近20余年来西北地区植被变化特征分析

Vegetation Cover Variation in Northwest China during the Past 22 Years

利用1982—2003年8 km分辨率的NDVI数据集,选中国西北地区森林、草原、灌溉农业、雨养农业区不同类型植被为研究区,分析了植被年、年际变化特征,并对植被覆盖空间变化进行动态研究.结果表明:森林、草原、灌溉农业区和以春小麦为主的雨养农业区NDVI年变化为单峰型曲线,以冬小麦为主的雨养农业区NDVI曲线呈双峰型;同一类型的植被NDVI受纬度或海拔高度的影响,绿峰出现时间存在1个月的位相差.22 a来森林植被NDVI多呈下降趋势,草原植被区为上升趋势;雨养农业区变化不大,灌溉植被区呈显著的上升趋势.西北东部雨养农业区植被波动频率和幅度最大,是受降水影响最敏感的地区;森林植被次之;有灌溉条件的绿洲植被,年际间波动最小.22 a间西北地区植被以增加趋势为主,增加面积约为20.5%,主要分布在新疆和河西走廊绿洲、黄河沿岸灌区以及青海草区,水分条件充足的绿洲是NDVI增加最显著的区域;NDVI减少地区面积为4.77%,主要分布在西北东部.

The vegetation cover annual and interannual variations were analyzed in the typical vegetation regions, including forest, grassland, oasis, rain-fed cropland and desert in Northwest China, using the GIMMS （Global Inventory Modeling and Mapping Studies） NDVI data set, which was collected at a spatial resolution of 8 km and 15 days interval, for the period from January 1982 to December 2003, At the same time, the vegetation cover dynamics in whole region was studied. The results show that the NDVI average annual curves had a single peak in these regions, such as forest, grassland, irrigating oases and rain-fed cropland where be planted spring wheat mainly. The curves have double peaks in those regions, where usually is planted winter wheat. For same type vegetation, the time when the NDVI peaks occurs delay one month according to different altitude and latitude.The NDVI variation trends of forest were decreased; the tread of grassland were increased; rain-fed cropland maintained flat and the irrigating oases had remarkable rising trends. The frequency and extent of NDVI variation was highest in rainfed cropland region, where is the most sensitive areas influenced by precipitation; forest taken second place and the irrigating oases were lowest. The characteristic of NDVI in the whole area was increasing during the past 22 years. The increased areas accounted for 20. 5% of Northwest China, where distribute mainly in oases Xinjiang and Hexi corridor, irrigating regions along the Yellow River and grassland regions in Qinghai Province. The increase of NDVI is the most notable in oasis . The decreased regions accounted for 4.8%, where primarily distributed in the eastern part of Northwest China.