of the Yangtze River, Yellow River, Lancang River and Nujiang River which is the sensitive and fragile ecosystem area and ecological barrier of the middle or lower reaches of the Rivers in our country as well. Under the background of plateau, the vegetation is sensitive to the climate change. With the special climate, the diversity of vegetation and the complexity of landform, the vegetation had significant spatial variation in this region. The main point in this paper is the differences of vegetation change and its response to the climate change of each district. This paper focuses on the characteristics of the spatial and temporal changes of the vegetation and the climate in the source region of the Yangtze and Yellow River based on meteorological data, multi-temporal GIMMS-NDVI and MODIS-NDVI data from 1982 to 2013.The correlation between vegetation change and climate factors was calculated. Combined with DEM data, the relationship between vegetation change and terrain factors in each district was calculated in two time periods of 1982-1999 and 2000-2013. Moreover, the differences of vegetation variation and its responses to climate change among different regions were discussed. During 1982 to 2013, the climate of Source region of the Yangtze and Yellow River presented the trend of first warming and drying and then warming and wetting. The annual temperature increased significantly with a growth rate of 0.593℃/10 a,the annual precipitation held stable with a slightly growth rate of 14.9mm/10 a.The temperature and precipitation in the western region increased faster than the eastern region. The annual temperatures in different regions were all increased. The increasing of annual temperature in Gonghe basin and Gannan plateau had slowed down after 2000 and the annual precipitation presented a trend of first decreased and then increased. The annual temperature in source regions of Yellow River, Yangtze River, Lancang River and Nujiang River had a consistent tendency to increase. The precipitation presented first decreased from 1982 to 1999 and then increased from 2000 to 2013 except source region of Nujiang River. And the precipitation of in source region of Yellow River, Yangtze River increased most significantly, the precipitation of the source region of Nujiang River presented a trend of not significantly decreasing in the two time stage. The maximum NDVI value presented a significantly fluctuate increasing trend in the study region with a growth rate of 0.0147/10 a.In season scale, the NDVI of four seasons all increased. As well, the maximum NDVI in six regions increased in the past 32 years. The NDVI in Gonghe basin and Gannan plateau presented a trend of first decreased and then increased. The NDVI of source regions of Yellow River, Yangtze River and Lancang River all presented a trend of first stable and then increased. The NDVI of source region of Nujiang River presented a trend of first increased and then decreased. The stable area of vegetation is biggest in all districts during both two time periods. And areas of vegetation increasing and decreasing in each region had differences. Analyze the altitude distribution of the rate of NDVI change in study region,the results showed that the vegetation in the region more than 4000 meter held stable with a growth rate of less than 0.01/10 a in both two time stage and the region of less than 4000 meter presented a trend of first slightly decreased and then significantly increased. Vegetation change in Source region of the Yangtze and Yellow River is influenced by both temperature and precipitation. The correlation between maximum NDVI and climate factors showed that the NDVI change of vegetation had a positive correlation with the temperature from July to August, winter temperature and precipitation in May. With the temperature increasing in winter, it may be good for soil thawing and mineral decomposition which leads to improve the heat and moisture condition. The growth of vegetation was improved as well. With summer temperature increasing, it’s conducive to decomposition of the organic matter and release nutrients needs of vegetation which make vegetation improve. Meanwhile, the precipitation is rare before vegetation grows. The precipitation in May is an effective supplement to soil moisture which is good for the growth of vegetation. In the low altitude of the region of Gonghe basin and Gannan plateau, the precipitation influenced on vegetation more than temperature. In the mid-mountain zone of Gannan plateau, the precipitation influenced on vegetation the same as temperature. The temperature influenced on vegetation more than precipitation in the high altitude of source regions.