People and the environment: how they interact
A human process is something people do: build houses, lay roads, run factories. A physical process is something nature does: rain, rivers, soil forming, plants growing.
In a city these two meet all the time:
- Concrete stops rain soaking in, so more water runs off and rivers flood faster.
- Cutting trees makes streets hotter (the urban heat island).
- Smoke from cars and factories makes the air dirty, which harms people's health.
Sustainable means we use things in a way that can go on for a long time without harming people later.
Water and energy saving
Saving water
- Rainwater harvesting: collect rain from roofs in tanks or let it soak into the ground.
- Grey water: reuse water from sinks and showers to flush toilets or water gardens.
- Low-flow taps, dual-flush toilets and water meters (people use less when they pay for what they use).
- Fix leaking pipes: many cities lose a large share of clean water through leaks.
Saving energy
- Renewable energy: solar panels, wind turbines.
- Insulation in walls and roofs, double-glazed windows, LED lights.
- Rules for new buildings so they use less energy.
Green space and waste
Green space
Parks, trees, green roofs and river paths cool the city, soak up rain, clean the air, give homes to wildlife and help people relax and exercise.
Waste
The waste hierarchy puts the best choices first:
- Reduce (make less waste)
- Reuse
- Recycle
- Recover energy (burn to make electricity)
- Landfill (last choice)
Sorting at home (food waste, dry recyclables, the rest) makes recycling and composting much easier.
Traffic management
Too many cars cause congestion (traffic jams), air pollution, noise and accidents. Cities use:
- Public transport: buses, trams, metro trains. One bus can replace dozens of cars.
- Bus lanes and park-and-ride (park outside the city, ride a bus in).
- Cycle lanes and bike-share schemes, safe footpaths.
- Congestion charge: pay a fee to drive into the busy centre (London, Singapore, Stockholm).
- Smart traffic lights and low-emission zones.
Try it: audit your street
Walk around your home or school for 10 minutes. Make a tally: rain tanks, solar panels, trees, recycling bins, buses and cars that pass in 5 minutes. Give each of the five taps (WEGWT) a score from 0 to 2. Then move the sliders in the 3D city to see which change helps most.
Key formulas and definitions
- Sustainable development: meeting today's needs without harming the ability of future people to meet theirs
- Rainwater (mΒ³) β roof area (mΒ²) Γ yearly rain (m) Γ collection share
- Waste hierarchy: reduce β reuse β recycle β recover β landfill
- Congestion: more vehicles than a road can carry, so traffic slows
- Urban heat island: a city is warmer than the countryside around it
- Green infrastructure: parks, trees, green roofs and rivers that do useful work in a city
Worked examples
1. A school roof is 200 mΒ². The town gets 0.9 m of rain a year and the tank catches 80% of it. How much water is collected?
Water = 200 Γ 0.9 Γ 0.8 = 144 mΒ³ a year. That is 144,000 litres, enough to flush toilets for months.
2. 60 people travel to work. Each car carries 1.2 people on average. How many cars are needed, and how many buses of 60 seats?
Cars = 60 Γ· 1.2 = 50 cars. Buses = 60 Γ· 60 = 1 bus. One bus takes 50 cars off the road.
3. A city wants to reduce flooding after heavy rain. Give two sustainable ideas and say why they work.
1) Green roofs and parks: plants and soil soak up rain, so less runs into drains. 2) Permeable pavements: water seeps through into the ground instead of flowing straight to the river.
Common mistakes
- Thinking recycling is the best choice. Reducing and reusing come first in the waste hierarchy.
- Thinking sustainable means only 'green'. It must also be fair to people and affordable.
- Saying a new road always cures traffic. New roads often attract even more cars.
- Forgetting that physical processes (rain, rivers) and human actions affect each other in a city.