Urban Metabolism: A How-To Guide

Published on Feb 06, 2017

With all the pressing environmental challenges that we currently face and the legally binding Paris Agreement, a lot of effort is put to accurately measure the human impact on the environment. Cities, are in the epicenter of most direct and indirect, local and global, environmental pressures. As they now host more than half of global population -and this share is expected to increase in the future-, urban areas are most definitely the place to start in order to reduce anthropogenic pressures.

Urban metabolism is a metaphor that has been used to conceptualise cities as living organisms that receive resource flows and reject pollution flows in order to function. Academia and urban environmental administrations are more and more using this tool to measure their environmental impacts of cities in order to mitigate them (see here our publication collection and our visualization collection).

But how do you actually do an urban metabolism study or a metabolic balance for your city? This blog and the illustration below will explain exactly that. Most studies boil down to an important and comprehensive data collection. More specifically, a collection of resource and pollution flows entering and exiting the urban system. Where do you find this data you might ask?



You can find this data through local or national statistical offices, urban and environmental administrations, grid operators (energy, water, etc.), transportation of goods and services agencies, academic literature, grey literature, etc. For instance, the following Figure detailing the flows of energy entering and the GHG emissions exiting NYC comes from the Inventory of New York City Greenhouse Gas Emission in 2014 Report.



More and more cities and administrations now provide their data in open access platform, which makes them easier to find. For instance, here below you can see the Electricity Consumption in London’s Borough for 2011 per different type of consumers (for more data visit London’s Datastore here). This type of data format are the easiest to use as they frequently provide data for other years as well.

Sometimes, you might be unable to find data for a specific flow or for a specific year. This is quite frequent and very often researchers have to find a proxy to estimate missing values. Of course, your hypothesis for using a certain proxy should be thoroughly discusses and any limitations should be put forward. If you still can’t find any possible way to approximate the metabolic flows, you might want to create some data yourself by doing surveys. You also might want to discuss with administrations and grid operators to know whether data really don’t exist or are just confidential, in which case you could perhaps sign a confidentiality agreement.

In any case, as soon as you have successfully establish a metabolic balance for your city (this step can typically take 2 to 3 months), you now need to understand the values. What do they represent? Are they too big, too small, and compared to what? Why does your city have these specific values? Would a different city with the same number of inhabitants would have the same flows? Are those flows specific for a year or they follow an increasing or decreasing trend?

Therefore, carrying out an urban metabolism is only the first step. In order to mitigate urban environmental pressures at local and global scale there is a need to understand what the context behind these values is and what the drivers are.