Techniques and crops for efficient rooftop gardens in Bologna, Italy

Urban rooftop farming favours local food production. Although rooftop farming is perceived as 33 a sustainable system, there is a lack of quantitative studies on rooftop farming. There we set up 34 experiments in the community rooftop garden of a public housing building in Bologna, Italy, 35 between 2012 and 2014. We grew lettuce, a leafy vegetable, using three techniques: nutrient 36 film, floating hydroponic and soil cultivation. We also grew tomato, chilli pepper, eggplant, 37 melon, watermelon on soils. Data was analysed by life cycle assessment for environmental and 38 economic performance. Results reveal that the best techniques of lettuce cultivation to address 39 global warming were floating in the summer, with 65-85% less environmental impact per kg 40 than nutrient film; and soil production in the winter, with 85-95% less environmental impact. 41 Furthermore, floating production was 25% cheaper in summer and soil was 65% cheaper in 42 winter, compared to the nutrient film technique. For soil production, eggplants and tomatoes 43 showed the best environmental performances of about 74 g CO2 per kg. Eggplant production in 44 soil gave in the cheapest crop of 0.13 € per kg

The valuation of public and private benefits of green roof retrofit in different climate conditions

Green roofs represent a suitable option for industrial buildings refurbishment, providing private and social benefits. Nowadays, in Italy green roof technology is still uncommon, because of high installation cost that drives the choice towards more traditional performing solutions, such as cool roofs (CRs). Thus, a thorough valuation of green roofs benefits in urban contexts is required to encourage their diffusion. This paper aims to valuate private and social costs and benefits generated by extensive green roofs (EGRs) compared with cool roofs in three Italian cities: Trieste, Ancona and Palermo. These contexts are characterized by different Mediterranean climate conditions (North, Centre and South Italy); moreover, residential areas overlooking industrial settlements take place in each of them, so it is possible to hypothesize a potential enhancement of landscape value in these properties, allowing to compare aesthetic benefits due to green roofs upon industrial buildings. The study has been based on literature review and on simulation of energy performances of EGR and CR alternatively considered as refurbishment solution for a reference industrial building taking place in each industrial settlement. For the social side, the externalities deriving from EGRs and CRs, such as aesthetic enhancement, biodiversity preservation and natural habitat provision, carbon reduction, air quality improvement, stormwater control, have been monetized according to available data for the cases of study. The analysis demonstrates that a private investor has a poor convenience to implement EGR rather than CR. On the other, a positive Net Present Value (NPV) derives from social cost-benefit analysis comparing EGR and CR, due to the EGR positive externalities. The valuation of the positive externalities let the calculation of economic incentives amount to promote the diffusion of green roofs in the Mediterranean area. On this basis, an annual reduction of local property tax has been considered as incentive form. Further, a sensitivity analysis with Monte Carlo simulation of both private and social benefits evaluation has been performed for each of three case studies. This technique properly evaluates the final effects on private investments in the presence of random unpredictable variables, depending either on climate conditions or on market observation, that influence their economic affordability. Finally, through the comparison of the three contexts, an overall discussion about of the influence of climate and urban conditions on the economic analysis has been conducte