Abstract: 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.

Key words: megacity, urban remote sensing ecological index (URSEI), ecological quality, remote sensing