An urban ecosystem is an urban area understood as a system in which human, built, and natural components interact. In IB ESS subtopic 8.2, this concept applies at both SL and HL.
An urban ecosystem includes biotic components, such as humans, animals, plants, and microorganisms, and abiotic components, such as air, water, soil, climate, roads, and buildings. Human institutions, technologies, economic activity, and infrastructure influence interactions between these components.
Urban ecosystems are open systems because energy and matter cross their boundaries. A city imports food, water, fuel, electricity, building materials, and manufactured goods. It exports solid waste, wastewater, air pollutants, greenhouse gases, and heat.
| System feature | Urban example |
|---|---|
| Inputs | Food, water, energy, materials, migrants |
| Storages | Buildings, reservoirs, soil, vegetation, human population |
| Flows | Transport, water distribution, energy transfer, migration |
| Outputs | Waste, sewage, atmospheric emissions, manufactured products |
| Transformations | Fuel combustion, food consumption, waste treatment |
Urban ecosystems also contain feedback mechanisms. For example, replacing vegetation with concrete increases heat absorption, contributing to the urban heat island effect. Greater demand for air conditioning may then increase electricity consumption and waste heat, amplifying warming through positive feedback.
Curitiba, Brazil, shows how urban planning can alter these flows. Its bus rapid transit system and extensive green spaces have aimed to reduce car dependence, manage flooding, and improve access to services. However, benefits may not be distributed equally, so environmental justice requires consideration of which communities receive green space, clean air, transport, and protection from hazards.
A common misconception is that an urban ecosystem means only wildlife living in a city. It includes the entire socio-ecological system, particularly people, infrastructure, institutions, and their interactions with natural processes.
Exam technique: For an ESS response, define the city as an open system, then identify specific inputs, storages, flows, transformations, and outputs. For higher-mark questions, connect these to sustainability, stakeholder perspectives, environmental justice, and a named urban example.
