Emergy-based urban ecosystem health evaluation of the Yangtze River Delta urban cluster in China

An evaluation framework of emergy-based urban ecosystem health indicators was established to measure and describe the urban ecosystem health status in terms of energy and materials metabolism, when combing with the classical urban ecosystem health factors. Set pair analysis was also employed to guarantee and promote the objectivity of the ecosystem health criteria. Set pair analysis defines the approximate degree of a real index set relative to an optimal index set, and this is evaluated to describe the relative health levels of urban ecosystems based on the emergy indicators. Six cities in the Yangtze River Delta urban cluster in China were selected as case studies using 2005 data, and the relative urban ecosystem health levels were evaluated using the emergy indicators and set pair analysis. The evaluation showed that the urban ecosystem health states of Shanghai and Hangzhou are relatively good, while the health states of Wuxi and Suzhou are relatively poor. The health states for the cities based on concrete factors were also analyzed to identify regulatory directions for the improvement of the health status of those cities with relatively poor ecosystem health. This paper presents a meaningful comparison between different urban ecosystems at different indicator levels, and provides a useful framework for urban ecological management with respect to urban ecosystem health status.