Conceptual Model for Integrating the Green-Blue Infrastructure in Planning Using Geospatial Tools: Case Study of Bucharest, Romania Metropolitan Area (2024)

1.1. Green-Blue Infrastructure Approach

Globally, natural landscapes are undergoing drastic changes due to anthropogenic pressures, which include habitat loss and fragmentation [1,2]. Neglecting ecological processes in urban land use decisions can lead to the degradation of the integrity and diversity of landscape structures, the deterioration of ecosystem functions in natural areas and urban green spaces, and fragmentation or even destruction of habitats [3,4,5]. The long-term effect of increased landscape fragmentation is the decline in biodiversity, ecosystem resilience and ecosystem services [6,7]. As a result, the quality of urban life and sustainability of cities decline.

Europe, as a territorial dimension, is characterized by a fragmented natural landscape, intersected with high human population densities. The need for measures to conserve habitat connectivity is of great importance and urgency as a result of the recognition that habitat fragmentation can exacerbate the potential impacts of climate change [8]. That is why, in 2013, the European Commission asked European countries to make a special effort to protect their last remaining natural habitat areas. The European Commission considers green-blue infrastructure as infrastructure capable of providing sustainable management of green and blue areas in the context of climate change and providing a wide variety of benefits to society [9]. The European Commission states that there is no need for legislation designed exclusively to enforce the implementation of the green-blue infrastructure concept in European countries and calls instead for the use of existing legislation, policy instruments and financing mechanisms [10]. These needs also call for studies on the green infrastructure, making it an important research topic.

1.2. Theoretical Aspects

The main attributes of green-blue infrastructure are spatial connectivity, multi-functionality, integration with other infrastructures and a multi-scalar approach. Connectivity is a particularly important value for green-blue infrastructure due to its ecological and social benefits [11,12,13,14]. Connectivity is the key principle of spatial organization to ensure a better opportunity for the provision of ecosystem services, which can affect urban hydrology, mobility, recreation and cultural assets. In addition, the functional and spatial connectivity of open spaces is essential for maintaining the ecological role of mitigating and adapting to climate change and increasing the value of ecosystem services, including those related to health and recreation [15].

Understanding multifunctionality is central to the green-blue infrastructure approach to land use and spatial planning. Where land serves a range of functions, multifunctionality is the ability of green-blue infrastructure to provide a much greater range of social, environmental and economic benefits than could otherwise be provided [16]. Integration expresses the physical and functional relationships of green-blue infrastructure with other types of infrastructure, and successful planning of green-blue infrastructure naturally requires an integration of different scales of planning and implementation [17].

1.3. Planning Approaches

Formal strategies such as green belts, green wedges and green ways can counteract spatial fragmentation by providing green spaces and open spaces close to residents and connecting to rural areas [18].

The green belt is the best-known model of green space for its connection with the idea of a garden city and its spread throughout the 20th century. The main function of the green belt is to ensure the control of urban sprawl. Over time, green belts have become multifunctional and continue to have a major impact on urban design. The idea of a ring of countryside surrounding an urban area to prevent sprawl emerged in the 1930s and spread to post-war London, being passed into national law in 1955 [19]. Currently, many Western European cities have demarcated and developed green belts with the role of stopping the unplanned expansion of the periphery in the territory and connecting the main areas with tourist and landscape potential.

Green wedges constitute a coherent structure of areas with high recreational, natural and cultural values. They form an amalgamation of green areas and watercourses in relation to built-up urban areas and provide good access to urban nature [20]. This type of green area planning was implemented in the Scandinavian countries, where both historical traditions and the topography of the designed surfaces were taken into account. Green belts and green wedges have in common that they often follow (public) transport corridors, and especially railways [21].

The concept of greenways appeared in North America at the beginning of the 20th century. Fabos [22] noted three types of benefits of greenways: ecological, recreational, and historical/cultural. They were created to develop greenway systems that interconnect cities with natural areas or forest areas in metropolitan areas [23,24].

Green corridors were designed as habitat areas for connecting wildlife populations (colonization, migration, etc.), areas that have become fragmented over time by human activities [25]. These corridors can include rural areas, river courses, lake areas, hill areas, natural forests or agricultural areas, being a logistical support for urban development, landscape protection and a healthy urban environment.

1.4. Implementing the Green-Blue Infrastructure

The new concept of green-blue infrastructure offers potential for a more comprehensive analysis and promotion of the connectivity of green and blue spaces and landscape integration. Initially, the concept included an aesthetic vision; it gradually morphed towards a very ecological view and later became a tool for sustainable land use planning [26].

The combination of methods that ensure the connectivity of green-blue infrastructure and its multifunctionality should be recommended, especially for city regions, due to the need to protect nature and biodiversity conservation, on the one hand, and sustainable development with its environmental, social and economic needs, on the other hand [17].

A positive example of green infrastructure implementation is the United Kingdom, which, in its national planning policy, indicates that plans at all levels must be approached strategically to conserve and enhance the network of habitats and green infrastructure [27]. The Good Practice Guide for Natural Environment Planning [28] states that green infrastructure requirements should be considered in the early stages of planning and should be included in drafting development proposals. A good practice example of implementing the concept of green-blue infrastructure is the revised planning legislation in Sweden, which recommends that Swedish cities develop a green infrastructure plan as an essential part of the urban development plan [29]. Thus, green infrastructure was implemented both at the local level (Stockholm city level) and at the regional level—the Regional Development Plan for Stockholm.

Unfortunately, in Eastern European countries, the concept of green-blue infrastructure has been approached to a much lesser extent than in Western European countries. The exceptions are the Czech Republic and Slovakia, which, since 1970–1980, have developed a multi-level ecological network, called the Territorial System of Ecological Stability of the Landscape (TSES) [30].

1.5. Green-Blue Infrastructure Planning Steps

Research shows that the implementation of green-blue infrastructure in European countries has focused on measures to improve ecological networks and preserve green space [31]. Compared to ecosystem services, landscape services take more into account the spatial patterns resulting from human and natural processes, and the social dimension [32]. According to the literature, the methods of planning and evaluating the green-blue infrastructure system in metropolitan areas of large cities include several stages:

However, the boundary between green-blue solutions and existing ones is still unclear. Nesshöver et al. [34] proposed the introduction under this umbrella of green-blue solutions by addressing the following four areas of intervention: (a) maintaining biodiversity, ecological functions and/or ecosystem services, where human management interacts with natural processes; (b) restoration of ecosystems affected by human activities; (c) design solutions that address challenges such as climate change or risk management, and (d) sustainable use of nature to mitigate challenges affecting quality of life, including vulnerability, social equity, economy and culture.

Even if the studies recommend using qualitatively different datasets at regional and local levels, they do not take into account the ownership regimes and the overlap of geodata obtained with high-resolution satellite images or obtained using UAVs. The overlay of processed geodata with satellite images creates the prerequisites for developing a much more consistent green connectivity analysis and avoiding, as much as possible, the intersection of green corridors connecting with private land surfaces. At the local level, the resulting green-blue connections can be numerous, many of which are difficult to implement. The choice of viable connections at the local level requires the use of old plans and maps of the city, which provide information on the fragmentation of green-blue areas over time.

1.6. Green-Blue Infrastructure in Romania

Although Romania is one of the first countries to ratify the European Landscape Convention, adopted in Florence on 20 October 2000, it has not taken any measures arising from this convention [35]. Ignoring the issue of landscape as a fundamental element of the national cultural heritage and as an essential mechanism of sustainable development has resulted in the loss of many unique natural areas. In this regard, the landscape represents the integrative tool of policies to protect cultural and natural heritage with development policies. However, its importance has remained until this moment only at the declarative level, as no operationalization mechanisms were provided in the territory [36].

In Romania, since 2001, as required by Law no. 351/2001 on the approval of the National Territorial Development Plan, Section IV—Settlement Network [37], it was necessary that urban plans provide for the establishment of green belts or green areas around the city of Bucharest (the country’s capital) and first-class cities. Later, Law 351/2001 was updated by Law no. 190/2019 [38] which provides for the establishment of green belts or green areas also in the case of second-class municipalities. Unfortunately, so far this requirement has not materialized.

In Romania, development strategies and plans are the most important documents for the integration of green-blue infrastructure at local and regional level [39]. But general urban plans and local action plans for the environment offer a rather limited vision in relation to the principles of implementing green solutions, and there is a low degree of implementation in the actions proposed at the level of cities in Romania [40].

The green-blue infrastructure of Bucharest and its dynamic were investigated by Petrişor et al. [14,41], based on Urban Atlas data. According to the aforementioned studies, the green-blue infrastructure of Bucharest consists mainly of agricultural areas (64%), followed by green spaces (20%), forests and natural areas (11%), and leisure areas (5%) [41]. As can be seen, landscaped areas make up one fourth of the green infrastructure. During the two periods covered by Urban Atlas Data (2006–2012 and 2012–2018) Bucharest experienced the fragmentation and loss of its green infrastructure; although some gain occurred in both periods, it was not sufficient to compensate for the loss [14]. For each category of green-blue infrastructure, the loss was proportional to its share.

Bucharest is one of the most polluted cities in Europe, with an average area of green space per inhabitant below 10 square meters, compared to the requirements of the European Union, which recommends 26 square meters of green space per inhabitant, or the World Health Organization, which recommends 50 square meters per inhabitant [42].

1.7. Need for Research

In Bucharest, a study regarding the identification of a green-blue infrastructure plan is absolutely necessary to make green-blue infrastructure an indispensable tool for territorial planning at all levels.

By addressing the previous shortcomings, the purpose of this study is to define an innovative methodology based on GIS tools that leads to the design of green-blue infrastructure both at the local level of a large city and at the regional level of a metropolitan area. Even though GIS tools are mainly used in connectivity analyses of wildlife habitats, they can also have very accurate results in green-blue connectivity analyses, provided that qualitative data is used and realistically processed to identify the resistance raster of moving through the landscape. The key to designing green-blue infrastructure at the local and metropolitan levels is to combine connectivity analysis with the conceptual model of this type of infrastructure. Data on the ownership of the studied areas and the use of high-resolution satellite and UAV images create the prerequisites for correcting the components of the green-blue infrastructure, so that the results are also validated on the field.

The results of this study contribute as a model of good practice, both to the creation of the institutional framework at the national level and to the provision of action models for the conservation of biodiversity and mitigation of climate change within the Urban Policy of Romania 2022–2035, a document to be approved by Government.

2.1. Principles

Since the lack of management plans for natural and cultural landscapes of national and local importance has led to the degradation of many of those from the metropolitan area of Bucharest, there is a need to develop and implement innovative methods of delimiting the green-blue areas and corridors of habitat. The methodology proposed in this endeavor starts from some basic principles related to the establishment of a functional connectivity both within Bucharest and between it and its peri-urban area.

• The first important aspect is establishing a balance between the interests of residential development and the use of open space. The key element is preserving the multifunctionality of open space, specifically green-blue areas and habitat corridors that must be secured in order to support ecological functions and benefits for people in terms of social well-being and recreation. Open urban areas remain the most important spaces of social contact for city dwellers despite technological progress and its impact on the social life of the individual (social networks, virtual reality, etc.), so their importance for cities remains undisputed [43]. Urban public spaces represent those places located in cities and which are open (squares, parks, as well as connecting spaces such as sidewalks and streets).

• Successful green-blue infrastructure planning naturally requires the integration of different planning scales (local/regional level). It is necessary to identify the corridors and blockages in the landscape for the connection of green-blue areas, the movement of species and their mapping.

• Another important aspect is the need to expand green areas inside and outside the city to improve the microclimate that contributes to lowering the temperature and the urban heat island (UHI) effect, reducing energy consumption in buildings, managing rainwater, increasing the resilience of ecosystems by improving their functional and spatial connectivity.

Starting from these principles, a territorial analysis scheme was created that includes the planning concepts of green-blue infrastructure connecting green space, open areas, road and rail systems and water sources as elementary components in built-up urban areas and in peri-urban areas.

2.2. Input Data

The methodology for identifying the green-blue belt of the Bucharest metropolitan area (Figure 1) was designed so that it can be used with input data at different scales, since necessary input data are available with different quality levels. The quality of results is based on the hom*ogeneity and quality of the input data.

Data used: For Bucharest, digital data taken from the Bucharest Urban Plan, government sources and digital data from the Urban Atlas were combined, and for the metropolitan area, CORINE 2018 database and data from the National Cadastre Agency were used.

Data processing was based on the authors’ experience in ecology and spatial planning and on European research on connectivity and the provision of landscape services.

The evaluation of the green-blue infrastructure connectivity was carried out based on innovative tools of the ARCGIS 10.6 (Figure 2).

Starting from applying ecological landscape principles and evaluating existing green spaces, the methodology proposes four green wedges and several green corridors from the suburbs to the center of Bucharest (Figure 3). The green wedges were designed along the future radial roads of the A0 belt. The two green belts are intended to protect the belt ring of Bucharest and the future A0 highway from the winds coming during winter from the east. These green belts have the role of stopping urban sprawl and supporting human activities such as walking, cycling and recreation.

3.1. Metropolitan/Regional Level

By using Linkage Mapper, the resistance raster and core areas from the metropolitan area of Bucharest, we obtained the map representing connectivity at the metropolitan level (Figure 6).

It can be seen that, in the south-west part around the belt ring of Bucharest (the first ring), there were no elements of the green-blue infrastructure, so that the green belt could not be closed. Instead, there were sufficient core areas and matrix areas to enclose the green belt around projected A0 freeway second ring). In Figure 6, we also see the links (ecological corridors), in purple, computed with Linkage Mapper, which connect with core areas.

From the maps published 100 years ago, we noticed that many green elements we proposed existed at that time. It is necessary for renatured rivers and streams to be re-arranged by including a wide variety of plant species. They must be used as easily accessible open recreational spaces for people, to bring vitality to the metropolitan area of the city. Also, there is much vacant land that needs to be ecologically restored and returned to nature as they had ecological functions in the past.

3.2. Local Level

At the local level, we used the data set from the Bucharest Master Plan, supplemented with geodata on green areas, lakes and rivers in the core of Bucharest, agricultural areas and all existing streets and boulevards in 2022. As core areas, we used green areas from Bucharest with a surface of more than 4000 m² and core areas around the central area of Bucharest.

Using Linkage Mapper, the resistance raster and core areas for Bucharest, we obtained a large number of green connections along some important streets and boulevards (Figure 7).

The analysis carried out (Table 1) shows that many of the resulting ecological corridors at local level (green color) develop along major boulevards, which means that there is a need to widen major boulevards and arteries and plant trees. We can see four compact areas (orange color in Figure 7) that contain a lot of fragmented green spaces and some areas—especially in the south and west of Bucharest—that require urgent implementation of green solutions. It results that in the urban area of Bucharest, especially in the city center, but also in certain neighborhoods, there are acute conflicts between high-density development and limited land, with insufficient open spaces for the population.

Taking into account the very high density of housing in Bucharest, innovative green solutions that can contribute to urban regeneration are recommended. Among these we mention green roofs (including solar roofs, for water drainage), green walls and vertical gardens, green street furniture, permeable pavements, and greening linear transport routes.

There is a continuous fragmentation of the areas that contained green spaces 70–80 years ago in Bucharest, caused by the continuous expansion of residential neighborhoods [45]. For this reason, there is also an urgent need for the regeneration of abandoned commercial and industrial areas [46], and, last but not least, the legal designation of some urban protected areas, as an absolutely necessary tool for Bucharest in order to achieve sustainability and resilience targets.

4.1. Scientific Significance and Importance of Results

From a scientific point of view, the research carried out represents a viable technical solution for stakeholders, taking into account the quantity and quality of data used, and the innovative IT solutions on green-blue infrastructure. The technical solution is safe and effective under the conditions of good knowledge of the research context and rich experience in using GIS tools. This study presents a way to connect the green-blue areas inside and outside Bucharest, so that road transport rings are surrounded by green belts that can stop uncontrolled urban expansion.

The GIS solutions chosen to define connectivity were designed to support wildlife habitat connectivity analyses. The tools Gnarly_Landscape_Utilities and Linkage Mapper used in this research are usually used in GIS mapping. When defining the models with lowest costs, cumulative cost maps are generated; they highlight areas with lowest costs, respectively, the least expensive ways to travel between core areas. These tools create very accurate connections if the data are of good quality and well processed. A disadvantage in implementing these tools is the very demanding hardware resources for computing connections. The use of high quality geodata in GIS creates the prerequisites for overlaying with high-resolution satellite or UAV images, which leads to the correction of identified errors and the correct definition of green connections.

At the same time, the research aimed to develop a methodology that would contribute to a better implementation of the green-infrastructure concept in the urban and territorial plans of the metropolitan area of large Romanian cities.

From previous experiences with landscape and connectivity analyses within national ecological networks, we have found that, for a proper assessment, a fundamental step in such studies is the collection of high quality data, as well as the ability to manage the large amounts of data available. Criteria are needed to determine which data to include or exclude from the different sets of information available for connectivity assessment. Assessment processes must be iterative in nature so that the data systems used are able to integrate new and better performing data to improve the quality of assessment tools.

Therefore, the data used in this study, both locally and regionally, required many data sources and additional compatibility analyses with GIS systems. GIS models are widely used tools for designing ecological corridors, and least-cost modeling allows for parameterization and testing through empirical studies. We used two GIS tools, extremely precise in defining the connectivity analysis. Starting from a conceptual model of extended green-blue network connectivity and mapping the components of the green-blue network of the Bucharest metropolitan area (core areas, ecological corridors, buffer zones and ecological reconstruction areas), we were able to obtain a green-blue infrastructure model that introduces mandatory environmental regulations for territorial planning, taking into account ecological resilience, ecosystem vulnerability and ecosystem support capacity.

Overall, our study makes a significant contribution towards the implementation of the concept of green infrastructure in urban and spatial planning, providing tools for planning the green-blue infrastructures of large cities and their metropolitan areas. Implicitly, our methodology helps towards reducing urban sprawl, improving air quality and mitigating environmental threats due to climate change, contributing ultimately to urban sustainability.

4.2. Internal Validation Related to Research Objectives

The lack of management plans for natural and cultural landscapes of national and local importance determined the need to develop an innovative study for designing the green-blue infrastructure of the Bucharest metropolitan area. This study approaches new ways and re-combines natural resources in different and creative ways, so as to control the environmental challenges that Bucharest encounters.

Three main elements contributed to the identification and operationalization of green-blue infrastructure in the Bucharest metropolitan area: Gnarly_Landscape_Utilities and Linkage Mapper GIS tools; data on the property regime in the studied areas; and high-resolution satellite images. With their help, connectivity analyses of green-blue areas were carried out and connections of green areas defined by intersecting as few private surfaces as possible.

The principles of implementing green solutions must be compatible with the general principles of territorial planning and environmental protection. The most difficult problem in the delimitation and management of a green-blue infrastructure of metropolitan areas in large cities is the collection of data and assessment of their quality.

For this reason, various sources of data are aimed at regional- and local-level coverage. It was necessary to join some data sources from the past with current ones and those from future plans and projects, using new technologies, in order to model connectivity needs in the face of imminent climate change. At the same time, we took into account that the spatial and temporal scale of assessing green-blue infrastructure connectivity in a large city (such as Bucharest) is one of the most important aspects of research [47].

Land cover maps available at European Union level, such as CORINE2018 database or the Urban Atlas, can help with a general assessment of green-blue infrastructure connectivity, but cannot provide accurate information on the local network of green-blue infrastructure elements. Therefore, the structure of the database had to be supplemented with the available, detailed regional and local data, such as data acquired from the National Cadaster Agency, Romanian Waters, Cadaster of green spaces in Bucharest, Agricultural Cadaster or data taken from Bucharest Master Plan. The IT solutions used in evaluating the spatial connectivity of green-blue infrastructure components are modern state-of-the-art solutions. The mapping of corridors also highlighted existing points of conflict between the continuity of connecting corridors and transport infrastructure [48]. These conflict points could be precisely identified by using satellite images from the Copernicus program. The use of high-resolution satellite images overlapped on processed geodata also led to accurate results in the assessment of spatial connectivity and green infrastructure components of the Bucharest metropolitan area.

4.3. External Validation Related to Research Objectives

The methodology used in this study presents the advantage of a simple and precise technical solution compared to other international studies [5,17,49]. The chosen technical solution requires very good quality data and good experience in processing and implementation in GIS. The use of land ownership data (either private or state) and the overlap of processed geodata with high-resolution satellite images constitute another advantage of the methodology in identifying the most correct green-blue infrastructure connections.

The study demonstrated the need to integrate the goals and related objectives of green-blue infrastructure planning strategy into as many policy areas as possible [50]. Policy areas particularly highlighted as suitable for this integration are climate, water, nature conservation, especially through the EU Biodiversity Strategy, regional policy, land and soil.

4.4. Methodological Limitations

The limitation of the study is the fact that green-blue infrastructure planning was only carried out at the metropolitan area and city level, as the necessary data on the ecological requirements of the landscape at a neighborhood level were missing. Even though green connectivity has been defined at a very high resolution using Copernicus satellite imagery, a future quantitative and qualitative assessment of green-blue infrastructure elements needs to be carried out at neighborhood level with the involvement of all stakeholders. Data must come from many fields, but green-blue infrastructure implementation projects require the coordination of local-level urban planning departments.

4.5. Future Research Directions

The future research directions will be oriented towards green-blue infrastructure planning within the Zonal Urban Plans of the six sectors of Bucharest. This can be facilitated by digital and GIS-enabled tools, such as mobile phones with GIS and GPS applications and UAV drones. All these activities must be based on a vision for implementing the green-blue infrastructure approved by the urban planning department and the establishment of collaboration and partnerships at a local level [51]. The identification and implementation of local-level projects must take into account the implementation strategy of the green-blue infrastructure of Bucharest.