We found 486 papers written in English and published in journals between 1991 and February 2021 in the Scopus database. However, 429 papers were selected according to the abstracts and pre-established criteria in the second step of the methodology. The analysis resulted in papers produced in 57 countries, 182 journals, 660 affiliations, by 1454 authors, who used a total of 1075 keywords. The first and most relevant results for each unit of analysis were listed to make the data presentation clarify.
As shown in Fig. 2, during the period between 1991 and February 2021, there was an increase in annual scientific publications according to the Scopus database. The first paper was written in 1991, and the second in 1992, with an interval without publication in 1993. Since 1996, more than one paper has been published each year, except for 1998, when there were no publications related to the topic. From 2011 onwards, at least 14 papers per year started to be published (disregarding the year 2021), showing the growth trend. Although a significant decrease in publications was observed between 2012 and 2014, during the following years, fewer differences in the number of publications were observed, indicating a more balanced scenario (i.e., between 2014 and 2018). On the other hand, the peak of publications was observed in 2020, the year in which authors published 60 papers related to the topic. In January and February 2021, 11 papers had already been published, which is a higher number than in the whole year of 2009 and the period before 2007. This result demonstrates a recent increase in studies on that have correlated climate change and the impact of storm surges on the coastal zone leading to erosion and flooding (inundation). Thus, the annual growth rate of publications related to the topic is 8.94%.
3.1 Analysis by country
Among 57 countries, at least 10 have 18 papers or more published. Table 3 shows the first 10 countries, in which the authors published more between 1991 and February 2021. Researchers from the United States published 132 papers, that is, 30.77% of the total of 429. Next is the United Kingdom, in which 54 papers were published. Authors from unlisted countries have published 36 papers or less. Table 2 also highlights the first 10 countries, in which the authors were most cited. Among 19,753 citations, the countries listed reached 15,821, which represents 80% of the total citations. The United States authors had 4,844 citations counted until February 2021: this reflects a percentage of 24.52%. The United Kingdom authors were cited 3,494 times (17.69%); whereas German researchers were cited 1,586 times (8.03%). In contrast, papers published by the authors from the Netherlands have 78 fewer citations. In France and Australia, citations reach 1,103 and 1,016, respectively. Papers published by researchers from Italy, Canada, India, and Bangladesh reach 11.49% of the total. The unlisted countries have 422 citations or less.
Comparing the number of published papers and citations, the United States and United Kingdom authors lead the rank, with 132 and 54 papers and 4,844 and 3,494 citations, respectively. However, the Netherlands has more papers than Germany, but no more citations. France researchers are not on the top of the papers list, but they have 1,103 citations in their 13 papers. Australia has fewer papers compared to Italy but has more citations, 1,016 and 917, respectively. Canada, India, and Spain have fewer papers than China but account for a greater number of citations, 470, 458, and 380, respectively. Finally, Bangladesh has fewer papers (14) than Spain (18) but adds 45 more citations.
Figure 3 shows the co-authorship network by country using a cluster approach. Colors separate countries into different clusters by collaborations; the size of the circle represents the number of publications, and the line thickness represents how strong the relationship between countries is. For example, lines are thicker between countries with more co-authorships. The results of co-authorship by countries are represented by 10 different clusters, in which 43 authors have at least two co-authorships (Fig. 3). A larger network among researchers was observed in 39 countries. The United States researchers were the most productive (132 papers) in the period and have established co-authorship with 22 different countries. Among them, China, the United Kingdom, Italy, Australia, and India presented a high relationship.
Researchers from the United Kingdom have 54 published papers and at least two co-authorships with 24 other countries. Among them, Ghana, China, Germany, and the Netherlands. Authors from the Netherlands, Germany, and Italy have 36, 35, and 33 papers (respectively) and at least two co-authorships with researchers from 17 countries. Authors from these three countries have a strong relationship. Both Australia and China had strong relationship, co-authorinig with 11 countries. In Canada, two co-authorships occur with 8 countries, and in India, with 6, which are represented in the same cluster as Iran. Despite being in tenth place in the publication ranking, Spain has at least two co-authorships with 18 countries. Brazil, which has 4 published papers, has a strong relation with Portugal and the United States.
3.2 Analysis by affiliations
Authors’ addresses recorded a total of 660 affiliations. It was found that 490 affiliations (74.24%) published only 1 paper. Figure 4 lists the 12 organizations with which authors were affiliated in terms of the most papers published in the period between 1991 and February. Pennsylvania State University is the most prolific affiliation with 20 papers, followed by Deltares and Princeton University, which published 15 papers each. The 12 affiliations represent 29.84%, with 128 papers out of a total of 429 publications on the topic. The other affiliations published 6 papers or less. Regarding countries, 7 affiliations are located in the United States. The Netherlands is the second country that most appeared in the rank, with 2 affiliations. The United Kingdom, Greece, and Taiwan are host countries for one affiliation.
3.3 Analysis by journals
The 429 selected papers were published in 182 indidivual journals. Table 3 shows the first 10 journals that published more papers on the topic in the period between 1991 and February 2021. The first paper published in our time series (Paw and Thia-Eng 1991) was published in Ocean and Coastal Management, which has only this paper related to the topic and 15 citations. The second and third (Daniels 1992, Toppe and Fiihrboter 1994) were published in the Journal of Coastal Research, in which a subsequent 22 further papers were publilshed. Natural Hazards has published 20 papers, the first in 2003 (Danard et al. 2003); Climatic Change has published 21 papers the first in 2008 (Kirshen et al. 2008). These first three journals represent 14.69% of the total number of published papers. The other 7 listed total 19.11%, with 82 papers published. In addition, 119 journals published only one paper, 24 journals published 2, and another 39 published 3 or more papers in the analyzed period.
The annual occurrence of papers related to the theme in the 7 most relevant journals is presented in Fig. 5. The journal Natural Hazards has become a greater focus on the vulnerability to, and impact of, storm surges over the years. It was the journal that published the most in January and February 2021. Water (Switzerland) also grew exponentially over the period and it was the second to publish more related papers in 2021. The Journal of Coastal Conservation published more in the period between 2017 and 2019. On the other hand, Climatic Change published more between 2013 and 2015, and Ocean and Coastal Management obtained the highest number of publications in the year 2017. The Journal of Coastal Research, which took an initial interest in the topic, has maintained this with a relatively consistent since 2009. Global and Planetary Change published less than the other 6 journals, with the peak between 2011 and 2015. Concerning all the highlighted journals, it it can be seen that there has been a marked increase in publications with a focus on impacts of the storm surges commencing in 2007.
The rank of the journals that have been published more is different, regarding the most cited journals. Table 4 shows the first 10 most cited journals by the 429 selected papers. Climatic Change, which published 21 papers, is the most cited journal. On the other hand, the Journal of Coastal Research, with 22 papers, is the fifth most cited journal (705). Plos One, which has 6 published papers, obtained 789 citations. Natural Hazards, third in the publications rank, appeared in the tenth position, with 443 citations. Journals, such as Global Environmental Change, Climate Research, Nature Climate Change, also do not appear in the ranking of those that have published more on the topic, but they total 763, 648, and 619 citations, respectively. The other journals, which are not in the rank of the first 10, were cited 412 times or less. Among the 13,548 citations, the first 10 journals have 6,778 (50.03% of the total). The results also demonstrate that 16 journals did not obtain citations, 14 had 1 citation, and 152 were cited 2 times or more.
Figure 6 shows 10 journals, in which at least 7 papers have been cited 65 times. In three clusters, represented by different colors, there are the journals that have the highest citation network. The Natural Hazards and Climatic Change have a greater relationship, forming a cluster represented by the color blue. In the green cluster are represented Water (Switzerland), Global and Planetary Change, Journal of Geophysical Research, and Science of the Total Environmental. Finally, the red group lists Ocean and Coastal Management, Journal of Coastal Research, Journal of Coastal Conservation, and Coastal Engineering. The size of the circles shows that among the journals with the highest citation network, Climatic Change, Global and Planetary Change, and Journal of Coastal Research were the three most cited journals.
3.4 Analysis by authors
The results indicate a total of 1,454 authors. The 10 most productive authors were highlighted, according to the number of publications on the topic. In addition, the number of citations, affiliations, country, and gender of the author is presented in Table 5. In our analysis, we have only selected the authors who have correlated climate change and the impact of storm surges on the coastal zone leading to erosion and flooding (inundation) in their papers.
Nicholls published the most papers on the topic. His first paper was published in 1996 in Ocean and Coastal Management Journal (Nicholls and Hoozemans 1996). Until February 2021, this paper obtained 31 citations of a total of 1,965 citations of the author. The author's most cited paper was published in 2015 in the Plos One journal and obtained 713 citations (Neumann et al. 2015). The second author of the rank is Lin, who has published 9 papers. The first paper produced having Lin as the main author was in 2010 (Lin et al. 2010) in the Journal of Geophysical Research: Atmospheres. That paper obtained 161 citations out of the 414 citations that have been reached by the researcher. Other authors are recorded in the database as having published 7 or fewer papers in the period.
The affiliations presented were described based on the profile of each researcher in Scopus. They were updated, according to the last paper published by the author until March 31, 2021. Thus, some authors may have more than one affiliation. According to Table 5, two prominent authors are affiliated with the Euro-Mediterranean Center on Climate Change: Critto and Torresan. The other authors are affiliated with different universities/centers. Regarding the countries, three authors develop researches in Italy (Critto, Marcomini, and Torresan), another three in the United States (Lin, Hagen, and Medeiros). Nicholls and Lowe are from the United Kingdom. Belgium and Germany also appear in the rank with the authors Vousdoukas and Weisse, respectively.
The discussion about gender aims to demonstrate that the frequency in which men and women occur in the field is mostly different. Holmam et al. (2018) found that prestigious journals have fewer female authors. Additionally, the authors estimated that men are invited by journals to submit papers at approximately double the rate of women. Gender equity guarantees women the same opportunities as men in benefiting from the fruits of research, contributing to society, earning a living, and choosing a fulfilling profession (Huyer 2015; Vila-Concejo et al. 2018). In the current times, in which gender equality is sought, it is necessary to present and show that women still do not dominate ranks, such as those presented in Table 5 and Table 6. Concerning the largest number of publications, Lin (female) occupies the second position. In the same sense, Torresan occupies the ninth position of the rank. However, the results point out that women are the minority compared to men, who account for 80% of the 10 authors on the top ranking.
Figure 7 shows the clusters of researchers who are co-authors in at least two papers. Among the 1454 authors, 183 are co-authors in the 429 papers analyzed. However, the largest set of connecting co-authorship consists of 49 authors. In this case, the cluster analysis allows the identification of the niches of co-authors. In the light blue cluster, Nicholls was the author who published the most, with 13 papers, and he is co-author with 10 other researchers. Among his strongest relationships are Brown, Hanson, and Vafeidis. Lin published 9 papers, thus being the author who has most published in the yellow cluster, co-authoring with 8 researchers. In the green cluster, Lowe, who published 7 papers, was the researcher with the highest co-authorship number (15). In the dark blue cluster, Weisse was the most prolific author with 5 published papers, and is a co-author with 10 researchers. Gonnert published 3 papers, hence is the most productive author in the red cluster, being the co-author with 9 other researchers. In the purple cluster, Kirshen, which published 4 papers, is co-authored with 5 researchers. Sterl was the most prolific publisher in the brown cluster with 3 published papers, and is co-author with 9 other authors. In the orange cluster, Dawson, which has 2 publications, is co-author with 4 researchers. Finally, in the pink cluster, Xian was the author who has written the most number of papers (3) and is co-author with 3 researchers.
Table 6 presents the first 10 most cited authors. The first 4 authors, Nicholls, Vafeidis, Neumann, and Zimmermann are co-authors of the same paper (Neumann et al. 2015), which obtained 713 citations until February 28, 2021. Lowe is the fifth author of the rank, with 529 citations in his 7 published papers. Dingman, Ericson, Meybeck, Vörösmarty, and Ward are also co-authoring of the same paper (Ericson et al. 2006), which has 453 citations to the same date.
Regarding affiliations, Vafeidis and Zimmermann are affiliated with Christian-Albrechts-Universität zu Kiel in Germany. Dingman and Ward are part of the University of New Hampshire Durham, located in the United States. The other authors of the rank are affiliated with different universities/centers. The first country in the rank is the United States, with four researchers. Next is Germany, with three authors, and the United Kingdom, with two researchers. France appears only once, in the seventh position in the ranks. As in the analysis of the number of papers published by the author (Table 5), the results related to gender in Table 6 also indicate that women occupy only 20% of the rank of most cited researchers. It is also noteworthy that Neumann and Zimmermann were co-authors of the same work, with Neumann being the first author. Again, it is shown that women are not the majority among the 10 authors on the top ranking.
Figure 8 presents the cluster analysis of the authors, in which at least 3 published papers were cited 4 times by other researchers. Divided into six clusters, the authors are associated with other authors, among whom they were cited. Nicholls was the most cited author, among the analyzed researchers. This author also presents a connection with the authors represented by the light blue, red, and purple clusters. This indicates that he also cites a significant number of authors from those clusters. Lowe appears as the second author who obtained at least 4 citations in 3 published papers. He was the researcher most cited by the authors of the light blue cluster. Lin was the third most cited author from the 429 papers in the database. The author was a reference, mainly of the works written by Emanuel, Xian, Donnelly, Horton, Kopp, Yin, and McInnes.
The co-citation patterns indicate the history of recognition and academic impact of publications since a publication can be relevant for future research and can, thus, potentially be cited (Hjørland 2013). The co-citation analysis by the author presents the group of researchers who are cited by a group of authors. Therefore, it becomes important to demonstrate to the authors that it is also related to the topic. The analysis of co-citation by the author demonstrates, from four clusters, the set of authors that were most cited by the 1454 authors of the 429 papers analyzed. In the selected papers, 24,623 researchers were cited, and the 36 researchers represented in Fig. 9 were cited at least 65 times. The authors' proximity to clusters refers to the list of their proposed themes within the general topic of storm surges and climate changes.
Nicholls appears as the most cited author, with 552 citations. In the same papers, authors, such as Woodroffe, Hinkel (the fifth most cited, with 144), Tol, Vafeidis, Hallegatte, and Corfee-Morlot are also cited. It does not exclude the fact that the authors of other clusters are also cited in the same paper, in which Nicholls appears. Emanuel is in the second position, with 247 citations. The authors most cited by the same paper are represented in the green cluster, in which Lin, fourth-most cited is part, with 146. Church is the third in rank, with 147 citations by base papers. The author is represented by the yellow cluster, in which also appears Cazenave, the sixth most cited author, with 141 papers. The other researchers were cited 121 times or less.
The paper entitled Sea-level rise and its impact on coastal zones (Nicholls and Cazenave 2010) was the most cited by the 429 papers analyzed. The authors discuss important issues in it, such as Global Sea-Level Rise in the 21st Century, Main Impacts of Sea-Level Rise, and Adaptation. The publication obtained 40 citations among the selected papers. The paper totaled 1.256 citations until April 2, 2021. Between January and April 2, 2021, the paper had already been cited 49 times, as indicated by Scopus.
3.5 Keywords’ analysis
The evolution of the first 5 keywords between 1991 and 2021 is shown in Fig. 11. The keywords plus (i.e., most commonly used words in titles, abstracts, and keywords list) were represented according to their annual and noncumulative occurrence. The main keywords are highlighted: Climate Change, Storm Surge, Floods, Sea Level, and Sea Level Change. In general, the terms appeared considerably since 2007. The most used keyword per year was climate change. Between the period of 2019 to February 2021, the curve is stable, with an annual occurrence of approximately 35. It shows that its use is constant and more elevated, concerning the other highlighted keywords.
Storm surge is the second most used keyword since 2007. Its usage peak occurred between 2017 and 2019. However, it must be considered that only papers from January and February of the year 2021 were selected. Studies related to the topic are growing exponentially until the year 2020, as seen in Fig. 2. In addition, only two months in 2021 account for more publications than several other years, such as 2009. The growth occurs due to the current situation of climate change and environmental impacts. Sea level change was the most used keyword in the papers since 2007. However, between 2015 and 2018, it remained stable, with a drop in its employment in 2019. After 2016, floods started to have a higher annual occurrence in keywords. Its peak was in the first two months of 2021. The use of the term sea level in keywords was stable between 2017 and 2019, slightly decreasing in 2020.
Among the 1075 keywords established by the authors, 17 occurred in at least 10 papers out of 429 analyzed. The co-occurrence network based on keywords occurrences in papers is shown in Fig. 12. The size of the node is proportional to the frequency of occurrence of the keyword, and the thickness of the line represents the intensity of co-occurrence between individual keywords (Mishra et al. 2020). Zupic and Čater (2015) point out the negative aspect of presenting co-word analysis. The authors show that words can appear in different forms, as well as they can have different meanings.
The keywords determined by the authors did not follow a pattern. It can occur in different research fields since different words can have the same interpretation meaning. In the case of the present study, words, such as sea level rise and sea-level rise, were found among the authors’ the 17 most used keywords. The researchers used it in 64 and 53 papers, respectively. Another example of duplicity is storm surge and storm surges, which appeared 82 and 26 times, respectively. Moreover, words like coastal flooding (24) and flooding (22) were used. Considering that the research only delimited studies related to the coastal area, the two terms can be classified as synonyms. The keyword inundation (13) may or may not give rise to the same interpretation as flooding. There is no consensus, among authors in the research area. In the same sense, erosion and coastal erosion appeared (both 13 times), which probably refer to the same topic. It should be noticed that, logically, when one of these keywords is used, the other one will not be used. It justifies the fact that they have the same interpretation.
An analysis of some papers by the three authors who published more on the topic revealed divergences in the keywords pattern. Nicholls (2002) used words like sea-level rise and flooding, while Lin et al. (2016) employed storm surge and sea level rise. On the other hand, Lin and Shullman (2017) used storm surge and sea-level rise. In the paper by Lowe and Gregory (2005), the expression storm surge may appear as a keyword. It is understood that the use of words in the singular or plural, as storm surge, may be related to the number of events that were analyzed by the authors. The three keywords most used by the researchers were climate change (168 times), sea level rise (sea-level rise), and storm surge (storm surges). The highlighting of these keywords is justified, as they are directly related to the keywords used in the query expression determined in the present study. Regarding keywords that did not show duplicity, there is vulnerability and adaptation, which appeared in 18 papers each, next to the sea level keyword, which was used 14 times. Risk assessment appeared in 11 papers, while the words coastal hazards, coastal management, and flood risk appeared in 10 papers. The other keywords were used 9 times or less.
Four clusters are represented in Fig. 12. In papers that the authors opted for the keyword climate change, the other 16 keywords presented were also used at least once. In the same green cluster, terms, such as sea level rise, coastal flooding, storm surge, sea level, and flood risk, appear. Storm surges appear related to the words represented in the blue cluster, considering its strong relationship with climate change and sea level rise, as well as sea-level rise, being more used in conjunction with words belonging to the red cluster, in addition to having a strong relationship with storm surge. Erosion and coastal hazards appear in the yellow cluster. Terms considered as synonyms appear in different clusters, which shows the fact that they are not used together in the keyword lists.