Research Highlights

What makes megacities tick

Published online 11 May 2015

A novel study of megacities’ energy and material flow finds a close correlation between electricity use and size of urbanized area.

Moheb Costandi

In the first study of its kind, researchers have measured the flow of energy and materials through the world’s 27 megacities, identifying those that use resources most efficiently and suggesting how megacities of the future can grow sustainably. 

In the past century, the number of city-dwellers has increased from 220 million to over 3.5 billion. Megacities — defined as metropolitan areas with populations exceeding 10 million — are now home to 6.7% of the world’s population, and this poses major environmental challenges.

Chris Kennedy of the University of Toronto and his colleagues collected relevant economic, geographic and meteorological data, and used them to compare manufacturing output, energy and water consumption, and waste production in each megacity. 

“Our aim was to find ways that megacities can develop with high quality of life while reducing global environmental impacts,” says Kennedy, “and we have already found examples of infrastructure systems that make progress, such as the transportation system in Paris, Tokyo’s water distribution, Seoul’s wastewater re-use and Moscow’s city-wide district energy system.” 

“Our findings support the established understanding that compact cities are the way to go – not just reducing transportation emissions, but also reducing electricity consumption.”

Corrected on 12 May, 2015: The original version of this article misrepresented the percentage of people living in megacities.


  1. Kennedy, C. A., et al. Energy and material flows of megacities. PNAS (2015)