Exploring the production capacity of rooftop gardens (RTGs) in urban agriculture: the potential impact on food and nutrition security, biodiversity and other ecosystem services in the city of Bologna

The present work, focusing on the theme of food production and consumption in urban areas, analyses the relationships among three factors: city, human well-being and ecosystems. A case study was carried out addressing the quantification of the potential of rooftop vegetable production in the city of Bologna (Italy) as related to its citizens' needs. Besides the contribution to food security of the city, the potential benefits to urban biodiversity and ecosystem service provision were estimated. The methodology consisted of: 1) experimental trials of potential productivity of simplified soilless systems in rooftop gardens (RTGs); 2) detection of all flat roofs and roof-terraces and quantification of the potential surfaces that could be converted into RTGs; 3) identification of the city's vegetable requirements, based on population and diet data; 4) calculation of the proportion of vegetable requirement that could be satisfied by local RTG production; 5) identification of other benefits (improvement of urban biodiversity through the creation of green corridors and estimation of carbon sequestration) associated with the increased area of urban green infrastructure (GI). According to the present study, RTGs could provide more than 12,000 t year(-1) vegetables to Bologna, satisfying 77 % of the inhabitants' requirements. The study also advances hypotheses for the implementation of biodiversity roofs enabling the connection of biodiversity rich areas across and close to the city: these would form a network of green corridors of over 94 km length with a density of about 0.67 km km(-2).