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Introduction
The current urban model is not sustainable in many cities and green policies are some of the most controversial issues. This paper explores a trending topic: green urban areas. The increasing trend of urbanization needs to consider useful tools to address the problems of lack of sustainability. Those tools include green areas, either at street level (parks and trees on the streets) or in buildings (green walls, green roofs, balconies, and courtyards). Achieving a green city, that is, an urban area with an adequate proportion of nature in its own environment, depends upon the available space, the economic resources and the positive attitude of the citizens towards greening their city. Currently, these urban green areas include a broader concept than their traditional meaning (parks and gardens), as they also refer to public and private actions, commercial transactions and even social movements; thus, they are termed ‘urban green markets’ ( De Felipe & Briz, 2015).
There is a strong relationship between how green a city is and the space available, as well as how the inhabitants accept the incorporation of urban agriculture into the existing city. Humans have a biological need for proximity and contact with nature. This ‘biophilic’ idea (Wilson, 1984) includes several dimensions with positive interactions. There are several scenarios where people who are involved with nature experience positive benefits. Living around nature encourages physical activity and helps develop good habits (Astell-Burt, Mitchell, & Hartig, 2014), it increases life and quality conditions (Koshimizu, 2015; Takano, Nakamura, & Watanabe, 2002), and the presence of green landscapes reduces stress (Stronegger, Titze, & Oja, 2010). These experiences are strong arguments in favor of promoting urban nature in order to improve the negative quality of life situation in megalopolises (Maas, Verheij, Groenewegen, Vries, & Spreeuwenberg, 2006). Urban environments that include green areas are more appreciated than those without any green recreation space (Hartig & Staats, 2006).
Local regulations and urban planning are the instruments by which urban green areas are created. There is a need to evaluate the potential alternatives and to check how the goals can be pursued with the available resources before making a decision.
Urban green markets include a multifunctional range of heterogeneous products and services, which are difficult to evaluate (Baycan-Levent & Nijkam, 2004). There are some attributes that are common to all greening activities, since all these activities involve nature. However, other aspects of greening activities may raise other issues, such as the carbon footprint of green roofs, the humidity of plant walls or the benefits for pollution control where plants act as filters (of noise, dust, and heavy metals) (Jim, 2015). Also, there are other specific aspects whose relevance depends upon the final use: the appearance of the landscape, food farming, building design and energy saving (Jaffal, Ouldboukhitine, & Belarbi, 2012).
The evaluation of urban green areas should also consider where the benefit of the action occurs. In general, green actions are focused on people’s enjoyment (parks and gardens) and other benefits such as food production or energy saving, that is, searching for the positive effects on the final users of the project (Peck, 2014). In other cases, there are positive effects for the whole community which include landscaping, pollution control, water management, or a lower carbon footprint, and the evaluation should also take into account these effects. For instance, neighbors living in the area surrounding a green roof may see the value of their houses increase, without any investment or sacrifice of their own, with other people having been the promoters and having been in charge of doing the maintenance. For this reason, experts have to analyze the situation and look for methodologies which optimize the available resources by using a new management procedure and technologies. However, most research activities are focused on the environmental and technical dimensions using cost-benefit and investment analyses, while socioeconomic studies which involve direct interviewing of the final users are only marginal and complementary to other studies.
The information required for a transparent and efficient study of urban green areas may be obtained from secondary and primary sources. Secondary sources include statistics and publicly available published documents, and a review of secondary sources is the first step in an analysis and evaluation procedure. As a complement, primary information data may be obtained in different ways. It could be done, for example, with personal direct interviews with stakeholders. The analysis may be focused on the historical evolution or may be done in a cross-sectional way. The objective of this work was to test the usefulness of a method for identifying urban green areas, through a case study in Madrid, and to know the attitude of the actors involved in the process of urban ground and roof greening.
Materials and methods
The motivation for the study of green areas and the selection of the appropriate methodology come from the need to change the current unsustainable city model. Vegetation improves air quality by providing oxygen, removing dust particles and heavy metals, retaining moisture, acting as a thermal and acoustic insulator, as well as providing space for enjoyment. All these arguments must be explained to residents to guide them in the decision-making process for urban plans and policies.
Green urban areas have been studied previously in the literature, focusing on limited problems and planning. Issues like the study of hedonic aspects (Bengoechea, 2003), urban density (Yamamoto, 2010), landscape ecology (Jim & Chen, 2003), food supply (Orsini et al., 2014), property values (Bolitzer & Netusil, 2000), wetlands (Mahan, Polasky, & Adams 2000), air quality (Smith & Huang, 1995), or urban trees and forest (Nowak & Stevens, 1996; Tyrvainen & Miettinen, 2000) have been the object of study. However, to our knowledge, there are no papers which combine the study of technical issues with personal opinions.
Traditionally, urban green areas were located at street level, in reserved spaces and generally public areas. Today, new construction techniques allow for utilizing available space (roofs, facades, patios) for vegetated areas. In this paper we focused on the roofs of buildings where the technical methodology has allowed us to identify the available surfaces in the districts of Madrid, Barcelona and Seville, and quantify their importance through a series of indexes. The next step was to apply in one of the selected districts (Salamanca, in Madrid) a socioeconomic methodology, which consisted of consulting the residents of the district about their opinion on the green areas and their willingness to collaborate in the installation and maintenance of a green roof on their own buildings.
Different methodologies provide information on urban green areas and are used for varied purposes. The techno-socioeconomic methodology is recommended when there is a direct interaction and dependency between both disciplines, technical and socioeconomic. It is useful when the decision makers have to pay attention to interdisciplinary teams. Contingent evaluation analyses projects with services to urban communities, and policy makers want to know the opinion of the final users prior to the development of the project. The total economic evaluation has a macroeconomic overview and considers the commercial and public values of the potential project. Its main utility arises in the first steps of urban planning. The hedonic price system, focusing on a microeconomic level, is oriented towards urban neighborhoods for a better understanding of the relevant factors included in urban green spaces. The forecast evaluation method may help to understand the potential impact of different projects in the coming future. It focuses on the opinion of experts in the area of analysis. Finally, the value chain evaluation is recommended when the performance of the project is related to different actors, and it is important to understand the attitude of each of them.
Below, we explain some of the most significant characteristics of the different methodologies that could be applied in the urban green areas, which finally leads us to the one selected for this paper, the techno-socioeconomic evaluation.
a) Techno-socioeconomic evaluation. This is a cross-sectional study that is particularly recommended for cities with spaces that may be underused and in which green activities could be developed. However, there are some restrictions to be noted in order to efficiently perform the study: i) Identification of the geographical spaces available. In the case of vertical agriculture, there must be underused areas (walls or roofs) on which green orchards/gardens may be installed; ii) Knowledge of the attitude of the main socioeconomic actors involved (neighbors, entrepreneurs, policy makers, civil servants, non-governmental organizations [NGOs] and associations); and iii) Benefit/cost ratio of the green project that is developed (Briz, Duran, & Röhrich, 2015).
With these goals, a combination of technological, innovation and socioeconomic analysis is carried out following the various steps below, and the costs should be shared by the promoters and the people of the city (through subsidies, taxes, administrative facilities, etc.). The steps of the process are: 1) The use of innovation technology applications to measure the available spaces that may support green activities; 2) interviews with the main actors in the urban district in which the project may be developed; and 3) an evaluation of the benefits that would be obtained from the creation of the green areas. The benefits may be tangible or intangible, and there may be a direct impact on the promoters (a better environment, food, recreation, and employment) and indirectly on the neighborhood (local climate, air quality, heat island effect, and landscape).
b) Contingent evaluation. This evaluation is based on information obtained from people who use the product or service through interviews (face-to-face, telephone, Internet, fax, mail, etc.). The goal is to know their opinion of the utility of the product or service, their willingness to pay and what modifications should be made to improve the product’s quality and efficiency. This is the first step in understanding the green market situation, and may be used for later action (Kallas, Gómez-Limón, & Barreiro, 2007).
c) Total economic evaluation. In this method there are two areas of study: the transaction value (the commercial value) and the public value (environmental and non-commercial factors). The commercial value is important for customers and entrepreneurs directly involved in the market transaction (that is, buyers and sellers), and includes prices, financial conditions and other matters. The environmental value is more related to externalities not considered by the market, and includes positive results for the neighborhood and the urban area as a whole (Dickinson & Calkins, 1988).
d) The hedonic price system. This method is applied when there are goods or services that are the result of the aggregation of several characteristics that satisfy different goals but cannot be split into isolated parts. This is the situation for multipurpose green areas that have an effect on air quality, food supply, biodiversity, landscape and leisure, water management, and energy and noise control. The area has to be evaluated on a global basis; some of these effects may not even be relevant for the particular city of analysis. In any case, each community has to establish its own attribute preferences (Shilling, 1992).
e) Forecast evaluation. The analysis of how the green city evolves, in response to different city planning policies and economic or social restrictions in future years, is very important for urban designers, social communities and firms. As a first approach the Delphi method may be used; this requires the researcher to obtain the personal opinions of the stakeholders involved in the urban greening activities. The interviewees may be community leaders, builders, urban planners, civil servants, policy makers, university researchers, or NGO employees. Different waves of interviews are carried out, with the intention of obtaining a convergent view about the state of the green areas in the future (Echenique, Hargreaves, Mitchell, & Namdeo, 2012).
f) The value chain evaluation. This method is recommended when there is a continuous flow of products and services in the urban green market, with different sources. This is the situation for urban food agriculture, where stakeholders, from producers to consumers, meet at the market. Urban and rural agriculture compete with their products, but from opposite positions. Rural food products usually have lower prices, because of their lower production cost, as farmers operate with economies of scale and are more specialized. By contrast, urban products are more expensive but have specific attributes (not always evaluated in traditional markets), such as lower energy and a smaller carbon footprint, and they provide positive benefits to urban dwellers. In this case, sustainability is a key factor in the decision buying process. A method that can be applied in this case, with a comparative analysis, is the value chain, which has been tested in several countries for regular markets (Briz & De Felipe, 2012).
The analysis carried out in this study covers vertical and traditional agricultures, using a techno-socioeconomic evaluation.
Techno-socioeconomic evaluation of vertical agriculture
This study consists of two parts. First, there is a technical identification of the available spaces (Torres & Arranz, 2015), and secondly, there is a search for socioeconomic information about the attitude of the subjects who live in the area. Following this methodology, the first step is to analyze the green roofs, with a techno-agronomical focus, that is, the degree of nature present in the environment. The traditional way is to study the characteristics of the facility and the maintenance needed for the roof (a structural focus), as explained in Table 1. This analysis provides valuable information, but we need a complementary view with a different focus, a landscape focus, for our study. Therefore, we propose a Willingness-To-Green (WTG) index, an index that provides information about the presence or absence of plants on roofs, in order to gain an initial view of the greening rooftop situation. This was the methodology applied in this study, as a pioneer method in this research area.
Table 1 Structural Analysis of Green Roofs.
| Type of Green Roof | |||
|---|---|---|---|
| Dimensions | Extensive | Semi-intensive | Intensive |
| Substratum-build | 60-200 mm | 120-250 mm | 150-400 mm |
| Weight | 60-150 kg·m-2 | 120-200 kg·m-2 | 180-500 kg·m-2 |
| Maintenance | Low | Periodic | High |
| Cost | Low | Medium | High |
| Irrigation | Low | Periodic | Regular |
| Plants | Sedum and grasses | Grasses and herbs | Perennials and trees |
Source: International Green Roof Association (IGRA, 2007)
In Table 2, several categories for the green density were established: Very High (VH), High (H), Medium (M), Low (L) and Non-Existent (N). As a first step, we define the Green Evaluation Weighted Index (GEWI), by the addition of green areas on roofs and walls:
where:
N = number of green spots (roofs [horizontal], walls [vertical]) located using Google Earth (for roofs) and by direct observation (for walls). In English, the literature on “vertical agriculture” includes roofs and walls, but the translation in Spanish, “agricultura de altura,” also refers to roofs and walls.
WTG = Willingness-to-green
For example, if in a certain street there were three roofs and walls with a High density (50-75 % green area), which means High WTG, and two roofs with a Low density (< 25 %), which means Low WTG, the GEWI will be:
Table 2 Willingness-to-Green (WTG) Index.
| WTG | Green Weight Index | Green area (%) |
|---|---|---|
| Very High (VH) | 6 | >75 |
| High (H) | 4 | 51-75 |
| Medium (M) | 3 | 25-50 |
| Low (L) | 1 | <25 |
| Non-existent (N) | 0 | 0 |
Source: Author-made (2015).
For the first part of the study, it was necessary to select the districts to be studied. In this case, a total of seven districts were randomly selected by convenience, provided the available resources, but with different population characteristics (income and age): three in Madrid, two in Barcelona and two in Seville (Spain). There were two main reasons for choosing these districts: firstly, they were urban neighborhoods with clear boundaries and, secondly, they had a high level of activity (houses, offices, shops, etc.), which would make direct interviews possible in the second phase of the evaluation.
The study of vertical agriculture was carried out with the aerial view information from Google Earth. This data was collected for the seven selected districts, and the green intensity was measured. In each district, the number of streets to be studied was identified, and the green areas on both roofs and courtyards were measured. Each roof and courtyard of the selected streets was carefully measured to see what percentage of it was covered in vegetation, using the WTG index. They were classified according to the categories defined above. With this, we obtained an overview of the greening situation on each street and the average area of courtyards and roofs that was green.
In what follows, we explain in detail the procedure that was followed in each one of the districts. For example, if we take the streets in Salamanca district and we measure the greenness of the roofs on those streets, we obtain 2 Very High (VH), 10 High (H), and 28 Low (L); we multiply those roofs by the WTG index for each type and the result is a GEWI of (12 + 40 + 28) = 80. As another example, if we consider the courtyards in the district of San Martí, in Barcelona, the total presence of urban agriculture in the studied streets is: 6 Very High (VH), 14 High (H), 49 Medium (M), and 193 Low (L). When multiplied by the coefficients (36 + 56 + 147 + 193), the GEWI was 432. A last example is a case from Seville: the courtyards in the district of Nervión. Urban agriculture has the following distribution in the courtyards of the 30 streets studied: 180 low (L), 10 medium (M), 8 high (H), and 22 very high (VH). The GEWI equals to 180 + 30 + 32 + 132 = 374.
Socioeconomic evaluation of vertical agriculture
For the in-depth socioeconomic analysis, one of the districts was selected, the Salamanca district of Madrid. This district was chosen because it is a central district with high traffic and commercial activity. Among European cities, Madrid has one of the higher green areas per capita (70 m2), and the Salamanca district has 13,000 street trees, but no big parks inside its perimeter. Because the area is very built up, one of the possibilities for increasing the number of green areas is through vertical agriculture, in patios (courtyards) and on roofs. The district is located in downtown Madrid, with an area of 540 ha and a total of 144,000 inhabitants according to the latest census in 2014. The economic activity is focused on offices and shops, with a yearly income per capita of 27,000 euros in 2009. The area was one of the first modern urban planning areas, developed by the promoter Marques de Salamanca, in a grid organization of parallel streets.
The socioeconomic study consisted of face-to-face interviews with residents in the area, in order to find out about their attitudes towards urban agriculture in their neighborhood. First, we tested the survey with a small pilot convenience sample (n = 16 people, University employees). Ultimately, a total of 178 face-to-face interviews were carried out during April 2015. Interviewers spent several days in the mentioned districts gathering the relevant information. In some cases, previous appointments were made with homeowners, office and store representatives, but in other cases, people who were entering houses in the district were directly approached. Some residents rejected taking part in the interview and some questionnaires were not fully completed, so they were not taken into consideration in the final number.
Results and discussion
Techno-socioeconomic study
Once all the districts had been studied, the results were compiled into Table 3. From these results, it can be clearly seen and quantified that the districts of Salamanca (Madrid), San Martí (Barcelona) and Nervión (Seville) have a higher GEWI, that is, a higher presence of urban agriculture on their streets. Since the index just refers to buildings and houses, it could be the case that there were parks and recreation areas with trees or gardens in districts with a lower GEWI. A lower GEWI does not mean “no trees” or “polluted” areas. The concern is just with urban agriculture.
Table 3 Districts studied in Madrid, Barcelona and Seville where places available for urban green areas were identified.
| District | Number of streets | Total | Average | ||
|---|---|---|---|---|---|
| Courtyards | Roofs | Courtyards | Roofs | ||
| Salamanca (Madrid) | 28 | 210 | 70 | 7.5 | 2.85 |
| Chamartín (Madrid) | 103 | 1,302 | 192 | 12.6 | 1.86 |
| Prosperidad (Madrid) | 16 | 94 | 21 | 5.9 | 1.3 |
| San Martí (Barcelona) | 34 | 432 | 128 | 12.7 | 3.7 |
| Eiample (Barcelona) | 23 | 238 | 45 | 10.3 | 1.9 |
| Nervión (Seville) | 30 | 374 | 32 | 12.5 | 1.1 |
| Cero-Amate (Seville) | 57 | 290 | 40 | 5.1 | 0.7 |
Source: Author-made, 2015
The technical study provides an easy, practical and affordable instrument to describe the green areas in the roofs or walls of an urban district. It is possible to measure and quantify the potential area to green, and its success depends on the final use by the residents of those buildings.
There are other sophisticated and expensive methods (which were not available for this study) that enable the possibility of not only measuring the surface, but also the inclination (tilt) of the roof (Torres & Arranz, 2015). These methods allow for designing specific green infrastructures to be installed on those roofs. Another important issue in the technical analysis is the capacity of the infrastructure to support a potential green area, either extensive (with a low density of plants) or intensive (with a high density of plants).
Socioeconomic study
The second part of this research involved a study in the Salamanca district of Madrid, which was selected because of its geographical and socioeconomic characteristics. It is located in downtown Madrid and it is one of the most dynamic districts regarding business and commercial activities. The pollution is very high in this district (Dirección General de Sostenibilidad y Control Ambiental, 2016) and the possibility of creating parks or gardens at street level is almost non-existent, given the layout of streets and buildings. However, the buildings offer many available roofs for green infrastructures, and the goal was to learn about the residents’ opinions on these issues.
Information on the attitudes, concerns and desires of the inhabitants of the buildings was gathered through personal interviews. The largest group of interviewees (60 %) were owners or tenants of their homes/offices. There were also doorkeepers (15 %) who had good information about the situation. Around 60 % of the people interviewed had a roof that could be transformed into a green space. The majority of the roofs (61 %) were managed by the community neighborhood, and only 26 % of the roofs had private owners. Some people did not know who was responsible for the management of their roof. The preference of end use of the roof or courtyard was even: either garden with flowers (50 %) or vegetable garden (50 %).
The main obstacles that interviewees expected to encounter if there were a new use of their space were a lack of knowledge on how to manage it (32 %), the probable cost of the new activity (29 %), and excessive bureaucracy that would have to be faced if the space were to be converted into an orchard or garden (15 %). In relation to the management of the new green space, most of the interviewees would prefer to delegate the tasks to an expert (either public or private) (30 %), while some would prefer to manage the area personally or with friends and family members (25 %). In some ways, these answers are related to a low level of knowledge of farming practices among urban citizens.
Moreover, there was a positive reaction to the idea of green roofs, and the interviewees were willing to use their roofs in a different way. The maximum amount they would invest in the reconditioning of their roofs, in their “new green adventure”, is, for 76 % of respondents, less than 3,000 euros, while 18 % would be willing to spend 3,001-5,000 euros and 6 % more than 5,000 euros.
In summary, the Salamanca district of Madrid has high potential for installing green roofs, according to the technical and socioeconomic information. Around 475,000 m2 gives many possibilities for transformation, either into regular green roofs or intensive capital and labor elements (greenhouses). Given the results of the personal interviews, we suggest that the promotion of green roofs in the Salamanca district follow different strategies. One action should be oriented towards community neighborhood roofs (61 % of the available ones), and the benefits for the residents: common activities, private parties, ornamental orchards, etc., depending on the use they want.
Another strategy could be aimed at private owners as they have the opportunity to expand their home space into outdoor space with recreational use. This possibility is very popular and there are already different initiatives to encourage activities. The Botanic Garden, University and City Hall Extension services offer introductory courses for people interested in creating their own orchard or garden. This is a key issue since many interviewees were interested in this option, but did not know how to manage it (33 % of the people). Also, almost one third of respondents (30 %) were in favor of delegating the maintenance of the gardens or orchards, so this is a great opportunity for private entrepreneurs who are already starting businesses focused on these specific urban areas.
Another important strategy is the simplification of bureaucracy and facilitating the conversion of the new green roofs. Residents were willing to install the roofs, but since the innovative investment is high, initiatives such as direct subsidies or credit would encourage the conversion, and could complement the initial outlay mentioned by dwellers which was between 3,000 and 5,000 euros.
Conclusions
Increasing the amount of green spaces in buildings could help alleviate the serious pollution problems faced by many cities. The task of this paper is to identify the main players in the urban green areas, their opinions and their reactions to the current conditions, and then show them the potential solutions. This paper proposes an original technical and socioeconomic methodology in two steps. It is an affordable and easy methodology that could be used by researchers. We propose a new index to measure the “presence of green” in an urban environment. This index, which was named Green Evaluation Weighted Index (GEWI), establishes the relationship between the number of roofs and the WTG of the inhabitants. This study showed the differences in potential green roofs between different districts. The second step was the socioeconomic study in the Salamanca district of Madrid because it is crucial to know the attitudes and needs of the urban residents, and there is a great opportunity to improve their quality of life through the creation of green roofs. With both analyses, we could define several strategies to improve urban quality of life through green roof infrastructure.
