How can you measure a city's sustainability? Here are three options

Index 1: how much lovely woodland does your city destroy each year? Image: Marianne Gagnon via Wikimedia Commons.

More than half of the world’s population lives in cities and that percentage continues to rise. That means cities are critical when it comes to preserving our natural resources. 

How green is your city? How does it match up to other cities? Is it making progress in becoming more sustainable?

We may be moving toward clearer answers to these questions. An exciting body of work is coming up with ways to measure the environmental impact of cities. Let’s look at three.

Land, energy, water

The ecological footprint measures how much land and water area a city requires to produce the resources it consumes and to absorb its wastes.

Ecological footprints are measured in global hectares (gha) per capital; the global average is around 2.6. The footprint of London stands at 4.5, slightly lower than the UK average of 4.6: more people in London use public transport than almost any other city in the UK, reducing the relative size of its footprint.

When the data are broken down by neighborhood, the biggest footprints are found in higher income areas where residents have larger homes and are more likely to have private cars. In San Francisco the value was calculated at 7.1 gha, while in Calgary, Canada, the value was 9.8 gha. Winters are cold in Calgary and most people use cars to get around.

Another measure is a city’s carbon footprint, which is the total amount of greenhouse gases it produces. The basic unit is kg or ton of CO2, and the global average is 1.2 metric tons per person.

One 2010 study measured the carbon footprint of 12 cities: Beijing, Jakarta, London, Los Angeles, Manila, Mexico City, New Delhi, New York, São Paulo, Seoul, Singapore and Tokyo. The number included direct emissions from the metropolitan area, as well as emissions produced in the metro area but consumed elsewhere, such as goods manufactured in cities.

A visualization of New York City’s daily carbon emissions with each bubble representing one ton of CO2.Image: Carbon Visuals.

Four of the cities have footprints smaller than the global average: Delhi, Manila, Sao Paulo and Beijing, in part because of relatively high usage of public transportation. London was close to the global average, while Los Angeles had by far the largest, followed by Singapore, New York and Mexico City.

Another study from 2009 measured the carbon footprint of the largest 100 metro areas in the US, and found the higher-density metro areas had the smallest footprint. An even more recent study of all US households found that those in suburban areas had a much higher footprint than those in the larger cities.

Finally, the water footprint of a city is a measure of all the freshwater used to produce all the goods and services consumed within it. This is a very difficult metric to compute because it includes the volume of freshwater consumed from surface water and ground water, the volume of rainwater consumed, and the volume of freshwater used to dilute the pollutants created by the production of all goods and services for the city.

Studies that assessed the footprint of Milan, Italy, and Lijiang City, China, showed how the increasing footprint was straining those cities' water supplies.

Imperfect measures – but they're a start

These metrics are still in the early stages of development. There are lots of problems, including assessing the leakage of impacts from outside the city’s boundaries; the quality of data, which is too often imprecise and collected at different times for other purposes; and the lack of comparability between studies. The work is more embryonic than definitive. For example, we have yet to agree upon standard protocols for the data used and methods employed.

While the three metrics have problems in estimation and calibration, they constitute a start. Even at this still rudimentary stage, they provide some startling findings. Notably, these initial studies show that larger cities have smaller carbon footprints than smaller cities. Higher density cities have lower carbon footprints, too.

With more than half of the world’s population living in cities, urban areas need to start measuring their ecological footprint. 

Singapore. Image: Getty.

As we transition into a more urban future, this could offer direction on effective city planning. Certain urban forms reduce the carbon footprint; these include more compact urban growth, more mass transit and greater use of cleaner, more sustainable energy supplies for buildings and transportation.

We need to refine these metrics, develop new ones and so create a standardised and easily understood index of city sustainability. Perhaps the protocols for developing a city sustainability index should be on the agenda at the United Nations Climate Change Conference to be held in Paris later this year.

With better data and a standard index, policies can be evaluated, targets set and institutions held to account. By comparing these metrics, planners and citizens can see how sustainability-related factors correlate to how livable cities are. And a robust city sustainability index would benchmark where we are now and provide a measure of progress in the future.

John Rennie Short is  a professor at the School of Public Policy, University of Maryland, Baltimore County.

This article was originally published on The Conversation. Read the original article.


Covid-19 is highlighting cities' unequal access to green space

In the UK, Londoners are most likely to rely on their local park for green space, and have the best access to parks. (Leon Neal/Getty Images)

As coronavirus lockdowns ease, people are flooding back to parks – but not everyone has easy access to green space in their city.

Statistics from Google show that park attendance in countries across the globe has shot up as people have been allowed to move around their cities again.

This is especially true in urban areas, where densely populated neighbourhoods limit the size of private green space – meaning residents have to go to the park to get in touch with nature. Readers from England can use our interactive tool below to find out how much green space people have access to in their area, and how it compares to the rest of the country.


Prime Minister Boris Johnson’s announcement Monday that people are allowed to mingle in parks and gardens with groups of up to six people was partially following what people were doing already.

Data from mobile phones show people have been returning to parks across the UK, and also across Europe, as weather improves and lockdown eases.

People have been returning to parks across the world

Stay-at-home requirements were eased in Italy on 4 May, which led to a flood of people returning to parks.

France eased restrictions on 1 May, and the UK eased up slightly on 13 May, allowing people to sit down in public places so long as they remain socially distanced.

Other countries have seen park attendance rise without major easing of lockdown – including Canada, Spain, and the US (although states there have individual rules and some have eased restrictions).

In some countries, people never really stopped going to parks.

Authorities in the Netherlands and Germany were not as strict as other countries about their citizens visiting local parks during lockdown, while Sweden has famously been avoiding placing many restrictions on people’s daily lives.

There is a growing body of evidence to suggest that access to green space has major benefits for public health.

A recent study by researchers at the University of Exeter found that spending time in the garden is linked to similar benefits for health and wellbeing as living in wealthy areas.

People with access to a private garden also had higher psychological wellbeing, and those with an outdoor space such as a yard were more likely to meet physical activity guidelines than those without access to outdoor space. 

Separate UK research has found that living with a regular view of a green space provides health benefits worth £300 per person per year.

Access is not shared equally, however, which has important implications for equality under lockdown, and the spread of disease.

Statistics from the UK show that one in eight households has no garden, making access to parks more important.

There is a geographic inequality here. Londoners, who have the least access to private gardens, are most likely to rely on their local park for green space, and have the best access to parks. 

However the high population in the capital means that on the whole, green space per person is lower – an issue for people living in densely populated cities everywhere.

There is also an occupational inequality.

Those on low pay – including in what are statistically classed as “semi-skilled” and “unskilled” manual occupations, casual workers and those who are unemployed – are almost three times as likely as those in managerial, administrative, professional occupations to be without a garden, meaning they rely more heavily on their local park.

Britain’s parks and fields are also at significant risk of development, according to new research by the Fields in Trust charity, which shows the number of people living further than a 10-minute walk from a public park rising by 5% over the next five years. That loss of green spaces is likely to impact disadvantaged communities the most, the researchers say.

This is borne out by looking at the parts of the country that have private gardens.

The least deprived areas have the largest gardens

Though the relationship is not crystal clear, it shows at the top end: Those living in the least deprived areas have the largest private green space.

Although the risk of catching coronavirus is lower outdoors, spending time in parks among other people is undoubtedly more risky when it comes to transmitting or catching the virus than spending time in your own outdoor space. 

Access to green space is therefore another example – along with the ability to work from home and death rates – of how the burden of the pandemic has not been equally shouldered by all.

Michael Goodier is a data reporter at New Statesman Media Group, and Josh Rayman is a graphics and data visualisation developer at New Statesman Media Group.