Investing in sustainable infrastructure and resource efficient technologies in cities offers a golden opportunity to deliver economic growth with lower rates of environmental degradation, according to a new report by the United Nations.

The study, City-Level Decoupling: Urban Resource Flows and the Governance of Infrastructure Transitions, produced by the International Resource Panel (IRP), which is hosted by the United Nations Environment Programme (UNEP), says sustainable development requires ‘decoupling’ city-based economic growth rates from the unsustainable consumption of finite natural resources.

The report says much greater effort is needed to support new and improved infrastructure for water, energy, transport, waste and other sectors - generally located in and around cities - to wean the world off unsustainable consumption patterns, and avoid serious economic and environmental implications for future generations.

Some 60 per cent of the built environment required to meet the needs of the world's urban population by 2050 still needs to be constructed.

The cost of meeting the urban infrastructure requirements of the world's cities between 2000 and 2030 is estimated at US$40 trillion - both through the building of new infrastructure (mainly in developing countries) or retrofitting existing facilities (mainly in developed nations).

There is a major opportunity, underlines the IRP report, to channel these funds into sustainable infrastructure that reduces carbon emissions, improves resource productivity, and avoids the resource-intensive urban planning of the past.

To date, the trend towards urbanization has been accompanied by increased pressure on the environment and growing numbers of urban poor," said UN Under-Secretary-General and UNEP Executive Director Achim Steiner at the launch of the report in Nairobi.

"But unique opportunities exist for cities to lead the greening of the global economy by increasing resource productivity and innovation, while achieving major financial savings and addressing environmental challenges. Although many cities are seizing such opportunities, a holistic vision for the urban centres of the future is still lacking."

Mark Swilling, one of the report's co-lead authors, said:

"When we look at the rising expenditures on urban infrastructure across the globe, we need to ask ourselves, what kind of cities of the future are envisaged by the designers and builders of these new infrastructures?"

"Are these infrastructures preparing cities for 21st century low-carbon transitions to fairer, more resource efficient futures? Or are they just fixing in concrete for the next 25 to 50 years 19th century urban planning modes and technologies that will need to be dismantled in 10 or 20 years from now?"

The report includes thirty case studies on effective efforts to reduce energy or water consumption or greenhouse gas emissions.

One such study is Singapore. Faced with a limited supply of natural resources, the city is implementing a national plan to reduce domestic water consumption by around 10 per cent by 2030. Advanced technologies are used to treat waste water (sewage) which is safe to drink and can be re-used by industry. Treated wastewater could meet 30 per cent of Singapore's water needs by 2030. Investments in desalination plants, repairs of leaking pipes and other efforts means the island state is on track to meet its 10 per cent goal.

Future urban projects aiming to achieve 'more with less' must be led by coherent visions for the city agreed by residents, businesses, governments, and other groups, which fully address poverty challenges and the need for greater equity, says the report.

'Ecosystem services' such as water from lakes, or flood prevention from wetlands play a critical role in supporting cities.

The report says maintaining healthy ecosystems, and factoring their economic value into urban development plans, will be key to achieving city-level decoupling. The city of Rio de Janeiro invested in reforestation to re-establish aquifers needed for water supply, while Johannesburg's urban forest of over 2.5 million trees in municipal areas supports biodiversity and better air quality.

The report outlines recommendations for city planners to minimize environmental damage and maximize the potential for using resources more sustainably.

• Government investments should support the role of cities in national sustainable development strategies, and support infrastructures that stimulate low carbon, resource-efficient and equitable urban development
• More investment is needed to support the capacity of city-level governments and universities to collect and analyze data on resource use and flows in cities as a basis for efforts to enhance sustainability
• Cities should set specific targets to use resources more efficiently, (eg. litres of water per unit of GDP, percentage of passenger trips by public transport) and formulate plans to achieve them
• For procurement activities, promote and use criteria favouring low-carbon, resource-efficient, green technology goods and services
• The private sector can play a key role in investing, and sharing expertise, to take small-scale sustainable infrastructure projects to a city-wide scale