Towards Productive Cities: Environmental Assessment of the Food‐Energy‐Water Nexus of the Urban Roof Mosaic

Abstract

Summary Cities are rapidly growing and need to look for ways to optimize resource consumption. Metropolises are especially vulnerable in three main systems, often referred to as the FEW (i.e., food, energy, and water) nexus. In this context, urban rooftops are underutilized areas that might be used for the production of these resources. We developed the Roof Mosaic approach, which combines life cycle assessment with two rooftop guidelines, to analyze the technical feasibility and environmental implications of producing food and energy, and harvesting rainwater on rooftops through different combinations at different scales. To illustrate, we apply the Roof Mosaic approach to a densely populated neighborhood in a Mediterranean city. The building‐scale results show that integrating rainwater harvesting and food production would avoid relatively insignificant emissions (13.9–18.6 kg CO2 eq/inhabitant/year) in the use stage, but their construction would have low environmental impacts. In contrast, the application of energy systems (photovoltaic or solar thermal systems) combined with rainwater harvesting could potentially avoid higher CO2 eq emissions (177–196 kg CO2 eq/inhabitant/year) but generate higher environmental burdens in the construction phase. When applied at the neighborhood scale, the approach can be optimized to meet between 7% and 50% of FEW demands and avoid up to 157 tons CO2 eq/year. This approach is a useful guide to optimize the FEW nexus providing a range of options for the exploitation of rooftops at the local scale, which can aid cities in becoming self‐sufficient, optimizing resources, and reducing CO2 eq emissions.

Analysis of urban agriculture solid waste in the frame of circular economy: Case study of tomato crop in integrated rooftop greenhouse

“…We found that the fraction of biomass generated in i-RTG is similar in composition (stems, branches and leaves) to the classification of "bio-waste" from parks and gardens that are part of municipal waste (European Council, 2008). Based on the above considering the great potential for the implementation of food production systems on rooftops (Safayet et al, 2018;Toboso-Chavero et al, 2019) and according to the growth projection for green roofs in Barcelona (Barcelona, 2017), an increase of 20% of this type of waste was calculated by 2030 within the city.…”

“…For 2019 the forecast of the covered area by green roofs was 5,431 m 2 and through the mosaic roof project, between 2020 and 2030 the creation of 22,000 m 2 will be promoted. The study by de Toboso-Chavero et al (2019) presents the "RoofMosaic" approach, which explores the concept of multiple uses on rooftops to create collective benefits at the local level and promote self-sufficiency in food, energy and water (FEW nexus). This by analyzing the technical, environmental and legal feasibility of the area.…”

“…3). Taking into account the great growth potential that RTGs have for food production (Toboso-Chavero et al, 2019) and according to the growth projection, for the case of Barcelona with the strategy of creating 22,000 m 2 of green roofs by 2030 (Barcelona, 2017), considering the results of the case study that shows the generation of organic SW of 6.63 kg per m 2 per average year (see table 2), the biomass that would be generated within the city from i-RTGs would be generated from i-RTG would be 145,860 kg. That is, there would be an annual increase in the municipal fraction of gardens and parks that would have to be managed within cities of approximately 20%, considering the generation of this fraction in 2017 (Ajuntament de Barcelona, 2018).…”

Perceptions on barriers and opportunities for integrating urban agri-green roofs: A European Mediterranean compact city case

“…Despite their quick growth, cities present a specific vulnerability with regard to managing the food-energy-water (FEW) nexus and its elements, which illustrates the need for efforts to be made in terms of the optimization and use of natural resources (Toboso-Chavero et al, 2018). In this regard, cities have increased the pressure and exploitation levels imposed on the ecosystems, both at local and global scale, as they are responsible, in direct or indirect ways, for nearly 75 % of global energy consumption and 80% of greenhouse gas (GHG) emissions (Ash, Jasny, Roberts, Stone, & Sugden, 2008), exerting high impacts on levels of atmospheric pollution and on the rising demand for natural resources (Cerón-Palma, Sanyé-Mengual, Oliver-Solà, Montero, & Rieradevall, 2012).…”

Implementing the urban food–water–energy nexus through urban laboratories: a systematic literature review

“…Dal Bo Zanon et al 2017), rooftop production(Sanjuan- Delmás et al 2018;Toboso-Chavero et al 2019;Salvador et al 2019), or urban aquaponics(Wu et al 2019).…”