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Urban agriculture takes many forms. These can range from household, school and community gardens to rooftop and indoor farms. A fundamental distinction is often made between urban agriculture (involving food production in an urban area) and peri-urban agriculture, which occurs on the fringes of cities. In the case of the latter, farming is largely undertaken by professional farmers on land that has often already been used for farming for decades. An urban farm is a part of a local food system where food is cultivated and produced within an urban area, and marketed to consumers predominantly within that urban area. Besides growing fruit and vegetables, urban farming can also include animal husbandry, beekeeping, aquaculture, and non-food products such as producing seeds, cultivating seedlings, and growing flowers. It can be characterized in terms of the geographic proximity of a producer to the consumer, and sustainable production and distribution practices. Urban farms can take a variety of forms, including non-profit gardens and for-profit businesses. They can provide jobs, job training, and health education, and they can contribute to better nutrition and health for the community by providing locally grown, fresh produce (McEldowney 2017). This chapter focuses on commercial food production within urban areas and, specifically, on rooftop greenhouses and other types of indoor farms.
As towns and cities continue to grow both in population and surface area, their infrastructural needs for transporting and distributing food are constantly spreading, pushing food production further and further away from the urban consumer and generating globalized food systems that contribute to 19-29% of global greenhouse gas emissions (Vermeulen et al. 2012). Currently, the flow of food to cities follows a linear model, resulting in a high consumption of energy resources and the generation of waste and CO2 emissions. Over two-thirds of the global population are projected to be living in cities by 2050, and with some experts being sceptical about the capacity of the biosphere to produce enough food for the entire human population, interest in local production to contribute to sustainable urban food systems has re-emerged among decision-makers. Urban horticulture has historically always contributed to the supply of fresh produce to urban dwellers, but recently it has been gaining popularity in the Global North, with growing awareness of environmental and health concerns. Over the past few years, commercial farms have been emerging in major northern cities, promoting a trend of environmentally friendly local food, grown in highly efficient installations on top of or inside buildings. Urban agriculture also provides opportunities for a closed cycle of resources in the urban metabolism, in stark contrast to the traditional unidirectional flow. Figure 1 shows the role of urban agriculture in an ideal resource circulation system: the red arrows indicate the unidirectional flow of classic urban metabolism, while the green arrows indicate the closed cycle in the urban metabolism with urban agricultural production, whereby waste can be transformed into biogas, digestates and technogenic (manmade) soils which can then be used for further agricultural production, all within the city itself. These ideas will be explored in more detail later in this chapter.
Figure 1: The role of urban agriculture in an ideal resource circulation system (after Nehls et al. 2016)
Figure 2: Typologies of commercial indoor farms
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