Worldwide, urban food producers are growing on an area the size of the European Union, according to the first comprehensive study on urban agriculture. The research, undertaken by the International Water Management Institute (IWMI), revealed that urban growing exists on a much larger scale than previously thought.

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The study's authors said the fact that urban agriculture already occupies 456 million hectares and is growing in line with population shifts towards towns and cities challenges the suitability of most agricultural research and development work, which is oriented to production in rural settings.

Most of the land under cultivation is on the edge of towns and cities, though 67 million hectares in urban centres also produce food. The researchers believe they may even have underestimated the extent of urban croplands worldwide, as they only looked at areas of 50,000 people or more, when in some countries smaller towns are also considered 'urban'.

Study co-author Pay Drechsel commented, "This is the first study to document the global scale of food production in and around urban settings, and it is surprising to see how much the table is definitely getting closer and closer to the farm."

Dr Dreschel continued, "We see this dichotomy where urban farming in wealthy countries is praised for reducing various footprints and enhancing a green economy, while in developing countries it is usually regarded as an inconvenient vestige of rural life that stands in the way of modernization. That's an attitude that needs to change."

Urban farms provide nutrition and efficiency, but need support

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As well as assessing the extent of urban agriculture, Dr Dreschel and co looked at resource use and differences in production between urban and rural farming. They found that urban farms typically produce more nutritious, higher value fruits and vegetables, rather than the more calorie-rich cereals grown in rural regions and that cropping intensity was higher in urban spaces.

However, their research also revealed that in drier regions, though they have great potential for better water use, urban farms are in some cases being fed with contaminated water. Dreschel said that, though urban farmers in Sub-Saharan Africa supply up to 90 percent of the leafy salad greens consumed in the region's rapidly growing cities, issues with water quality could lead to serious public health concerns.

He elaborated, "In urban areas of Ghana, everyday there are about 2,000 urban vegetable farmers supplying greens to 800,000 people. [However], most of these farmers irrigate their fields with highly polluted water. In Accra, for example, up to 10 percent of household wastewater is indirectly recycled by urban vegetable farms. These farms are now 'recycling' more wastewater than local treatment plants."

Even so, Dr Drechsel and his colleagues found that urban agriculture, in addition to contributing to food security, puts marginal lands into productive use, assists in flood control, increases income opportunities for the poor and strengthens urban biodiversity.

Though the researchers feel confident that urban agriculture is supporting meaningful food security, by providing nutritious food where people need it, they said more research is needed to look at water use issues in particular. Though urban growing has the potential for better water use, there are still concerns that, without support or infrastructure, these farms could come into conflict with other urban water needs and issues of water quality could persist in some areas.

The researchers said it is their hope that "Better understanding [of] the extent and characteristics of urban crop production… should support better decisions on urban policy and planning."

Their study can be read here