Remote sensing monitoring the spatiotemporal changes of alpine grassland coverage in northern Tibet

Ranging from 83°41' to 95° 11' east longitude and from 30° 27' to 35°39' northern latitude, Northern Tibet in the highest of Tibet is known as the ridge of world with the mean elevation of 4500 meter. Northern Tibet is the headstream of Yangtze River, Nu River and Lancang River. The environmental condition of this area has significant effect on the mainly rivers, climate and eco-environment of Tibet and the whole country, so much as the global for the rigorous natural condition and fragile ecosystem. Based on the Normalized Difference Vegetation Index (NDVI) data (from 1981 to 2004), this paper has revealed the dynamics of grassland vegetation coverage of Northern Tibet by the method which the remote sensing technique integrated with ground measurement. The preliminary results are as follows: The grassland vegetation coverage of Northern Tibet is very low that the average value is only 29.7% for many years. In terms of spatial distribution of grassland vegetation coverage, the eastern region of Northern Tibet has a relatively higher coverage of grassland vegetation; the western has the lowest vegetation coverage. During the period of 1981-2004, the average grassland vegetation coverage had a slight decreasing trend, but fluctuation is relative greatly; the grassland vegetation coverage in the western region had a marked rising trend while the coverage in the middle, eastern and northern regions had a decreasing tendency.