In the particular historical moment, we are experiencing, due to the recent COVID-19 epidemic, which has brought to light the vulnerability of our supply-chain and the inadequacy of our consumption habits, shortening the supply chain of agri-food products would be very necessary for the creation of more resilient local communities.

A recent study by the University of Sheffield has outlined a possible scenario; it calculates how much fruit and vegetables the town would produce from the conversion of its urban greenery.

Sheffield has a green area of 10,600 hectares, equal to 45% of its total extension. Part of this is already devoted to allotments, while the rest, consisting of 40% private gardens and 15% parks and street greenery, according to the study of British researchers could be used for the cultivation of food.

If Sheffield were to choose to cultivate all this available land - i.e. all the gardens, parks and roadside greenery - there would be enough space to devote 98 square metres of land per resident to the daily production of fruit and vegetables. To understand the scale, consider that the UK's agri-food sector currently has a per capita area ratio of 23 square metres, which still covers the country's fruit and vegetable needs. This means that the conversion of all of Sheffield's potentially suitable green areas would be enough to feed 709,000 people, well over 518,000 of the city's population.

However, it is unrealistic to think of turning all the private gardens into vegetable gardens, as well as depriving the city of public parks. For this reason, researchers in Sheffield have also developed a more conservative estimate that, considering the conversion of only 10% of the suitable areas, would produce enough fruit and vegetables to cover the needs of 87,375 people.

The study, recently published in Nature Food, also highlighted the availability of areas suitable for cultivation on the roofs of Sheffield. They are about 32 hectares, which could host greenhouses with thermo-hygrometric conditions to grow high-density, such as tomatoes, currently almost entirely imported from other countries.

Considering that only 16% of fruit and 53% of vegetables in the UK are grown locally, the role that cities can play in making food supply more sustainable becomes even more evident. The case of Sheffield can be extended to the whole country, as it is representative of all urban areas in the UK in terms of the green area that can be grown.

By projecting the results of this study to other cities, considering the presence of buildings potentially suitable for hydroponics, the principle of fruit and vegetable producing cities takes on global validity.