PNAS – Proceedings of the National Academy of Sciences of the United States
of America
http://www.pnas.org/content/early/
(Accessed 2 May 2015)

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Energy and material flows of megacities
Christopher A. Kennedya,1, Iain Stewarta, Angelo Facchinib, Igor Cersosimob, Renata Meleb,
Bin Chenc, Mariko Udaa, Arun Kansald, Anthony Chiue, Kwi-gon Kimf, Carolina Dubeuxg, Emilio Lebre La Rovereg, Bruno Cunhag, Stephanie Pincetlh, James Keirsteadi, Sabine Barlesj, Semerdanta Pusakak, Juniati Gunawank, Michael Adegbilel, Mehrdad Nazariham, Shamsul Hoquen, Peter J. Marcotullioo, Florencia González Otharánp, Tarek Genenaq, Nadine Ibrahima,
Rizwan Farooquir, Gemma Cervantess, and Ahmet Duran Sahint
Author Affiliations
Edited by Susan Hanson, Clark University, Worcester, MA, and approved April 2, 2015 (received for review March 6, 2015)
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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.
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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.