Energy and material flows of megacities
- aDepartment of Civil Engineering, University of Toronto, Toronto, ON M4J 3K1, Canada;
- bEnel Foundation, 00198, Rome, Italy;
- cSchool of Environment, Beijing Normal University, Beijing, China 100875;
- dDepartment of Energy and Environment, TERI University, Vasant Kunj, New Delhi, DL 110070, India;
- eDepartment of Industrial Engineering, De La Salle University, Malate, Manila, 1004 Metro Manila, Philippines;
- fDepartment of Landscape and Ecological Planning, Seoul National University, Seoul, South Korea 151-742;
- gCoimbra Institute of Postgraduate Research in Engineering, Federal University of Rio de Janeiro, University City, Rio de Janeiro, RJ 21941-901, Brazil;
- hInstitute of the Environment and Sustainability, University of California, Los Angeles, CA 90095;
- iDepartment of Civil and Environmental Engineering, Laing O'Rourke Centre for Systems Engineering and Innovation, Imperial College London, London SW7 2AZ, United Kingdom;
- jInstitute of Geography, University of Paris, 75005 Paris, France;
- kDepartment of Accounting, Trisakti University, Jakarta Barat, DKI Jakarta 11440, Indonesia;
- lDepartment of Architecture, University of Lagos, Lagos 23401, Nigeria;
- mDepartment of Environmental Engineering, College of Engineering, University of Tehran, Tehran, Iran;
- nDepartment of Civil Engineering, Bangladesh University of Engineering and Technology, Dhaka-1000, Bangladesh;
- oDepartment of Geography, Hunter College, New York, NY 10065;
- pEnvironmental Strategies Department, Environmental Protection Agency, Government of Buenos Aires City, Buenos Aires, Argentina;
- qEcoConServ Environmental Solutions, Zamalek, Cairo, Egypt 11211;
- rDepartment of Civil Engineering, Faculty of Civil Engineering and Architecture, NED University of Engineering and Technology, Karachi 75270, Pakistan;
- sDepartment of Civil Engineering, University of Guanajuato, CP 36000, Guanajuato, Mexico; and
- tFaculty of Aeronautics and Astronautics, Istanbul Technical University, Maslak, 34469, Istanbul, Turkey
See allHide authors and affiliations
Edited by Susan Hanson, Clark University, Worcester, MA, and approved April 2, 2015 (received for review March 6, 2015)

Significance
Our quantification of energy and material flows for the world’s 27 megacities is a major undertaking, not previously achieved. The sheer magnitude of these flows (e.g., 9% of global electricity, 10% of gasoline; 13% of solid waste) shows the importance of megacities in addressing global environmental challenges. In aggregate the resource flows through megacities are consistent with scaling laws for cities. Statistical relations are established for electricity use, heating/industrial fuels, ground transportation, water consumption, waste generation, and steel production in terms of heating-degree days, urban form, economic activity, and population growth. Analysis at the microscale shows that electricity use is strongly correlated with building floor area, explaining the macroscale correlation between per capita electricity use and urbanized area per capita.
Abstract
Understanding the drivers of energy and material flows of cities is important for addressing global environmental challenges. Accessing, sharing, and managing energy and material resources is particularly critical for megacities, which face enormous social stresses because of their sheer size and complexity. Here we quantify the energy and material flows through the world’s 27 megacities with populations greater than 10 million people as of 2010. Collectively the resource flows through megacities are largely consistent with scaling laws established in the emerging science of cities. Correlations are established for electricity consumption, heating and industrial fuel use, ground transportation energy use, water consumption, waste generation, and steel production in terms of heating-degree-days, urban form, economic activity, and population growth. The results help identify megacities exhibiting high and low levels of consumption and those making efficient use of resources. The correlation between per capita electricity use and urbanized area per capita is shown to be a consequence of gross building floor area per capita, which is found to increase for lower-density cities. Many of the megacities are growing rapidly in population but are growing even faster in terms of gross domestic product (GDP) and energy use. In the decade from 2001–2011, electricity use and ground transportation fuel use in megacities grew at approximately half the rate of GDP growth.
Footnotes
- ↵1To whom correspondence should be addressed. Email: christopher.kennedy{at}utoronto.ca.
Author contributions: C.A.K., A.F., I.C., R.M., B. Chen, A.K., A.C., K.-g.K., C.D., E.L.L.R., S. Pincetl, J.K., S.B., S. Pusaka, J.G., M.A., M.N., S.H., P.J.M., F.G.O., T.G., R.F., G.C., and A.D.S. designed research; C.A.K., I.S., I.C., B. Chen, M.U., A.K., A.C., K.-g.K., C.D., E.L.L.R., B. Cunha, S. Pincetl, J.K., S.B., S. Pusaka, J.G., M.A., M.N., S.H., P.J.M., F.G.O., T.G., N.I., R.F., G.C., and A.D.S. performed research; C.A.K., I.S., A.F., I.C., M.U., J.K., and F.G.O. analyzed data; and C.A.K. and I.S. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1504315112/-/DCSupplemental.
Citation Manager Formats
Article Classifications
- Social Sciences
- Sustainability Science