A Quantitative Study Assesses the Aggregate Benefits and Potential of Urban Agriculture Worldwide
February 14, 2018 | seedstock
Though urban agriculture (UA), defined here as growing of crops in cities, is increasing in popularity and importance globally, little is known about the aggregate benefits of such natural capital in built-up areas. Here, we introduce a quantitative framework to assess global aggregate ecosystem services from existing vegetation in cities and an intensive UA adoption scenario based on data-driven estimates of urban morphology and vacant land. We analyzed global population, urban, meteorological, terrain, and Food and Agriculture Organization (FAO) datasets in Google Earth Engine to derive global scale estimates, aggregated by country, of services provided by UA. We estimate the value of four ecosystem services provided by existing vegetation in urban areas to be on the order of $33 billion annually. We project potential annual food production of 100–180 million tonnes, energy savings ranging from 14 to 15 billion kilowatt hours, nitrogen sequestration between 100,000 and 170,000 tonnes, and avoided storm water runoff between 45 and 57 billion cubic meters annually. In addition, we estimate that food production, nitrogen fixation, energy savings, pollination, climate regulation, soil formation and biological control of pests could be worth as much as $80–160 billion annually in a scenario of intense UA implementation. Our results demonstrate significant country-to-country variability in UA-derived ecosystem services and reduction of food insecurity. These estimates represent the first effort to consistently quantify these incentives globally, and highlight the relative spatial importance of built environments to act as change agents that alleviate mounting concerns associated with global environmental change and unsustainable development.
More than half of the world’s population lives in cities, a proportion expected to increase to 67% by 2050 (United Nations, 2012). Since urbanized (i.e., built-up area) land represents less than 1% of the Earth’s land surface (Liu et al., 2014; Zhou et al., 2015), efforts to increase resiliency, adaptive capacity, and habitability of cities will require substantial investments over small areas that will impact a disproportionately large fraction of society. This issue is particularly prominent for regions whose local relative share of global urban population continues to rise. For example, while Asia’s share of global urban population is projected to peak around 2030, urban populations in Africa are expected to grow at increasingly rapid rates for many decades to come (Georgescu et al., 2015). Consequently, Africa will make up an increasingly larger fraction of total urban land (Güneralp & Seto, 2013). Such recognition of anticipated urban expansion has implications for prioritization of strategies guiding sustainable urban development (i.e., retrofitting relative to planning of future cities), which have largely focused on reduction of greenhouse gas emissions and on land-based solutions such as green and cool roofs (Georgescu et al., 2014; Sailor, 2008), increased vegetation fraction (Krayenhoff et al., 2014; Middel et al., 2015), and local engineering-based solutions (Meggers et al., 2016). In addition to potentially beneficial aspects of landscape configuration (Connors et al., 2013), deployment of natural capital within built environments may provide considerable additional human and environmental cobenefits.
Urban agriculture (UA) is a form of natural capital for growing food and other crops within cities (van Veenhuizen & Danso, 2007). Here we define natural capital to mean the biotic and abiotic components of a plant growth system, maintained in an area otherwise classified as urban (we exclude livestock, aquaculture and other secondary productivity). UA offers potential to ameliorate a host of urban environmental problems by increasing vegetation cover and therefore contributing to a decrease in the urban heat island (UHI) intensity (Susca et al., 2011), improving the livability of cities (Frumkin, 2003; Turner et al., 2004) and providing enhanced food security to over half of Earth’s population (de Bon et al., 2009; Pearson et al., 2010). UA is connected to multiple metabolic pathways in the urban ecosystem including food provisioning (Zezza & Tasciotti, 2010), regulation of local microclimate and hydrology (Oberndorfer et al., 2007), consumption of nutrient rich “waste” water and biosolids/organic matter (Armstrong, 2009; de Zeeuw et al., 2011; Smit & Nasr, 1992), and fixation of atmospheric nitrogen (Herridge et al., 2008) and carbon (Beniston & Lal, 2012). For pollinators and other wildlife, habitat is created in the city (Goddard et al., 2010). It has been suggested that UA can also alleviate poverty (van Veenhuizen & Danso, 2007; Zezza & Tasciotti, 2010), increase resiliency (to market fluctuations and climate change) (de Zeeuw et al., 2011), serve as a repository of agricultural knowledge (Koohafkan & Altieri, 2010) and an incubator of new technologies (Despommier, 2010), provide measurable improvements to human health and wellbeing (Joye, 2007; Ulrich, 2006), and reunite urbanites with natural systems from which they have been separated (McClintock, 2010; Turner, 2011). There is evidence that UA shifts dietary intake toward more fresh fruits and vegetables (McCormack et al., 2010), which may reduce emissions from fossil fuels (Weber & Matthews, 2008) and nitrogenous waste (Sutton et al., 2011), while contributing to human nutrition and reducing the risk of multiple chronic diseases (Boeing et al., 2012). Conversely, UA may introduce disease and agricultural pollutants to the urban ecosystem (Smit et al., 2001), create conflicts over land use (Schmelzkopf, 1995), and add complicated, maintenance intensive systems to the urban infrastructure. Based on the economies of scale enjoyed by industrial agriculture, some have argued vigorously against the potential of UA to provide economic and environmental benefits (Desrochers & Shimizu, 2012). Meharg (2016) noted that UA will require monitoring to avoid consumption of food contaminated by urban pollutants.
The incorporation of agroecosystems into cities represents a significant paradigm shift in urban planning and design (Doron, 2005), and its success will require a sufficiently broad inquiry from the scientific community that addresses existing (e.g., environmental) concerns. Given the many and varied potential benefits of UA, it is largely absent from discussions of global food security (Foley et al., 2011; Godfray et al., 2010; Nature Editors, 2010; Tilman et al., 2002) and urban ecology (Grimm et al., 2008). Despite “a groundswell of interest” (Whitfield, 2009), little is known about the cumulative impact of broad UA adoption. In the United States and elsewhere, UA implementation is outstripping policy (Viljoen & Bohn, 2012). Recent reviews of UA in developing (Hamilton et al., 2013) and developed countries (Mok et al., 2013) still have not established a consistent, quantitative framework for analyzing the costs and benefits of UA at global scale, despite acknowledging that “the time is ripe for urban agriculture to be taken seriously and its potential contribution assessed rigorously” (Hamilton et al., 2013). Recent efforts (Badami & Ramankutty, 2015; Martellozzo et al., 2014) estimated the extent to which UA production of vegetables for urban dwellers is constrained by urban area, concluding that UA has minimal potential to alleviate food insecurity in developing countries. However, because these “nutritional footprint” approaches focus on constraints of urban area to meet dietary needs (100% devotion of urban area to agriculture is infeasible in any reasonable scenario), they may not appropriately assess UA potential multifunctionality (i.e., food production, ecosystem services, or economic returns) from realistic scenarios of UA adoption. A recent attempt has been made to estimate the amount of urban area under active cultivation (Thebo et al., 2014). Prior work therefore highlights the need to carry out a comprehensive examination that simultaneously incorporates multiple environmental and societal aspects, setting the basis for the data-driven quantitative approach used here. . . . Continue reading the study here: