Why green cities?

Worldwide, cities are growing rapidly. Not only because the world population is rising, but there is also an increase in the urbanisation of the population. According to the United Nations, around 50% of the world population is now urban, with 60% expected to be urban by 2030. Growing cities place increasing pressure on the natural environment, and there is increasing pressure within cities and their suburbs to provide the houses, services, space, and quality-of-life that residents expect.

Development pressures extend to peri-urban areas where agriculturally productive lands and natural vegetation are often found. But the pressures of urban development do not end there. They extend to the places from where we obtain energy, water, food, and construction materials, where we recreate, and where we discard waste. In this way, the impact of cities on the environment is global.

Growth in population and affluence increases resource consumption. To this end, fuels, foods, minerals and fibres are transported around the globe. But there are limits to growth. New lands for cultivation are only available at the expense of natural areas, the waste we expel is changing the environment, and the fuels we rely on today, oil, gas, and coal, are limited in their supply.

Cities are changing to accommodate more people. They are also changing to accommodate an understanding of development pressures, the scarcity of resources, and the importance of conserving the natural environment. A diverse set of knowledges and skills are required to continue these changes and create truly green cities. BioCity@UniSA research includes urban and regional planning, biodiversity, engineering, spatial sciences, construction and surveying, and earth sciences, to plan and build green cities.

Creating green cities

Cities can create rather than consume. For example, electricity can be produced using photo-voltaic (PV) solar cells, wind turbines, and geothermal processes. According to South Australia’s Strategic Plan, South Australia already has the capability to produce over half of Australia’s wind-generated electricity, and almost all of its geothermally produced electricity. Other strategies for changing the energy balance, from consumption to production, include using solar hot water, biomass energy, passive solar design, and carbon offset schemes. The use of all resources in cities can be rationalised through reduction, reuse, and recycling.

The improvement of transport systems is integral to the creation of green cities. Modern, post-industrial cities are dominated by car transport, causing problems including excessive energy use and pollution. Importantly, the layout of cities largely determines people’s transportation choices. Green cities, through Transit-Oriented Design (TOD), can encourage the use of public transport, cycling, and walking. For example, urban planning can ensure access to services and facilities within a reasonable distance. Therefore, consolidated, mixed use areas function best, where housing is interspersed with the commercial, administrative, health, and educational facilities.

Urban consolidation reduces the way in which cities encroach on natural and productive lands. Ideally, high-density areas are located around transport nodes, such as train stations, allowing lower-density areas to be developed between them. Low density areas can include areas for food production, water management, corridors for transport between urban agglomerations, and parks and corridors for biodiversity and recreation.

Most urban planning research supports the argument for high-density cities. In such cities it is more cost and resource efficient to provide infrastructure such as water, sewage, and energy, transport for people and goods, and there are more opportunities for social interaction. Biocity@UniSA researchers are focussing on the complex relationships between housing densities, transportation, energy consumption, housing affordability, and urban biodiversity

Green buildings

Building performance can be assessed in economic, social, and environmental terms. Economic performance includes initial cost of construction, plus ongoing costs that affect profitability. Social performance includes the comfort and satisfaction of occupants. Environmental performance includes energy and water consumption, as well as physical integration with the natural environment. While energy efficiency has long been understood as an issue in building design, it has only been mandated through the Building Code of Australia as recently as 2003 for residential buildings. However, this revision has provided only a minimum standard for new houses.

The Green Star System, introduced for non-residential buildings by the Green Building Council of Australia, allows further assessment of a building’s materials, construction management and techniques, and ongoing energy, water, transport, and management efficiency. The system has a maximum attainable score of six stars for a building that leads the world in green construction and performance. An important component of a building’s energy consumption is embodied energy, which includes the energy used to produce the building, including materials, transport, and management costs. Adelaide has a number of good examples of highly-rated Green Star buildings, including the 5-star City Central Tower 1. A major challenge for the future is to refit existing buildings to improve their performance and contribute to the development of green cities.

Sustainable materials and infrastructure

Green cities require efficient design and use of materials in housing and commercial buildings, and in the infrastructure for water and electricity supply, waste disposal, and transport systems. There are a number of approaches: building water and energy efficiency into the design of new structures, and retrofitting existing structures to improve their efficiency or capacity. Increasing the capacity of existing structures can reduce the need for additional structures, thereby avoiding additional environmental disturbance. Researchers at BioCity@UniSA are currently focussed on the embodied energy of residential developments, Water Sensitive Urban Design (WSUD), cold-form steel frame construction techniques, transmission towers for communications and electricity transmission, recycled pavement materials, and how trees impact on built structures.

Trees are an important component of urban design, increasing both biodiversity and people’s satisfaction with urban areas. As they remove soil moisture through evapotranspiration, their impact on infrastructure can be positive or negative, depending on whether water is scarce or overabundant. Soil movement, arising from fluctuation in soil moisture levels, can cause damage to footings, pavements, roads, and rail infrastructure. Therefore, the suitability of trees is site specific and should consider the natural and built environments.

Innovative cities

Cities must innovate in order to become green. A good example of innovative urban design in Adelaide is Christies Walk. This development uses roof and wall gardens containing an edible landscape, minimising the intensity of runoff, insulating buildings from both heat and noise, and providing habitat for urban biodiversity. A larger-scale roof garden has been created at the Ford Rouge River Plant in Dearborn, Michigan. These two developments demonstrate the advantages of integrating the natural and built environments.

We are learning from nature, and there are many lessons to be learnt. For example, how do termites build solar-oriented cooling towers to regulate their nest temperature, and how does the form and physiology of drought-resistant trees conserve water? Biomimicry explores the use of natural products and processes in human endeavour. By integrating nature into the city we receive many environmental, psychological and physiological benefits. How much life can we incorporate into built environments?