8.2 Urban systems and urban planningIB Environmental Systems and Societies HL: Revision notes

An urban area is a built-up area with a high population density, buildings and infrastructure. It works as a system with inputs (people, food, water, energy) and outputs (waste, heat, pollutants). Urban areas contain urban ecosystems: parks, gardens, rivers and the organisms in them.

Urbanisation is the population shift from rural to urban areas, driven by rural-urban migration. The proportion of people living in urban areas is increasing: about 30% in 1950 and about 56% in 2020. Suburbanisation is movement from dense central areas to lower-density peripheral areas. When working with data, calculate the numbers from the percentages and total population (e.g. 130 million × 0.52 = 67.6 million).

Expansion causes habitat loss, more surface runoff from impermeable surfaces, the urban heat island, and higher energy use, waste and pollution.

Urban planning decides the best use of land and buildings. Modern planning may consider sustainability. Ecological urban planning treats the city as an ecosystem, looking at the complex relationships between biotic and abiotic components (e.g. tree planting that improves air quality, cools the city and supports biodiversity).

Ecological urban planning follows three principles:

• Urban compactness: dense development in a smaller area, shorter journeys, more efficient public transport, less land taken.
• Mixed land use: homes, workplaces, shops and services close together, reducing travel and emissions and keeping streets active.
• Social mix practice: people of different ethnic, income or age groups live in the same neighbourhoods, avoiding segregation and supporting social sustainability.

Example: Singapore: compact, mixed-use housing estates with ethnic mix quotas and large reserves of green space.

A linear economy extracts resources, makes, uses and discards. A circular economy keeps materials in use through reuse, repair and recycling, cutting waste and the use of new raw materials. Doughnut economics has a social foundation (basic needs for everyone) and an ecological ceiling (limits of Earth's systems); the aim is to live in the safe and just space between.

Example: Amsterdam adopted the doughnut in 2020 and aims to halve its use of new raw materials by 2030 and be fully circular by 2050.

Green architecture minimises the harmful effects of construction projects on human health and the environment, safeguarding air, water and earth. It chooses environmentally friendly materials (recycled, reused, locally sourced, low-toxicity) and construction practices, and designs for energy and water efficiency.

Example: Bosco Verticale in Milan, where trees and shrubs on balconies absorb carbon dioxide and particulates, give shade and provide habitat. Evaluate with costs, maintenance and embodied emissions.