1982-2006年新疆植被活动的年际变化及其季节差异

NDVI-based Interannual and Seasonal Variations of Vegetation Activity in Xinjiang during the Period of 1982-2006

利用1982-2006年NOAA/AVHRR归一化植被指数(NDVI)时间序列,结合植被、地形和气候等资料,研究新疆植被活动的年际变化及其季节差异。结果表明:过去的25年,占新疆植被面积27%的地区生长季(4～10月)NDVI显著增加(P<0.05),其中近一半地区年增加速率大于0.003,而显著减少地区的面积仅占4%。与20世纪80年代相比,21世纪初植被覆盖度较高地区(生长季NDVI>0.3)的面积增加了5%,同时植被覆盖度较低区域(生长季NDVI<0.1)的面积下降了5%。不同季节的NDVI年变化趋势表明,秋季NDVI上升趋势极显著(P<0.01),并且增加速率最快(0.57%/a)。另外,不同植被类型NDVI的季节变化存在明显差异。草地和荒漠植被在春夏秋三季都显著增加;农作物在夏、秋两季增加显著且夏季增加速率最大(1%/a);森林NDVI仅在秋季呈显著增加趋势。因此,生长季的延长和生长加速是新疆植被活动增强的主要原因,而温度上升和夏季降水量的增加以及农业活动的加强可能是其主要的驱动因子。

Interannual and seasonal variations of vegetation activity in Xinjiang during the period from 1982 to 2006 were studied using the time series data of normalized difference vegetation index （NDVI） derived from remote sensing images （NOAA/AVHRR）,information of vegetation distribution and observed climatic data. The results show that the NDVI in growth season （from April to October） increased significantly in 27% of the study area but decreased in 4% of the study area in recent 25 years. The area with a high NDVI （0.3） in growth season was enlarged by 5% during the period of 2002-2006 compared with that in the 1980s （1982-1986）,and the area with a low NDVI （0.1） in growth season was reduced by 5%. Seasonal NDVI in Xinjiang increased significantly in spring,summer and autumn in recent 25 years. Seasonal variation of NDVI reveals that the NDVI increase in autumn was the most significant （P0.01）,and the mean increase rate was 0.57%. However,the seasonal NDVI varied from different vegetation types. NDVI of grasslands and desert vegetation increased significantly in spring,summer and autumn,that of crops increased significantly in summer and autumn,especially in summer （increased by 1%/a）,but that of forests increased significantly only in autumn. Therefore,our study suggests that the overtime of growth season and acceleration of plant growth were the main factors resulting in the increase of vegetation activity in Xinjiang,and the increase of temperature,rainfall in summer and agricultural practices might be the important driving factors.