Resumen de Integració del nexe aliments, energia i aigua en les cobertes urbanes
Sustainable urban strategies are worldwide spreading with the common goal of improving the habitats where most population lives, i.e., cities. These strategies cover many different fields and are key to transforming cities into healthier, fairer, and greener sites. Cities are often based on a linear economy system, and three of the most essential resources required in urban areas are food, energy and water (FEW). Hence, cities must find circular solutions, closing loops of energy and materials, and avoiding the generation of waste and emissions. Therefore, one of these circular solutions is the use of underutilized rooftops to implement the production of vegetables, energy or rainwater harvesting, i.e., the Roof Mosaic approach named by authors. To this end, this dissertation aims to assess the environmental and socio-economic impacts, and the benefits of the implementation of food production, renewable energy infrastructures and rainwater harvesting, on available rooftops for the purpose of self-sufficient cities. We use a set of different methodologies from different fields, assessing the Roof Mosaic from an environmental, social and economic perspective, and using different approaches such as urban metabolism, life cycle and public participation. We first propose a complete guideline to the accurate implementation of these systems on urban roofs, from the technical aspects to environmental, social and economic indicators. Subsequently, to assess the Roof Mosaic, we apply it at different scales and different urban areas. The two first studies are based on housing estates, and the third is based on a municipality with three characteristic urban forms. We evaluate the FEW metabolism of these urban areas, concluding that housing estates have the lowest electricity (0.75-0.82 MJ/hour), vegetable and water metabolic rates. In contrast, the single-family housing areas display the highest rates in vegetable and electricity metabolic rates. Regarding the different sustainability indicators, we find a relevant share of self-sufficiency in vegetable supply, from 17 to 115% through the implementation of open-air farming or greenhouses on roofs, and also in energy production with percentages of 7-71% through solar panels. In the case of water self-sufficiency, the percentage is high 66-227% for the irrigation of crops, but for specific uses, such as flushing and laundry the percentages are low, from 18-38% for single use, or laundry or flushing. In terms of environmental indicators, scenarios with more rooftops implementing photovoltaic panels depict high CO2 savings but simultaneously high environmental impacts in their construction phase (98 kg CO2 eq/m2/year). Socio-economic indicators illustrate that these new FEW systems could cover between 9-71% and 7-18% of energy and water poverty, respectively. Concerning monetary savings, households could save between 335-1801 ?/year depending on the scenario implemented. To engage stakeholders in the design of future scenarios, we evaluate the public perception of these strategies through participatory processes and surveys, revealing that most residents prefer to implement photovoltaic panels on their rooftops (65-77%). However, for the implementation of urban rooftop farming, the percentage willing to accept is lower. In one of the municipalities only 7%, and in the second one the proportion augments to 20-21%. Therefore, there is a necessity for policies aimed at the use of rooftops for other systems than photovoltaic panels such as open-air farming, rooftop greenhouses or green roofs. Considering the findings of this dissertation, future research lines proposed are setting up different pilot projects in different urban forms and types of residents, aiming to monitor and test the Roof Mosaic and the inclusion of all stakeholders in the design of urban strategies to match their preferences and needs with effective climate change solutions in cities.
