1999-2007年祁连山区植被指数时空变化

Spatiotemporal Variation of Vegetation NDVI in the Qilian Mountains during the Period from 1999 to 2007

基于SPOTVGT-NDVI数据,结合累积平均法、均值法、趋势线分析和影像差异法,分析了祁连山地区植被时空变化。结果表明:祁连山区植被覆盖东多西少;1999年以来植被呈增加趋势,植被指数(NDVI)增速为1.1%/10a,东段增速(1.6%/10a)大于中段(1.4%/10a)和西段(0.6%/10a);NDVI年内月和旬变化曲线均呈单峰型,7～8月达到最大。7～8月雨热达到最佳,适宜植物的生长;而从10月到翌年2月祁连山草地处于枯黄期;3～4月草地处于返青期,植物生长缓慢,NDVI都较低。祁连山NDVI增加和减少的面积分别占总面积的37.39%和10.95%。植被覆盖增加的地区主要分布在高山和亚高山森林草地,东段、中段、西段NDVI最大增加量分别为0.15,0.21和0.12。植被覆盖减少的地区主要分布在河流河谷以及青海湖周边,东段、中段、西段NDVI最大减少量分别为0.19,0.28和0.17。

As a body of terrestrial ecosystem,vegetation affects energy balance and climatic,hydrologic and biochemical cycles.Simultaneously,it is also affected by the factors mentioned above.So it is of great significance to monitor the dynamic change of vegetation.In this paper,the spatiotemporal variation of NDVI of vegetation in the Qilian Mountains during the period from 1999 to 2007 is analyzed by using the cumulative average method,average method,trend line analysis and image differencing analysis based on the SPOT VGT-NDVI data.The results show that the NDVI in the eastern part of the Qilian Mountains is higher than that in the western part;the annual average NDVI had been increased by 1.1%/10 a in the Qilian Mountains since 1999;the increase rate in the eastern part （1.6%/10 a） was also higher than that in the central part （1.4%/10 a） and western part （0.6%/10 a）.The annual NDVI curve was unimodal and reached the maximum in July or August because precipitation and temperature were suitable for vegetation growth in July or August.The areas with increase and decrease of NDVI accounted for 37.39% and 10.95% of the total area respectively.The increase of NDVI occurred mainly in the alpine and subalpine natural forests and grasslands in the Qilian Mountains,and the NDVI was increased by 0.12,0.22 and 0.12 in maximum in the eastern,central and western parts,respectively.The decrease of NDVI occurred mainly in the river valley and the peripheral region of the Qinghai Lake,and the NDVI was decreased by 0.27,0.18 and 0.19 in the eastern,central and western parts,respectively.