What this lesson teaches
I can explain how cities draw on local and distant environments for resources and what that costs.
Syllabus 9173, Topic 3.1, 1. Sustainable Urban Development. How does the demand placed on natural environments by urban areas influence progress towards sustainable development?
Make a guess
A compact city has very clean streets and small built-up area. Is its environmental impact small?
- Yes, because its built-up area is so small.
- No, because compact cities pollute the most.
- Yes, because clean streets prove low impact.
- No, not necessarily. It may use land far away.
Show the answer
No, not necessarily. It may use land far away.
A city's ecological footprint includes the land and water needed to supply its food, energy and materials and absorb its waste, wherever that is.
Cities pull in food, water, energy and materials, and send waste and pollution beyond their boundaries.
Cities need constant flows. Water, food, energy and materials come in. Products, waste and emissions go out. A big, busy population creates huge demand, often drawing on surrounding and faraway areas.
An urban area can be defined by population size, economic activity, official status or function. A functional area is a core plus the places linked to it by commuting. Countries use different definitions, so check before comparing.
Cities also have zones. The central city is the core. Suburbs are built-up areas around it. The rural-urban fringe is where city and countryside meet. New housing, roads and dumps put different pressures on each zone.
An ecological footprint is the area of productive land and water needed to supply what people use. It includes the area needed to absorb their waste, wherever it is. It is not the city's built-up area. A compact city may depend on a much bigger area elsewhere.
Cities concentrate waste. If materials are just thrown away instead of reused or recycled, new raw materials must be extracted. Sending waste outside the city moves the harm to others. Recovering materials can cut some demand, but needs working systems and buyers. Urban water use can also reduce supplies downstream, and food supply areas can lose habitats. A full assessment follows consumption and waste across city boundaries and asks which communities bear the costs.
- Urban zones
- Central city, suburbs and rural-urban fringe.
- Ecological footprint
- Land and water needed for consumption and waste.
- Displaced impacts
- Waste and pollution moved to other places.
Step by step
Find inputs
Water, food, energy and materials, and their sources.
Follow outputs
Waste, emissions and what could be recovered.
Look beyond the boundary
Effects on nearby and distant places.
Real examples to use
Urban heat island, Singapore
NUS researchers report that outdoor air in Singapore's built-up areas can be up to 7 degrees C hotter than in its green areas. Hard surfaces store heat, and air-conditioners pump waste heat outside. Hotter air then raises the demand for air-conditioning.
Worked example: A clean centre, a polluted edge
A city collects rubbish well and trucks it to an unlined dump outside its boundary. Streets are cleaner, but polluted liquid from the waste, called leachate, threatens nearby water. Residents there face smells and pests.
Watch out for this
A city's ecological footprint is the land its buildings cover.
It is the area needed to supply its consumption and absorb its waste, wherever that is.
Check your understanding
A city sends all its waste elsewhere and reports cleaner streets. What is missing?
- The effects on people and places where the waste goes.
- Nothing, because the city boundary ends its responsibility.
- Whether it has enough rubbish trucks for the trips.
Show the answer
The effects on people and places where the waste goes.
Yes. The harm has moved, not disappeared.