Commercial farming within the urban built environment – Taking stock of an evolving field in northern countries
Introduction
Global population is projected to reach almost 10 billion by 2050, resulting in a higher demand for food by around 50% compared to 2013 – in a scenario of moderate economic growth; at the same time, income growth in low- and middle-income countries is expected to hasten a dietary transition towards higher consumption of meat, fruits and vegetables, requiring changes in agricultural output and intensifying pressure on natural resources (FAO, 2017). However, while an acceleration in productivity growth is needed, it is also hampered by the fast degradation of natural resources caused by agricultural practices, that have already led to massive land use change in order to meet demand for food, which in turn has amplified the environmental effects.
Agriculture and climate change are interconnected: the former not only contributes to the latter, but is also affected by its manifestations. The effects of agriculture on climate change have been largely demonstrated, mainly through GHG emissions, depletion of underground aquifers, and impacts of tillage, fertilizers and pesticides on soil, air and water quality, and on biodiversity (Clark and Tilman, 2017). Furthermore, the use of fossil fuels, jointly with land degradation such as desertification and deforestation, are the major anthropogenic sources of carbon emissions worldwide (IPCC, 2013). At the same time, rising carbon levels and the effects of global warming on temperatures and precipitations are projected to have impacts on crop yields (Zhang and Cai, 2011). In spite of the uncertainty in defining its net impact on the food system, it is likely that climate change will affect the suitable land area for crops, leading to significant socio-economic costs (Stevanovic et al., 2016).
In a context of climate change and increasing urbanization – over two-thirds of global population are projected to be living in cities by 2050 (United Nations, 2014), while some experts are skeptical about the capacity of the biosphere to produce enough food for the entire human population (Gilland, 2006), interest for local production to contribute to sustainable urban food systems has re-emerged among decision-makers (Baker and de Zeeuw, 2015), and the practice of urban agriculture as a food, income and employment generator is likely to expand (Caputo, 2012). Today, urban cultivation has been widely recognized not only to enhance food security by shortening and thus improving the resilience of food supply chains, but also to provide economic development opportunities, enhance urban public health (Brown and Jameton, 2000), and contribute to mitigate environmental impacts of the food system by reducing food losses and wastage and cutting transportation distances (Benis and Ferrao, 2016).
However, in spite of the growing awareness of its significant benefits for the environment and for communities, urban agriculture has been largely absent in urban planning strategies and policies (Pothukuchi and Kaufman, 2000, Steel, 2008) until very recently, and establishing its viability as compared to conventional agricultural practices is a challenge when it comes to land accessibility, scalability, resource efficiency, and cost-effectiveness. Over the past decade, hundreds of cities, both in the Global North and South, have developed policies and programs on urban food security, nutrition, and urban agriculture (Baker and de Zeeuw, 2015). At the same time, there has been large debate about defining sustainable cities and urban forms that alleviate pressure on natural resources. Some planners defend that “rurban” areas like the Oosterworld in the Dutch city of Almere, which combine housing and farming, can provide great sustainability (Jansma et al., 2014). Others advocate the concept of “green urbanism”, which promotes compact resource-efficient urban development with mixed land uses, as a way of preserving agricultural land (Lehmann, 2010).
Whereas livestock, cereals and oilseeds require large areas of land, horticultural crops offer high yields in small areas and can thus be easily grown in urban gardens, backyards, vacant lots, rooftops or even indoors. Worldwide, a study has shown that urban agriculture would require around one third of the total global urban area to meet the global vegetable consumption of urban dwellers (Martellozzo et al., 2014). Other researchers have measured the potential of large North American and European cities for self-reliance in food if they were to use only their currently vacant urban space, estimating that 77–100% of urban vegetable demand can be met, depending on available areas and farming methods to be implemented, which would lead to different yields (Grewal and Grewal, 2012, Haberman et al., 2014, Orsini et al., 2014, Saha and Eckelman, 2017). Such proposals include large-scale implementation of high-yield urban horticultural production within the built environment. One of the commonly used concepts in the literature of such practices, Building-Integrated Agriculture (BIA), was coined in 2007 (Caplow and Nelkin, 2007) and consists of adapting soilless cultivation techniques such as hydroponics or aquaponics, for use on top of or in buildings in a way that exploits synergies between the buildings and the agricultural activities. On-site production through urban BIA cuts transportation distances and avoids land use change while creating urban jobs. Furthermore, when involving Controlled-Environment Agriculture (CEA), advantages of BIA include year-round production, higher yields, enhanced water use efficiency (Gould and Caplow, 2012) and improved building energy efficiency through the creation of symbiotic relations between the farm and its host building (Nadal et al., 2017). BIA systems can be applied: (i) on the building envelope, i.e., on the rooftop or facades, to take advantage of the availability of natural light; or (ii) indoors, in a fully controlled environment. In the literature, the term Zero-acreage Farming (ZFarming) can also be found, describing all types of urban agriculture characterized by the non-use of farmland or open spaces, and rather using otherwise unused spaces in the urban built environment (Specht et al., 2014). In this category, authors usually also include low-tech alternatives such as rooftop open-air on-soil farming.
Fig. 1 shows examples of different forms of farming systems that are currently sprouting within the built environment of major cities worldwide.
Among existing forms of envelope-integrated systems, rooftop farming is the most popular since rooftops represent large unutilized solar exposed urban areas. Rooftop farming is either practiced on intensive green roofs, or in Rooftop Greenhouses (RG) equipped with hydroponic equipment. In the latter, state-of-the-art installations generally include recirculating water systems, waste heat captured from the building's HVAC system, local renewable energy production such as solar PV, rainwater harvesting systems and evaporative cooling (Gould and Caplow, 2012). A few North American and European companies have already proven that significant amounts of local food can be produced year-round for urban dwellers on unutilized rooftops in dense cities where affordable land is rare.
For facades, Vertically-Integrated Greenhouses (VIG) have been developed as a concept and patented (Adams and Caplow, 2012). VIG systems consist of double skin building facades combined with hydroponic systems. However, to the best of our knowledge, there is currently no existing significant example.
Vertical Farming (VF) is another form of high-yield urban food production that consists of raising crops in controlled environments and using soilless cultivation methods, in multistory buildings within the urban context. Some scientists defend the legitimacy of VF for environmental reasons, arguing that plant cultivation inside the buildings involves less embodied energy and releases less pollution than some agricultural practices on natural landscapes, in addition to the fact that periurban lands are often too toxic for agricultural production (Despommier, 2010). These intensive closed growing systems – using skyscrapers to grow food – are also called Skyfarms (Germer et al., 2011), or Plant Factories (PF) (Kozai, 2013).
Another emerging trend in the field of commercial urban farming are modules that can be operated within the built environment, such as outfitted and insulated Shipping Containers (SC). Equipped with state-of-the-art climate control technology and hydroponic growing equipment, SC farms allow for year-round production and can be installed in vacant lots, warehouses, basements or rooftops. Advantages of shipping containers include their compactness and modularity, large availability, low cost, and ease of shipping.
Section snippets
Methods
Today, approaches of farming the urban built environment as a viable solution to feed cities are gaining momentum among some of those who believe that current sustainable farming methods will not be sufficient or the most effective method to meet the demand for food of a growing urban global population. At the same time, although intensive urban farming is a nascent area, numerous research questions are already emerging around it, from uncertainties about its environmental and economic
Food miles vs. resource intensity
Located within the city and therefore closer to the consumer, high-yield urban agriculture has been claimed by several authors to have a lower carbon footprint than its counterpart rural food production, by cutting transportation distances – “food miles” (Cerón-Palma et al., 2012; Specht et al., 2014). However, depending on local climate conditions and farm typologies, crop production in controlled environments can also be highly energy-intensive, which can considerably exacerbate its
A deferred revolution
On the one hand, the technology behind high-yield indoor farming – controlled-environment soilless culture – has been around for almost eighty years. In 1940, William Frederick Gericke, a professor at the University of California Berkeley, coined the term “hydroponics”, a plant cultivation method where, instead of using nutrients to improve soil quality, the researcher wanted farmers to replace their fields with the indoor soilless system that he had developed throughout years of testing
Beyond food production: community building
Social impacts of conventional on-soil urban horticulture on vacant plots or in open-air rooftop gardens have been widely investigated (Proksch, 2011, Eigenbrod and Gruda, 2015), and were shown to include a large set of benefits to local communities. In addition to providing access to fresh and nutritious food, urban horticulture involves volunteer and social works, youth educational programs and job trainings, stimulating the creation of powerful community ties and giving urbanites the chance
Conclusions
Rather than spreading out across hectares of land, the farms of tomorrow might grow food within climate-controlled, artificially-lit urban facilities, using less land, less water, yet producing year-round fresh, colorful and tasty vegetables anywhere in the world. This would allow our growing urban areas to provide food to their residents while mitigating desertification and deforestation, whereas commercial farming industry would offer urban jobs, contributing to offset the unemployment
Acknowledgments
Generous support for this work has been provided by FCT (Portuguese Science and Technology Foundation), under the MIT Portugal Program in Sustainable Energy Systems, through the doctoral degree grant SFRH/BD/52306/2013. Interviews were carried out in the Netherlands during a research visit by the main author at the University of Amsterdam, partially supported by the InnoEnergy Ph.D. School funding for special activities.
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