New strategy for Sustainable Urban Areas: The Water-Energy-Food Nexus Implementation on Rooftops

Through sustainable urban planning cities can become healthier, greener and more self-sufficient. Cities might benefit from a transition towards a circular economy that uses renewable resources and energy, and designs cyclical and efficient systems. For example, the use of underutilized areas, such as rooftops and public spaces, may help improve urban sustainability. In this sense, rooftops are a valuable asset in areas where space is scarce and expensive, which might increase self-sufficiency in urban areas when used to produce food and clean energy or to harvest rainwater. We developed the Roof Mosaic approach, which poses the utilization of urban rooftops to implement agriculture, solar panels and to harvest water through different combinations at neighbourhood scale. In this study, we use a comprehensive methodology that includes participatory processes and quantitative data through the Multi-Scale Integrated Analysis of Societal and Ecosystem Metabolism (MuSIASEM). The objective is to establish a link between the socio-economic and ecological processes of our housing estate case study at three distinct scales: households, buildings and neighbourhood. All the buildings included in this research have roofs suitable for the implementation of any mosaic combination (agriculture, solar panels and rainwater harvesting), as they receive direct solar radiation, are flat and the load capacity of the roofs is ideal. The first scenario proposed unveils a self-sufficiency of 100% some vegetables like tomatoes and lettuces, 25% of electricity, and 100% of rainwater for crop irrigation and 25% for flushing, which means a total saving of 2,372 tonnes CO2 eq/year, i.e. a reduction of 8.5% in the carbon footprint of the residents. This novel strategy can promote circular, environmental and socially inclusive solutions for lower income groups and save millions of euros in utilities and food products.