1. Introduction

In 2015, the world population reached 7.3 billion people [ 1 ], 54% of whom lived in urban areas. Urban populations are projected to increase by 66% before 2050 [ 2 ]. With many countries experiencing rapid urbanization and urban areas often facing many complex problems related to governance and decision-making, governments continue searching for sustainable solutions to improve the resilience of urban areas [ 3 ]. At the same time, local governments face problems with the maintenance of public spaces because of high costs [ 4 ]. This situation is expected to exacerbate in the future due to aging society [ 5 ].

Urban agriculture (UA) may be one affordable alternative for the maintenance of public green spaces [ 6 ]. In the present study, UA is defined as production of fruits and vegetables within or in proximity of an urban area [ 7 ]. Historically, cities transformed agricultural lands for more profitable land uses, and sustainable food systems were integrated into the New Urban Agenda to ensure sustainability of urban development [ 8 ]. To pursue this agenda, more research is needed to identify current and potential agricultural production in urban areas and meet the demands of the urbanites; UA is one way to address food security in cities.

UA plays different roles for food security in developed and developing countries. In developed countries, UA improves nutrient intake in food deserts for underserved populations and serves as a general source of healthy, locally-sourced food, closing the loop of the circular economy [ 9 ]. In developing countries, UA can be the main source of food amidst challenges of rapid urbanization for low-income populations [ 10 ]. It can also provide income to enable purchases of other foods [ 11 ]. UA has also provided common benefits to developed and developing countries, e.g., in the aftermath of a disaster in Haiti [ 12 ] where survivors were temporarily cut off from conventional sources of food.

Research shows that UA farmers specialize in small-scaled practices that provide greater diversity and fresher crops compared to those of rural farmers [ 13 ]. The main reason for this is that urban farmers are disadvantaged in production areas, making it difficult for them to compete in the wholesale market. Rather, UA farmers tend to focus on direct and local sales (e.g., farmers’ markets) that require greater varieties of crops to meet the local demand [ 14 ]. Although there are exceptions, urban farmers plant high-quality, labor-intensive, perishable crops, instead of staple crops in order to differentiate themselves in competition with rural farmers [ 15 ].

UA has already been proven to address many urban challenges (such as food security, access to fresh food, resilience, dietary diversity, nutrition intake, social inclusion, heat island effect, and a source of income for urban poor [ 16 ]). It has also been said that UA can be practiced on land of any size or shape [ 17 ], making it a land use type that can easily be adapted on underutilized lands, such as vacant lands that are often unsuitable for other purposes because they are small in size and irregular in shape. Furthermore, UA can be practiced on floodplains and land with earthquake risks [ 6 ], improving the resilience of the population. These benefits show that UA contributes to the sustainability of urban areas, especially by developing underutilized land. However, few empirical studies focus on the spatial distribution of UA or its nutritional contribution to cities.

Fresh food is important for public health [ 18 ]. However, more than 60% of urban areas are prone to earthquakes, floods, and tropical cyclones, which can affect the food supply from other areas [ 19 ]. Increasing urban resilience through disaster preparedness and adaptation strategies, especially in relation to the social, environmental, and economic infrastructure, has been a critical agenda item for governments [ 20 ]. One example, Japan, is a country prone to natural disasters, but with densely-populated cities, narrow roads, and complex utility systems. The Japanese government has developed a system that solicits UA farmers to register their lands as disaster prevention cooperation farmland [ 21 ]. Registered farmers agree to have affected populations temporarily evacuate to their farmlands, and permit the construction of temporary shelters where emergency food is distributed. This is an UA strategy with co-benefits of overcoming temporary food crises after a natural disaster and securing space for temporary shelters contributing to public safety. Indeed, recent studies report on the health benefits of UA activities due to improved access to fresh produce [ 22 ] and dietary nutrition [ 23 ] in the context of natural disasters.

Current emergency relief mainly consists of carbohydrates, and case studies of cities struck by large earthquakes have reported the need for more nutritious diets [ 24 ]. For example, increases in health issues (e.g., cardiovascular disease) caused by deficiency in nutrients, such as vitamin C, were reported by previously-healthy people after the Great East Japan Earthquake [ 25 ]. Increased intake of fresh fruits and vegetables from UA has been linked to the prevention of cardiovascular diseases, cancer, and other dietary-related health problems [ 26 ]. In this context, UA has been discussed as one source of disaster preparation food. Although current emergency food fulfills its purpose of providing sufficient energy, UA can help to provide nutrients lacking in post-disaster situations (e.g., [ 24 27 ]).

UA also has benefits beyond emergency food. Lifestyle habits and health have been linked in several food studies (e.g., food desert studies) [ 28 29 ]. One study in New York City found that participation in community-supported agriculture increased people’s vegetable consumption, induced positive changes in dietary pattern, and increased consumption of seasonal, local foods [ 30 ]. This study also demonstrated that participation in UA was associated with increases in physical activity. Another study, in Milan, found that hobby farmers are aware of these health benefits, as their main motivations for engaging in UA was their conviction that growing one’s own food is healthier than buying it in the market [ 31 ]. One study in the Netherlands showed that participants of all age categories experienced health benefits, and that older participants experienced the greatest benefits [ 32 ]. These studies indicate that UA can provide coupled psychological and physical health benefits, and that these benefits may be especially useful in combatting the health challenges reported in emergency situations [ 33 ].

36, There are, however, differences in the availability of UA land. Duany and colleagues [ 34 ] categorized UA zones based on the gradient of land uses of the city from urban core to the nature zone. Their classification scheme was adapted and modified for the present study to quantify how UA can better local food security through land use pattern analysis. At present, there are no studies combining spatial and self-sufficiency analysis of UA despite the heavy dependency of self-sufficiency rates on yield, availability of agricultural land [ 35 37 ], and local demand. To assess the potential contributions of UA to food security, it is necessary to understand how produce from UA can contribute to food self-sufficiency in different parts of the city.