The big idea: Urban environmental stress is the damage that city growth and city living do to the local environment — to the air, the climate, the water, the land and the green space around people.
As cities grow quickly, more people, traffic, buildings and waste crowd into a small area. This concentrates pressure on the environment, creating problems like the urban heat island, air pollution, water pollution and loss of green space.
This micro is about the environmental stresses; the social stresses (deprivation, inequality) are the next micro (13.3.2).
Key terms for urban environmental stress
- Urban heat island (UHI) — a city being warmer than the rural land around it, especially at night.
- Urban microclimate — the city's own local climate: its temperature, wind and rainfall, changed by buildings and activity.
- Albedo — how much sunlight a surface reflects. Dark concrete and tarmac have low albedo, so they absorb and store heat.
- Air pollution — harmful gases and particles (from traffic and industry) building up in city air.
- Green space — parks, gardens, trees and verges that cool the city, clean the air and store water.
- Rapid urban growth — fast population and built-up growth that outpaces planning and services.
Stress = a pressure on the environment: Every environmental stress has a cause (what city living does) and an effect (the damage).
Exam answers almost always want the chain: more traffic and concrete -> warmer, dirtier air -> harm to people and nature. Name the link, don't just name the problem.
How this is tested: Paper 1 Option G opens with a data-response that makes you read a figure — a transect of temperatures, a graph of remaining green space, or a city map. You State or Identify a value, then a short Outline [2] asks why a city is warmer than the countryside, or how a design change alters the microclimate.
Always quote the figure (a temperature, a percentage, a grid square) — never just describe in words.
| Point along transect | Land use | Air temperature (degC) |
|---|---|---|
| 1 (rural edge) | Farmland and woodland | 18 |
| 2 (suburbs) | Low-density housing + gardens | 20 |
| 3 (inner city) | Dense terraces + main roads | 23 |
| 4 (city centre / CBD) | High-rise concrete + offices | 26 |
| 5 (inner city) | Dense terraces + main roads | 23 |
| 6 (suburbs) | Low-density housing + parks | 20 |
| 7 (rural edge) | Farmland and woodland | 18 |
Reading a heat-island transect: A transect crosses the city from one rural edge to the other. The temperature is lowest at the rural edges and peaks in the dense, concrete city centre — that dome of warm air is the urban heat island. Read the centre value and a rural value and find the difference.
| Cause | How it warms the city |
|---|---|
| Concrete + tarmac (low albedo) | Dark surfaces absorb sunlight by day and release stored heat slowly at night |
| Tall buildings | Trap heat in 'street canyons' and cut the cooling wind |
| Less vegetation | Fewer plants means less shade and less cooling from evaporation |
| Waste heat | Cars, factories, air conditioning and people all give off heat |
| Air pollution | A dome of pollution traps outgoing heat over the city |
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The biggest environmental stresses come from traffic and industry (which pollute the air and warm the microclimate) and from building over green space (which removes the city's natural cooling and water store). Real cities show both the stress and the response.
How human activity changes the urban microclimate
- Hard surfaces — concrete and tarmac replace soil and plants, lowering albedo and raising temperatures.
- Vehicle and factory emissions — exhaust fumes add particles and gases that thicken the pollution dome and trap heat.
- Tall buildings — channel wind into gusty street canyons and block the breeze that would cool the city.
- Waste heat — engines, factories and air conditioning pump heat straight into the city air.
Beijing and London — air pollution: Beijing suffers heavy smog from traffic, coal heating and industry; on bad days fine-particle (PM2.5) levels soar far above safe limits, harming health. The city responded with factory relocation, coal-to-gas switching and traffic limits.
London charges drivers to enter its Ultra Low Emission Zone (ULEZ), pushing out the dirtiest vehicles. Roadside nitrogen-dioxide levels fell sharply in the central zone — though traffic and pollution simply shifted to some edges.
Barcelona and Curitiba — traffic and green space: Barcelona's 'superblocks' group nine blocks together and close the inner streets to through-traffic, turning road space into squares and greenery. This cuts emissions and noise, lowers temperatures and adds green space — though some traffic is just displaced to the edges.
Curitiba (Brazil) built a fast Bus Rapid Transit network and protected parkland, so far fewer people drive and the city floods less — green space doing real environmental work.
How this is tested - the [10] Examine essay: Paper 1 Option G ends with a 10-mark Examine / Evaluate essay, marked on markbands. The recurring versions are: how human activity changes urban microclimates and air pollution, and how far strategies have actually reduced air pollution or traffic congestion in named cities.
Top band needs: accurate terms, two or more strategies/factors developed with a named city and data, a weighing of how successful each is (and for whom), and a clear judgement.
Strategies to reduce urban environmental stress
- Clean-air / low-emission zones — charge or ban dirty vehicles (London ULEZ).
- Public transport + cycling — Bus Rapid Transit and bike lanes cut car use (Curitiba).
- Traffic-free design — superblocks and pedestrian zones cut emissions and add greenery (Barcelona).
- Green infrastructure — parks, street trees and green roofs cool the city and clean the air (Singapore).
- Cleaner energy + industry — coal-to-gas switching and moving factories out of the centre (Beijing).