2000-2019年京津冀地区植被覆盖状况变化及驱动因素

近20年来中国和印度通过土地利用活动改变地表覆盖使植被变得更绿，京津冀地区是植被变得更绿的典型地区。收集京津冀地区2000-2019年MODIS增强型植被指数（EVI）、植被覆盖百分比数据，以及年平均温度和降水量等数据，分析该区近20年来自然植被和农田植被EVI变化过程和趋势，揭示其变化的驱动因素，结果显示2000-2019年京津冀地区自然植被和农田植被EVI显著增加，自然植被EVI增加速率是农田植被的1.8倍。99.51%的自然植被和96.95%的农田植被生长状况改善。2000-2019年京津冀地区自然植被EVI与年平均温度和年降水量相关性不显著。农田植被EVI与年平均温度显著相关，与年降水量相关性不显著。农田灌溉和年平均温度变化是农田植被EVI显著增加的主要驱动因素。近20年京津冀地区通过实施以造林为主的生态建设工程，自然植被生长覆盖状况呈现极显著变好。同时森林植被比非森林植被覆盖百分比增加趋势更明显。以造林为主的生态建设工程是京津冀地区自然植被生长覆盖状况显著变好的主要驱动因素。

Change of vegetation coverage and the driving factor in the Beijing-Tianjin-Hebei region from 2000 to 2019

With the development of remote sensing technology, large-scale vegetation change monitoring becomes possible. It was found that global vegetation had become greener in last decades. China and India have changed the vegetation coverage through land use activities to make land greener in the past 20 years under climate change. The Beijing-Tianjin-Hebei region is a typical area where land has become greener. The remote sensing vegetation index was widely used in monitoring the coverage change of surface vegetation. In this study we collected MODIS Enhanced Vegetation Index(EVI) data, MODIS vegetation growth and coverage data, land use and land cover data of the Beijing-Tianjin-Hebei region from 2000 to 2019, as well as annual average temperature and precipitation data. Then we analyzed the annual average EVI variation process and trend of the natural vegetation and cropland vegetation of the study area in the past 20 years, and revealed the driving factor, with the expectation of providing a scientific basis for objectively evaluating the effectiveness of the Beijing-Tianjin-Hebei ecological construction and coordinated development, and building the regional ecological security. The results showed that the EVI of natural vegetation and farmland vegetation in the Beijing-Tianjin-Hebei region increased significantly from 2000 to 2019. The increase rate of natural vegetation was 6.96%/10 a, the rate of increase of farmland vegetation was 3.91%/10 a, and the rate of increase of natural vegetation EVI was 1.8 times that of farmland vegetation. The growth of 99.51% of natural vegetation and 96.95% of farmland vegetation had improved. From 2000 to 2019, the EVI of natural vegetation in the Beijing-Tianjin-Hebei region had no significant correlation with annual average temperature and annual precipitation. The EVI of farmland vegetation was significantly correlated with the annual average temperature, but not significantly related to the annual precipitation. The main reason was that the irrigation water for the farmland vegetation in the Beijing-Tianjin-Hebei region comes from groundwater and agricultural water for the South-to-North Water Diversion Project. The growth of the farmland vegetation was not correlated with the fluctuation of the annual precipitation in the area. The annual average temperature was directly related to the growth of farmland vegetation. Farmland irrigation and annual average temperature changes were the main driving factors for the significant increase in farmland vegetation EVI. In the past 20 years, the Beijing-Tianjin-Hebei region had implemented a number of ecological construction projects focusing on afforestation, and the growth and coverage of natural vegetation have shown a remarkable improvement. Statistics showed that in 2019, the total afforestation area in the Beijing-Tianjin-Hebei region was 5712.66 km², accounting for about 2.62% of the total area of the region. The accumulated afforestation area in the Beijing-Tianjin-Hebei region from 2000 to 2019 was 84367.27 km², and the afforestation area in the Beijing-Tianjin-Hebei region had increased year by year since 2006. At the same time, the percentage increase of forest vegetation coverage was more obvious than that of non-forest vegetation. The ecological construction project focusing on afforestation was the main driving factor for the remarkable improvement of the growth and coverage of natural vegetation in the Beijing-Tianjin-Hebei region.