中国西北地区植被NDVI的时空变化及其影响因子分析

利用GIMMS/NDVI数据分析了中国西北地区1982-2006年植被NDVI时空变化特征及其影响因子。近25年来,中国西北地区年均植被NDVI增速为0.5%/10a,并存在明显的空间差异。天山、阿尔泰山、祁连山、青海的中东部等地区植被NDVI显著增加;青海南部地区、陕西和宁夏交界地区、甘肃部分地区,以及新疆部分地区的植被NDVI下降。从不同植被类型看:林地、草地和耕地的年均NDVI都在提高。研究表明:中国西北地区植被NDVI变化是各种自然和人为因素综合作用的结果。植被NDVI与气温、降水的年际变化整体上都呈弱的正相关。但与其年内变化则都呈显著的线性关系,当月均温量超过20℃时,植被NDVI呈下降趋势;当月降水量在0¹00mm期间,植被NDVI随降水线性增长,当月降水量超过100mm之后,不再有明显的增长趋势。农业生产水平提高和植被生态建设等人类活动对西北地区植被NDVI增加有重要影响。

Spatio-temporal Change of Vegetation Index NDVI in Northwest China and Its Influencing Factors

In this paper the spatio-temporal variation of vegetation cover in Northwest China and its influencing factors were analyzed by average method,trend line and correlation analysis during 1982 to 2006 using GIMMS/NDVI data.The annual average NDVI has been increased significantly with a rate of 0.5%/10a in Northwest China in recent 25 years.There were some significant spatial differences of the vegetation cover change.The trend line slope of NDVI were higher than 0.0005 in Xinjiang（Tianshan,Artai Mountains）,Gansu（Qilian Mountains） and the eastern part of Qinghai,and it indicated the vegetation cover was significant increased in this areas.The trend line slope of NDVI were lower than-0.000 5 in the southern region of Qinghai,Shanxi and Ningxia border region,parts of Gansu and Xinjiang（Talimu Basin,Tulufan,Tahe,Tuoli）,and it indicated the vegetation cover was degraded in this areas.The NDVI of woodland,grassland and cultivated land had an ascending tendency during the study period.Studies showed that： the vegetation cover change was caused both naturally and artificially in Northwest China.The temperature rose significantly in past 25 years in northwest China by an average rate of 0.67℃/10a,and precipitation increased by an average rate of 8.15mm/10a since 1986.There was a weak positive correlation between vegetation cover and temperature and precipitation inter-annual changes.However,there was a significant linear relationship between vegetation cover and the monthly average temperature and precipitation during the years.But when the average monthly temperature exceeded 20℃,the NDVI decreased and the correlation coefficient is 0.29;when the average monthly precipitation was 0~100mm,the NDVI increased and the correlation coefficient is 0.63.However,when the average monthly precipitation was more than 100mm,a clear growth trend no longer existed.The improvement in agricultural production and the ecological construction project are the very important reasons to increase the NDVI in Northwest China.