基于2005—2020年北京地区NDVI数据,采用NDVI等级划分、差值分析等方法,分析植被空间分布特征、时间分布特征和时空特征,揭示北京地区NDVI变化的时空规律,分析近15年北京地区植被覆盖变化和变化原因。研究结果表明:北京地区整体植被覆盖处于较高水平,从区域上看,2005—2020年北京地区NDVI平均值为极高覆盖等级的区域都分布在军都山和西山两个山脉,门头沟区、怀柔区、延庆区、房山区、昌平区、平谷区的植被覆盖处于北京地区最高水平等级;从时间上看,植被覆盖水平从2005—2020年发生了巨大变化,NDVI年均值由0.659 0上升到0.756 6,提高了14.81%;极高覆盖等级的面积比例由5.31%提高到47.79%,等级低的面积比例由5.91%下降到1.25%;从植被时空变化特征看,明显改善和轻度改善的面积比例超过了80%。两个“百万亩造林”和山区森林经营是提升北京地区植被覆盖质量的主要驱动力。

Based on NDVI data from 2005—2020,the spatial distribution characteristics,temporal distribution characteristics and spatio-temporal characteristics of vegetation were analysed using NDVI classification and difference analysis to reveal the spatio-temporal patterns of NDVI changes in Beijing,and to explore the reasons for the changes by analysing the vegetation cover changes in Beijing in the past 15 years.Through analysis,it is found that,the overall vegetation cover in the Beijing area is at a high level.From a regional perspective,the areas with very high NDVI mean coverage classes in Beijing from 2005 to 2020 were all located in the Jundu and Xishan mountain ranges.The vegetation coverage of Mentougou District,Huairou District,Yanqing District,Fangshan District,Changping District and Pinggu District was at the highest level in Beijing.In terms of time,the level of vegetation coverage changed significantly from 2005 to 2020,with the average annual NDVI value increasing from 0.659 0 to 0.756 6,an increase of 14.81%.The proportion of area with "very high" vegetation coverage increased from 5.31% to 47.79%,and the proportion of area with "low" vegetation coverage decreased from 5.91% to 1.25%.In terms of spatiotemporal change characteristics of vegetation,the area with obvious improvement and slight improvement accounted for more than 80%.Two "million mu afforestation" projects and mountain forest management were the main driving forces to improve the quality of vegetation coverage in Beijing.