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Flashcards · IB Diploma Programme Environmental Systems and Societies · Topic 8

Human populations and urban systems flashcards

17 cards on Topic 8, subtopics 8.1 to 8.3. Pick a subtopic or study them all.

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8.1 Human populations

How do you calculate the natural increase rate and doubling time?
NIR (%) = (CBR − CDR) ÷ 10, with CBR and CDR per 1,000. Doubling time ≈ 70 ÷ growth rate (%). Example: CBR 25, CDR 10 → NIR 1.5% → doubling time about 47 years. Assumes a constant rate and no migration.
What is the total fertility rate (TFR)?
The average number of children per woman over her lifetime at current rates. Replacement level ≈ 2.1. Unlike the crude birth rate, it does not depend on the age structure, so it is better for comparing countries.
How do you calculate the dependency ratio?
(people aged 0–14 + people aged 65+) ÷ people aged 15–64 × 100, giving dependants per 100 people of working age.
Describe stages 1–4 of the demographic transition model
1: high birth and death rates. 2: death rate falls fast (clean water, sanitation, vaccination); birth rate stays high. 3: birth rate falls (contraception, education of women, urban living). 4: both low.
Limitations of the demographic transition model
Based on European history; assumes birth rates will follow death rates down; ignores migration; gives no timescale; stage 5 was added later and is not explained by the original model.
Malthus versus Boserup
Malthus: population growth is limited by resources (food), leading to checks such as famine. Boserup: population pressure drives innovation that raises food production.
What is population momentum?
Continued growth after fertility falls to replacement level, because many young people are still entering child-bearing age.

8.2 Urban systems and urban planning

Urbanisation versus urban growth
Urbanisation: an increase in the proportion of people living in urban areas. Urban growth: an increase in the number. Both can happen together.
Why is a city described as an open system?
Food, water, energy, materials and people flow in; waste, pollutants, heat and goods flow out. It relies on land far beyond its boundary, so its ecological footprint is much larger than its area.
What causes an urban heat island?
Dark surfaces absorb and store heat; waste heat from vehicles, buildings and air conditioning; less vegetation, so less evapotranspiration; tall buildings trap heat and reduce wind. It is most marked at night.
Give push and pull factors in rural–urban migration
Push (rural): few jobs, low incomes, poor services, drought, land degradation, farm mechanisation. Pull (urban): jobs, wages, education, healthcare, perceived opportunity.
Name five features of sustainable urban planning
Compact mixed-use design; brownfield before greenfield; public transport and cycling; green roofs, parks and street trees; energy- and water-efficient buildings; waste separation and recycling.

8.3 Urban air pollution

Primary versus secondary pollutants
Primary: emitted directly from a source (CO, NOx, SO₂, particulates, VOCs). Secondary: formed by reactions between primary pollutants in the atmosphere (tropospheric ozone, PANs).
How does photochemical smog form?
Traffic emits NO and VOCs; NO oxidises to NO₂; sunlight splits NO₂ → NO + O, then O + O₂ → O₃; VOCs and nitrogen oxides form PANs and more ozone. Sunny, warm, still weather favours it.
What is a thermal inversion?
A layer of warm air above cooler surface air, which stops pollutants rising and dispersing, so smog is trapped near the ground.
Tropospheric versus stratospheric ozone
Tropospheric (ground-level) ozone is a harmful secondary pollutant. Stratospheric ozone absorbs UV and protects life.
Two strategies for urban air pollution and their limits
Low-emission zone (controls release): traffic may divert and it needs enforcement. Catalytic converters (control release): work only if fitted and maintained, and do not cut vehicle numbers. Congestion charge (alters activity): can fall hardest on lower-income drivers.

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