The 21st century will be the century of the city, whose size and complexity outlines a prominent role in the global economy and, at the same time, poses huge problems of sustainability. Currently the global urban system account for only about 2% of the Earth surface but for about 70% of GHG gas emission. Global urbanization might well be defined by the emergence of ‘megacities,’ i.e., metropolitan areas of more than 10 million people, which number passed from 4 in 1970 to 30 in 2015.
As of 2011, there were 27 megacities in the world, with 10 more expected by 2020. The flows of energy, water, and materials into megacities and the wastes produced—which together define the ‘urban metabolism’—likely have environmental effects on a planetary scale.
Despite the huge populations of these cities, their complex governance structures and socio-economic systems have thwarted comparative study, without which policy development is hampered. To help fill the need for data on megacities, we conducted a major investigation into the urban metabolism of these regions.
Objective of this research is to conduct urban metabolism (UM) studies of the world’s 27 megacities as of 2011, collecting data on a small number of UM parameters, specifically energy (all sources), water, material, and waste flows. For the first time a study compares the UM of megacities, providing a view about the energy use and outlook for the future and the main results have been published on Proceedings of the National Academy of Science of the United States of America
The data gathered for this purpose allowed us to assess the efficiency of resource flows and service delivery in each megacity. Statistical correlations were established between biophysical parameters (climate, urban form, economy) and measures of urban metabolism (energy use, water consumption, waste production).
Particular focus was given to the role of utilities (electricity, natural gas, water, etc.), and how they can affect the urban metabolism. The perspective was to investigate the role of utilities in megacities looking, for example, at how electric mobility, energy efficiency, and integrated infrastructure solutions can influence the UM and quality of life in megacities. The study identified low-carbon electrification of cities as the key strategy for urban sustainability and provide a general ‘roadmap’ to the low-carbon electric city.