Science of the Total Environment 689 (2019) 945–957 Contents lists available at ScienceDirect Science of the Total Environment journal homepage: www.elsevier.com/locate/scitotenv Structuring an integrated water-energy-food nexus assessment of a local wind energy desalination system for irrigation Tarik Serrano-Tovar a, Baltasar Peñate Suárez b, Ana Musicki b, Juan A. de la Fuente Bencomo b, Violeta Cabello a, Mario Giampietro a,c,⁎ a Institute for Environmental Science and Technology, Universitat Autònoma de Barcelona, 08193 Bellaterra, Spain b Water Department, Canary Islands Institute of Technology (ITC), Playa de Pozo Izquierdo s/n, 35119 Santa Lucía- Las Palmas, Spain c ICREA, Pg. Lluís Companys 23, 08010 Barcelona, Spain H I G H L I G H T S G R A P H I C A L A B S T R A C T • A novel approach for integrated assess- ment of water-energy-food systems is provided. • It is validated for a local desalination system in the drought-prone Canary Islands. • The system uses wind energy to provide desalted water for agriculture. • Inputs, outputs and wastes are assesses in biophysical and economic terms. • Trade-offs across different levels and di- mensions of analysis can be anticipated. a r t i c l e i n f o a b s t r a c t Article history: Desalination is increasingly put forward as a sustainable local solution to water scarcity in combination with the Received 9 December 2018 exploitation of renewable energy sources. However, the complexity of the resource nexus entails the unavoidable Received in revised form 11 June 2019 existence of pros and cons across its various dimensions that can only be assessed at different scales of analysis. In Accepted 25 June 2019 turn, these pros and cons entail different winners and losers among the different social actors linked through the Available online 26 June 2019 nexus. To address these challenges, a novel approach to resource nexus assessment is put forward, based on Editor: Deyi Hou multi-scale integrated analysis of societal and ecosystem metabolism (MuSIASEM) and recognizing the resource nexus as a wicked problem. The integrated representation identifies the existence of biophysical constraints de- Keywords: termined by processes both under human control (in the technosphere) and beyond human control (in the bio- WEF nexus sphere). The approach is illustrated with a local case study of desalination in the Canary Islands, Spain. The Wicked problem material presented has been generated in the context of the project “Moving towards adaptive governance in Desalination complexity: Informing nexus security” (MAGIC) for use in participatory processes of co-production of knowledge Renewable energy claims about desalination, a prerequisite for informed policy deliberation. MuSIASEM © 2019 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http:// Canary Islands creativecommons.org/licenses/by/4.0/). 1. Introduction ⁎ Corresponding author at: Institute for Environmental Science and Technology, Universitat Autònoma de Barcelona, 08193 Bellaterra, Spain. Desalination is increasingly put forward as a sustainable local E-mail address: mario.giampietro@uab.cat (M. Giampietro). (decentralized) solution to water scarcity, notably in combination https://doi.org/10.1016/j.scitotenv.2019.06.422 0048-9697/© 2019 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). 946 T. Serrano-Tovar et al. / Science of the Total Environment 689 (2019) 945–957 with the exploitation of renewable energy sources (RES), such as wind The entanglement of resource flows is inherent in the complex met- and solar energy (Alkaisi et al., 2017; Chandrashekara and Yadav, abolic pattern of social-ecological systems and requires a complex sys- 2017; Fornarelli et al., 2018; Gold and Webber, 2015; Gude, 2016; tems approach based on relational analysis. The current use of Manju and Sagar, 2017; Shahzad et al., 2017). However, while desalina- deterministic models trying to optimize or maximize individual objec- tion can certainly be an essential option for resource security purposes tive functions in specialized governance structures simply makes the in isolated and islands areas, an effective assessment of the performance nexus invisible to the analyst. A novel approach addressing these chal- of desalination in relation to nexus security requires a comprehensive lenges is proposed and illustrated with a case study on desalination. understanding of the nature of the entanglement over water, energy, The rest of the paper is organized as follows. Section 2 provides a and food flows. Literature on the water-energy-food (WEF) nexus short presentation of the case study and the accounting method pro- shows a general consensus on the urgent need to improve both: posed for the analysis of the nexus across multiple scales and dimen- (i) the effectiveness of scientific analysis in integrating quantitative sions of analysis (MuSIASEM). Section 3 illustrates the type of results analyses across different dimensions and scales; and (ii) the process of generated by the approach through a characterization of the factors de- governance across the existing ‘institutional silos’ dealing with water, termining the performance of the desalination plant in the Canary energy and food separately (Al-Saidi and Elagib, 2017; Bazilian et al., Islands. Section 4 discusses the strength and limitations of the approach 2011; Biggs et al., 2015; Cairns and Krzywoszynska, 2016; Endo et al., (section 4). The last section concludes. 2017; Garcia and You, 2016; Gulati et al., 2013; Hák et al., 2016; Hoff, 2011; Howarth and Monasterolo, 2016; Howells et al., 2013; Khan 2. Materials and methods et al., 2017; Leese and Meisch, 2015; Mohtar and Lawford, 2016; Pittock et al., 2015; Rasul, 2016; Ringler et al., 2013; Verhoeven, 2.1. The case study 2015). Hence, there is the need to improve the process of generation and use of scientific information relative to the nexus. In particular, it Gran Canaria forms part of the Canary Islands, a Spanish volcanic ar- is essential to integrate the information about two different types of chipelago located in front of the Moroccan coast in the Atlantic Ocean. trade-offs: (i) between the ecological and socio-economic side; and Although the islands have diverse climatic areas and ecosystems, a sub- (ii) within the socio-economic process among different social actors, tropical climate and arid areas predominate. Indeed, the amount of pre- both within—e.g., producers and consumers—and across hierarchical cipitation in Gran Canaria is low, with an average of 300 mm per year. levels—e.g., administrators and tax-payers. The porosity of the volcanic terrain further challenges storage of water The study presented in this paper has been developed within the in reservoirs. The monthly average wind speed at the east coast of context of the Horizon2020 project “Moving towards adaptive gover- Gran Canaria is 8.5 m/s with predominant NE direction. Strong ‘trade nance in complexity: Informing nexus security” (MAGIC). It addresses winds’ are produced between March and August (Rybar et al., 2011). Al- three systemic problems in WEF nexus research: though traditionally an agricultural area, the main economic sector today is tourism. Due to population growth and the rapidly increasing 1. It is difficult to use scientific information on the nexus in participa- demand of services for tourists, the freshwater requirement has dra- tory processes because of the nexus being a ‘wicked problem’ matically increased (CIAGC, 2015). Underground water has traditionally (Rittel and Webber, 1973); a problem impossible to simplify without been used, but depletion of water resources from the subsoil has losing relevant information. Indeed, the analysis of the resource exhausted the insular aquifers aquifers. Additionally, the over- nexus is extremely complex and requires the consideration of exploitation of groundwater has triggered saltwater intrusion from many factors and functional elements operating at different scales. the sea (Instituto Tecnológico de Canarias, 2008). The underground wa- This makes it impossible to adopt simple standard models (of the ters of the southeastern part of the island of Gran Canaria suffer the type ‘one size fits all’) that identify ‘optimal’ solutions and eliminate highest degree of marine intrusion (CIAGC, 2015). Carrying freshwater uncertainty from the results. The quantitative analysis of the nexus is from the mainland to the islands is not a viable option given the long incompatible with the paradigm of reductionism that currently dom- distances and enormous costs involved, and the local government of inates the generation of quantitative information. When dealing with the Canary Islands has been forced to seek alternative solutions, using the nexus things are not simply ‘black’ or ‘white’, costs or benefits, alternative water sources such as desalted water. and quantitative results heavily depend on the assumptions made At the east-coast of Gran Canaria island (Playa de Vargas) a seawater in the pre-analytical phase. reverse osmosis (SWRO) desalination plant was constructed by 2. It is hard to generate scientific information referring to the nexus Soslaires Canarias S.L. in 2002. It also includes water pumping, pipelines with the existing model of scientific inquiry being divided into disci- and a water reservoir. The capacity of the desalination plant plinary fields. The reductionist strategy of addressing and solving one (5000 m3/day) was designed to exceed the initial water demand of issue at the time (using water models, energy models or food crops in this area. The plant and water pumping are driven by the elec- models) has created a practice of considering one data set at the trical grid but are also connected to an on-shore wind power farm time – i.e. models dealing only with water, with energy or with (2.64 MW). The SWRO consumes energy from the electrical grid when food. Although results of these mono-dimensional models may be wind power is insufficient. When the wind farm produces more elec- contrasted with each other, the assumptions (and their credibility) tricity than needed by the SWRO, it is sold to the grid at market price underlying each one of these models are still based on the ceteris (with an investment bonus of 12€ per MW). paribus hypothesis. Hence the causal relations described by the The SWRO facility produces and sells water to local farmers. The models in the different specific disciplinary domains are assumed desalted water from Soslaires Canarias S.L. irrigates up to 230 ha of ag- to be independent of events that can only be observed from within ricultural crops pertaining to farmers of a local agricultural cooperative, a different disciplinary domain. growing mainly fresh vegetables and fruits. The water derived from the 3. It is difficult to use scientific information referring to the nexus for desalination plant is stored in a 2500 m2 reservoir with a capacity of governance within the actual silo structures found in existing 200,000 m3, located at 200 m above sea level. This reservoir is a strategic institutions. The division into specific issues, addressed one at buffer element aimed at optimizing the wind energy used by the system the time by specialized bodies, does not provide the diversity of by storing desalted water in periods when irrigation is not needed. information that would be required to gain policy relevance – Farmers in the area have the option to combine the desalted water i.e., who are the winners and who are the losers (at different levels with other water sources: groundwater and reclaimed water. of analysis) of a given policy in relation to the implications of the The seawater inflow happens in four catchment wells that are 50 m nexus? inland. The brine produced by the desalination plant is discharged into a T. Serrano-Tovar et al. / Science of the Total Environment 689 (2019) 945–957 947 specific beach-well (diluted with a concentration of between 58 and ecological system metabolize flows. Hence, flow-fund ratios are qualita- 60 g/l) that is 10 m away from the sea. The distance between the seawa- tive benchmarks linked to a specific typology of functional elements. ter catchment and brine discharge wells is sufficiently high to avoid any This approach was originally proposed by Georgescu-Roegen under brine recycling into the production wells. Hydro-geological studies are the name of the flow-fund model (Georgescu-Roegen, 1971). For in- done before any beach well exploration, not only to warrant the flow re- stance, the flow ‘annual crop production’ (measured in t) is accounted quired but also to study underground pollution. The spatial distribution for as the product of yield (in t/ha) and land in production (in ha), but of the facilities is shown in Fig. 1. also as the product of labor productivity (in kg/h of human activity) At first glance, the Soslaires Canarias S.L. plant seems to be a perfect and labor required in production (in h). In this way the system of ac- WEF nexus system: (1) it allows an isolated semi-arid social-ecological counting creates redundancy in the information space, which is useful system to produce its own food by supplying irrigation water, (2) the for integrating information across different dimensions and scales of supply of water is obtained from the sea, so it does not stress the analysis. exhausted aquifers, and (3) the energy for desalination is obtained One of the key features of MuSIASEM is that it provides different from the wind, so it does not require import of fuels from outside. How- types of quantitative information relevant for discussing three distinct ever, at closer look, not all the flows required and supplied by the sys- types of constraints (Giampietro et al., 2014): tem match each other in time. (i) Feasibility in relation to external constraints determined by pro- 2.2. MuSIASEM rationale cesses outside of human control. Feasibility refers to the availabil- ity of natural resources or environmental services in relation to Similar to organisms, social-ecological systems (and their constitu- the required supply and sink capacity (in terms of supply of re- ent components) must metabolize material and energy inputs to sur- quired inputs and sink of wastes/emissions generated). This vive and evolve, thereby producing useful outputs and wastes quantitative information is based on data referring to topogra- (Giampietro et al., 2012). Using this concept of metabolism, MuSIASEM phy, climate, soil types, availability of renewable resources such describes the functioning of social-ecological systems in terms of meta- as wind, solar radiation, water or biodiversity, and availability bolic patterns of flow and fund elements. Flow elements describe what of non-renewable resources such as fossil energy, mineral ores. the system does in terms of metabolic activity (consumption of fuels, Feasibility refers to the interactions taking place between the generation of electricity, production of crops, generation of brine), biosphere and the technosphere. whereas fund elements describe what the system is ‘made of’ (hectares (ii) Viability in relation to internal constraints determined by processes of crops, workers, wind turbines). Fund elements provide a metric to under human control. Viability concerns the nature of the internal describe the size of the metabolic system. MuSIASEM differs from constraints imposed on the metabolic pattern by the human so- other approaches to ‘social metabolism’ in that it does not simply quan- cioeconomic system. This quantitative information refers to de- tify ‘flow elements’, as done for example by material and energy flow mography, labor force, productivity of economic activities, analysis (MEFA) (Suh, 2005), but it relates the various flows to the spe- availability of technology and know-how. Viability refers to in- cific fund elements that produce or consume them. In this way, a family teractions taking place within the technosphere. of benchmarks is obtained (represented by the values of flow-fund ra- (iii) Desirability in relation to normative values and institutions keeping tios) that describes how the various functional elements of the social- together the social fabric. Desirability implies the need of carrying Reservoir 4 wind turbines Seawater Inflow Brine Discharge Desalination Plant Fig. 1. Aerial view of the facilities of Soslaires Canarias S.L., scale 1:8000, standard north-up representation (IDECanarias, 2018). 948 T. Serrano-Tovar et al. / Science of the Total Environment 689 (2019) 945–957 out an additional check on the performance of the metabolic pat- given process or function. An analogy of the processor is the concept tern of social-ecological systems in relation to the expectations of enzyme in biochemistry or the concept of production function in eco- and preferences of the social actors involved. This check cannot nomics. In MuSIASEM processors represent an integrated description of be based on quantitative analysis carried out by ‘experts’, it re- the characteristics of the metabolic units of the system (González-López quires the implementation of participatory processes to involve and Giampietro, 2017). An example of a processor characterizing the the social actors in the integrated assessment. specific profiles of inputs and outputs required to carry out a particular process (task) within a multi-scale metabolic pattern is illustrated in MuSIASEM is based on an application of relational analysis (Louie, Fig. 2. Corresponding data are stored in the form of a data array (a spe- 2013, 2009; Rosen, 1985, 1977) to the flow-fund model of Georgescu- cific data structure). Roegen (1971) in three main steps: (1) identification of the hierarchical The upper part of the processor in Fig. 2 represents the profile of in- structure determining the functional relations of the metabolic ele- ternal inputs, both flows (left side, in blue) and funds (right side, in red), ments of the social-ecological system under analysis; (2) characteriza- obtained from the socio-economic system (technosphere). Whereas tion of the specific metabolic patterns of each one of the relevant flows are consumed, fund elements are not. Funds are maintained functional elements using the concept of processors, and (3) generation along the process (e.g., laborers, land, and machinery). They provide in- of a series of non-equivalent representations of the metabolic perfor- formation about the size of the processor (in terms of hectares of land, mance of the WEF elements of the system considered at different levels hours of labor, or watts of power capacity). and dimensions of analysis depending on the questions to be answered. The lower part of the processor represents the interaction with the MuSIASEM distinguishes itself from other methods in that it is se- biosphere (i.e., the environment or context of the system). It is de- mantically open (possibility to mix semantic information to formal scribed in terms of external input and output flows. On the left side, analysis). In the pre-analytical framing (step 1) one has to decide the flows directly taken from the biosphere (in green) are shown, that which metabolic elements are relevant for the definition of the hierar- is, materials and energy from natural resources—the supply side of the chical structure of functional relations. This process can be done in con- metabolism. The lower right part (in orange) represents the output sultation with stakeholders. Then, in step 2, it must be decided which flows of unwanted by-products that are dumped in surrounding ecosys- formal categories (associated with quantitative assessments) are tems, like wastes (brine) and emissions (CO2)—the sink side of the needed for a meaningful characterization of the metabolic characteris- metabolism. tics of the selected elements using the concept of processors. Finally, The useful output of the processor (going into the socio-economic in the last step, the information space generated in the first two steps system) is represented by the grey arrow exiting to the right. This out- is used to produce non-equivalent assessments (feasibility, economic put represents a measurable quantity of useful product (or a mix of use- viability, technical viability, dependence on subsidies, etc.) tailored to ful products) and corresponds to a defined amount of required flows specific research questions of interest to specific stakeholders. and funds (top arrows) and a defined level of interaction with the bio- sphere (bottom arrows). 2.3. The concept of processors This structure of accounting thus provides information about: (i) inputs required/obtained from the socio-economic system (flows The concept of processor is key to MuSIASEM. First introduced by and funds on the top); (ii) outputs going into the socio-economic sys- Rosen in relational analysis (Rosen, 1958), a processor is a description tem (on the right); and (iii) inputs and outputs exchanged with the bio- of the profile of inputs and outputs associated with the expression of a sphere (flows on the bottom). It can be applied to a specific process Fig. 2. Graphic representation of a processor. T. Serrano-Tovar et al. / Science of the Total Environment 689 (2019) 945–957 949 (e.g., an individual wind turbine producing electricity), a wind farm (the level of self-sufficiency), the dependence on imports or subsidies, made up of many wind turbines, a complex of alternative electricity and the overall environmental pressure exerted can be checked. The production combined with a desalination plant used for irrigation, the procedure is illustrated for the selected case study in the Results section. agricultural sector, or an entire society. Clearly at each specific hierarchi- cal level of analysis the definition of inputs and outputs in the proces- 2.4. Data and material sources for the case study sors and the corresponding accounting must be adjusted (semantically open approach). Data used in this study were obtained from various sources. Primary Processors represent metabolic relations and are described using data on the water and energy flows were provided by Soslaires Canarias physical quantities (e.g. surface for land, volume for water, time for S.L (personal communication) and cover technical coefficients of wind labor, power for machinery, electricity for energy). However, they can power plant, desalination plant, pumping, storing infrastructure, and ir- also be used to track economic costs and benefits by using the costs of rigation related to the year 2015. Primary data on crop production were the input flows and funds and the revenues of the useful outputs. By in- obtained from the agricultural cooperative and complemented with tegrating the two types of information, a picture about both economic secondary data from statistics. Gross revenue and food prices are from viability and biophysical viability and feasibility is obtained, which is the records of the official food wholesale market on the island where useful to assess the operative and amortization costs, the net profits of farmers sell their produce, using the most frequent food prices for the the outputs, or the possible subsidies that are required for achieving year 2015. Labor costs were calculated from the average salary of oper- economic viability. ation and maintenance workers and farmers in the area. The costs for ir- Processors can be represented either as ‘unitary’ or ‘sized’ processor. rigation and agrochemicals were estimated from the profile of required In unitary processors, the values of the flows and funds exchanged are inputs. The cost of fertilizers was estimated using benchmark average normalized per unit of output (e.g., the inputs and outputs per cubic values found for Spain. Data used for the processors are available in meter of desalinated water produced, or inputs and outputs per ton of the Supplementary data files. Note that the analysis provided in this crop produced) or per unit of input fund element (e.g., the profile of in- paper is but a starter for the process of co-production of knowledge puts and outputs per hectare of land use for crop production). Hence, claims. The quality of this preliminary characterization will be checked the unitary processors represent the ‘technical coefficients’ of the pro- in the second phase of the project using participatory processes to duction process. They are useful for two main purposes: (i) to visualize build a validated representation useful for an informed process of and compare differences across different metabolic elements express- deliberation. ing the same function; and (ii) to scale up the effect of a change in size or technical characteristics of a specific processor in simulations of 3. Results scenarios. Sized processors, on the other hand, refer to the actual size of the flows and funds observed in the system. Unitary processors can 3.1. System description easily be converted into sized processors and vice-versa by, respec- tively, multiplying or dividing the profile of inputs and outputs by the The first step is to identify the functional elements required to stabi- size of the fund element used for the scaling. lize the flows of water, energy and food metabolized by the WEF system Distinction between functional elements (a wind farm) and struc- and define the relations among these elements starting from the big pic- tural elements (wind turbines) is essential for scaling up the quantita- ture of the whole system. This includes a definition of a boundary for the tive representation of metabolic performance. Processors describing system in order to distinguish between exchanges of input and output specific structural elements (e.g., specific model of wind turbine) can flows that take place inside the WEF system and those taking place be combined into a higher-level processor describing a functional ele- across the boundary with either the wider environmental context (the ment (e.g., a wind farm made up of a combination of different types of biosphere) or other socio-economic systems (e.g., the market or elec- wind turbines). Therefore, representing the metabolic pattern with pro- tricity grid in this case). A hierarchical set of relations over the different cessors (relational analysis) allows the analyst to move across the hier- functional elements is then established up till the lowest level where it archical levels of the system. This is an important feature of MuSIASEM's is still possible to identify structural elements. relational analysis. In this way, it is possible to handle a simultaneous As shown in Fig. 3, in this case, there are three functional compo- representation of the metabolic system across different levels of analy- nents expressing three processes: (i) the production of electricity by sis (e.g., an individual wind turbine; a wind farm; the WEF system as a the wind-farm (local wind electricity supply); (ii) the production of whole). The metabolic characteristics of the lower-level structural com- fresh water by the desalination plant (local desalted water supply); ponents weighted by their relative size define the metabolic character- (iii) the production of crops on the local farm (local crop supply). Crop istics of the upper-level functional element. This approach can be used production uses: (i) electricity from both the local wind energy provider in both diagnostic and anticipatory mode. The diagnostic mode explains and the national grid, (ii) blue water from the local desalination plant the relations among metabolic characteristics observed across different and possibly from the nearby supply of reclaimed water (some farmers levels, that is, how the characteristics observed at the upper level de- alternate these two water sources); (iii) green water in the form of pend on those observed at the lower level. In the anticipatory mode, privately-managed groundwater. MuSIASEM is used to visualize expected changes in metabolic charac- The electricity generated by the wind farm is used mainly, but not teristics of the functional components at the upper level in response to exclusively to power the desalination plant. As shown in Fig. 3, the elec- changes in metabolic characteristics or relative size of lower-level ele- tricity from the wind farm and the grid do not meet all the energy re- ments (e.g., introduction of new models of wind turbines or an increase quirements of local crop production. For instance, the fuels consumed in the relative contribution of certain types of wind turbines in the wind by the tractors operating on the farm have to be imported from outside farm). the system (the socio-economic context). The desalted water is used ex- The procedure for aggregating processors of lower-level metabolic clusively for the local crop supply. However, some of the farmers who elements into processors describing functional elements at a higher use the desalinated water also use a nearby supply of reclaimed water level is simple: inputs and outputs of the sized processors are summed and/or groundwater to irrigate their crops. The ground water is man- respecting the common structure of the data array (blue water is aged by a private company. The crops produced by the farm are for summed to blue water, labor hours to labor hours, and so on). Moving the market and therefore go outside of the system. up in this way in the hierarchical structure of the system, an overall as- The three functional elements in the WEF system (electricity supply, sessment of the profile of inputs and outputs for the entire WEF system water supply, and crop supply) are each composed of a mix of different is formalized. At this level of analysis, the level of openness of the system structural types (Fig. 4). The crop supply consists of eight different 950 T. Serrano-Tovar et al. / Science of the Total Environment 689 (2019) 945–957 Fig. 3. Relational analysis of functional metabolic elements of the local WEF system in the island of Gran Canaria. production systems (structural types: cantaloupe, watermelon, tomato, dammed pond used for storing the desalted water for irrigation (buffer), zucchini, beans, pumpkin, banana and moringa), the local electricity and the pumping devices, located outside the desalination plant, re- supply consists of four wind turbines, and the local desalted water sup- quired for the water system supply. For each of these structural compo- ply consists of three structural elements: a desalination plant, a nents a processor is created, as shown in Fig. 4. Fig. 4. Representation of the hierarchical relations between the processors of the three functional elements and their composing structural elements. T. Serrano-Tovar et al. / Science of the Total Environment 689 (2019) 945–957 951 Fig. 5. Contextualizing the representation of functional elements in relation to the socio-economic context (top) and environmental context (bottom). Establishing a bridge across the information carried by the proces- this pre-analytical phase will determine the usefulness of the resulting sors of structural and functional elements at the different levels of anal- quantitative characterization. For example, considering the require- ysis (Figs. 3 and 4), it is possible to understand the relation that the ment of water, is it important to distinguish between blue and green system has with both its socio-economic (economic reading) and envi- water? What are the relevant outflows that could represent a measur- ronmental context (biophysical reading) as shown in Fig. 5. The eco- able impact on the environment? nomic reading is essential to check the economic viability of the Based on the biophysical reading of the processes taking place inside system; the biophysical reading to check the environmental compatibil- the system, a parallel economic reading can be generated by converting ity. As regards the latter, note that the arrows on the bottom of the the flows of biophysical inputs into economic costs, and the flows of scheme of Fig. 5 represent environmental pressures on the environment. useful outputs into economic revenues. As noted earlier, processors They are not necessarily associated with environmental impact. For ex- can be represented as either unitary or sized processors. ample, in this specific case, the production of brine as a by-product does not represent a big threat to the environment because, at the current 3.2.1. Local wind energy supply scale of production, it is diluted into the sea. A similar assessment can Fig. 6 illustrates the sized processor characterizing the wind farm be done for the other indicators of environmental pressure. A given complex. In this representation, funds and flows are expressed in abso- level of abstraction of water from the local aquifer becomes dangerous lute terms, reflecting the size of the local wind electricity supply system. and generates impact only when it exceeds the recharging capacity. This information is about how much electricity is produced on a year Therefore, an analysis based on processors per se does not provide infor- basis and the total amounts of inputs (flows and funds) necessary to mation about ‘environmental impacts’, but only about ‘environmental guarantee this supply. The unitary processor (normalized to one unit pressures’. of output, that is, 1 GWh/y) is available in the Supplementary data. The information conveyed by the processor—including the power 3.2. Characterization of the processors of the various metabolic elements capacity (PC) installed—permits us to calculate the capacity factor (the maximum possible energy output of the device). Wind turbine power Variables relevant for characterizing the performance (the profile of output depends on the strength and intermittency of the wind and inputs and outputs) of the functional and structural elements in the hence is variable. The wind farm cannot provide maximum power ca- form of processors have to be selected. This includes: (i) in the inputs: pacity year round. Moreover, the desalination plant cannot use all the the required funds (land, human activity, power capacity), internal electricity produced by the wind farm at maximum power capacity. flows (electricity, blue water), and the external flows from the socioeco- Hence part of the output of electricity of the wind farm is sold to the nomic system (electricity, fuels, blue water) and the embedding natural electricity grid of the island and part of the requirement of electricity ecosystems (green water, abstraction from the aquifer); (ii) in the out- of the desalination plants is obtained from the grid. Hence, the socio- puts: the flow of useful products generated (electricity, desalted water, economic context plays an essential role (as a ‘virtual’ functional ele- crops) and the waste flows released into the environment (brine, car- ment of external electricity supply) in providing electricity when it is bon dioxide emissions). The definition of the profile of inputs and out- needed but not produced by the local supply system. puts can be different for different types of processors. Desalted water Information on the monetary costs and revenues associated with is an output of the local water supply system (one of the functional ele- this processor is also shown in Fig. 6 (in yellow). Part of the electricity ments) but is consumed inside the system and therefore no longer an produced by the wind farm is used for the desalination plant. However, output when considering the WEF system as a whole. Moreover, de- as the local supply systems of wind electricity and water are both pending on the scope of the analysis, some of the inputs and outputs owned by the same company, no revenue is involved. Excess electricity may be neglected if they result as irrelevant. Semantic decisions in outflow is sold to the electric grid at market price (with an investment 952 T. Serrano-Tovar et al. / Science of the Total Environment 689 (2019) 945–957 Fig. 6. Sized processor of the functional element local electricity supply (wind farm, aggregating data from the four structural elements), biophysical and economic (in yellow) reading. bonus of 12€ per MW). The costs of the wind farm include operational pond are located; (v) the annual amortization costs of the fix invest- costs (labor, and maintenance) and fixed costs of the installation of ments (estimated); and (f) the revenues of selling the desalted water the infrastructure and technical devices. The fixed costs have been to the local agricultural cooperative. The price of the desalted water is discounted over the expected life span of the infrastructure or devices. higher (ranging from 0.6 to 0.83 €/m3 in the period 2010–2016) than The external subsidies that Soslaires Canarias S.L. received at start up that of groundwater (between 0.5 and 0.6 €/m3) and of (subsidized) were also accounted for. In 1999, Spanish policy supporting renewable reclaimed water (between 0.45 and 0.53€/m3), but there is not suffi- energies fostered premiums to promote private investments in wind cient underground water for agricultural irrigation in the area. energy. An amount of 526 Spanish Pesetas (3.16 EUR) per kWh was paid to facilities with power lower or equal to 50 MW for several 3.2.3. Local food supply years (IDAE, 1999). Additionally, the Spanish national entity responsible The flows and funds related to the agricultural production of the co- for renewable energy policies (IDAE - Institute of Diversification and En- operative (functional element ‘local crop supply’) are shown in Fig. 8. ergy Saving) provided financial support to ensure proper execution This sized processor represents the aggregated output of the eight from 2002 until 2010. However, since 2010, the only subsidies the crops cultivated. Water inflows to the cooperative are divided into the WEF system has received have been agricultural subsidies. desalted water from Soslaires Canarias S.L. and underground water. The carbon dioxide emission involved in the operation of this wind Groundwater can be obtained either directly from the biosphere farm has been estimated based on an average of 6 g of carbon dioxide (through wells operated by the farmers) or from the techno-sphere emitted per kWh (EWEA, 2018). (from the grid against payment by the farmer). In this case, the input from the biosphere is accounted for in the ‘virtual processor’ associated 3.2.2. Local desalted water supply with the system of abstraction and distribution of water to the farmers The sized processor for the functional element local desalted water operating outside the boundary of the analysis. supply (integrating the characteristics of its three lower-level elements) Depending on the purpose of the analysis, selected information pro- is shown in Fig. 7. The unitary processor is not shown but available in vided by this multi-scale system of accounting can be further elabo- the Supplementary data. The desalination plant uses electricity from rated. For example, when looking for indicators of environmental the grid when the wind farm does not meet its demand. Brine outflow pressure, the following information would be relevant: (i) the biophys- represents a potential impact on the environment, but in this particular ical information conveyed by the processors describing the structural el- desalination plant, so close to the sea, it may be assumed insignificant as ements inside the system boundaries, such as the flow of nutrients and the brine is not poured directly into the sea but through a filtered well. pesticides, the extraction of underground water; and (ii) the depen- The economic data (Fig. 7, in yellow) provides relevant additional in- dency of the system on imported flows (externalization of the environ- formation, such as: (i) the cost of the electricity purchased from the mental pressure to the producers of the imported flows). As noted grid; (ii) the cost of the labor required for the operation of the plant; earlier, information about environmental pressure has to be (iii) the cost of external services for the maintenance of the machinery; georeferenced to assess environmental impact. On the other hand, if (iv) the annual cost of renting the land where the desalination plant and the information generated is to be relevant for economic agents, the T. Serrano-Tovar et al. / Science of the Total Environment 689 (2019) 945–957 953 Fig. 7. Sized processor of the functional element local desalted water supply (aggregating data from the three lower-level structural elements); biophysical and economic (in yellow) reading. functional elements associated with the activities of the relevant eco- example, there are two economic agents operating in the system: nomic agents have to be identified first. (1) the private company Soslaires, uniting the two functional elements Regarding agricultural subsidies, farmers who cultivate certain veg- local electricity supply and local water supply into one single economic etables, fruits, ornamental or medicinal plants can receive subsidies agent; and (2) the farming cooperative, corresponding to a single func- under the “Community Support Program to the Agrarian Productions tional unit made up of eight different structural elements (the crop pro- of the Canary Islands” (POSEI, 2015). The extent of the economic sup- duction systems). As shown in Fig. 9, MuSIASEM not only provides port depends on whether or not the farmers are consolidated in agricul- useful information on the biophysical performance of this WEF system, tural cooperatives, the type of crop cultivated, and whether or not crops but also on the performance of the local economic agents through the are destined for marketing outside of the Archipelago. For example, the assessments of monetary flows. production of banana and tomato receives greater support, especially if The economic narrative can also be applied to the big picture of the marketed outside of the Archipelago. Thus, in principle, it is possible to entire WEF system by moving up another level in the hierarchy. At this know the amount of agricultural subsidies received by the farmers who level, the economic interaction of the local system (composed of differ- applied for it for each of the crop systems studied. However, this infor- ent local economic agents) with its wider socio-economic context can mation was not disclosed in this case study. be studied. For example, the role of the various monetary flows (e.g., subsidies and taxes) in stabilizing the metabolic pattern can be 3.2.4. Processor of structural elements quantified and evaluated. In fact, the WEF system can be perceived as Moving down in the hierarchy of levels of analysis, we arrive at the a functional unit that supplies society not only with crops and the sur- characterization of the individual structural elements that make up plus of electricity but also with other socio-economic services, such as the functional elements. For example, looking ‘inside’ the functional el- employment and hence the reproduction and livelihood of the local ement local crop supply, we find the processors describing the opera- community. Thus, MuSIASEM provides two different visualizations of tions of the eight individual crop systems (as described earlier in the economic reading: (i) one providing information relevant for the Fig. 4). Processors characterizing individual structural elements are specific economic agents operating inside the system; and (ii) one pro- not shown here but illustrated (for the eight crop systems) in the Sup- viding information relevant for the discussion of policies at the commu- plementary data. nity or regional level. 3.3. Aggregation of processors across the various functional elements 4. Discussion As indicated earlier in Section 2.3, the procedure for aggregating the Given the illustrative nature of this study, approximate data have information carried by the processors is flexible and depends on the been used and some of the inputs and outputs of the various processors purpose of the analysis. The pre-analytical decision about the choice have been estimated for lack of data. A more robust assessment will be and definition of functional and structural metabolic elements is essen- obtained through participatory processes with local farmers in the sec- tial in this process. Especially when adopting an economic narrative, the ond phase of the project. Nevertheless, this preliminary analysis shows definition of functional units operating inside the system depends en- that MuSIASEM is a powerful approach to study the sustainability of in- tirely on the choices made by the analyst. In this particular case, for tegrated WEF systems. It can answer questions such as: How much net 954 T. Serrano-Tovar et al. / Science of the Total Environment 689 (2019) 945–957 Fig. 8. Sized processor of the functional element local crop production; biophysical reading complemented with economic data (in yellow). energy, water and food are being produced? Is this WEF system self- analytical approach helps analysts to contextualize its results in relation sufficient? What are the possible external and internal constraints? to the specificity of the considered situation in order to avoid endorsing What is the economic viability of the system? Is it feasible to extrapolate misleading narratives. When dealing with sustainability issues, there this system to other areas? are pros and cons for each technical solution and these must always The wind turbines provide part of the energy used by the desalina- be contextualized in relation to the biophysical limits determining the tion plant and the desalination plant provides part of the water used option space. The local case study presented here is relatively simple by the farms. In the same way, the farms provide part of the food used and manageable, but the same principles and outputs apply to larger by the population in the island. An informed discussion of the perfor- and more complicated WEF systems. mance of this system requires an identification and analysis of the rela- The WEF system studied is not self-sufficient. It relies on other exter- tive importance of the various functional elements and the significant nal systems for its supply of energy carriers (fuels and electricity) and constraints affecting the performance of the system. In relation to this water for its operation. Naturally, this does not imply that alternative point, the interaction with the context is essential to assess the desir- energy generation and desalination are useless or bad. On the contrary, ability, viability and feasibility of this solution. For example, wind tur- they help improve the sustainability of economic activities. The point bines produce electricity that cannot always be used by the made here is that in order to get the most out of proposed alternative desalination plant (water demand is not linked with wind availability). solutions, it is essential to develop an analytical framework capable of: So, the unused electricity has to be sold to the grid. The local supply sys- (i) providing a clear vision of the degree of openness of the WEF system; tem needs to be backed-up by an external supply/demand system. Also, (ii) understanding its possible limitations; and (iii) characterizing the the desalination plant requires electricity that cannot always be pro- pros and cons across different levels and dimensions. duced by the wind turbines, so a grid must be available to guarantee It is important to keep in mind that in this area it is possible to use the continuity of operations. Additionally, if agriculture needs more different kinds of water (groundwater, desalted water, reclaimed water than the desalination plant can supply, the option of extra supply water) but that these are not necessarily apt in quality (salinity and ag- of water must be available. Again, the local supply system needs to be ronomic requirements) and quantity to the different crops cultivated. backed-up by an external supply system. Finally, the people of Gran Moreover, the use of underground water relies on a private market Canaria require a larger quantity and variety of products compared to and management and hence is subject to availability and price varia- the few vegetables and fruits produced in this system. The local crop tions beyond control. So, for the farmers, the desalted, more expensive supply system must be integrated in a larger food supply system. water is a warranty of supply under stable conditions (price and man- These observations might seem obvious, but the adoption of this agement). The possible subsidies received by the wind farm and T. Serrano-Tovar et al. / Science of the Total Environment 689 (2019) 945–957 955 Fig. 9. Economic representation of the WEF system relevant for local economic agents. desalination plant should guarantee their economic viability. The over the various functional elements (i.e., what should be considered farmers can assume the high cost of desalted water considering (i) the relevant information?). existence of agricultural subsidies, and (ii) the local market price policy. It is important to be aware of these location-specific arguments when 5. Conclusion considering similar solutions for other areas. Gran Canaria depends on desalted water in spite of its cost, because Water-Energy-Food (WEF) nexus security becomes extremely im- desalination is one of the very few viable water sources. However, the portant in isolated areas and islands when one or more of the natural re- supply of desalted water is normally prioritized for urban consumption. sources are scarce. However, the entanglement between water, energy Water requirements of the agricultural sector are high, and the eco- and food flows associated with the nexus entails a formidable epistemo- nomic return of agricultural water use is much lower compared to logical challenge for conventional reductionist science (Giampietro, other socioeconomic sectors. This means that agricultural activity re- 2018). This challenge calls for new approaches to the quantitative anal- quires a large quantity of water resources to produce comparatively lit- ysis of the nexus. tle value added. For this reason, agriculture flourishes only where water In this paper, a local case study in the Canary Islands—a private desa- resources are not limited or where the water used in agriculture does lination plant that uses wind electricity to provide water for an agricul- not represent an opportunity cost to the development of other sectors. tural cooperative located in the southeast of the island of Gran Canaria— On the other hand, the heavy dependency on external food sources was used to illustrate the potential of MuSIASEM in providing an inte- does severely affect the food security and food sovereignty of this terri- grated assessment of the WEF nexus in relation to sustainability. tory. This is why the Canary Islands try to control as much as possible The illustration of the MUSIASEM approach has shown that it is pos- their internal food production. However, a close look at this particular sible to generate a robust quantitative assessment of the energy, water local WEF system shows that the mix of crops produced does not supply and food nexus using insights from complexity theory, by establishing the basic elements of the local diet (based mainly on cereals, tubers, relations over processors conveying information referring to different grains, oils, and animal products), but focuses on fresh crops with high dimensions and scales of analysis. This allows a holistic reading of the costs to import due to their relatively high water content and perishable big picture as well as of the functioning of the various constituent com- nature. Hence, the food production of this local WEF system contributes ponents of the system, each of which provides relevant information only marginally to the food security of the archipelago. about the WEF system performance. In this way it becomes possible to This discussion seeks to emphasize the variety of issues and con- explain the characteristics observed at the large scale from the charac- cerns involved in a comprehensive assessment of the performance of a teristics of the functional elements operating at lower levels and to local WEF system in relation to its socio-economic and environmental identify limiting factors. context. Given the complexity of the picture, relevant information The flexible information space created by MuSIASEM can be used ei- should be gathered in the form of participatory research involving the ther (i) in a ‘diagnostic mode’ to explain the observed metabolic perfor- local actors. 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