北京城市绿化的时空动态分析

城市绿化覆盖是城市生态系统的重要组成部分,合理的绿化率和绿化布局可以改善城市环境,提高城市人居适宜性。研究中将2005、2010、2015年北京市土地利用（LUC）数据中的城市居民用地作为城区范围,应用Landsat 5、GF-1影像数据和MODIS产品,利用支持向量机的监督分类方法,提取了2005、2010、2015年的北京市城市绿化覆盖数据,并获取了同期的植被指数（NDVI）数据;继而以城市绿化覆盖率、绿化覆盖均匀度和植被指数为评价指标,在公里栅格和行政区2个尺度上探讨了北京市城市绿化覆盖的空间分布格局和时间变化动态特征。研究表明：① 3个指标在空间和时间2个维度、区县和栅格2个尺度上都表现一致。这反映北京市过去10年中,在绿化面积增加的同时,绿化的空间布局得到优化改善,绿化的质量得到提高。② 2005-2015年,北京市城市绿化覆盖面积由518.93 km² 增加到1405.54 km²,绿化覆盖率由39.9%增加到49.13%,绿化覆盖均匀度由0.598增加到0.653,植被指数由0.42增加至0.5。③ 北京市城市绿化建设存在明显的时空差异。中心城区绿化建设缓慢,成效不明显;重大绿化建设成果主要集中在城市边缘地区和远郊区县。城市绿化改善过程主要发生在2005-2010年。

Analysis of Spatial and Temporal Dynamics of Green Coverage and Vegetation Greenness in Beijing

Urban green coverage is an important part of urban ecosystem. Reasonable green coverage layout can improve urban environment and improve urban human suitability. In this paper, urban residential land in the Land Use/Land Cover（LUC）data in 2005, 2010 and 2015 were chosen as the urban area. Based on Landsat 5 and GF-1 remote sensing images, we used the support vector machine classification method to acquire the urban green coverage data of Beijing in 2005, 2010 and 2015. We also got the normalized difference vegetation index (NDVI) at the same time based on the MODIS and GF-1. Then, the rate of urban area green coverage, uniformity degree of green coverage and normalized difference vegetation index were considered as the evaluation indexes. We analyzed the spatial pattern and dynamic changes of Beijing urban green coverage at the scale of 1km raster and district. This study indicated that: (1) three indexes were consistent in two dimensions of space and time, raster and district. This reflected that the green space layout and the quality of greenness and the actual effect had been improved when green areas increased. (2) From 2005 to 2015 in the past 10 years in Beijing,, the urban area of green coverage increased from 518.93 km² to 1405.54 km², the rate of green coverage increased from 39.9% to 49.13%, the uniformity degree of green coverage increased from 0.598 to 0.653, and the vegetation greenness increased from 0.42 to 0.5. (3) There were obvious differences in time and space between urban greenness and overlay construction in Beijing. Greenness of the downtown was slow and the effect was not obvious. The results of major greenness were mainly concentrated in the urban fringe and suburban counties. The improvement process of urban greenness mainly occurred in 2005 - 2010.