Megacity growth and urbanisation challenges for QCE Geography Unit 4
“Explain the processes of urbanisation and megacity growth and the challenges they create for people and environments”
A megacity has over 10 million people. Megacities grow through rural-to-urban migration, high urban natural increase, and reclassification as urban areas expand. Rapid growth, especially in the global south, outpaces housing, services and infrastructure, producing informal settlements, congestion, water and sanitation stress, pollution and environmental hazard exposure. Lagos, Delhi, Jakarta and Dhaka show these challenges. Strong answers name a megacity, separate the growth processes, and link each process to specific people and environment challenges.
What this dot point is asking
QCAA wants you to explain how megacities grow and the challenges that growth creates. A megacity is an urban area with more than 10 million people. Urbanisation is the rising proportion of a population living in towns and cities. "Explain" means showing the processes (rural-urban migration, natural increase, reclassification) and then the challenges they produce for people and environments. This dot point sets up the Topic 2 investigation where you study one megacity in depth. Strong answers name a specific megacity, use real data, and link process to challenge.
The answer
Megacities and urbanisation
In 1950 only a couple of cities exceeded 10 million; by the 2020s there were more than thirty megacities, most in Asia and Africa. Urbanisation is the increasing share of people living in urban areas, distinct from urban growth (the absolute rise in city population). The fastest urbanisation is now in the global south, where cities are growing far faster than the European and North American cities did during their industrial era, and with far less time and resource to build infrastructure.
Process 1: rural-to-urban migration
The classic driver is migration from countryside to city, propelled by push factors (rural poverty, lack of land, mechanised agriculture, drought) and pull factors (jobs, services, education, the perception of opportunity). Lagos and Dhaka draw millions of rural migrants seeking work, often arriving faster than formal housing and jobs can absorb them.
Process 2: natural increase
Many megacity populations are young, with high birth rates, so the city grows from within through natural increase (births minus deaths) as well as from migration. In rapidly growing African and South Asian cities, internal natural increase now contributes as much growth as migration.
Process 3: reclassification and expansion
As cities sprawl, formerly rural settlements on the edge become absorbed into the urban area and reclassified as urban. This statistical and physical expansion adds to measured city population without new migration, and it consumes farmland and natural land cover on the fringe.
Challenges for people
Rapid growth outpaces the capacity to house and service people, producing:
- Informal settlements (slums). A large share of megacity residents in the global south live in informal housing without secure tenure, often built on hazard-prone land. Dharavi in Mumbai and the informal settlements of Lagos are large examples.
- Inadequate services. Water, sanitation, electricity, health and education struggle to keep pace, raising disease risk.
- Congestion and transport stress. Jakarta is notorious for severe traffic congestion that costs hours and billions in lost productivity.
- Inequality. Wealthy enclaves sit beside informal settlements, with sharp differences in access to services.
- Employment in the informal economy. Many migrants work in insecure, unregulated informal jobs.
Challenges for environments
- Water and sanitation. Demand outstrips supply; Jakarta's over-extraction of groundwater is causing the city to subside, with parts sinking and flooding.
- Air pollution. Delhi suffers among the world's worst air quality, driven by traffic, industry, construction and crop burning.
- Land cover loss. Sprawl converts farmland, wetland and bushland to built surfaces, increasing flood risk and heat.
- Waste. Solid waste and untreated sewage overwhelm systems.
- Hazard exposure. Informal settlements on floodplains, steep slopes and coasts expose poor residents to flooding and landslides, a vulnerability worsened by climate change. Dhaka faces severe flood and cyclone exposure.
Linking process to challenge
The analytical move is connecting growth process to challenge. Rapid in-migration plus natural increase (process) outstrips housing supply, producing informal settlements (challenge). Sprawl and reclassification (process) destroy fringe land cover and push settlement onto hazard-prone land (challenge). This sets up Topic 2, where you propose management action for one challenge in a chosen megacity.
Across the global south, a large share of urban residents live in informal settlements, and the United Nations projects that almost all future urban growth will occur in Africa and Asia. This is why megacity management is a central twenty-first century challenge and a core Unit 4 case-study theme.
A common Unit 4 task asks you to explain growth and its challenges. Work through it in steps.
Step 1: Define the terms
Distinguish urbanisation (rising share living in cities) from urban growth (absolute increase in numbers).
Step 2: Set out the three growth processes
Cover rural-to-urban migration, natural increase, and reclassification or expansion.
Step 3: Identify people challenges
Connect rapid growth to informal settlements, service gaps, congestion and inequality.
Step 4: Identify environment challenges
Connect growth to water stress, pollution, land cover loss and hazard exposure.
Step 5: Link process to challenge with a named city
Tie each challenge to its driving process at a named megacity (Jakarta subsidence, Delhi air quality).
- Confusing urbanisation with urban growth
- Urbanisation is the rising proportion living in cities; urban growth is the absolute increase in numbers. A country can have urban growth without rising urbanisation if rural areas grow too.
- Only mentioning migration
- Megacity growth comes from migration, natural increase AND reclassification. Naming all three lifts the response.
- Listing challenges with no place
- Name Lagos, Delhi, Jakarta or Dhaka and attach a specific challenge (Jakarta subsidence, Delhi air quality) with data.
- Treating slums as simply negative
- Informal settlements also house workers and host vibrant informal economies; nuanced answers note both the problems and the function.
Examples in context
Example 1. Lagos. Rapid rural-to-urban migration and high natural increase produce explosive growth, large informal settlements and severe infrastructure pressure.
Example 2. Jakarta. Over-extraction of groundwater for a megacity population causes land subsidence and worsening coastal flooding, prompting plans to relocate the capital.
Example 3. Delhi. Traffic, industry, construction and surrounding crop burning combine to give the megacity some of the world's most hazardous air quality, a direct people-and-environment challenge of rapid growth.
Exam-style questions
Questions in the style of QCAA exam questions on this dot point, each with a worked answer. They are written by ExamExplained unless tagged "Past paper"; the year shows the paper a question is modelled on.
Practice6 marksUse the stimulus on a developing-world megacity to explain two processes driving its growth and link each process to a challenge it creates.Show worked answer →
A QCAA Paper 2 data-response is marked for the correct processes, the process-to-challenge link, and use of the stimulus.
Process 1. Explain rural-to-urban migration (push and pull factors) and link it to the challenge of informal settlements that outpace formal housing.
Process 2. Explain high urban natural increase and link it to the challenge of overstretched water, sanitation and education services.
Markers reward two distinct processes, each tied to a specific challenge, using stimulus evidence.
Practice7 marksAnalyse the challenges that rapid megacity growth creates for people and environments. Support your response with evidence from a named megacity.Show worked answer →
A QCAA Paper 2 extended response analysing challenges.
- People challenges
- Informal settlements, inadequate services, congestion (Jakarta traffic) and inequality.
- Environment challenges
- Water stress and subsidence (Jakarta groundwater), air pollution (Delhi), land cover loss and hazard exposure (Dhaka flooding).
- Link to process
- Connect each challenge to the growth process driving it. Markers reward named-city evidence and an explicit process-to-challenge link.