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Environmental problems caused by intensive economic development and rapid urbanization have seriously constrained the sustainable development of social economy. Ecological security assessments have become an effective tool for measuring the unsustainability bottom line. Although Shanghai, Nanjing, Suzhou, Hangzhou, Wuhan, Hefei, Chongqing, and Chengdu are developed megacities in the Yangtze River basin of China, they are located in a fragile ecological environment. The megacities of the Yangtze River basin must achieve sustainable development based on an appropriate assessment of ecological security so that suitable suggestions can be proposed. To quantitatively measure and analyze the ecological security levels in these eight megacities in 2007–2016, this study applied the improved emergy ecological footprint model which optimizes the traditional emergy ecological carrying capacity by adding the new account of the socioeconomic emergy ecological carrying capacity. To improve accuracy, the environmental technology investment efficiency in the socioeconomic account was introduced using the slack based measure model of undesirable output. Then, this study constructed a framework of ecological security assessment. The results showed that from 2007 to 2016, the renewable resources carrying capacity varied greatly among these eight megacities which had an absolute effect on the contribution of emergy ecological carrying capacity. Environmental technology investment efficiency failed to increase. However, in the short term, it effectively increased the socioeconomic carrying capacity for megacities with poor renewable resources. The emergy ecological footprint followed a growth trend in Shanghai, Nanjing, Hangzhou, Hefei, and Chongqing, and a decreasing trend in Suzhou, Wuhan, and Chengdu. Across the study period, ecological deficits were identified in Shanghai, Suzhou, Nanjing, Wuhan, and Hefei. Hangzhou, Chengdu, and Chongqing had ecological surplus because of their superior renewable resources and their ecological security. Nanjing and Wuhan changed their status from sub-secure to secure. Except for Shanghai, the ecological footprint diversity indexes of all other megacities followed a growth trend, indicating that their consumption structure improved. Finally, this paper provides policy recommendations to help decision-makers formulate ecological security and sustainable development strategies. The results of this study provide a scientific reference for other megacities to mitigate ecological pressures by considering their local situations.
Liu et al. (Wed,) studied this question.