A new study on ‘megacity metabolism’ has assessed how large metropolises around the world use resources such as water and energy and treat their waste, revealing those with the worst and best environmental impact.
Among the 27 metropolitan areas involved in the study with a population greater than 10 million, New York impressed researchers the least.
"The New York metropolis has 12 million fewer people than Tokyo, yet it uses more energy in total - the equivalent of one oil supertanker every 1.5 days," said Professor Chris Kennedy from the University of Toronto who led the research. "When I saw that, I thought it was just incredible."
Comparing New York and Tokyo was significant, as both cities lie within the temperate climate zone and have a wealthy population.
"Wealthy people consume more stuff and ultimately discard more stuff," said Kennedy. “The average New Yorker uses 24 times as much energy as a citizen of Kolkata [formerly Calcutta, the capital of the Indian state of West Bengal] and produces over 15 times as much solid waste."
Tokyo’s impressive performance is due to the city’s complex network of public transport and smart urban policies guiding the use of resources, the researchers concluded. As a result, the city is becoming more energy efficient despite the rising GDP and increasing population.
Tokyo has also managed to perfect its water-consumption efficiency by fixing leaky pipes across the city. Only three per cent of potable water is now being lost in the ground in Tokyo. By comparison, Brazilian megapolises Rio de Janiero and Sao Paolo lose up to 50 per cent of water through holes in the pipes, despite both cities struggling to secure enough potable water for its inhabitants.
London fared reasonably well in the comparison, being the only megacity which saw a reduction in its electricity consumption per head despite the rising GDP. The researchers believe that the UK’s rising electricity costs, as well as taxes on the disposal of solid waste, may have contributed to the positive situation.
The study found that megacities around the world, despite housing only 6.7 per cent of the world’s population, consume a disproportionate 9.3 per cent of global electricity and produce 12.6 per cent of global waste.
The environmental footprint of these settlements is likely to get worse as they continue to grow in size. In 1970, there were only eight megacities across the world with a population over 10 million. This number grew to 27 in 2010 and is expected to reach 37 by 2020. These urban areas currently generate 14.6 per cent of the globe's total GDP.
In the study, published in the journal Proceedings of the National Academy of Sciences, the researchers focused on various energy inputs and outputs including heating, transport, the use of electricity and disposal of solid waste and waste water.
They identified several strategies that could improve the overall sustainability of the megacities.
Moscow was praised for its centralised heating system, the largest in the world, which provides heat and power to buildings housing 12 million people. According to the researchers, such a system is more energy efficient than separate heating systems in every building.
Seoul impressed the researchers with its system for reclaiming used waste water for secondary uses, such as flushing toilets.
"What we're talking about are not short-term, one-election issues, but long-term policies on infrastructure that shape cities over years or decades," said Kennedy.
"The evidence is that megacities can make some progress in reducing overall resource use and I think that's encouraging."
While Kennedy and other researchers have studied resource use in big cities before, they have often been limited either by a small sample size or by a definition which did not include the entire metropolitan region. This new study is the first to capture detailed information from 27 megacities around the world.