Environmental performances and energy efficiencies of various urban green infrastructures: A life-cycle assessment

Abstract

Urban green infrastructures have been well recognized for their roles in providing ecosystem services in cities. However, their environmental performances have not been fully understood from a life-cycle perspective. In this study, we evaluated the life-cycle environmental performances and energy efficiencies of three types of green infrastructure, i.e. green roof, greenway, and grove that are increasingly built in cities. Our analysis covered all phases of the life-cycle including extraction and construction, use and maintenance, end-of-life, and transportation. Results confirm the environmental improvements of the green roof, greenway, and grove in most of the addressed impact categories. The energy saving in the use and maintenance phase contributed a significant part to these improvements, while the construction material in the extraction and construction phase had a dominant share in the environmental impacts. The grove and greenway showed better environmental performances than the green roof. The extensive use of compost for the greenway and grove could release toxic substances to the environment, and offset environmental improvements or even resulted in a negative consequence to EP of the greenway. The utilization of substrate and waste disposal for the green roof caused relatively high impacts on the environment. Sensitivity analysis shows a 50% reduction of the energy saving weakened the environmental improvements of the green roof, greenway and grove in all categories, and particularly exacerbated the environmental impacts on EP and CADP for the green roof, AP for the greenway and EP for the grove; and an increased waste recycling and reuse rates will greatly enhance the environmental improvements of the green roof.