Emerging Trends and New Developments on Urban Resilience : A Bibliometric Perspective

Urban resilience is concerned by the scholars in the world, especially in light of new uncertainty challenges for cities such as natural disasters and man-made disasters. We performed a bibiometric analysis on urban resilience research based on the 1296 articles in the SCI, SCIE, SSCI and A&HCI database from 1986 to 2015. Publication trends were discussed in HistCite to reveal the publication outputs, subject categories and publication pattern, most prolific authors and international productivity. The document co-citation analysis was made in CiteSpace III to explore the research basements and research trajectories, emerging trends and new developments. Growth of article output has emerged since 2003. Environmental studies and environmental sciences came out the most urban resilience articles. Ecology and Society was the most productive journal in this area. Barthel was the most prolific author. USA and UK were the most productive countries, and Arizona State University was the most high-productive institution, but the cooperation is lacking in the worldwide. Two streams were detected from the co-cited papers. “Governance”, “climatechange” and “city” are research hotspots of urban resilience according to the strongest citation bursts of keywords, and Folke’s paper published in 2006 has the strongest bursts. Future research will focus on ecosystem service, adaptive capacity and human-dominated ecosystem.

B. Pu, Y. J. Qiu increased from 28.3% to 50% in 2010.While man is facing all sorts of emerging uncertainty challenges in social progress, such as natural disasters (e.g.earthquake, flood, drought, climate change, etc.) and man-made disasters (e.g.environmental pollution, war, terrorism, etc.).Urban resilience is a significant capacity to adjust to stress from hazards and to recover quickly from their impacts from catastrophe.Indeed, urban resilience can be seen in the context of risk and vulnerability assessments, institutional and social governance structures, resilience in (or of) different sectors (e.g.ecosystem, economy, etc.), and transformations of urban areas.In other words, to strengthen urban resilience is beneficial to reduce the influence of urban disaster.
Some scholars have made some reviews on urban resilience or resilient cities (Lang, 2011;Müller, 2011;Chelleri, 2012;Jha et al., 2013;Cartalis, 2014), and bibliometric analysis could display the research performance and trajectories, emerging trends and new developments (Chen, 2006;Chen et al., 2014;Wang & Liu, 2014;Kim & Chen, 2015), but a review used bibliomeric analysis has been not much.However some researchers focused on resilience research (Xu et al., 2015;Meerow & Newell, 2015) with bibliometric analysis.These studies could not get the map of the urban resilience research.
In this article, we will provide a comprehensive survey of the advance of urban resilience.More specifically, it aims to 1) present mainly publication outputs, subject categories and publication pattern, most-prolific authors and international productivity; 2) emerge the research basements and research trajectories by visualizing the citation network using CiteSpace III; 3) identify the research trends and new developments according to the keywords and cited references with strongest citation bursts.

Data and Methods
We established an analysis database of urban resilience from the Science Citation Index (SCI), Science Citation Index Expanded (SCIE), Social Science Citation Index (SSCI) and Arts and Humanities Citation Index (A&HCI) supported by Web of Science."Urban resilience" or "resilient city" or "resilient cities" were used as keywords to search from 1st January, 1986 to 5th August, 2015.Then we removed duplicate articles and got 1296 related articles.
Many available tools are used by bibliometric research, such as HistCite, CiteSpace, VOSviewer and Sci 2 etc. HistCite is a flexible tool to provide research perspectives and information in our analysis database (Garfield, 2009) through GCS, LCS, LCR, LCS/t and GCS/t indicators, such as to analyze the classical literatures, to look for the productivity authors and institutions.Meanwhile, CiteSpace is popular to study the knowledge domain in a scientific field (Chen et al., 2014), can be used to analyze the knowledge basement and development track, to detect emerging trends and new developments.

Publication Outputs
There has become a rapid increase on urban resilience work since 2003, as showed in Figure 1.According to the curve of publication number on urban resilience research, two stages can be notified.Before 2003: The articles number kept a low level.In this period, many workers paid great attention to the high-risk and resilient children, psychosocial resilience, urban children with stress resilient and stress affect outcomes, talked about that how to improve the human development in the city.After 2003: With the climate change and disasters increasing in the world, how to promote the orderly development of the city had attracted the attention of scholars.
Pursuers of diverse disciplines to conduct researches on the resilient city and urban resilience from different angles.And the publication number grew from 12 in 2003 to 215 in 2014 steeply.

Subject Categories and Publication Pattern
Several ISI-defined subject categories were included, such as environmental studies, environmental sciences, urban studies, ecology, geography etc.We presented the uppermost 10 subject categories in Table 1.The most common categories were environmental studies (260; 20.06%), environmental sciences (203; 15.66%), urban studies (176; 13.58%), ecology (141; 10.88).Meanwhile, we find out the urban resilience research has the nature of multidisciplinary, involves the environmental science, ecology, geography, psychology and social work etc.

Most-Prolific Authors and International Productivity
3624 authors concentrated on the urban resilience and published related articles.However, only 67 scholars produced more than 4 papers, accounting for 1.85% of the total scholars, 3267 authors only had one article.Table 3 lists the 18 most productive authors, each with more than 5 published articles on related study.The most prolific author, Stephan Barthel and Rajib Shaw, had published 10 papers.Stephan Barthel work at Stockholm University in Sweden, with 47 LCS and 245 GCS.Rajib Shaw service for Kyoto University in Japan, with 4 LCS and 18 GCS.Other prolific authors included Kylie Bail, Emory L. Cowen, Peter A. Wyman, and so on.It is useful to mention that all the 18 most prolific scholars in Table 3, who come from developed countries.The 1296 urban resilience research articles were scattered geographic distribution in the world, and gathered mainly in the developed country.Five countries or regions contribute to the urban resilience research articles more than 50 papers, most of the countries or territories published less than 10 articles.United State was the most industrious country with 510 articles, and got the largest LCS (452) and GCS (8391), and had the largest average citation rate of LCS (0.89) and GCS (16.45).UK was the succeeding productive country with 203 articles, and received the second LCS (134) and GCS (1987).Australia was the third productive country (125), followed Canada (80) and Netherlands (52).Other prolific countries included Sweden (46), Germany (43), China (39), South Africa (39), and so on.More interestingly, the result confirmed that most of developed countries with post-urbanization paid attention to the urban resilience specially, and just a few developing countries with rapid urbanization has begun to emphasize the related research, such as China, South Africa, Brazil, India (see Table 4).
Institution distribution of urban resilience research was gathered, and mainly concentrated in several developed countries, such as USA, UK and Australia.

Temporal Evolution of Keywords
Keywords are vital components of the article, and it will show the research focus to analyze the keywords frequency and keywords centricity.As Table 7 showed, in the past study, according to frequency the top 10 keywords were resilience, vulnerability, management, cities, risk, adaptation, systems, children, climate change and urban.However, the top six keywords were biodiversity, adolescents, youth, resilience, ecosystem services and vulnerability, looking from the keywords centrality.United-states as a keyword, had been mentioned 43 times with 0.01 centrality.There are limited reasons, firstly many scholars are interested in urban resilience in USA, and secondly USA is the representative of the developed country.

Burstness of the References
Burst detection and visualization can be implemented to different types of nodes for finding out the research basement of future research.(2000) has the second strongest citation burst in the period of 2005 and 2011.However, some papers will be research basements for future research, such as Folke ( 2006), Cutter et al. (2008) and Barthel et al. (2010) in the field of environmental change, Walker et al. (2006) in the theory of resilience, Davoudi et al. (2012) in planning areas, Walker et al. (2004) and Folke et al. (2010) in the ecological society areas.
Table 9. Top 20 references with strongest citation bursts.

Clusters of Co-Cited References from 1986 to 2015
To identify further development clearly, we showed a timeline visualization based on the dataset which we gathered.Visualized clusters are defined based on citation instances made by the top 50 most-cited articles per three years from 1986 to 2015.Timeline visualizations can be revealed the newly emerged threads.Timeline visualization for T 1986-2015 is showed in Figure 3, animatedly.The largest cluster is cluster #0 on ecosystem services, and the largest circles with red rings depict the references to Holling (1973).Some recent developments since 2010 are presented in Figure 3 as the clusters' labels.New clusters include #2 on adaptive capacity and # 11 on human-dominated ecosystem.
A more detailed visualization was obtained to further investigate new developments about urban resilience as showed Table 10.The largest cluster #0 ecosystem service has over 30 references as its members with an average year of publication of 1999.It was high silhouette value of 0.932 indicates a high homogeneity of the cluster.
The largest cluster was formed by more recently published articles, which was #11 and labeled as humandominated ecosystem.This cluster had ten members and an average year of publication of 2007.And Table 11 showed seven articles in cluster #11 with the strongest citation bursts.Folke is undoubtedly the major contributors of social-ecological system on urban resilience.Meanwhile, Folke's (2006) paper held the strongest citation bursts in this cluster.Table 12 showed three most-representative articles of cluster #11.Ernstson et al.'s (2010) work had combined urban resilience and human-dominated ecosystem.This is a mainstream of the present study on urban resilience.
The other cluster included cluster #2, which was labeled as disaster resilience indicator and adaptive capacity.Table 13 lists nine articles in cluster #2 with the strongest citation bursts.Tilte terms include Resilience, vulnerability, hazards and adaptability.Cutter has been focused on the social vulnerability and social resilience, and published a large number of articles.Davoudi et al. (2012) has the strongest citation bursts in this cluster.

Conclusions
In this paper, we have provided bibliometric techniques on research trends in the urban resilience research, based on the 1296 articles, which were downloaded in the Web of Science during the period from 1986 to 2015.The paper presented publication outputs, subject categories and publication pattern, most prolific authors and international productivity, research basements and research trajectories, emerging trends and new developments.Works show that the article number on urban resilience has increased since 2003.Environmental studies and environmental sciences came out the most related papers.Meanwhile, Ecology and Society and Environment and Urbanizations were the most-prolific journal; Barthel was the most-prolific author.In addition, most research of urban resilience was dominated by USA and UK, and Arizona State University was the most highproductive institution.Two streams were identified.One stream paid attention to social-ecological system of urban, others focused on psychology and resilience.According to the bursts of the node, these keywords were research hotpots, such as "government", "climate-change" and "city"; the articles were the research basement of future research, such as Cutter et al. (2008), Folke (2006), Davoudi et al. (2012) and Walker et al. (2006).Future research will focus on three areas mainly, such as ecosystem service, adaptive capacity and human-dominated ecosystem.With the development of global city, more topics will be concerned, such as the metrics of urban resilience, the relationship between leisure city and resilient city, urban vulnerability and urban resilience.

Figure 1 .
Figure 1.Growth of urban resilience study publications from 1986 to 2015.

Figure 3 .
Figure 3.A timeline visualization for T 1986-2015 is shown.New developments since 2010 are included in the visualization, notably in association with clusters #2 and #11.

Table 1 .
Distribution of the subject categories: the top 10.Table2showed the 18 most common journals on urban resilience research, along with the number of articles, the number of the LSC, LSC/t, GCS, GCS/t and LCR received.The main publication journal for urban resilience research included Ecology and Society, Environment and Urbanization, Landscape and Urban Planning, Sustainability, Urban Studies and Cities.

Table 2 .
Most active scholarly journals in urban resilience research.
TA, total number of articles; TA%, the percentage in the 3085 articles; LCS, local citation scores; LCS/t, local citation scores per year; GCS, global citation scores; GCS/t, global citation scores per year; LCR, local citied references.
TA, total number of articles; LCS, local citation score; LCS/t, local citation scores per year; GCS, global citation score; GCS/t, global citation scores per year.

Table 5
displayed the 21 most fruitful research institutions, each with more than 13 articles.Arizona State University was the most high-producing institution with 27 articles (2.08% of the 1296 articles), followed closely by Stockholm University (24), University of Maryland (21), Yale University (21).About the urban resilience research, there are several sub-institutions in Arizona State University, such as school of sustainability, school of social work, school of geography science and urban planning et al.It is necessary to say that Stockholm Resilience Centre was established on 1st January 2007, to advances research on the governance of social-ecological systems with a special emphasis on resilience.

Table 4 .
Top 20 productive country of urban resilience research.
TA, total number of articles; TA%, the percentage of the 3085 article; LCS, local citation score; GCS, global citation score.

Table 5 .
Top 21 productive research institutions of urban resilience research.
TA, total number of articles; TA%, the percentage in the 3085 article; LCS, local citation score; GCS, global citation score.Figure 2. Co-cited of paper on the urban resilience.B. Pu, Y. J. Qiu

Table 6 .
Research basements and research streams.

Table 8 .
Top 20 keywords with strongest citation bursts.

Table 9
Folke (2006) top 20 high citation bursts of articles about urban resilience.From the list,Folke (2006)has the strongest bursts among articles published in Global Environmental Change, with 14.1352 burst value and burst duration from 2013 to 2015.It is further curious to note that Luther et al.

Table 10 .
Largest clusters of co-cited references among the 43 clusters.

Table 11 .
Articles with strongest citation busts in cluster #11.

Table 12 .
Articles that cite over 20% members of cluster #11.

Table 13 .
Articles with strongest citation busts in cluster #2.