Urban and suburban expansion converts natural or agricultural land into built environments, changing habitats, water flows, local climate, resource use and pollution. Suburban expansion often has a larger impact per person because low-density development requires more land, roads and private transport.
This is SL and HL core content in IB ESS subtopic 8.2 Urban systems and urban planning.
An urban area can be modelled as an open system. It receives energy, water, food and materials as inputs, while releasing wastewater, solid waste, atmospheric pollutants and heat as outputs. Expansion increases these flows and replaces permeable vegetation and soil with buildings and impermeable surfaces.
| Environmental change | Mechanism and consequence |
|---|---|
| Habitat loss and fragmentation | Clearance reduces habitat area, isolates populations and may lower biodiversity and resilience. |
| Altered hydrology | Concrete and asphalt reduce infiltration and groundwater recharge but increase run-off, erosion and flood risk. |
| Urban heat island | Dark surfaces absorb solar radiation; reduced vegetation decreases evaporative cooling; vehicles and buildings release waste heat. |
| Air and climate impacts | Construction, electricity use and transport emit air pollutants and greenhouse gases; car-dependent suburbs often increase emissions. |
| Resource use and waste | Expansion raises demand for water, energy, food and materials and outputs of sewage, solid waste, noise and light pollution. |
Impacts are also social. Lower-income communities may face greater exposure to pollution, flooding or limited green space, creating an environmental justice issue.
Compact planning, public transport, mixed land use and green infrastructure can reduce impacts. Curitiba, Brazil, is a named example where integrated public transport and planned development have helped limit dependence on private cars.
Exam technique: For an “explain” question, link each change to a mechanism and consequence rather than listing impacts. Use systems terminology and distinguish dense urban growth from suburban sprawl. Avoid the misconception that all expansion has identical effects: severity depends on density, planning, transport and management.
