快速城市化时期中国城市建成区植被状况的时空分异特征

Spatial-temporal Difference of Vegetation Changes in Built-up Areas in China during the Period of Rapid Urbanization

基于植被变化视角,以中国656个建制城市的建成区为研究对象,选择1992、2000和2010年DMSP/OLS夜间灯光数据和植被数据,选用城市建成区内归一化植被指数(Normalized Difference Vegetation Index,NDVI)的均值反映建成区植被的状况;用建成区内NDVI均值和背景区内NDVI均值的比值(NDVI比值)衡量人为因素对城市建成区植被的影响情况。结果表明:①同一年份,城市规模越大,建成区植被越差;近20 a来,除小城市植被变差外,其他等级城市植被总体在变好。②同一年份,规模小的城市人为因素产生的不利影响相对较小。近20 a来,人为因素对特大城市和大城市植被产生的不利影响在减小,而中等城市基本不变,小城市则变大。③同一年份,从湿润半湿润森林带、半干旱草原带到干旱荒漠带的城市建成区内的植被逐渐变差;近20 a来,干旱荒漠带的建成区植被状况略微变差,其余植被带内建成区植被变好。④同一年份,从湿润半湿润森林带、半干旱草原带到干旱荒漠带人为因素对建成区植被的不利影响逐渐减小;近20 a来,湿润半湿润森林带内人为因素对建成区植被的不利影响在减小,而其他植被带内,人为因素的不利影响在增加。

Since the 1978 reform and opening up of China, the level of urbanization has increased rapidly. Rapid urban expansion and restructuring have had significant impacts on the ecological environment especially within built-up areas. This study used ArcGIS 10, ENVI 4.5, Visual FoxPro 6.0, and Python software to analyze vegetation changes, and the impact of human factors on vegetation in the built-up areas of 656 Chinese cities from 1992 to 2010. The data mainly include DMSP/OLS nighttime light data and vegetation data. Firstly, an existing algorithm for extracting urban areas based on statistical data was refined to extract the boundaries of built-up areas. Secondly, we selected the mean Normalized Difference Vegetation Index （NDVI） of a built-up area to represent absolute vegetation, and mean NDVI can reflect vegetation cover and vegetation biomass in the built-up area. We constructed a mathematical model （ratio of mean NDVI in a built-up area to a background region, RMNDVI） to measure the impact of human factors on vegetation. RMNDVI values greater than 1 indicate relatively beneficial effects, and RMNDVI values less than 1 indicate proportionally adverse effects. The results clearly indicated three aspects of vegetation changes and human influence in built-up areas during rapid urbanization： the size of cities （metropolises, large cities, medium-sized cities, and small cities）, administrative divisions of China （provinces, autonomous regions, and municipalities） and vegetation zones （humid and semi-humid forest zone, semi-arid steppe zone, and arid desert zone）. Finally, we discussed the mechanism of human factors on vegetation changes in built-up areas. The findings provide a scientific basis for municipal planning departments and a decision-making reference for government, and also provide scientific guidance for sustainable development in China.