北京市植被指数变化与影响因素分析

利用MODIS归一化植被指数(NDVI)数据分析了北京市2001—2010年植被覆盖的时空变化特征，并从气候因子和人类活动两个方面分析影响植被覆盖变化的因素。北京市近10年的植被覆盖变化大致可分为两个阶段:2001—2003年植被覆盖小幅度下降时期；2004—2010年植被覆盖上升时期。空间上植被覆盖变化则存在显著差异:怀柔、密云北部和延庆东北部的林地和部分草地，以及西南地区即门头沟和房山地区的林地植被覆盖显著提高；植被覆盖显著下降地区分布较为特殊，昌平、延庆、顺义、大兴和房山的东部地区，以海淀、朝阳、城市中心为圆心的外围向四周延伸。研究表明，植被覆盖变化是气候因素和人类活动共同作用的结果。北京市近10年气温和降水量总体都呈现增加趋势，分别以每10年0409 ℃和每年156 mm的速度增加，植被覆盖与降水的关系更为密切，月际水平的相关程度明显高于年际水平的相关程度。人类活动也是影响植被覆盖变化的重要因素，土地利用类型的改变、农业生产水平的提高以及植被建设的管理对植被覆盖都有不同程度的影响。 

Temporal and spatial variation of normalized difference vegetation index and its influencing factors in Beijing

In this paper,we analyzed the spatio-temporal variations of normalized difference vegetation index (NDVI) based on the 250 m MODIS data from 2001 to 2010 in Beijing.We also examined the drivers of such variations,mainly climate change and human activities.Vegetation cover changes had experienced two stages in Beijing:a declining phase with small fluctuations during 2001-2003 and an increasing phase during 2004-2010.There were some significant spatial differences of vegetation cover changes.The vegetation cover had obviously increased in north of Huairou,Miyun and the northeast of Yanqing districts.NDVI of forest also increased in Mentougou and Fangshan districts.However,the vegetation cover evidently decreased in Changping,Yanqing,Shunyi,Daxing and the east of Fangshan districts,around the center of the city.The results showed that the spatio-temporal variations of vegetation cover were the results of climate change and human activities.The temperature and precipitation were increasing at a rate of 0.409 ℃/10 years and 15.6 mm/year during the past 10 years in Beijing.The correlation between NDVI and precipitation was more obvious than temperature.The relationship between monthly NDVI and monthly climate factors was obvious during the study period.Human activities also played an important role in vegetation cover changes.There were some different impacts in vegetation cover changes by land cover change,improved agricultural production and vegetation construction.