Communities that are concerned with ecological sustainability can use “urban metabolism” studies as a way to understand how much energy and materials are flowing through a neighbourhood, the city, or even the whole metropolitan region. These flows provide important information about how much energy is being used in daily activities of residents and municipal operations. For example energy used in buildings for heating and lighting, or in fuel to support transportation of goods or people on public transit or in privately owned cars. An urban metabolism can also track how much water is being consumed and by whom. It can also be used to identify the types of materials such as paper, textiles, clothing, that is passing through the city and ultimately ending up as wastes or being recycled and repurposed or composted. Comparing the amount of energy and materials a city consumes to the amount of energy and materials a bioregion can provide helps indicate whether a city is existing in balance with nature.
However, did you know that there are is an additional flow of hidden or embodied energy and materials that are also associated with the flows tracked in an urban metabolism? These are the resources that are used outside of a city to manufacture the products that are then imported into the city and that get consumed therein. Often the energy and materials used outside the city to create exceed what actually passes through a city. Paying attention to the embodied energy and materials in buildings and automobiles, consumer goods and food is an important part of understanding our impact on Earth and how we create cities in balance with nature.