The Living City

A city is like a living thing. It consumes raw materials, fuel and water and transforms them into a streets, buildings, houses – and waste. But the metaphor of city as organism isn’t just a literary conceit. It’s an idea that is shaping efforts at creating sustainable cities, says Chris Kennedy, professor of civil engineering.

In 1965 an American civil engineer named Abel Wolman suggested the idea that researchers could study an “urban metabolism.” Interest in the concept waxed and waned for a few decades, but in the past 10 years seems to have taken hold, says Kennedy in a paper he wrote for the journal Environmental Pollution. In the past decade, 30 substantial papers have used the idea. At least 10 cities have undergone a full-scale metabolism analysis, including Vancouver and Toronto.

In humans, metabolic studies measure all of the food, air and water that go into a person’s body, and the carbon dioxide, heat and waste that come out. A metabolic study of a city rigorously quantifies the inputs, which include water, fuel, and raw materials like cement and steel, and the outputs, including solid waste and air pollution.

Kennedy used the urban metabolism idea to measure the greenhouse gas emissions for 44 cities last year, and is helping to develop a method that can measure the metabolism of a neighborhood or residential or commercial development.

Ultimately, the urban metabolism idea can be used by planners to design sustainable cities, Kennedy says. His own students have designed a sustainable neighborhood that could be built at the Toronto Port Lands. Among other things, it would cut per-person CO2 emissions for residents to one tonne annually, compared with the national average of 23 tonnes.