An environmental and economic life cycle assessment of rooftop greenhouse (RTG) implementation in Barcelona, Spain. Assessing new forms of urban agriculture from the greenhouse structure to the final product level

Abstract

Purpose: Rooftop greenhouses (RTGs) are increasing as a new form of urban agriculture. Several environmental, economic, and social benefits have been attributed to the implementation of RTGs. However, the environmental burdens and economic costs of adapting greenhouse structures to the current building legislation have already been pointed out as a limitation of these systems in the literature. In this sense, this paper aims to analyze the environmental and economic performance of RTGs in Barcelona. Methods: A real RTG project is here assessed and compared to an industrial greenhouse system (i.e., multi-tunnel), from a life cycle perspective. Life Cycle Assessment (LCA) and Life Cycle Costing (LCC) methods are followed in the assessment. The analysis is divided into three parts that progressively expand the system boundaries: greenhouse structure (cradle-to-grave), at the production point (cradle-to-farm gate), and at the consumption point (cradle-to-consumer). The applied LCIA methods are the ReCiPe (hierarchical, midpoint) and the cumulative energy demand. A Cost-Benefit analysis (CBA) approach is considered in the economic analysis. For the horticultural activity, a crop yield of 25 kg•m-2 is assumed for the RTG reference scenario. However, sensitivity analyses regarding the crop yield are performed during the whole assessment. Results and discussion: The greenhouse structure of an RTG has an environmental impact between 17 and 75% higher and an economic cost 2.8 times higher than a multi-tunnel greenhouse. For the reference scenario (yield: 25 kg•m-2), 1 kg of tomato produced in an RTG at the production point has a lower environmental impact (10-19%) but a higher economic cost (24%) than in a multi-tunnel system. At the consumption point, environmental savings are up to 42% for local RTGs tomatoes, which are also 21% cheaper than tomatoes from multi-tunnel greenhouses in Almeria. However, the sensitivity assessment shows that the crop efficiency is determinant. Low yields can produce impacting and expensive vegetables, although integrated RTGs with energy from the building can lead to low impacting and cheap local food products. Conclusions: RTGs face law limitations that make the greenhouse structure less environmentally-friendly and less economically competitive than current industrial greenhouses. However, as horticultural systems and local production systems, RTGs can become an environmentally-friendly option for further develop urban agriculture. Besides, attention is paid to the crop yield and, thus, further developments on integrated RTGs and their potential increase in crop yields (i.e., exchange of heat and CO 2 with the building) are of great interest.

Urban versus conventional agriculture, taxonomy of resource profiles: a review

“…Conversely, increasing accessible roof area significantly diminished life cycle energy savings (16 to 4 %) for green roofs in Singapore (Wong et al 2003), a challenge Improved yields (Smit et al 2001;Despommier 2013;Besthorn 2013) -Urban greenhouse in NL provided improved yields above traditional agricultural for numerous products (Besthorn 2013) a Reduced food waste (Sanyé-Mengual et al 2012, 2015b -Assumed 17 % reduction in food losses over distribution (Sanyé-Mengual et al 2012) Reduced packaging (IBID) -Packaging savings potentially reduce carbon footprint with urban agriculture in Barcelona, ES (Sanyé-Mengual et al 2012, 2015b In situ ecosystem improvement Improved biodiversity (Knowd and Mason 2006;Havaligi 2011) -Green roofs shown to increase local biodiversity (Hoffman 2007;Oberndorfer et al 2007;Forman 2014) Urban heat island attenuation (Pearson et al 2010;Wong et al 2003) -Satellite models showed appreciable UHI reduction in New York City, USA, with hypothetical urban agriculture scenario (Ackerman 2012) -50 % green roof cover could reduce ambient temperatures by 2°C in Toronto (Bass and Baskaran 2003) Stormwater attenuation (Ackerman 2012;Sida 2003) -Significantly slower runoff rate and runoff retention observed at green roofs around North America (Oberndorfer et al 2007) a -Green roof significantly mitigated runoff in Mediterranean (Fioretti et al 2010) a Soil quality (Smit et al 2001;Jansson 2013) -Compost on UK urban agriculture improved soil structure and nutrients (Edmondson et al 2014) (Jaffal et al 2012). Moreover, these benefits to building energy diminish when well-insulated buildings considered (Castleton et al 2010;La Roche and Berardi 2014).…”

“…The former has been implemented (Nelkin and Caplow 2008), with over 100 operations in New York City utilizing this practice (Cohen et al 2012), though risks exist for rain to deliver airborne contaminants acidifying the soil or depositing heavy metals (Forman 2014). Rainwater collection has also been seen in rooftop greenhouses, such as the Fertilecity project in Barcelona, ES reducing water impacts by 98 % compared to a traditional tomato (Sanyé-Mengual et al 2015b), the Arbor House in New York City (Green Home NYC 2011), and Lufa Farms in Montreal, CA (Lufa Farms 2014). Benefits of rainwater capture must be balanced against the embodied burdens additional structural buttressing, which can be significant depending on the installed system, and pumping energy requirements.…”

“…Lastly, analyses of rooftop greenhouses posit that UA could reduce both packaging and food waste (Sanyé-Mengual et al 2012, 2015b. The former is a logical consequence of lower food-miles and is potentially important in reducing selected environmental impacts (IBID).…”

Global Trends and Current Status of Commercial Urban Rooftop Farming

“…A total of 73 projects were analyzed in terms of specific criteria, such as typology, farming methods, and spatial diversification. Other practical studies assessed and tested the environmental performance of URF and potential techniques for improvement [9][10][11][12]. A number of studies have calculated that cities can achieve significant levels of local self-reliance in terms of food production [1,[13][14][15].…”

Techniques and crops for efficient rooftop gardens in Bologna, Italy

“…Sanyé-Mengual et al (2013) quantified the environmental benefits of the local supply chain of tomatoes produced in rooftop greenhouses in Barcelona (Spain) and contrasted with the conventional supply chain of tomatoes from Almeria (Spain). Sanyé-Mengual et al (2015c) accounted for the environmental burdens of the structure of a rooftop greenhouse and compared it to a conventional greenhouse, since more resources are consumed for reinforcing rooftop greenhouses to meet legal requirements of buildings' technical codes. Tomato production in local rooftop greenhouses in Barcelona could be 33 % more environmentally friendly, in terms of global warming, and 21 % cheaper than conventional production in Almeria.…”