The global rise of urban rooftop agriculture: A review of worldwide cases

Rooftop agriculture (RA) is a building-based form of urban agriculture that includes both protected and nonprotected farming practices, such as rooftop greenhouses as well as open-air rooftop gardens and farms. The use of underexploited urban spaces on buildings for farming purposes is considered a useful strategy for targeting global concerns (e.g., the limitations in food security and land access, impacts of climate change or social exclusion). While previous studies have addressed selected RA cases and the general worldwide dissemination of RA, a systematic evaluation integrating the constantly evolving sector and its diversity (both commercial and noncommercial) is currently lacking. Here, we provide an overview of the current status of RA based on a metadata analysis of 185 publicly accessible cases. This paper summarizes the global trends and spatial distribution of RA cases and presents their main features. The results present the global distribution of different RA types over time, their diverging farming purposes and further characteristics (such as farm sizes, building typologies, growing systems, products and reported yields, activities, implementation of resource-efficient practices, or economic and social activities). The results indicate an emphasis on RA cases in North America (44% of the analyzed cases) and show that RA practices are mainly represented by open-air farms and gardens (84%), as the growing sector of rooftop greenhouses is still relatively small. Similarly, commercial cases are scarce, with the majority of RA cases targeting social-educational goals or the improvement of urban living quality. This tendency suggests a range of currently untapped business opportunities that, if developed, may contribute to the evolution of more sustainable and resilient city food systems providing fresh crops from the inner urban fabric. In conclusion, the research showed a rising global interest in RA, although stronger policy intervention is crucial to upscale RA practices to reach decisive environmental, economic and social benefits at the city level.