Time is running out for many developing countries like India to protect their growing cities from future environmental risks and resource scarcity, a report by an engineering and design consultancy, Atkins, showed on Wednesday.
Atkins, together with the University College of London's Development and Planning Unit and the UK government's Department for International Development, assessed the risks, vulnerabilities and capabilities of 129 cities in 20 countries.
It found that cities in developing countries are most at risk from climate hazards as populations grow and development is fast-paced, putting pressure on natural resources and energy.
More than half the world's population already lives in cities and this is expected to grow to 75% by 2050.
"Given that 95% of this urban expansion is projected to take place in the developing world, it is cities in developing countries which will be at the front line of managing this challenge," the report said.
"The earlier cities in developing countries take steps to future proof their urban development, the better. There is an important - but closing - window of opportunity for many cities to act now before they are locked into unsustainable and unsuitable development pathways."
Cities account for 60 to 80% of energy consumption and 75% of carbon emissions even though they only occupy 2% of the earth's land.
Natural hazards such as storms and flooding already have a devastating impact on cities, and that is only forecast to get worse as they increase due to climate change.
Last month, Hurricane Sandy hit the US East Coast, causing an estimated $71 billion damage in New York and New Jersey.
Environmental degradation has cost countries such as Pakistan, Nigeria and Ghana up to 10% of their gross domestic product, according to the report.
"Few cities have a low risk profile. These are often cities that are currently small but with significant growth prospects," it said.
Some of the world's largest cities such as Bangkok, Delhi, Jakarta and Mumbai have high energy use and the most environmental risks from flooding and cyclones, as well as threats to water and food and natural ecosystems.
Other cities need to focus on one risk area. Bangalore, for example, has a high energy and carbon footprint due to new high- rise glass facade developments, while Karachi faces water and food supply risks due to drought and the limited availability of agricultural land.
"Cities with the highest number of vulnerable people continue to remain in the largest cities in South Asia such as Kolkata, Mumbai, Karachi and Dhaka," the report said.
In those four cities, over 32 million people live in poverty which highlights the scale of the challenge.
To respond to risks, cities will have to work closely with national and regional government to strengthen their urban governance, planning, finance and services.
Policies which can reduce urban poverty and boost short-to- medium-term economic growth include improvements to walking and cycling infrastructure.
Policies such as urban agriculture, micro-generation, public transport information improvements and enhanced bus services are easy to implement and low cost.
However, much more financial assistance will be needed as many developing country cities are dependent on transfers from national governments and do not have projects which meet private sector investment criteria.
(Editing by Jason Neely)