近几十年来，京津冀经历了快速的人口增长过程，快速城市化的过程会导致城市及城市周边地区的生态变化。植被是受到城市化影响的地表生态环境中重要的组成部分，对于分析城市化进程中生态环境变化具有重要意义。城市的扩张会直接导致地表覆盖由植被向不透水层转变，改变地表下垫面情况，对植被覆盖度造成负面的影响，同时城市化也会改变城市局部气候，从而影响植被的变化。但是随着城市化的推进，为打造更宜居的城市生态，城市的规划更加关注城市内植被的状况和重视城市建成区公园绿地的建设。因此评估城市化对植被覆盖度变化的影响以及判断城市内的公园绿地建设能否发达到预期十分重要。然而，以往的研究更多关注城市化进程中土地利用变化造成的植被覆盖度变化，定量化研究城市化对植被覆盖度变化贡献的较少，结合城市政策规划探究城市内公园绿地覆盖率的也较少。

考虑到城市化和气候变化以及政策的综合影响，本研究的第一部分利用灯光数据表征城市化，结合京津冀气候站点数据，定量化分析了2000-2010和2011-2018年这两个城市化阶段内，城市化进程和气候变化对植被覆盖度变化的影响；第二部分中利用土地利用数据和时间序列的NDVI数据提取城市公园绿地，计算2000、2010、2016、2020年的城市公园绿地服务半径覆盖率，预测北京市能否完成市政府规划的公园绿地建设目标。结果表明：

（1）2000-2018年京津冀有89.22%的区域植被覆盖度增加（显著增加的有83.3%，p<0.05），有10.78%的区域植被覆盖度减少（显著减少的有46.91%，p<0.05）。增加的区域主要位燕山-太行山和衡水、沧州等小城市的周边区域。减少的区域主要分布在北京、天津、石家庄、唐山、保定等周边地区。将植被覆盖度的变化分为2000-2010年的人口快速增长时期和2011-2018人口增长趋势变缓时期两个时间段分析。在2000-2010年期间，植被覆盖度下降的区域主要是张家口坝上区域和6个大城市的扩展区和边缘区以及周边区域；在2011-2018年期间北京西部植被覆盖度显著上升，京津冀东南部植被覆盖度显著且成片下降。

（2）在2000-2018年间，城市化、气候变化和其他因子对植被覆盖度变化贡献都是1/3左右。城市化对植被覆盖度变化的贡献率最高，为28.44%，不同城市之间有较为明显的差异。气候因子对植被覆盖度变化的贡献为34.17%（温度和降雨分别为17.39%和16.78%）。在城市发展的前一阶段（2000-2010年），城市化和降雨对植被覆盖度的影响较大，分别是30.26%和22.24%。但是在城市化的后一阶段（2011-2018年），城市化的影响和降雨的影响都有所降低（贡献为22.72%和13.06%），温度成为了植被变化的主导因子（贡献为42.35%）。

（3）在2020年，在公园绿地服务半径内的居民地占大部分，为88.91%，符合《北京城市总体规划（2016年-2035年）》中对于建成区2020年城市公园绿地服务半径覆盖率的预期。根据两种遥感评估得到的未来公园绿地服务半径覆盖率显示，不考虑土地利用类型的限制，2035年北京公园绿地服务半径覆盖率为大于99.51%，2035年的公园绿地服务半径覆盖率（>99.51%）符合《北京城市总体规划（2016年-2035年）》的要求。

本文分析了京津冀地区2000-2018年植被覆盖度动态变化状况，并在此基础上定量评估了城市化和气候变化对植被覆盖度变化的贡献；并根据北京市的统计数据和政策实施情况判断了2020年城市公园绿地能否完成建设目标。本文的研究对于了解未来城市内植被状况有重要意义，可以为城市的宜居环境发展目标提供理论支持。

In recent decades, the Beijing-Tianjin-Hebei region has experienced rapid population growth. The rapid urbanization process will lead to ecological changes in the city and its surrounding areas. Vegetation is an essential part of the surface ecological environment affected by urbanization. It is of great significance to analyze the changes in the ecological environment in the process of urbanization. The expansion of urban areas will directly lead to the transformation of land cover from vegetation to impervious layer, change the underlying surface conditions, and have a negative impact on vegetation coverage. At the same time, urbanization will also change the local climate, thereby affecting vegetation change. However, with the advancement of urbanization, to create a more livable city, the government planning pays more attention to the urban ecological environment and urban green spaces in built-up areas. Therefore, it is crucial to evaluate the impact of urbanization on the change of fractional vegetation coverage and determine whether the city's urban green spaces can meet expectations. However, previous studies have paid more attention to changes in vegetation coverage caused by direct changes in land cover in the process of urbanization. There are few quantitative studies on the contribution of urbanization to the change of vegetation coverage and the urban green space coverage in combination with urban planning policy.

Considering the comprehensive impact of urbanization, climate change and policies, the first part of this research quantitatively analyzed the impact of urbanization and climate change on (Fractional Vegetation Coverage, FVC) changes in two urbanization phases from 2000 to 2010 and from 2011 to 2018. In the second part, land use data and time-series (Normalized Difference Vegetation Index, NDVI) data were used to extract urban green space, and calculated the coverage rate of urban green space service radius in 2000, 2010, 2016, and 2020. Then we predicted whether Beijing city could complete the green space construction target planned by the municipal government. The results indicate that:

(1) From 2000 to 2018, 89.22% of the total area in the Beijing-Tianjin-Hebei region showed an increase in the FVC. The increased areas are mainly natural areas with less human activities like the surrounding areas of small cities such as Yanshan-Taihangshan, Hengshui and Cangzhou. The reduced areas are mainly distributed in surrounding areas of megacity such as Beijing, Tianjin, Shijiazhuang, Tangshan, and Baoding. The change of vegetation coverage is divided into two time periods: rapid population growth from 2000 to 2010 and slower population growth from 2011 to 2018. From 2000 to 2010, the vegetation coverage declined mainly in the Bashang area of Zhangjiakou, the expansion and fringe areas and surrounding areas of six megacities; from 2011 to 2018, the vegetation coverage increased significantly in western Beijing, and decreased significantly in the southeastern Beijing-Tianjin-Hebei region.

(2) During the period from 2000 to 2018, urbanization, climate change and other factors contributed about 1/3 of the change in vegetation coverage. The contribution of urbanization to the change of vegetation coverage was the highest, which was 28.44%. The contribution of temperature and precipitation change to vegetation coverage change is relatively small, being 17.39% and 16.78%, respectively. In the previous stage of urbanization (2000-2010), urbanization and rainfall had a greater impact on vegetation coverage change, which were 30.26% and 22.24%, respectively. However, in the latter stage of urbanization (2011-2018), the impact of urbanization and rainfall have decreased (contributions of 22.72% and 13.06%), and temperature has become the dominant factor of vegetation change (contribution of 42.35%).

(3) In 2020, residential areas within the service radius of urban green spaces account for 88.91%, which is in line with the expected coverage of urban green spaces in built-up areas in 2020. The future service radius of urban green spaces obtained from two remote sensing evaluations shows that, regardless of land use restrictions, the service radius of green space in 2035 is greater than 99.51%, which is in line with the requirements of the 2035 coverage rate in the "Beijing City Master Plan (2016-2035)".

This study analyzed the dynamic changes of fractional vegetation coverage in the Beijing-Tianjin-Hebei region from 2000 to 2018. On these basis, the impacts of natural factors and urbanization on fractional vegetation coverage changes were quantitatively evaluated. Then, based on the statistics data of Beijing urban green space and the implementation of policies, it was judged whether the goal of urban green spaces construction can be achieved in 2020. This research is of great significance for understanding the vegetation conditions in cities in the future and can provide theoretical support for the development goals of the city's livable environment.