21世纪以来青藏高寒草地的变化特征及其对气候的响应

利用遥感数据和气象观测资料探索气候因子对区域植被变化的驱动作用具有重要意义。以1980-2012年气象数据和2000-2012年MODIS-NDVI数据为数据源，借助线性回归和相关分析分别分析了青海和西藏两个地区21世纪以来气候变化对青藏高寒草地的影响机制。结果表明：（1）1980-2012年，青海和西藏地区均呈暖湿化的发展趋势。但21世纪以来，西藏地区降水呈不显著的减少趋势；整个青藏高原中部和西部地区增温趋势明显（>0.05 ℃·a-1）。（2）在年际尺度（2000- 2012年）上，青海地区NDVI呈显著增加的趋势，增长率为0.003·a-1（P<0.05）；西藏地区NDVI无变化趋势，区域尺度统计中植被退化与改善相互抵消。在空间上，青藏高原东北部地区NDVI呈良性趋势，部分区域增长斜率超过0.01·a-1。青藏高原南部地区NDVI呈变差趋势，变化斜率为0.008·a-1。（3）区域上的相关分析显示，在青海地区，降水量的增加和温度的升高共同促进了该区域植被的良性发展趋势；在西藏地区，降水量的减少和温度的升高可能是南部地区植被变差的重要原因。

Variation of alpine grasslands and its response to climate warming in the Tibetan Plateau since the 21st Century

As one of the major issues in global environmental research，the impacts of climatic factors on regional vegetation variability has attracted widespread attention from scientists and it is important to understand the driving mechanism of this variation by using remote sensed data and meteorological observations. In this study，based on meteorological data in the period of 1980-2012，MODIS-NDVI data in the period of 2000-2012 and methods of linear regression and correlation analysis，our aim is to explain how climate changes impact on Qinghai and Tibet alpine grasslands since the 21st century. Results indicated as follows：（1） Qinghai and Tibet regions both showed warm and humid trends over 1980-2012. But in Tibet region，annual precipitation performed a decreasing trend with less significant in the period of 2000-2012. Warming trend was significantly throughout the central and western regions of the Tibetan plateau （>0.05 ℃·a^-1）. （2） At the interannual scale （in 2000-2012），NDVI showed a significantly increasing trend in Qinghai region，with the rate of 0.003·a^-1 （P<0.05）. However，unchanged trend in NDVI was found in Tibet region owing to that vegetation degradation and recovery mutually offset at the regional scale. Spatial NDVI largely presented rising trends in northeastern of the Tibetan Plateau with the slope of 0.01·a^-1，but in southern Tibetan Plateau，NDVI trends were worse at the slope of 0.008·a^-1. （3） Regional correlation analysis expounded the different trends in Qinghai and Tibet regions. In Qinghai region，increasing precipitation and warming temperature together promote positive trends of regional vegetation. Reducing precipitation and rising temperature might be important reasons causing vegetation deterioration in the south of Tibet region.