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7 October 2021

Susana Toboso-Chavero, PhD number 36 from Sostenipra

The researcher Susana Toboso-Chavero from the Institute of Environmental Science and Technology (ICTA-UAB; https://www.uab.cat/web/icta-1345819904184.html) and the research group Sostenipra (https://www.sostenipra.cat/en/)  successfully defended her thesis on “Integrating the food, energy and water nexus on urban rooftops”, under the supervision of Professor Xavier Gabarrell, Professor Gara Villalba and Dr. Cristina Madrid-López. The evaluation committee was composed of Professor Francesco Orsini, Dr. Johannes Langemeyer and Dr. Jorge Sierra-Pérez.


The doctoral thesis is focused on sustainable urban strategies. 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.First, it was proposed 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, it was applied 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. The FEW metabolism of these urban areas was evaluated, 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, finding 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, the public perception of these strategies was assessed 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, between 7-21%. 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.