(Re)Defining Restorative and Regenerative Urban Design and Their Relation to UNSDGs—A Systematic Review

Abstract

The 1992, the Rio Declaration on Environment and Development highlighted that human impacts on the environment should be reduced. Against this backdrop, publications on restorative and regenerative urban design first appeared in the mid-1990s, and both disciplines have developed rapidly up to the present time. However, there is still some uncertainty regarding the interrelationships and differences between these two terms, and their association with the United Nations Sustainable Development Goals. Based on a search of the Web of Science database, a total of 117 papers were studied with the help of VOS viewer and R studio. The differences between the two disciplines and their respective associations with the United Nations Sustainable Development Goals were analyzed using key performance indicators. Detailed analysis was used to explore their current development status. Scientific publication and citation network analyses were used to examine the historical developments and interrelationships between two disciplines. The review revealed that both disciplines are closely related to the United Nations Sustainable Development Goals, especially regenerative urban design, but they have developed independently in the field of urban design. Unlike the descriptions found in many of the identified papers, restorative urban design not only focuses on ecological aspects but also attempts to create a built environment that allows its users to thrive both physically and mentally. Regenerative urban design is more inclined to restore or create an “ability”. Further, both disciplines are in their infancy but have evolved from internal conceptual development to the stage of exploring external relationships and frameworks as well as mechanisms. This review found that although many frameworks and models are used to support and evaluate these two disciplines, almost all of them fail to integrate necessary aspects of the ecosystem, e.g., elements, relationships, processes, etc. Moreover, future work should examine the design patterns that are closely related to restorative and regenerative urban design to better guide the concrete practice.

1. Introduction

Urban areas are vibrant and complex entities, which comprise a heterogeneous mixture of built environments, plants, animals, and modified habitat for human use [1]. However, increasing urbanization is resulting in residents facing the challenge of urban environmental deterioration. Urbanization has been defined as the shift of population from rural areas where agriculture is the predominant economic activity to urban areas dominated by industry and services [2]. According to the United Nations, 55% of the world’s population lived in the cities in 2016, and this is projected to surge to 68% by 2050 [3]. The continuous growth of the urban population inevitably drives the disorderly expansion of cities, which have long established the habits of resource consumption and waste disposal, with little regard for the consequences [4]. As a result, a series of complex issues have emerged, such as environmental degradation, biodiversity degradation, social dysfunction, scarcity of natural resources as well as increased anthropogenic climate change [5,6,7,8]. As our societies become more complex and the urban environment deteriorates, the built environment we rely on will become increasingly unsustainable [6].

The 1992 Rio Declaration on Environment and Development emphasized the integral and interdependent nature of our earth’s ecosystem and defined sustainable development in 27 principles. These principles highlighted human responsibility for sustainable development while providing important guidance for the practice of sustainable development; for example, principle four states that in order to achieve sustainable development, environmental protection cannot be considered in isolation in the process of development [9]. This principle gives environmental protection equal importance as development. As stated by [10], the Rio Declaration provides an ideal perspective for other approaches that attempt to clarify sustainable development and, to some extent, contribute to the emergence of relevant guidelines and frameworks. Based on this milestone declaration, the 2000 Millennium Summit identified eight Millennium Development Goals (MDGs). However, many MDGs are difficult to achieve as there is a lack of direct participation of social organizations and weak integration between economic, social, and environmental priorities [9]. As such, the 2012 Rio + 20 conference highlighted seven fields of priority attention, which guided the emergence of 17 United Nations Sustainable Development Goals (SDGs) in 2015. The SDGs have many objectives which cover environmental, social, and economic aspects. One of them is to build viable cities and communities that are resilient, long-lasting, inclusive, and safe [11]. However, according to the Sustainable Development Goals Report 2022 [12], although some progress has been achieved toward this goal, there are still serious challenges; for example, over 90% of global urban residents still live in areas where the air quality exceeds the new standards set by the World Health Organizations.

A significant number of studies have noted that sustainability represents an equilibrium point, which is insufficient to accomplish long-term development that improves the urban environment [13,14]. As such, the concept and practice of sustainability is evolving towards restorative and regenerative design, which, rather than seeking to do no further harm to the status quo, aims to remediate harms that previous practices have caused [15]. ‘The term “regenerative” refers to a process that repairs, recreates, or revitalizes its own sources of energy, air, water, or any other matter’ [8] (p. 19). In addition, regenerative urban design is also regarded as the process of replacing the present linear system with a cyclical system that aims at achieving the rebirth of life itself, and therefore provides hope for the future [16]. Similarly, restoration involves repairing the damage caused by human activities and returning the environment to its original state through thoughtful development [17].

Research in restorative and regenerative urban design has steadily increased in recent years. Due to the complexity of balancing multiple goals in the built environment, both research fields are multidisciplinary in nature, which leads to integrative research. For instance, urban regeneration and public health development regarding the social and built environment [18]; urban regeneration and energy balance [19]; urban restoration and ecological network construction [20]; urban regeneration and higher education [21]; urban regeneration and ecosystem services biomimicry [22]. Although these studies in different areas provide inspiration and insights into the practice of restorative and regenerative urban design, it is difficult to find implementations of regenerative design at the urban scale [23].

Regenerative approaches have also introduced standards for architecture design, such as the WELL building standard. However, similar parameters do not exist in urban design [23]. Furthermore, the definitions of restorative and regenerative urban design are often misunderstood. As stated by [24], there is currently a tendency to confuse regenerative design methods with the design scope that emerged in the 1990s in pursuit of ecosystem sustainability. This confusion may arise because these two definitions only roughly describe their respective characteristics and do not involve specific design parameters or indicators [17].

In an attempt to remove this confusion, the objective of this research is to deliver a holistic overview of restorative and regenerative urban design. The aims of this research include: (1) analyzing the historical development of these two terms; (2) using key performance indicators (KPI) to explore the differences in these research fields and attempt to delineate the two concepts; (3) to employ key performance indicators (KPI) to demonstrate whether these two terms have a significant relationship with the United Nations Sustainable Development Goals (SDGs); (4) to explore the emerging principles, methods, assessment tools, and current barriers to the two fields through detailed analysis of recent publications; (5) to employ citation network analysis to investigate the interrelationship and mutual influence between these two research fields.

2. Literature Collection and Survey

2.1. Publication Collection

Restorative and regenerative urban design have attracted widespread attention from government sectors and urban designers for many years [25]. In order to identify relevant publications, the study conducted a search via the Web of Science database using the time span of 1960 to 2021. There were no restrictions on document type, data category, document year and country, but inclusions were limited to English language. The following search terms were used to collect publications:

• ‘Restorative urban’ AND ‘design’
• ‘Regenerative urban’ AND ‘design’
• ‘Restorative urban’ AND ‘planning’
• ‘Regenerative urban’ AND ‘planning’
• ‘Restorative urban’ AND ‘study’
• ‘Regenerative urban’ AND ‘study’

The publications obtained using the above search terms in the Web of Science database were not all entirely within the scope of this study. As such, the obtained publications were first screened by interpreting the titles and abstracts. Then, the remaining publications were further refined by reviewing their content. Finally, the results of the search were downloaded in the form of a citation report, which contained key information about the publications, such as title, citations, abstract and authors, publication year, etc. To systematically and holistically analyze the relationship between the publications, the downloaded data was analyzed with the help of VOSviewer and Rstudio, which have been widely utilized in similar works, such as [26,27]. Two functions from the software were used to generate bibliographical maps of the scientific realm: (1) extracted the number of annual scientific productions, document types and relevant sources; (2) extracted citation relationships between the publications.

2.2. Data Analysis

The following four methods were employed to generate the required results: scientific publication analysis, key performance indicators, detailed analysis, and citation network analysis.

2.2.1. Scientific Publication Analysis

Scientific publication analysis was used to explore the historical development of these two disciplines. Based on the downloaded details of selected publications, such as publication year, source abbreviation and document type, a line chart was generated by Rstudio to visualize the annual scientific publications and to count the main document types and most relevant sources.

2.2.2. Key Performance Indicators (KPI)

The key performance indicators (KPI) analysis was used as an initial qualitative assessment to confirm the relationship between restorative and regenerative urban design and the SDGs, and to identify differences between the two disciplines. The KPI analysis serves as a tool for assessing the actions corresponding to the goals previously established for the city [28]. To collect the relevant KPIs, this study reviewed many publications that focused on assessing sustainability, urban restorative design, and urban regenerative design [7,29,30,31,32,33,34,35,36]. The overlapping indicators from these publications were identified and employed in this analysis. In this study, the structure of KPIs have three dimensions, namely, dimensions, sub-dimensions, and indicators (Appendix A). In the dimension level, there are five indexes, including economy, environment, society, scale, and the SDGs. Each index has related sub-dimensions, except for SDGs.

During the process of analysis, the sub-dimensions of KPIs involved in each paper were marked and counted (see Appendix B). Then, the cumulative marks of each sub-dimension of KPIs were calculated and visualized in a diagram; for example, if the KPI marks in the productivity sub-category affiliated to the economic dimension were 10, this means that 10 articles mentioned the indicators in the sub-dimension of productivity. However, one publication may involve multiple sub-categories. Hence, these marks cannot match the total number of publications. This analysis helped to categorize and reorganize the collected publications. Therefore, the fields mentioned in the papers of restorative or regenerative urban design could be identified and the differences between them could be noted. Moreover, it also facilitated counting the number and types of SDGs mentioned in the downloaded data, which in turn allowed verification of the relationship between these two terms and SDGs.

2.2.3. Detailed Analysis

Detailed analysis aims to explore the emerging principles, methods, assessment tools, and current barriers to these two fields. Strictly speaking, the text mining and KPI analysis were insufficient for deeply exploring the current internal development status of restorative and regenerative urban design. As such, conducting detailed review was necessary. The data collection identified papers spanning from 1960 to 2021. While earlier studies undoubtedly stimulated the development of later urban restorative and regenerative studies, they could not shed light on the current hot topics, obstacles and new tools, or make predictions for future research trends. As such, the detailed analysis concentrated on the literature published within the last 6 years (after 2015). To systematically review these publications, this study divides the collected data on restorative and regenerative urban design into five themes: (1) documenting and describing the theoretical development of these two disciplines, as well as the emerging principles and methods; (2) determining how to support, monitor and evaluate them (mainly referring to assessment tools and approaches); (3) identifying cases of current practice; (4) identifying barriers and enablers that need to be understood and addressed to make faster progress in implementing restoration and regeneration in the urban built environment; and (5) other themes. A table is generated to show each category of the themes and the papers involved. In addition, some research may use case studies to test their proposed theories or methods; therefore, one article may involve two themes.

2.2.4. Citation Network Analysis

The citation network analysis was used to identify the interaction between urban restorative and urban regenerative design. The study investigated the citations of all publications with the help of VOSviewer. Specifically, the cited information of each collected publication was run in the VOSviewer to visualize the citation network in a diagram. Of special attention are papers that appeared in both restorative urban design and regenerative urban design, as they were the best candidates to understand the interaction between the fields. In addition, the study explored the reasons why these publications appeared in both disciplines.

3. Results

3.1. Publication Collection Overview

A total of 1637 publications were initially identified by using the search terms described in Section 2.1. However, only 86 publications remained after eliminating a significant number of overlapping and irrelevant documents (e.g., landscape or medicine restoration, wetland and riverfront regeneration as well as mental health restoration, etc.). Meanwhile, 31 additional papers were found by searching the references of these 86 papers. However, since they are not included in the database of Web of Science, their details could not be downloaded. To generate the required diagrams, the detailed information of these 31 papers was manually inputted in the software. However, the software of VOSviewer was unable to recognize and read the manually added references cited by these 31 papers. As a result, these 31 articles feature in all the analyses except for the citation network analysis.

In short, a total of 117 documents were studied in this research, of which 37 publications related to urban restorative design and 80 related to urban regenerative design.

3.2. The Results of Data Analysis

The results of data analysis are illustrated in Figure 1, Figure 2, Figure 3, Figure 4 and Figure 5.

3.2.1. The Result of Scientific Publication Analysis

The annual publications from 1960 to 2021 are shown in Figure 1. Generally speaking, the number of publications on restorative and regenerative urban design has been increasing but fluctuating. The publications of urban regenerative design have increased much faster than those of urban restorative design, particularly in the last decade. During this time, publications in these two research fields accounted for 68% of total publications. The number of articles on urban regenerative design reached its highest level in 2012. This might relate to the 2012 Rio + 20 conference, which stimulated the establishment of the United Nations Environment Assembly and emphasized the need for a set of sustainable development goals [9]. However, papers on restorative urban design started to decline after peaking in 2015. The first publications on regenerative and restorative urban design appeared in 1996 and 1998, respectively.

Figure 2 shows the document types and the top five most relevant sources of publication. More than half of the publication types are articles. Proceedings papers rank second with 16 papers. The number of publications in the remaining document types is under 10. Articles in book chapters are the lowest number. In terms of the most relevant sources of publication, the dominant publication source is Sustainability with nine papers, followed by Building Research and Information with eight papers. Landscape and Urban Planning and Urban Studies have four and five publications, respectively. European Planning Studies rank last.

3.2.2. The KPI Fields Involved in Restorative and Regenerative Urban Design

In Figure 3, there is an exceptionally clear difference in research fields between restorative and regenerative urban design. Regenerative urban design involves all the sub-dimensions of KPIs. In contrast, restorative urban design is mainly concentrated on environmental restoration and community benefit. In addition, the sub-category of environmental restoration was dominant in both research fields, and the indicator of enriching biodiversity was significantly emphasized. Apparently, addressing the existing environmental problems is the mutual objective of restorative and regenerative urban design. In the community benefit sub-category, restorative and regenerative urban design have 22 and 8 papers, respectively. In this sub-category, the indicator of mental and physical health attracted significant attention in both disciplines. Additionally, the indicators of housing and citizen participation were frequently mentioned in regenerative urban design studies. This indicates that the process of regenerative design requires active participation from the public and the community (this part is further discussed in 4.4). Building or space restoration, and productivity were the prevalent research topics in regenerative urban design studies, especially relating to resource efficient building and employment improvement. On the contrary, only three publications on restorative urban design concentrated on these two sub-categories. Further, resource-efficient or consumption and urban governance correspond to 12 and 11 publications, respectively. Among them, the indicators of renewable energy supply and consumption, and policy guidance and support were frequently mentioned. Only seven publications involved both cultural regeneration and scale.

3.2.3. The SDGs Involved in the KPIs of Restorative and Regenerative Urban Design

Figure 4 and

Table 1. The corresponding information of 17 SDGs (United Nations, 2022).

SDG 1 No Poverty	SDG 10 Reduced Inequalities
SDG 2 Zero hunger	SDG 11 Sustainable cities and communities
SDG 3 Good health and well-being	SDG 12 Responsible consumption and production
SDG 4 Quality education	SDG 13 Climate action
SDG 5 Gender equality	SDG 14 Life below water
SDG 6 Clean water and sanitation	SDG 15 Life on land
SDG 7 Affordable and clean energy	SDG 16 Peace, justice and strong institutions
SDG 8 Decent work and economic growth	SDG 17 Partnerships for the goals
SDG 9 Industry, innovation and infrastructure

show the SDGs involved in restorative and regenerative urban design as well as detailed description of SDGs, respectively. Eighty papers directly referenced or were related to the SDGs, representing 68% of the total number of publications, while restorative and regenerative urban design relate to 8 and 15 sustainable development goals, respectively. In terms of urban regenerative design, SDG3 was associated with the largest number of publications, compared with other SDGs. This might relate to the indicator of mental and physical health as it was frequently mentioned in the publications. SDG7 and SDG11 were both referenced by 13 articles. According to the explanations of the United Nations [13], SDG 11 contains several specific targets, such as providing affordable housing, protecting cultural and natural heritage, expanding public transport, improving air quality and waste management, etc. Therefore, it corresponds to more indicators of KPIs than the other SDGs. Providing decent work and economic growth (SDG 8) ranks third with ten papers. To some extent, the indicators in the productivity sub-category of KPIs made a significant contribution to SDG 8, such as the indictors of increasing the percentage of the GDP of the knowledge economy, and new capital investment. Notably, SDGs 2, 4, 5, 9, and 10 were only mentioned in one related paper. As for urban restorative design, only SDG 15 was referenced in more than 10 articles, while 7 papers mentioned SDG 14. The indicator of enriching biodiversity has a significant association with both SDGs 14 and 15. Moreover, SDG 3 and SDG 13 were mentioned by 8 and 6 articles, respectively. The high involvement of SDG 13 in the publications is related to its association with multiple indicators. The number of papers related to SDGs 6, 7, 8, 11 was less than two. In addition, for SDGs 3, 6, 7, 8, 11, 13, 14, and 15, there is overlap between restorative and regenerative design.

Overall, this analysis confirmed that restorative and regenerative urban design have a significant relationship with the SDGs, especially regenerative urban design. Restorative urban design is very limited in terms of addressing SDGs as it mainly focuses on four SDGs. Therefore, it is necessary for this discipline to take more comprehensive approaches and integrate sustainable thinking in order to add significant value to the field. In addition, both terms are closely associated with SDG 3 and SDG 15.

3.2.4. The Result of Detailed Analysis

Fifty-two papers were published after 2015, of which only nine papers related to urban restorative design.

Table 2. The type of themes and articles involved.

The Type of Themes	Related Papers
1. Describing the theoretical development or proposing principles and methods	[4,13,15,19,22,31,37,38,55,56,57,58,59,60,61,62]
2. Evaluating these two terms or providing new assessment tools and approaches	[7,25,63,64,65,66,67,68,69,70]
3. Cases of current practice	[20,25,39,57,60,62,65,69,71,72,73,74,75,76,77,78,79,80,81]
4. Current barriers and enablers	[71,82,83,84]
5. Others	[27,72,79,80,81,85,86,87,88,89,90,91,92]

shows the themes included in each article.

As shown in Table 2, many articles describe the theoretical development of these two terms or propose some new research methods or conceptual theories. One study stated that urban regenerative design requires transforming traditional urban planning and design into sustainable practices and then into more regenerative ones, and additionally requires changes to the urban fabric at three scales including urban, neighborhood, and individual plots [55]. Similarly, several researchers suggest incorporating ecosystem services analysis (ESA) into the process of urban regenerative design, avoiding the human-centric goals and useless design metaphors that are hard to quantify [15,22,56]. Other studies proposed a new decision support tool to aid urban regeneration [64,65,66]. Several articles discussed urban regeneration in terms of social sustainability and institutions [57,58]. Only three articles depicted the general characteristics of restorative and regenerative design, of which two were related to regenerative design [13,31,37]. Although these papers belong to the same theme, they are involved different research topics.

In terms of Theme 2, it can be divided into two categories based on the type of data: first, evaluating the output of restorative and regenerative design (e.g., health assessment); second, proposing new models or indicators to guide the process of restorative and regenerative urban design. As a result, five papers belong to the second type, of which four are related to urban regenerative design [7,63,64,67,68]. This part will be further described in the discussion. The remaining articles are devoted to evaluating the results of restorative and regenerative design, such as resident satisfaction, health and cultural identity.

As for Theme 3, strictly speaking, it cannot be treated in isolation because most of the articles, to some extent, are related to the other themes. In other words, many scholars have used former urban design cases to reflect on the results in order to identify current barriers or propose new strategies, and sometimes to directly verify their theories or models through case studies at an appropriate scale. Furthermore, four papers discussed the current barriers and enablers. One of these articles proposed three strategies based on the current barriers to urban regeneration including public action, certification standards, and corporate responsibility [82]. The rest of the papers mentioned the topics of gentrification, private and public collaboration, public attitudes and ecosystem health. In addition, many articles do not belong to the above four research themes. Their research themes are diverse, including rain gardens, industrial landscape restoration, urban greenery, etc.

3.2.5. The Result of Citation Network Analysis

The citation network analysis was conducted on the 86 collected papers by using the VOSviewer software.

Figure 5 illustrates the citation network between restorative and regenerative urban design. Twenty citation relationships could be found, which means 66 papers were not cited by any other publications. Furthermore, these citation relationships were divided into two groups, with one group having 15 papers and the remaining 5 papers belonging to the other group. These groups of 15 papers and 5 papers will be referred to as Groups 1 and 2 in the following description.

Concerning the cited urban regenerative design publications, 14 citation relationships were identified, all of which were in Group 1. The citation relationships of urban restorative design were identified in six papers, mainly belonging to Group 2, except for one article. More importantly, there is no direct citation link between these two groups. This implies that the citation interrelationship between restorative and regenerative urban design was not present in Group 2. In terms of Group 1, with the exception of one paper, the rest of the citation interrelationships occurred after 2010, revealing that studies in urban regenerative design have developed significantly over the last decade. This finding is the same as the result found in Section 3.2.1. In contrast, all citation interrelationships of restorative urban design in Group 2 occurred before 2011, implying that the rapid development stage of restorative urban design theory began earlier than that of regenerative urban design.

4. Discussion

4.1. Publications on Restorative and Regenerative Urban Design

The results revealed that the publications in these two fields have emerged in the last 25 years and that there were no publications related to restorative and regenerative urban design before 1996. This result could be explained by the process of urban regeneration development. Early research on urban regeneration began in the 1970s [93]. However, this early research in the subsequent decade focused on adjusting urban intervention strategies to enhance the maintenance of existing urban fabric and address non-dominant urban issues [15,94]. This may not raise public awareness of the environmental limitations of modern society. The real turning point was the appearance of the concept of sustainable urban development in the late 1980s, and the signing of the Rio Environment and Development Declaration in the early 1990s, which highlights the integrated and interdependent nature of humans and the environment, as well as prescribes the need for urban policies to integrate environmental problems and contribute to sustainable urban development [15]. First proposed by John T. Lyle in 1994, the term regenerative design can be understood as an evolution of sustainable development pioneered by researchers in the fields of built environment and architecture [95]. Shortly after the term was coined, further studies laid the theoretical and technical foundation for restorative and regenerative design [96]. Accordingly, the first publications on restorative and regenerative urban design appeared in 1996 and 1998, respectively.

Furthermore, in the following decade, many experts and researchers proposed a series of core principles and strategies for building a sustainable urban environment. These emerging insights and terms have contributed to the further development of urban regeneration theory, which may be the reason for the rapid increase in the number of publications between 2011 and 2021; for example, the concept of urban regeneration design was defined in 2000 [97], the term Resilient Cities was proposed in 2002 [98], and the principles of Green Urbanism were introduced in 2010 [99].

4.2. The Differences in Research Fields between Restorative and Regenerative Urban Design Identified through KPI Analysis

As shown in Section 3.2.2, there is a clear difference in research fields between restorative and regenerative urban design. Urban regenerative design involved all the sub-dimensions of KPIs. In contrast, the marks of ecological restoration in the subcategory of urban restorative design account for 70% of all KPI marks. Furthermore, the rest of the KPI marks of urban restorative design mainly concentrate on the subcategory of community benefits, the majority of which are associated with the indicator of mental and physical health. This means that urban restorative design is closely linked to community benefits rather than the previously described definition of merely focusing on environmental restoration. In other words, in practice, urban restorative design is not focused on maximizing certain ecological goals. This significant association may be related to biophilic design. Urban restorative design has a strong association with biophilic design [24], which seeks to systematically integrate nature into the urban fabric in a way that improves the connection between man and nature [100]. The health benefits of contact with nature, such as stress reduction and decreasing cardiovascular disease [101], are increasingly accepted by the public. This deliberate behavior of bringing natural elements into urban landscapes and building interiors while mimicking natural geometry or forms could enhance the healing effect of the built environment. From this perspective, urban restorative design is committed to building a close relationship between man and nature, thereby placing physical and mental health alongside ecological restoration at the core of urban design.

In terms of urban regenerative design, many papers define it as an integrated approach that seeks to have a long-term impact on living systems. However, this is a relatively abstract concept. In this study, urban regenerative design included 33 out of 51 indicators, which covered the economic, environmental, and social fields. In the economic dimension, the most frequently mentioned indicators were employment growth and new capital investment. Many papers also mentioned increasing the proportion of the knowledge-based economy in the local economic structure. In the environmental dimension, enriching biodiversity had the highest score. However, the indicator of decreasing greenhouse gas emissions was not present in the majority of articles. Greenhouse gas emission is closely associated with the rising global temperature, and it has become a significant part of the United Nations Framework Convention on Climate Change [13]. However, as the research on integrating climate policy into urban regeneration is still in its infancy, the current progress is limited to conveying the mitigating measures through examples of regeneration projects [102]. Nevertheless, the process of regenerative design involves different forms of spatial intervention, which can transform existing urban forms and land use patterns to achieve a more sustainable future. Moreover, the related measures have the potential to improve the efficiency of energy and resource utilization as well as reduce greenhouse gas and waste emissions. Therefore, it is necessary to consider this indicator in urban regenerative design. In addition, renewable energy supply and waste recycling indicators have also attracted widespread attention. This may be related to the fact that regenerative design is considered as a transition from the current linear system to a cyclic system in which the life cycles of all materials are carefully considered [17].

Regarding the social dimension, the indicators of resource efficiency of buildings, policy guidance and support, and housing were all frequently mentioned in the literature. In addition, the indicators of recreational facilities, physical health, and mental health also attracted attention. However, only two papers mentioned the accessibility of green space. This is surprising as improving livability by integrating healthy outdoor spaces has become a significant topic in urban regenerative design [71]. The multiple benefits of green space within the community have already been demonstrated, for instance, providing a social space, enhancing the property value of the real estate and improving community cohesion, etc. [103]. In fact, urban regenerative design should not only provide physical environments to be shared, but also consider the durability and convenience of the daily services delivered by these facilities. In other words, ‘The urban design principle of diversity is about what people can do in the locality’ [72] (p. 8). The accessibility of public space is an important principle in measuring a good urban design and is also used to assess environmental justice [104,105]. Without accessibility in design practice, regenerative design cannot optimally realize the potential benefits contained in green spaces, such as individual emotional perceptions and functional requirements, even if they are comfortable and inviting spaces. To a large extent, this also reflects the necessity of building neighborhood parks as part of urban regenerative design at the community scale. These spaces often encourage people to come out of their houses and provide opportunities for contact with nature. They also allow family gatherings and informal sporting events to take place and thus become focal points for surrounding communities. However, the occurrence of these activities depends on accessibility. That is, these spaces should be located within close proximity of the community, and they should also be physically accessible for residents, regardless of their physical and mental ability. Furthermore, neighborhood parks require adequate natural features and supplementary facilities. For example, playing structures for children and pavilions or other shelters. Another key requirement for neighborhood parks is that their edges are also actively used, which avoids the emergence of dead zones, thereby preventing the separation of the park and community spaces.

The additional indicators of making sense of space and improving bicycle and pedestrian infrastructure were frequently mentioned. The high scores for the parameter of bicycle and pedestrian infrastructure reflect the return of human-scale urban design. This requires the spatial connectivity of different activity spaces and the accessibility of different services, which is a fundamental principle in sustainable urban design [105]. However, the close linkage in physical distance, to some extent, does not mean that there is a closer internal relationship between different spaces and their elements. The further design requirement is the establishment of a “place network”. At the micro-level, urban space is not a completely homogeneous space, but rather a spatial system comprising various spatial elements [106]. This physical connectivity does not erode the boundaries of these spaces, as people are inclined to mentally separate these elements from each other. For example, they mentally define the border of squares, streets, and even public and private spaces [107]. This is related to the capacity of people to control their contact with others [108]. Nevertheless, the geometric relationship between places determines what kind of feeling a place brings to people. It is also an important factor in judging the success of a place. Accordingly, buildings and streets or other components should be regarded as a part of a system of space. As such, when planning an environmental structure (e.g., square or plaza), it should first be considered as part of a place network. Subsequently, these places and many points of modulation, such as hedges, windows, and fences, are expressed as part of a continuous network with some connections. Therefore, the enhancement of the space network not only requires accessibility at a physical distance but also the ability of different spaces to self-organize into regional structures [109].

In short, urban regenerative design has not only frequently mentioned many conventional indicators, but also has included some indicators that emphasize the long-term nature of self-regeneration, such as increasing the percentage of knowledge economy of the GDP, solid waste reuse and recycling, renewable energy supply and consumption, developing a sense of place, etc. It could be inferred that urban regenerative design supports and facilitates the formation of an ability to fulfill the long-term needs of urban development.

Based on this analysis, the most appropriate definitions of restorative and regenerative urban design could be:

Urban restorative design not only restores the polluted and damaged ecosystems to a healthy state, but also integrates nature into life through appropriate design patterns while ensuring consistent interaction and contact with nature to create a built environment that allows its users to thrive both physically and mentally.

Urban regenerative design resolves urban problems from an integrated perspective of economy, society and environment, while not only seeking the growth of conventional indicators (e.g. increased employment, enriching biodiversity), but also attempting to restore and establish an “ability” to adapt and meet long-term or future development requirements.

With respect to the overlapping indicators, the following five were identified: physical and mental health, freshwater supply, renewable energy supply and consumption, recreational facilities, and enriching biodiversity. Notably, physical and mental health as well as enriching biodiversity were strongly emphasized. Since biophilic design aims to integrate nature into urban or architectural fabric, it can meet the innate requirement of human connection with nature while contributing to our health and well-being. Thus, there is a need to integrate the design pattern of biophilic urbanism into the practice of restorative and regenerative urban design. This is not a stylistic suggestion or personal preference but is completely related to the improvement of the relationship between man and nature as well as human health. The work of biophilic urbanism combines two mechanisms: intimate contact with living organisms and human response to the geometries created by following biological rules. It also includes many elements that contribute to the enhancement of human experience, such as curves, color, fractals, water, and organized complexity. As such, in practice, restorative and regenerative urban design should ensure repeated and constant contact between man and nature by integrating nature and biophilic elements (e.g., fractal patterns, curves), internally and externally, into buildings, built infrastructure and across urban spaces across various scales of urban structure.

4.3. The Association between Restorative and Regenerative Urban Design and SDGs

The results from the KPI analysis reveal a close relationship between restorative and regenerative urban design as well as the UN SDGs. Restorative and regenerative urban design all tend to deliver good health and well-being to the public (SDG 3) as well as build sustainable cities and communities (SDG 11). However, one of the unintended outcomes in some areas of urban regenerative practices was gentrification, which stimulates economic development and increases household income in a given area, but also results in many low-and middle-income residents being replaced by wealthier newcomers. In this sense, this is not consistent with SDG 10 (reduce inequalities). In other words, urban regeneration must reconsider the current one-sided design pattern because this phenomenon results in the destruction of diversity. As stated by [108], a decrease in diversity due to increased wealth is perhaps as bad as reducing wealth (when a declining area becomes a slum). The optimal result is to achieve economic growth in poor areas while considering social diversity. This suggests that urban regeneration should not be a catalyst for the homogenization of communities. Instead, it should facilitate heterogeneity, that is, neighboring different groups to live next to each other. Urban regeneration should integrate the social mixing of different groups and classes with economic development to ensure both integration and diversification [110]. According to [111], in the design of urban regeneration projects, the social aspects of the initiative should be equally important as environmental and economic considerations. This means that when gentrification is observed during regeneration, it is necessary to introduce measures or social policies to maintain the low-income housing stock and minimize social inequality [112]. This could be achieved by providing a range of new housing at different prices while introducing or increasing commercial investment opportunities in multiple locations to avoid overheating investment in individual regions [113,114]. Moreover, the significant differences in building quality and image between social and private housing within a short distance should be avoided [71]. Therefore, urban regeneration should retrofit the current one-sided design pattern to create optimum wealth and maximum diversity through active and reasonable policies.

In addition, SDG 14 and 15 are mentioned by more literature in restorative urban design than regenerative urban design. One possible interpretation is that a secondary relationship exists. On the one hand, there are many articles on restorative design that mentioned ecosystem services, which significantly relate to enhancing the environment and ecology. On the other hand, life below water (SDG 14) and life on land (SDG15) are partly associated with addressing existing environmental and ecological problems. Furthermore, restorative and regenerative urban design all have an association with SDG 8 of decent work and economic growth, especially regenerative urban design. Promoting the economic development of declining areas has always been one of the priorities of urban regeneration [24]. However, it is necessary to integrate the economic pattern of the regeneration area into the local context. In other words, the standardized economic pattern does not necessarily apply in any place. Although the standardization of the current economy undoubtedly reduces the cost of production and obtains economies of scale [115], it also leads to the runaway production of unadapted and undifferentiated structures. This goes against the principles of sustainability. However, this pattern of standardization and scale has also infiltrated into the urban design domain resulting in low adaptability, non-resilience, and unsustainability of the urban environment. In fact, urban design and development systems as well as underlying economic systems need to take into account and coordinate the relationship between standardization, scale, differentiation, and localization to prevent a nearly unified, non-resilient environment from emerging. Many current standards, norms, models, and other subsystems make it difficult to change elements in specific practice. Therefore, to prevent the emergence of an unsustainable urban environment, it is necessary to gradually change the excessive reliance on standardization and scale. Attempts at differentiated and localized design patterns at all scales must be made in future practice.

In sum, restorative and regenerative urban design all have a significant relationship with SDGs, but some new design patterns need to be integrated in the practice of regenerative design, such as coordinating the relationship between standardization, scale, differentiation, and localization, as well as optimum wealth and maximum social diversity.

4.4. The Current Development Status of Restorative and Regenerative Urban Design

As discussed in Section 3.2.4, only three papers reviewed the theoretical development of these two terms. One article aimed to identify differences between regenerative design and regenerative development [95]. It interpreted regenerative design as a method of forming and shaping systems designed to reverse environmental degradation and deliver positive effects, while regenerative development was defined as an approach that enables the co-evolution of human communities and natural living systems. Apparently, regenerative development is regarded by some researchers as an upgraded form of regenerative design. However, in another study, regenerative design and development were not defined differently [37]. At the same time, the pattern of co-evolution also was termed as regenerative sustainability in that paper rather than regenerative development [37]. Nevertheless, they all collectively emphasize the role of the human in regenerative development. It is clear that there is no consensus on the definition of regeneration, resulting in each paper interpreting the subject using its own preferred definition.

In addition to differences in existing definitions, some scholars have suggested incorporating ecosystem services analysis (ESA) into the process of regenerative design: ‘The purpose of ESA is to measure past, current and potential future environmental performance of the built environment in terms of ecosystem services provision so that future spatial and temporal ecology derived performance goals can be devised’ [68] (p. 6). However, this approach focuses solely on the provision of ecosystem services and thus leads to a lack of deep understanding of the ecological processes behind ecosystem services. As stated by [22], the theoretical formulation and practice of ecosystem-level biomimicry focusing only on regenerative urban design at the end of the ecosystem service cascade will lead us to oversimplify our understanding of ecosystems. In recent years, a more complex approach has been proposed by some scholars in the form of the “Ecosystem Services Cascade Framework” (ESCF), which emphasizes the connection between ecosystem biophysical structures, its health and integrity, as well as the ecosystem service provision [22]. However, a recent study has further pointed out the shortcomings of the above two models. It explained that the lack of translation work between ecological concepts and practical examples of ecosystem service design in the built environment results in the difficulty of wide application of these two frameworks [68]. In simple terms, these two frameworks could not bridge the gap between the results of design practice and the proposed ecological concept. In addition to this criticism, the study also introduced an online interactive tool based on an ecosystem services diagram and urban ecosystem service categories depicted by Pedersen Zari [116]. This is also the theoretical foundation of the above two frameworks. More importantly, this tool can connect ecosystem services concepts with design strategies and case studies [68]. It is indicated that the approaches and tools which support incorporating ecosystem services into urban regenerative design have been developing and evolving.

Furthermore, many articles emphasized that regenerative design requires the active participation of communities and stakeholders, with several articles obtaining this finding from the perspective of preserving local identity. This is because community residents are best aware of what aspects of their cultural heritage need to be protected and preserved [58,75]. The general opinion of the remaining articles is that the participation of communities and different stakeholders in the regenerative process could, in addition to meeting people’s requirement-orientated design goals, establish a consciousness of engagement in continuous healthy relationships [38,57,73,74]. However, the collaboration of different stakeholders also brings obstacles to the process of urban regenerative design, especially in the collaboration of private and public sectors. The cooperation of public and private sectors undoubtedly brings substantial resources to the site, but this involves a wide range of multi-level governance relationships and resources, even for small regenerative projects. As a result, in this complicated network of relationships, it is sometimes difficult to determine decision-making processes [83]. When this occurs, public accountability is hindered by lack of transparency in decision-making [83]. Moreover, due to seeking profit maximization, the higher decision-making power of the private sector in such cooperation perhaps leads to gentrification, resulting in the displacement of original residents in the regeneration area [71]. Furthermore, urban regenerative design emphasizes a holistic paradigm. Therefore, a single-category assessment tool is not able to meet the requirements. Many scholars in the articles used or introduced assessment tools such as ‘Sustainably Performed Urban Regeneration’ (SuPerUrban), ecosystem services analysis (ESA), and restorative urban design (RUD). However, almost all the evaluation tools are based on a series of key performance indicators. As explained by [63], the ecological and sustainable indicators in the majority of current assessment tools have failed to integrate the necessary aspects of the ecosystem, such as relationships, flows, and processes. As a result, research by [63] proposed a new evaluation tool that goes beyond the original checklist pattern and attempts to describe the elements and relationships required to regenerate living systems rather than the final state. However, our study found that this model completely abandoned the general urban regenerative design indicators and strategies, making the model somewhat difficult to understand for those people without relevant background knowledge.

The time span of data in this analysis is the last six years, but only a few studies have explored and described the concepts of these two terms in detail. Most studies aim to present new insights into urban regenerative design or explore the models and frameworks that support and evaluate these two approaches. Thus, it could be inferred that restorative and regenerative urban design have evolved from internal conceptual development to the stage of exploring external relationships and frameworks as well as mechanisms.

4.5. Citation Relationship between Restorative and Regenerative Urban Design

The results show that only one urban restoration publication had a citation interrelationship with urban regenerative design. Two papers on urban regenerative design were cited by this publication, which concentrates on studying how to apply the analysis of ecosystem services to the urban built environment and analyzes the starting point of regenerative design. However, one of the articles it cited was published in 2015 and deals with urban stormwater management. This cited relationship seems unusual. However, this cited paper proposed a new conceptual framework and recommends approaching the regenerate urban built environment paradigm with a holistic view by integrating urban sustainable drainage systems with resource management and climate mitigation and adaption. Regarding another cited publication, this cited paper calls for whole system thinking and living systems thinking, which is a holistic way of linking the natural environment with the built environment [24]. It recommends using this approach in sustainable practices to promote urban regeneration. As such, the description and analysis of the “natural environment” and “built environment” sections may bring an interconnection between these three articles. Moreover, although the paper of urban restorative design focuses only on the feasibility of urban regeneration from an ecological perspective, the cited article provides it with an entirely theoretical framework for urban regenerative design. This seems an important reason for the citation relationship between them.

Besides, as mentioned in Section 3.1, since 31 articles are not included in the database of the Web of Science, it is impossible to directly generate such a schematic diagram of the citation relationship by software. As such, the study manually checked the remaining 31 articles, of which 11 papers belong to urban restorative design. Among them, only two dissertations mentioning “regenerative” focus on regenerating natural systems. The rest concentrated on discussing health and ecosystem restoration. In addition, most of the remaining 20 urban regenerative design papers are conceptual articles. Five articles directly mentioned the definitions and purposes of restorative and regenerative design. To some extent, this cannot be used as evidence of an internal relationship between them. Furthermore, two articles may have associations with urban restorative design. One paper mentioned the use of biomimicry theory to drive a paradigm shift in urban regenerative design, however, it relied on an understanding of ecological theory and analysis of ecosystem services. Thus, the health and integrity of ecosystems are highly valued. Similarly, another article suggested incorporating the analysis of ecosystem services into built environment design and using a practical case to demonstrate the benefits. Therefore, “ecosystem services ” are the reason for their correlation to urban restorative design.

In general, there are three possible relationships between restorative and regenerative urban design: namely, development independent of each other, a partial overlap between these two disciplines, and one discipline completely including the other (Figure 6). Strictly speaking, the citation analysis demonstrated that there is no significant internal relationship between urban regenerative and urban restorative design. Instead, they have developed almost independently of each other, as shown in Figure 6a. However, in the KPI analysis, urban regenerative design involves more indicators and dimensions than does urban restorative design, but the former does not fully include the indicators of urban restorative design (Figure 6c). The indicators involved in restorative and regenerative urban design overlap with each other (Figure 6b). To some extent, this indicates that restorative and regenerative design should be interrelated with each other.

In the pioneering work of regenerative design research, Lyle pointed out that to achieve sustainable development, the supply system of raw materials and energy must discard the original ideas and strategies that destroy the environment, replacing the original linear systems with regenerative design and circular flow [117]. Based on this, advocates of restorative environment design called for the restoration of the damaged ecological environment to its original health, while other scholars advocating for regenerative buildings tend to use a holistic approach to building human settings [16]. It is clear that the focus of the former is to return to an unspecified original state. Moreover, urban regenerative design is considered as a representative of implementing the “cradle-to-cradle” pattern. During this process, the material flow is based on closed-loop cycles [16]. It emphasizes an “ability” rather than a “state”. In simple terms, if restorative design signifies returning something to its original state, regenerative design represents making it better than the original state.

There are two possible reasons to explain why the findings of restorative and regenerative urban design in the citation analysis differ from the KPI analysis. First, for different research fields, the citation relationship will occur only when a common research topic or theme emerges. The results show that urban regenerative design is a broad research field, while in contrast, urban restorative design mainly concerns physical and mental health as well as ecological restoration. In other words, the citation relationship will only emerge when the research on urban regenerative design is focused on or has some connections with the above two aspects. The second reason is lack of data volume. Mining association and correlation between different items is best served by large amounts of data [118]. However, only 117 documents were studied in this research, of which only 37 publications related to urban restorative design. The insufficient data volume and the large differences in the number of publications between these two fields, to some extent, could further reduce the probability of finding citation relationships. As a result, the superimposed influence of the above two reasons may have led to the weak citation relationship between restorative and regenerative urban design in this study.

Overall, the citation relationship suggests that restorative and regenerative urban design developed independently of each other. This contradicts the findings of former KPI analysis in this research as well as the opinions of many researchers. It is necessary to reassess this association based on a large quantity of data in the future.

5. Limitations

A few limitations of this study should be noted. First of all, this study highly relies on the quality and quantity of the data. Even though this study employed the logical combined search terms to collect the publication, it is impossible to ensure that all the related publications have been collected. Some researchers may use other search terms; for instance, using urban environmental restoration rather than restorative urban design. Besides, the Web of Science database indexes contain SCI-EXPANDED, SSCI, A & HCI, CPCI-S, and SPCI-SSH. This means some important papers are excluded from publication collection, such as doctoral dissertations. Moreover, utilizing only English papers has further reduced the amount of data. Thus, only 117 publications involved in the research may render the results less persuasive.

Another limitation is that 31 publications, which accounted for nearly 26% of the total number of publications, could not be included in the citation relationship analysis through the software. Although the study manually checked these papers, their omission from the software analysis creates the possibility of errors. Thus, the final output might be unreliable.

6. Conclusions

The disciplines of restorative and regenerative urban design are in their infancy but are growing rapidly. There are still ambiguities in terms of the tangible differences and internal relationships. Although this study is framed as a systematic review of these two disciplines, the higher goal is to clearly define and differentiate them so that they can better support and guide the practice of future urban design.

This study illustrates that restorative and regenerative urban design are closely related to the SDGs, especially urban regenerative design. Restorative urban design is very limited in terms of addressing SDGs as it mainly focuses on four SDGs. Therefore, in order for this discipline to improve its relevance and increase the value it offers, it is necessary for it to take more comprehensive approaches and better integrate sustainable thinking. Although there are obvious differences between restorative and regenerative urban design, both disciplines tend to mitigate or minimize the negative impacts of design and development on natural systems, and also use the built environment to promote a closer relationship between man and nature.

Rapid urbanization has tested our ability to develop cities in a sustainable way. Undoubtedly, the majority of interventions compromise, to some extent, the natural environment. As such, urban development must go beyond simply maintaining sustainability. This requires the thinking of urban design to go beyond the logic of co-existence between man and nature. Rather, the logic of co-evolution between man and nature needs to be pursued. This is a vital and necessary transformation, as attitudes are more important than gains in driving change in urban development. As such, urban design practice requires an integrated planning and design perspective that considers the built environment as a system in which humans and nature support and co-evolve with each other, thereby obtaining net positive benefits for social and natural dimensions. In addition, in the process of practice, there is a need to coordinate and integrate the priorities of economic, social, and environmental aspects, such as promoting the development of renewable energy and reducing greenhouse gas emissions. Urban development beyond sustainability requires a long process, and it is also dependent on meaningful engagement in that process. This means that a participatory approach should not be ignored. The active participation of citizens helps design teams or academies to identify the needs of the users as well as the potential gaps that must be filled to enable cities to move beyond sustainable design to restorative or regenerative design. There is an urgent need for design teams to bridge the gaps by raising awareness of and improving understanding of restorative and regenerative urban design. They must also leverage these advances by generating more active and holistic approaches to address the most urgent and important issues in order to meet requirement-orientated design goals to improve the overall livability.

The Sustainable Development Goals Report is categorical in that the desired progress in achieving the SDGs has not been realized. Therefore, consideration must be given to how progress can be accelerated and what can be done to better guide specific practice. There is no doubt that clear and robust urban design frameworks are required, and that such frameworks need to be flexible enough to respond to changing conditions. However, frameworks alone are not enough. Although they give direction for urban design practices to achieve the SDGs from a macro perspective, frameworks are not project oriented and cannot provide solutions to certain issues. As such, other means are required to drive and direct projects. Design patterns are an effective tool to guide and support designers and stakeholders within specific projects. As explained by Alexander [119], design patterns consist of three parts which indicate the relation between the context, the common design problem, and the fundamental nature of a solution to resolve the problem. Compared with the approaches of guidelines and heuristics, design patterns are focused on providing concrete solutions to specific problems rather than abstract advice. Thus, it is necessary to combine frameworks with design patterns to better guide urban design practices from the perspectives of macro and micro. Future work should examine the design patterns that are closely related to restorative and regenerative urban design so as to make rapid progress in achieving SDGs.