Abstract: The characteristics of temporal and spatial variations in the grass growing season of Tibet during the period of 1982 to 2010 were analyzed using NDVI data and GIS technology. Results show that the grass growing season of Tibet is short and only four months per year. During the research period, the NDVI of grass growing season shows increasing trend, but the increase of NDVI is slow and the rising rate is only 0.009·(10 a)^-1. The cumulative growth rate is 15.24%. The NDVI of grass growing season decreases from southeast to northwest in Tibet and the high value of NDVI is located in the Naqu and Changdu of northeast Tibet. The NDVI of grass growing season elevates from 1982 to 2010 accounting for the 71.77% of total grassland area. The NDVI of grass growing season in the south wing of eastern Himalaya area in southern Tibet is significant increase, while the NDVI in parts of the Yarlung Zangbo River is significant decrease during the period of 1982 to 2010. The above results indicate that human beings do not have a devastating effect on the grassland vegetation coverage of the area in recent 30 years. The change of climatic condition in the central areas of Tibet is unsuitable for vegetation growth. Vegetation in the north central and northwest region of Tibet is the most sensitive part in response to climate change.

Key words: Grassland in Tibet, Growing season, NDVI, Temporal and spatial variations

摘要： 利用NDVI数据结合GIS技术，定量分析了西藏草地1982—2010年生长季时空变化特征。结果表明：西藏草地生长季较短，全年仅4个月。研究期内，西藏草地生长季NDVI总体呈现上升趋势，上升速率仅为0.009·（10 a）^-1，累计增长率为15.24%；西藏草地生长季NDVI在空间上呈现由东南向西北递减的趋势，其高值区位于东北部的那曲-昌都一线。与1982年相比，2010年西藏草地生长季NDVI升高的面积占草地总面积的71.77%，其中位于西藏南部的东喜马拉雅山南翼地区增幅最为显著；而降幅则以雅鲁藏布江中下游部分地区最为显著。因此，近30年间，人类对该地区草地植被覆盖尚未造成破坏性影响。中部地区气候条件逐渐向不利于植被生长方向转变，西藏中北部和西北地区植被则是响应气候变化的敏感区。

关键词: 西藏草地, 生长季, NDVI, 时空变化