VARIABILITY OF NDVI IN WINTER AND SPRING ON THE TIBETAN PLATEAU AND THEIR RELATIONSHIP WITH SUMMER PRECIPITATION

The Tibetan Plateau has a complex topography and landscape, a large variety of vegetation, and huge heterogeneity and salient geographical variability in landcover, ranging from the evergreen rainforest of the southern Himalayas to the semiarid and arid lands of the northern plateau. The Tibetan Plateau is a sensitive region in climate change, where the manifestation of global warming is particularly noticeable. The large climate variability over this region significantly affects the local land ecosystem and could consequently lead to notable vegetation changes. Based on the 20 years normalized difference vegetation index (NDVI) dataset from the Inventory Modeling and Mapping Studies (GIMMS) and precipitation station data from the National Climate Center (NCC) of China Meteorological Administration (CMA), the relationship between winter and spring NDVI and summer precipitation in the Tibetan Plateau is investigated using the singular value decomposition method. The results show that vegetation coverage is best in the eastern and southern plateau regions and deteriorates toward the west and north. On the whole, the vegetation activity evinces a gradual enhancement with an oscillatory manner during 1982-2001. The temporal variation also exhibits striking regional differences: an increasing trend is most apparent in the north, northwest, and south, whereas a decreasing trend is present along the southern plateau boundary and in the central-east region. There exist a preferable correlation between NDVI in winter and spring and summer precipitation in the Tibetan Plateau and the lag correlation also exhibits striking regional differences. The correlation of NDVI in winter and spring to summer precipitation put up strongly positive. The respond is sensitive especially in north and south region. However, in the central-east region NDVI in winter is negative correlated to the summer precipitation. The SVD analysis between the NDVI and the precipitation suggests that the vegetation change is closely related to the precipitation change. The vegetation variability should be considered as the factor of the long forecasting for the precipitation in the Tibetan Plateau.