中外超大城市生态质量遥感评价

Remote Sensing-based Comparative Study on the Urban Ecological Quality between Chinese and Foreign Megacities

超大城市生态系统和地表生物物理组分之间存在复杂的潜在非线性关系,且其产生的生态效应大于中小城市和乡村地区,这使得超大城市生态质量客观评估遇到了技术挑战。该文针对性选取空气质量指数、路网密度、生态连接度、热度、绿度、干度和湿度7个超大城市生态重要影响因子,利用主成分分析方法实现指标集成和阈值自动设定,建立城市生态评价遥感指数(URSEI),对比快速城市化背景下中国超大城市(北京、上海和广州)与进入城市化后期的发达国家超大城市(伦敦、纽约和东京)的城市生态状况差异。URSEI指数评价结果表明,6个城市URSEI均值分布在0.445~0.542之间,伦敦生态质量最好(URSEI为0.542),其后依次为广州(0.533)、北京(0.517)、纽约(0.511)和上海(0.495),东京最差(0.445)。对比URSEI指数的7个指标分量,伦敦与广州URSEI分量中,对生态质量起正向作用的生态连接度和绿度值较高,对生态质量起负向作用的空气质量指数、路网密度、干度和热度值较低,使得这2个城市的生态质量较好。从空间分布来看,城市中心不透水面覆盖率高,植被覆盖少,生态用地的生态效益较低,热岛效应严重,空气质量差,导致其生态质量差;城市大块绿地覆盖区,绿度和湿度高,干度和热度低,空气质量较好,完整连续的生态用地发挥的生态效益也更高,因而生态质量较好。URSEI指数既能作为一个量化指标来刻画区域生态质量,还可以反映城市空间的生态差异性。

Megacities are likely to have more significant impacts on regional ecological quality than smaller cities and country areas.Owing to the complex,potentially nonlinear relationship between urban ecological systems and biophysical surface components in megacities,selecting the right quantitative models to evaluate their urban ecological quality is not always clear.Six typical megacities inside and outside China(Beijing,Shanghai,Guangzhou,London,New York,and Tokyo)were taken as examples.7 ecological indicators,including Air Quality Index(AQI),Road Density(RD),Ecological Connectivity Index(ECI),Wetness,Greenness,Dryness,and Heat,were integrated to a new model named as urban remote sensing ecological index(URSEI)using principal component analysis.The URSEI was used to quantitatively evaluate the ecological quality of Chinese and foreign megacities.Results show that London had the best ecological quality(0.542),followed by Guangzhou(0.533),Beijing(0.517),New York(0.511)and Shanghai(0.495).Tokyo had the lowest ecological quality(0.445).Comparing the 7 indices within the URSEI,the ECI,Wetness and Greenness indices had positive effects on the ecology,while the AQI,RD,Dryness and Heat indices had negative effects.London and Guangzhou had high ECI and Greenness values and low AQI,RD,Dryness and Heat values.Hence,they had better ecological quality than those of the other four megacities.According to the spatial distribution of the URSEI,urban centers that were covered by high ratio of impervious surfaces and low ratio of vegetation had low ecological connectivity between the ecological land patches and had severe heat island effects and air pollution,which resulted in poor ecological quality.Areas covered by large amounts of vegetation had high Greenness and ECI values,and low Dryness,Heat and AQI values,which helped to improve the ecological quality.The URSEI can be used both as a quantitative indicator to describe the regional ecological quality,and to describe the spatial difference in the ecological quality of megacities.