Research articles published in water resources journals: A bibliometric analysis

Abstract

This study was designed to evaluate the global scientific output in the ISI subject category of “water resources” for the past 16 years. Data were based on the online version of the Science Citation Index Expanded, Web of Science, from 1993 to 2008. Articles referring to water resources were assessed for many aspects, including distributions of source countries, institutes, words in the title, author keywords, and KeyWords Plus. The h-index was also calculated in terms of the characteristics of publications. Distributions of paper titles, the author’s keywords, and KeyWords Plus at different periods were applied to evaluate research trends. The analysis showed that researchers paid most attention to groundwater and water quality parameters. Modeling and adsorption were the most popular techniques in water resources research. In addition, the relationship between the impact factor and h-index was significant for journals in the first group. The impact of the most cited articles each year were also discussed along with the article life information.

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Desalination and Water Treatment
www.deswater.com
1944-3994/1944-3986 © 2011 Desalination Publications. All rights reserved
doi: 10/5004/dwt.2011.2412
*Corresponding author.
28 (2011) 353–365
April
Research articles published in water resources journals: A bibliometric analysis
Ming-Huang Wang
a
, Jinfeng Li
a
, Yuh-Shan Ho
b,c,
*
a
Department of Environmental Sciences, College of Environmental Sciences and Engineering, Peking University, Beijing, 100871,
People’s Republic of China
b
Trend Research Centre, Asia University, Taichung 41354, Taiwan
c
Department of Environmental Sciences, Peking University, The Key Laboratory of Water and Sediment Sciences,
Ministry of Education, Beijing 100871, People’s Republic of China
Tel. 866 4 2332 3456 ext. 1797; Fax: 866 4 2330 5834; email: ysho@asia.edu.tw
Received 01 October 2010; Accepted 15 February 2011
ABSTRACT
This study was designed to evaluate the global scientifi c output in the ISI subject category
of “water resources” for the past 16 years. Data were based on the online version of the Sci-
ence Citation Index Expanded, Web of Science, from 1993 to 2008. Articles referring to water
resources were assessed for many aspects, including distributions of source countries, insti-
tutes, words in the title, author keywords, and KeyWords Plus. The h-index was also calcu-
lated in terms of the characteristics of publications. Distributions of paper titles, the author’s
keywords, and KeyWords Plus at different periods were applied to evaluate research trends.
The analysis showed that researchers paid most attention to groundwater and water quality
parameters. Modeling and adsorption were the most popular techniques in water resources
research. In addition, the relationship between the impact factor and h-index was signifi cant for
journals in the fi rst group. The impact of the most cited articles each year were also discussed
along with the article life information.
Keywords: Scientometrics; Research trend; Power model; Exponential model; Water resources
1. Introduction
Three-quarters of the Earth’s surface is covered
by oceans, which dominate the overall impact on the
weather and climate system [1]. Water is the most pre-
cious global commodity with its myriad uses like drink-
ing, industrial production, irrigation and the production
of fi sh, waterfowl and shellfi sh [2]. These include water
for freshwater systems that provides many nonextrac-
tive or instream benefi ts like fl ood control, transporta-
tion, recreation, waste processing, hydroelectric power,
and habitat for aquatic life [3]. Some benefi ts, such as
irrigation and hydroelectric power, are achieved only
by major changes to the fl ow regime and fl ow paths
from dams and water diversions [4]. Degradation of
water resources with time is a social concern. Therefore,
researchers have investigated the unbalanced distribu-
tion of water resources [5–7]. According to a review on
history of water resource studies, the earliest research
was presented in 1910 [8], and many investigations
were implemented in the following years, for example
about central and east African water resources [9], and
the geology and ground-water resources of Iwo Jima
[10], whereas today, water resources science has become
one of the most important areas in the water research
fi eld. The issue of water resources plays an important
role in the global environment. Over the years, a great
deal of progress has been made in water resource moni-
toring [11,12], water treatment techniques [13–15], and
water resource management [16–18]. The bibliometric

M.-H. Wang et al. / Desalination and Water Treatment 28 (2011) 353–365
354
method has been widely applied to the analysis of sci-
entifi c production and research trends in environment-
related topics, for example, geostatistics [19], adsorption
technology [20], aerosol [21], hydrologic sciences [22],
hydrogeology [23,24], wetland [25], solid waste [26], and
desalination [27]. The Science Citation Index Expanded
(SCI-Expanded), from the Institute for Scientifi c Informa-
tion (ISI) Web of Science databases, is the most important
and frequently used source database of choice for a broad
review of scientifi c accomplishment in all fi elds [28].
Many bibliometric investigations have been carried out
in various subject areas, for example the medical fi elds
of oncology [29], radiology, nuclear medicine and medi-
cal imaging [30], otolaryngology [31], tropical medicine
[32], virology [33], and dentistry, oral surgery & medi-
cine [34] as well as the science and engineering fi elds
ecology [35], microbiology [36], psychology [37], biol-
ogy [38], and ocean engineering [39]. Conventional bib-
liometric methods often evaluate research trends by the
publication outputs of countries [40], research institutes
[21], journals [41], and research fi elds [42] as well as by
citation analysis [22–24,70]. However, merely depending
on the change in the citations or publication counts of
countries and organizations cannot completely defi ne
developmental trends or the future orientation of the
research fi eld. More information, closer to the research
itself, such as words in the title [21,43], author keywords
[21], KeyWords Plus [44], and words in the abstract [45]
should be introduced in the study of research trends.
The KeyWords Plus in the SCI-Expanded database sup-
plies additional search terms extracted from the titles
of articles cited by authors in their bibliographies and
footnotes [46]. Recently, data was separated into 4 four-
year periods in order to analyze the variations of trends
thoroughly and more precisely [21,43]. In this study, we
aimed to synthetically use the traditional method, such
as the analysis of languages, source countries, source
institutes, and the most cited papers to describe perfor-
mance in water resources research. In addition, the dis-
tributions of words in the title, author keywords, and
KeyWords Plus were analyzed.
2. Data sources and methodology
The data were collected by analyzing articles and
citations from the Thomson Reuters Web of Science
database which is based on the online version of SCI-
Expanded. According to Journal Citation Reports (JCR),
it indexed 6,426 major journals with citation references
across 172 scientifi c disciplines in 2007. All journals that
publish articles mostly on water resources, were selected
from among 59 journals listed in the category of “water
resources” indexed by ISI in 2007. Articles originating
from England, Scotland, Northern Ireland, and Wales
were reclassifi ed as from the United Kingdom (UK).
Papers addressed in Hong Kong were not included in
China. The impact factor (IF) of a journal is defi ned by
the JCR, and is derived by dividing the number of cur-
rent citations to articles published in the two previous
years by the total number of articles published in the
two previous years. It is a measure of the frequency with
which the average article in a journal has been cited in
a particular year. The IF is used to evaluate a journal’s
relative importance, especially when compared to oth-
ers in the same fi eld [37,58]. The IF of each journal was
obtained from the 2008 JCR. Contributions from differ-
ent institutes and countries were estimated by the affi li-
ation of at least one author to the article. Collaboration
type was determined by the addresses of the authors,
where the term “single country article” was assigned if
the researchers’ addresses were from the same c ountry.
The term “internationally collaborative article” was
designated to those articles that were coauthored by
researchers from more than one country. The term
“single institute article” was assigned if the research-
ers’ addresses were from the same institute. The term
“inter-institutionally collaborative article” was assigned
if authors were from different institutes. All the articles
referring to the subject category of water resources dur-
ing 1993–2008 were assessed from the following aspects:
document type and language of article, characteristics of
article output, distribution of output in journals, article
output of source country, source institute, author num-
ber per single country or institute article, and analysis
of words in the title, author keywords, and KeyWords
Plus. Keywords were defi ned as comma-separated
items of one or more words. All keywords, both those
reported by authors and those assigned by ISI, as well
as words in the title were identifi ed and separated into
4 four-year spans (1993–1996, 1997–2000, 2001–2004,
and 2005–2008), then their ranks and frequencies were
calculated, and different words with identical meaning
and misspelled keywords were grouped and consid-
ered as a single keyword. In addition, the h-index was
also calculated as a representative indicator of scien-
tifi c achievement [47]. It was defi ned as the number of
papers with citation number greater than or equal to h
[47]. Hirsch suggests that the h-index has a better predic-
tive power than other measures such as total number of
published papers and total number of acquired citations
[48]. Studies assessing the effi cacy of the h-index have
pointed out its convergent validity as a major advan-
tage [49–51]. Moreover, quantity and quality of output
are usually assessed by “number of publications” and
“total citation counts”, respectively [50,51]. Therefore,
as a quality measure of publication activity, the h-index
of languages, journals, research institutes and countries
were calculated to evaluate achievements.

M.-H. Wang et al. / Desalination and Water Treatment 28 (2011) 353–365
355
3. Results and discussion
3.1. Document type and language of publication
The distribution of document type identifi ed by ISI
was analyzed. From this study, 18 document types were
found in the total 96,574 publications during 1993–2008.
Journal articles (62,258) were the most-frequently used
document type with 64% of the total production, followed
by proceedings papers (19,769; 20%), editorial materials
(5,743; 5.9%), and reviews (1,806; 1.9%). The others were
less signifi cant, including news items (799), letters (660),
corrections (569), discussions (513), notes (485), addi-
tion corrections (208), biographical items (136), software
reviews (38), meeting abstracts (30), items about an indi-
vidual (25), reprints (21), bibliographies (8), book reviews
(6), and database review (1). As journal articles were domi-
nant in the document types and peer-reviewed within
this fi eld, they were identifi ed and further analyzed. The
emphasis of the following discussion was to determine
the pattern of scientifi c production and research activity
trends which consisted of authorship, institutes, countries,
and trends in the research subjects addressed. Ninety-
eight percent of all these journal articles were published
in English (60,793) with an h-index of 151. Compared with
other investigations, English was the dominant language
[21,43,52], followed by French (913), Spanish (407), Ger-
man (130), Afrikaans (10), Dutch (2), Rumanian (2), and
Danish (1) with h-indexes of 14, 6, 11, 2, 0, 1, and 1 for each
respectively. A signifi cant correlation was found between
the yearly cumulative number of articles and the year from
1993 to 2008 [53,54]. The relationship between the cumu-
lative number of articles published each year (P) and the
number of consecutive years (Y) studied from 1993 to 2008
was found to be: P = 2088Y
1.144
(r
2
= 0.997) until 2002 and
P = 9568exp (0.1173Y) (r
2
= 1.000) for 2002–2008 (Fig. 1).
3.2. Distribution of outputs in journals
All journals with their impact factor, impact factor
rank, number of articles in 2007, and h-index were sta-
tistically analyzed (Table 1). In total, 62,258 articles were
published in the 59 searched journals under the category
of water resources. Seventeen journals had more than
1,000 published articles referring to water resources
research from 1993 to 2008. The h-index provides a new
indicator for the research performance and the impact
factor is a mature indicator. Water Research published the
most articles (6,880; 11%), and had the highest h-index
(117). The coeffi cients of determination between the
h-index and the impact factor of journal outputs were
calculated (Figs. 2 and 3). Group 1 journals had a coeffi -
cient of determination (r
2
) of 0.81 while group 2 had 0.63.
Moreover, Bradford’s Law of Scattering [55] was
applied. The journals were sorted in descending order in
terms of number of articles, and then divided into three
“zones”. Zone 1 represents the most productive one-
third of the total articles, with 5 (8.5%) of 59 journals.
Zone 2 represents the next most productive one-third of
total articles, with 14 (24%) of 59 journals, and Zone 3
represents the least productive one-third of total articles
with 40 (68%) of 59 journals. The number of journals
in the three zones approximately followed Bradford’s
law. To reiterate, the number of journals was approxi-
mately 1: n: n
2
(1: 2.8: 8). The water resources category
contained fi ve Bradford’s core journals, Water Research,
Water Resources Research, Journal of Hydrology, Water Air
and Soil Pollution, and Environmental Geology.
3.3. Distribution of country/territory articles
The contributions of different countries/territories
were estimated by the location of the affi liation of at
least one author of the published paper. The 914 articles
without any author address information were excluded.
Of all the 61,334 articles with author addresses, 49,338
(80%) were single country articles and 12,006 (20%)
were internationally collaborative articles. Among the
top 20 productive countries/territories were two North
American countries, ten European countries, six Asian
countries, South Africa, and Australia (Table 2). There
was no country from South America in the top produc-
tive countries. Most of the 7 major industrial countries
(G7: Canada, France, Germany, Italy, Japan, the UK,
and the USA) were among the top 10 productive coun-
tries except for Japan (ranked 11th). The USA, the UK,
and Canada had high productivity in terms of total,
i ndependent, internationally collaborative, fi rst author,
Fig. 1. Cumulative number of articles by year during 1993–2008.

M.-H. Wang et al. / Desalination and Water Treatment 28 (2011) 353–365
356
Table 1
All journals in the category of water resources in SCI-Expanded
Journal title TA (%) IF IFR TA (2007) h-index
Water Research 6,880 (11) 3.587 1 509 117
Water Resources Research 5,345 (8.6) 2.398 2 505 109
Journal of Hydrology 4,223 (6.8) 2.305 3 404 78
Water Air and Soil Pollution 2,961 (4.8) 1.398 15 249 50
Environmental Geology 2,674 (4.3) 1.026 31 459 26
Hydrological Processes 2,396 (3.8) 2.002 7 415 50
Journal of Hydraulic Engineering-ASCE 1,855 (3.0) 1.272 20 185 30
Journal American Water Works Association 1,678 (2.7) 0.561 51 91 21
Desalination 1,602 (2.6) 1.155 25 747 15
Ground Water 1,522 (2.4) 1.304 18 84 34
Water Environment Research 1,480 (2.4) 0.966 36 153 25
Ocean Engineering 1,444 (2.3) 0.857 41 163 19
Agricultural Water Management 1,386 (2.2) 1.646 12 138 29
Journal of the American Water Resources Association 1,285 (2.1) 1.208 23 117 39
Journal of Contaminant Hydrology 1,253 (2.0) 2.106 6 97 63
Clays and Clay Minerals 1,169 (1.9) 1.171 24 47 2
Advances in Water Resources 1,129 (1.8) 2.235 4 137 47
Journal of Hydraulic Research 991 (1.6) 0.883 40 92 22
Journal of Soil and Water Conservation 984 (1.6) 1.121 28 87 31
Journal of Irrigation and Drainage Engineering-ASCE 981 (1.6) 0.822 42 115 23
Water SA 946 (1.5) 0.721 46 82 20
Catena 907 (1.5) 1.874 11 147 44
Hydrological Sciences Journal-Journal des Sciences Hydrologiques 906 (1.5) 1.216 22 90 43
Houille Blanche-Revue Internationale de L Eau 815 (1.3) 0.096 57 66 7
Water Science and Technology 757 (1.2) 1.005 33 604 19
Journal of Water Resources Planning and Management-ASCE 750 (1.2) 1.275 19 61 37
Hydrogeology Journal 732 (1.2) 1.100 29 115 28
Hydrology and Earth System Sciences 719 (1.2) 2.167 5 104 39
Ocean & Coastal Management 697 (1.1) 1.036 30 72 32
Journal of Hydrologic Engineering 694 (1.1) 1.007 32 134 11
Natural Hazards 684 (1.1) 0.989 35 108 27
China Ocean Engineering 659 (1.1) 0.430 53 46 11
Water International 616 (1.0) 0.315 55 30 8
Journal of Waterway Port Coastal and Ocean Engineering-ASCE 602 (1.0) 0.789 43 32 18
Ground Water Monitoring and Remediation 583 (0.94) 0.957 37 25 28
Vadose Zone Journal 567 (0.91) 1.441 14 122 41
Environmental Toxicology 531 (0.85) 1.899 9 92 39
Aquatic Conservation-Marine and Freshwater Ecosystems 506 (0.81) 1.619 13 107 35
Journal of Water Supply Research and Technology-Aqua 489 (0.79) 0.626 49 57 11
Water Resources Management 488 (0.78) 1.350 16 112 53
Acta Hydrochimica et Hydrobiologica 476 (0.76) 0.907 39 0 19
Environmental Geochemistry and Health 457 (0.73) 1.238 21 61 28
Natural Hazards and Earth System Sciences 448 (0.72) 1.345 17 131 50
Ingenieria Hidraulica en Mexico 409 (0.66) 0.112 56 51 14
River Research and Applications 387 (0.62) 1.959 8 92 52
Water Quality Research Journal of Canada 373 (0.60) N/A 59 N/A 5
Stochastic Environmental Research and Risk Assessment 367 (0.59) 0.951 38 77 31
Irrigation Science 331 (0.53) 1.891 10 49 50
Irrigation and Drainage 318 (0.51) 0.480 52 45 10
Physics and Chemistry of the Earth 287 (0.46) 1.138 27 186 29
Nordic Hydrology 270 (0.43) 0 58 40 8
International Journal of Water Resources Development 243 (0.39) 0.738 45 42 25
Lake and Reservoir Management 209 (0.34) 0.746 44 0 5
Water and Environment Journal 173 (0.28) 0.648 48 36 24
Clean-Soil Air Water 170 (0.27) 1.145 26 118 40
Environmental Fluid Mechanics 142 (0.23) 1.000 34 42 29
Proceedings of the Institution of Civil Engineers-Water Management 133 (0.21) 0.333 54 38 8
Journal of Hydroinformatics 107 (0.17) 0.681 47 24 17
Proceedings of the Institution of Civil Engineers-Maritime
Engineering
72 (0.12) 0.571 50 14 18
TA (%): total number and percentage of articles; IF: impact factor in 2008; IFR: rank in descending order of impact factor; TA (2007): total
number of articles in 2007.

M.-H. Wang et al. / Desalination and Water Treatment 28 (2011) 353–365
357
for 42% of all the internationally collaborative articles.
However, the collaborative articles represented only
23% of the total articles from the USA, which was
lower than that of European countries (Table 2). The
article impact of the USA was excellent with the high-
est h-index (123) among all the countries, followed by
Fig. 2. Relationship between h-index and impact factor
(Group 1).
Fig. 3. Relationship between h-index and impact factor
(Group 2).
Table 2
Top 20 most productive countries/territories of articles during 1993–2008
Countries Region TA TA R (%) SA R (%) CA R (%) FA R (%) RA R (%) %C h-index
USA American 21,851 1 (36) 1 (34) 1 (42) 1 (31) 1 (31) 23 123
UK European 4,647 2 (7.6) 2 (5.9) 2 (14) 2 (6.1) 2 (6.1) 37 77
Canada American 4,293 3 (7.0) 3 (5.7) 3 (12) 3 (5.7) 3 (5.6) 34 76
China Asian 3,209 4 (5.2) 4 (4.0) 5 (10) 4 (4.2) 4 (4.3) 39 47
France European 3,158 5 (5.1) 6 (3.7) 4 (11) 5 (3.9) 5 (3.9) 42 62
Germany European 2,847 6 (4.6) 8 (3.3) 6 (10) 7 (3.4) 7 (3.5) 43 66
Australia Oceania 2,693 7 (4.4) 7 (3.5) 7 (8.2) 6 (3.5) 6 (3.5) 37 66
India Asian 2,338 8 (3.8) 5 (3.7) 13 (4.1) 8 (3.4) 8 (3.4) 21 49
Italy European 2,326 9 (3.8) 9 (3.0) 10 (6.9) 9 (3.1) 9 (3.2) 36 59
Spain European 2,171 10 (3.5) 10 (3.0) 11 (5.8) 10 (3.0) 10 (3.0) 32 57
Japan Asian 2,138 11 (3.5) 11 (2.5) 9 (7.3) 11 (2.6) 11 (2.7) 41 53
Netherlands European 1,834 12 (3.0) 14 (1.9) 8 (7.6) 12 (2.2) 12 (2.1) 49 61
Taiwan Asian 1,282 13 (2.1) 12 (2.1) 24 (2.1) 13 (1.9) 13 (2.0) 20 51
Turkey European 1,216 14 (2.0) 13 (2.0) 25 (2.0) 14 (1.8) 14 (1.9) 20 42
Switzerland European 1,142 15 (1.9) 20 (1.0) 12 (5.3) 17 (1.3) 18 (1.3) 56 51
South Korea Asian 1,127 16 (1.8) 16 (1.3) 14 (3.9) 16 (1.5) 16 (1.5) 41 46
South Africa African 1,093 17 (1.8) 15 (1.8) 27 (1.7) 15 (1.7) 15 (1.6) 19 29
Sweden European 1,026 18 (1.7) 17 (1.2) 15 (3.8) 18 (1.3) 17 (1.3) 44 47
Israel Asian 872 19 (1.4) 19 (1.1) 17 (2.7) 19 (1.1) 19 (1.2) 37 45
Belgium European 814 20 (1.3) 23 (0.76) 16 (3.7) 22 (1.0) 22 (1.0) 54 41
TA: total number of articles; TA R (%), SA R (%), CA R (%), FA R (%), RA R (%): rank and percentage of total articles of one country, single
country articles, internationally collaborative articles, fi rst author articles, corresponding author articles in total articles; C%: percentage
of internationally collaborative articles in total articles of one country.
and corresponding author articles. Domination in arti-
cles from the mainstream countries was not surprising
since this pattern occurs in other scientifi c fi elds [43].
The USA was predominant in global water resources
research and published the most articles (21,851; 36%).
The USA was also the most frequent partner a ccounting

M.-H. Wang et al. / Desalination and Water Treatment 28 (2011) 353–365
358
Fig. 4. Comparison of the trends of the top 5 productive
countries during 1993–2008.
Table 3
Top 20 most productive institutes during 1993–2008
Institute TA TA R (%) SA R (%) CA R (%) FA R (%) RA R (%) h-index
U.S. Geological Survey, USA 1,343 1 (2.2) 1 (1.9) 1 (2.5) 1 (1.5) 1 (1.6) 64
Agricultural Research Service, United
States Department of Agriculture (USDA
ARS), USA
820 2 (1.3) 3 (0.83) 3 (1.8) 4 (0.8) 4 (0.85) 56
Chinese Academy of Sciences, China 813 3 (1.3) 5 (0.74) 2 (1.9) 3 (0.86) 2 (0.87) 33
Indian Institute of Technology, India 765 4 (1.2) 2 (1.1) 6 (1.4) 2 (0.89) 3 (0.85) 35
University of Arizona, USA 693 5 (1.1) 6 (0.73) 4 (1.5) 5 (0.71) 5 (0.60) 58
US Environmental Protection Agency,
USA
607 6 (1.0) 11 (0.49) 5 (1.5) 9 (0.53) 8 (0.54) 41
University of California (Davis), USA 596 7 (1.0) 8 (0.59) 7 (1.4) 8 (0.58) 9 (0.53) 38
University of Waterloo, Canada 591 8 (1.0) 7 (0.67) 8 (1.3) 6 (0.66) 7 (0.55) 51
University of California (Berkeley), USA 548 9 (0.89) 4 (0.77) 12 (1.0) 7 (0.60) 6 (0.56) 49
Texas A&M University, USA 491 10 (0.80) 10 (0.50) 10 (1.1) 11 (0.49) 11 (0.46) 27
Colorado State University, USA 473 11 (0.77) 21 (0.38) 9 (1.2) 13 (0.45) 14 (0.40) 37
University of Illinois, USA 458 12 (0.75) 13 (0.46) 11 (1.0) 12 (0.47) 12 (0.44) 41
National Taiwan University, Taiwan 419 13 (0.68) 9 (0.54) 18 (0.82) 10 (0.52) 9 (0.53) 33
University of Colorado, USA 411 14 (0.67) 16 (0.40) 14 (0.94) 14 (0.42) 15 (0.38) 47
Cornell University, USA 402 15 (0.66) 31 (0.32) 13 (1.0) 17 (0.37) 21 (0.32) 41
Spanish National Research Council
(CSIC), Spain
391 16 (0.64) 16 (0.40) 17 (0.88) 16 (0.39) 13 (0.41) 35
University of Florida, USA 356 17 (0.58) 19 (0.39) 20 (0.77) 15 (0.41) 17 (0.36) 30
Delft University of Technology,
Netherlands
353 18 (0.58) 60 (0.23) 15 (0.92) 27 (0.31) 32 (0.27) 36
University of British Columbia, Canada 344 19 (0.56) 26 (0.35) 20 (0.77) 23 (0.33) 26 (0.30) 35
Oregon State University, USA 343 20 (0.56) 68 (0.21) 16 (0.90) 30 (0.30) 34 (0.26) 37
TA: total number of articles; TA R (%), SA R (%), CA R (%), FA R (%), RA R (%): rank and percentage of total articles of one institute, single
institute articles, inter-institutionally collaborative articles, fi rst author articles, corresponding author articles in total articles.
the highest growth rate in the number of articles and
ranked second in 2008.
3.4. Distribution of institute analysis
The contributions of different institutes were esti-
mated by the affi liation of at least one author. Taking EU
member states as an example, a previous study pointed
out the complexity in the use of address data, and con-
cluded that this can be used at the level of “main orga-
nization”, such as a university, a company, or a research
institute [56], but for countries with a complex system,
such as France, a list of organizations should be compiled
beforehand. In our data we used institute names from the
ISI database. Furthermore, country and institute infor-
mation were used jointly to avoid errors in aggregating
papers to institutions. Of all the 61,334 articles with author
addresses, 30,619 (49.9%) were independent articles
and 30,725 (50.1%) were collaborations by two or more
in stitutes. Among the top 20 institutes (Table 3), 13 were
in the USA, 2 in Canada and one each in China, India, Tai-
wan, Spain, and the Netherlands. A bias in institute anal-
ysis should be noted that both the Chinese Academy of
Sciences and the Indian Institute of Technology have over
100 branches in different cities. At present, the articles of
Canada (77) and the UK (76). The trends of the top 5
productive countries in 2008 with more than 400 arti-
cles are shown in Fig. 4. Besides the USA, China had

M.-H. Wang et al. / Desalination and Water Treatment 28 (2011) 353–365
359
these two institutes were pooled under one heading, and
articles divided into branches would result in different
rankings [58]. This kind of identity raised these two insti-
tutes’ ranks in global water resources research. The U.S.
Geological Survey (USGS) published the most total arti-
cles (1,343), independent articles, inter-institutionally col-
laborative articles, fi rst author articles and corresponding
author articles. Furthermore, the h-index (64) of USGS was
the highest among all the institutes. The most cited paper
from the USGS was “evaluating the use of goodness-of-fi t
measures in hydrologic and hydro-climatic model valida-
tion” [57]. The USGS is a scientifi c agency of the United
States government, and its major aim is to study the land-
scape of the United States, its natural resources, and the
natural hazards that threaten it. This organization has four
major science disciplines, hydrology, biology, geography,
and geology (www.usgs.gov).
4. Distribution of paper titles, author keywords and
KeyWords Plus
4.1. Distribution of paper titles analysis
The title of an article always includes the information
that the author would most like to express to the readers.
It can be used to identify the subjective focus and empha-
sis specifi ed by authors. The analysis of paper titles was
fi rst applied in mapping trends in aerosol research [21],
and then in stem cell [43], and atmospheric simula-
tion research [58]. All single words in the title of water
resources-related articles were statistically analyzed
in this study. Some prepositions, articles and common
words such as “using”, “under”, “the”, and “during”
were discarded, as they were meaningless for further
analysis. The 25 most frequently used substantives in
titles were grouped in 4 four-year periods (Table 4).
“Model” ranked second and was the most frequent
method used in the analysis of paper titles. In 1998, Arnold
et al. developed a conceptual, continuous time model
called SWAT (Soil and Water Assessment Tool) to assist
water resource managers in assessing the impact of man-
agement on water supplies and nonpoint source pollution
in watersheds and large river basins [59]. This paper in
the Journal of the American Water Resources Association had a
great impact on the subsequent water resources research.
4.2. Distribution of author keywords analysis
Author keywords offer information about research
trends that concern researchers. Bibliometric methods
Table 4
Top 25 most frequent substantives in article titles during 1993–2008 and 4 four-year periods
Words in title
93-08
TA
93-08
R (%)
93-96
R (%)
97-00
R (%)
01-04
R (%)
05-08
R (%)
water 8,892 1 (14) 1 (8.6) 1 (14) 1 (16) 1 (16)
model 3,937 2 (6.3) 2 (5.3) 2 (6.5) 2 (6.1) 2 (6.8)
Flow 3,696 3 (5.9) 5 (4.6) 3 (6.4) 2 (6.1) 3 (6.1)
Soil 2,992 4 (4.8) 4 (4.7) 4 (4.8) 5 (5.0) 7 (4.7)
River 2,989 5 (4.8) 11 (2.6) 7 (4.3) 4 (5.2) 4 (5.7)
Analysis 2,931 6 (4.7) 8 (3.5) 5 (4.6) 6 (4.6) 5 (5.4)
Groundwater 2,668 7 (4.3) 7 (3.8) 8 (3.7) 8 (3.9) 6 (5.1)
Transport 2,477 8 (4.0) 3 (4.8) 6 (4.4) 7 (4.0) 11 (3.4)
Modeling 2,308 9 (3.7) 6 (4.2) 10 (3.4) 10 (3.5) 8 (3.8)
Effects 2,276 10 (3.7) 9 (3.4) 9 (3.5) 9 (3.8) 9 (3.7)
Management 1,880 11 (3.0) 15 (2.4) 13 (2.9) 14 (3.0) 10 (3.4)
Effect 1,860 12 (3.0) 10 (3.1) 12 (2.9) 11 (3.1) 16 (2.9)
System 1,843 13 (3.0) 20 (2.2) 11 (3.0) 12 (3.1) 14 (3.2)
Treatment 1,748 14 (2.8) 24 (2.0) 18 (2.4) 15 (2.9) 12 (3.3)
Removal 1,706 15 (2.7) 18 (2.3) 16 (2.6) 13 (3.0) 17 (2.9)
Sediment 1,512 16 (2.4) 22 (2.0) 19 (2.4) 19 (2.4) 22 (2.6)
Assessment 1,506 17 (2.4) 48 (1.3) 29 (2.0) 23 (2.3) 13 (3.2)
Wastewater 1,495 18 (2.4) 179 (0.58) 20 (2.3) 17 (2.5) 15 (3.1)
Evaluation 1,467 19 (2.4) 21 (2.0) 26 (2.1) 20 (2.4) 23 (2.6)
Aquifer 1,452 20 (2.3) 12 (2.6) 17 (2.5) 25 (2.3) 31 (2.2)
Systems 1,452 20 (2.3) 14 (2.4) 15 (2.6) 27 (2.1) 28 (2.3)
Basin 1,446 22 (2.3) 39 (1.4) 31 (2.0) 18 (2.5) 18 (2.8)
Surface 1,424 23 (2.3) 28 (1.7) 14 (2.7) 24 (2.3) 27 (2.3)
Distribution 1,412 24 (2.3) 26 (1.8) 24 (2.3) 22 (2.3) 25 (2.4)
Quality 1,392 25 (2.2) 63 (1.1) 23 (2.3) 16 (2.7) 26 (2.4)
Irrigation 1,392 25 (2.2) 23 (2.0) 36 (1.7) 26 (2.2) 20 (2.7)
TA: total number of articles; R (%): rank and percentage of substantives in titles in total articles.

M.-H. Wang et al. / Desalination and Water Treatment 28 (2011) 353–365
360
of author keyword analysis have been developed in
recent years [52,60], whereas using the author key-
words to analyze the trend of research in different
periods is rare [21,43,58]. Examination of author key-
words in this study revealed that altogether 74,992
were used, among which, 54,235 (72%) appeared only
once and 8,731 (12%) appeared twice. The large num-
ber of once-only keywords probably indicates a lack of
continuity in research and a wide disparity in research
foci [61]. The author keywords which ranked top 25
in all articles are listed in Table 5. The top two most
frequently used keywords were “groundwater” and
“water quality”, which are the most important topics
in water resources research. Two highly cited articles
with the author keyword “groundwater” were found.
The fi rst was “tracking persistent pharmaceutical
residues from municipal sewage to drinking water”
in the Journal of Hydrology [62]. This article had been
cited 150 times from its publication in 2002 until 2008.
The other was “arsenic in groundwater in six districts
of West Bengal, India” in Environmental Geochemis-
try and Health [63]. Arsenic in groundwater above
the WHO maximum permissible limit of 0.05 mg l
-1
was found in six districts of West Bengal covering an area
of 34,000 km
2
with a high population of 30 million [63].
This paper was cited 141 times up to 2008. The constant
focus on “groundwater” during 1993–2008 is consistent
with previous research results which demonstrated
this mature but also challenging theme [23,64,65]. “The
importance of trace metal speciation to water quality
criteria” with “water quality” in the title was pub-
lished in Water Environment Research [66] and was cited
131 times up to 2008. An interesting phenomenon in
author keywords was found; the researchers paid more
attention to the water resources issue that humans
can really “use” such as “fresh water resources” than
“ocean water”. “Adsorption” and “modeling” were the
most popular techniques in author keyword analysis.
Some topics, such as “runoff”, “wastewater”, “irri-
gation”, and “evapotranspiration” became new foci,
whose ranks went up markedly. In contrast, the author
keywords “activated sludge”, “biodegradation”, and
“denitrifi cation” decreased from 1st, 4th, and 5th during
1993
−1996 to 18th, 35th, and 56th during 2005−2008.
Table 5
Top 25 most frequent author keywords used during 1993–2008 and 4 four-year periods
Author keywords
93− 08
TA
93− 08
R (%)
93−96
R (%)
97− 00
R (%)
01− 04
R (%)
05− 08
R (%)
Groundwater 1,193 1 (2.9) 3 (2.9) 2 (2.8) 1 (3.1) 1 (2.7)
water quality 1,077 2 (2.6) 11 (1.9) 1 (2.9) 2 (2.9) 2 (2.4)
Adsorption 674 3 (1.6) 2 (3.1) 5 (1.7) 3 (1.5) 6 (1.4)
heavy metals 668 4 (1.6) 7 (2.1) 3 (2.3) 4 (1.5) 8 (1.3)
Runoff 584 5 (1.4) 99 (0.48) 6 (1.6) 6 (1.4) 3 (1.5)
Activated sludge 562 6 (1.4) 1 (4.8) 4 (1.8) 20 (0.91) 18 (0.89)
Modeling 540 7 (1.3) 8 (2.0) 8 (1.5) 5 (1.5) 13 (1.0)
Wastewater 538 8 (1.3) 68 (0.58) 7 (1.5) 8 (1.1) 5 (1.4)
Irrigation 524 9 (1.3) 43 (0.85) 28 (0.86) 7 (1.3) 4 (1.5)
Phosphorus 459 10 (1.1) 24 (1.2) 12 (1.2) 21 (0.91) 9 (1.2)
Sediment 450 11 (1.1) 24 (1.2) 11 (1.2) 13 (1.0) 11 (1.0)
evapotranspiration 445 12 (1.1) 68 (0.58) 38 (0.75) 16 (1.0) 7 (1.4)
modeling 424 13 (1.0) 89 (0.51) 15 (1.2) 9 (1.1) 12 (1.0)
Drinking water 422 14 (1.0) 20 (1.2) 17 (1.1) 12 (1.0) 16 (0.92)
Biodegradation 419 15 (1.0) 4 (2.7) 9 (1.3) 19 (0.93) 35 (0.63)
Nitrogen 403 16 (1.0) 34 (1.0) 13 (1.2) 14 (1.0) 23 (0.82)
Nitrate 385 17 (0.93) 43 (0.85) 24 (0.95) 10 (1.1) 24 (0.82)
Simulation 383 18 (0.92) 68 (0.58) 19 (1.0) 17 (0.94) 17 (0.92)
Hydrology 379 19 (0.91) 77 (0.54) 21 (1.0) 11 (1.1) 20 (0.84)
denitrifi cation 375 20 (0.90) 5 (2.4) 10 (1.3) 27 (0.82) 56 (0.53)
Climate change 351 21 (0.84) 153 (0.34) 34 (0.78) 26 (0.83) 14 (1.0)
Precipitation 350 22 (0.84) 37 (1.0) 34 (0.78) 22 (0.89) 26 (0.81)
GIS 349 23 (0.84) 372 (0.17) 51 (0.65) 28 (0.80) 10 (1.1)
Wastewater treatment 342 24 (0.82) 32 (1.0) 31 (0.82) 36 (0.72) 19 (0.87)
Sorption 340 25 (0.82) 24 (1.2) 16 (1.2) 24 (0.85) 43 (0.59)
TA: total number of articles; R (%): rank and percentage of author keywords in total articles.

M.-H. Wang et al. / Desalination and Water Treatment 28 (2011) 353–365
361
4.3. Distribution of KeyWords Plus analysis
KeyWords Plus provides search terms extracted from
the titles of articles cited by authors in their bibliogra-
phies and footnotes in the ISI database, and substantially
augments title-word and author-keyword indexing [46].
Unlike segmenting a whole title into single words as
in paper title analysis, precise words that the authors
wanted to transmit to the readers are preserved in author
keywords analysis. The KeyWords Plus analysis, as an
independent supplement, reveals the article contents
in more details. There were some similar and dissimi-
lar trends between their statistical results in this study
period. The top four most frequently used KeyWords
Plus were “water”, “model”, “fl ow”, and “transport”
(Table 6). The rank of “management”, “waste-water”,
“runoff”, and “variability” went up markedly from
62nd, 40th, 43rd, and 59th during 1993-1996 to 7
t
h, 13th,
14th, and 15th during 2005-2008. Similar to the results of
author keyword analysis, “waste-water” and “runoff”
were also emphasized in KeyWords Plus analysis. The
most cited article in 2004 was written by Carballa et al.
who did a survey of “waste-water” treatment in Spain.
The aim of this study was to investigate the behavior of
Table 6
Top 25 frequent KeyWords Plus used during 1993–2008 and 4 four-year periods
KeyWords plus 93–08
TA
93–08
R (%)
93–96
R (%)
97–00
R (%)
01–04
R (%)
05–08
R (%)
Water 3,960 1 (8.2) 1 (8.5) 1 (9.2) 1 (8.6) 2 (7.4)
Model 3,510 2 (7.3) 2 (5.9) 2 (6.9) 2 (7.5) 1 (7.8)
Flow 2,698 3 (5.6) 3 (4.9) 3 (5.1) 3 (5.7) 3 (6.0)
Transport 2,271 4 (4.7) 4 (4.4) 4 (5.0) 4 (4.7) 4 (4.7)
Soil 1,627 5 (3.4) 5 (4.0) 5 (3.4) 5 (3.3) 5 (3.2)
Porous-media 1,478 6 (3.1) 7 (3.8) 6 (3.2) 6 (3.2) 12 (2.7)
Groundwater 1,423 7 (3.0) 6 (3.8) 7 (3.1) 7 (2.8) 11 (2.7)
Simulation 1,376 8 (2.9) 11 (2.5) 9 (2.7) 9 (2.6) 6 (3.2)
Systems 1,348 9 (2.8) 10 (2.7) 11 (2.5) 10 (2.5) 9 (3.1)
Removal 1,273 10 (2.6) 17 (1.8) 14 (2.0) 8 (2.7) 8 (3.2)
Adsorption 1,168 11 (2.4) 8 (2.8) 8 (2.7) 11 (2.4) 16 (2.2)
Soils 1,097 12 (2.3) 12 (2.5) 10 (2.6) 13 (2.2) 23 (2.1)
System 1,049 13 (2.2) 38 (1.2) 25 (1.5) 12 (2.2) 10 (2.8)
Management 1,040 14 (2.2) 62 (0.80) 35 (1.2) 18 (1.9) 7 (3.2)
Waste-water 1,023 15 (2.1) 40 (1.2) 24 (1.5) 14 (2.2) 13 (2.7)
Solute transport 993 16 (2.1) 9 (2.8) 12 (2.4) 17 (2.0) 29 (1.7)
Runoff 986 17 (2.0) 43 (1.1) 19 (1.7) 16 (2.0) 14 (2.5)
Hydraulic conductivity 981 18 (2.0) 14 (2.0) 13 (2.2) 20 (1.9) 21 (2.1)
Models 921 19 (1.9) 18 (1.8) 16 (1.8) 25 (1.7) 17 (2.2)
Variability 917 20 (1.9) 59 (0.85) 43 (1.2) 15 (2.2) 15 (2.4)
Degradation 856 21 (1.8) 21 (1.7) 17 (1.8) 19 (1.9) 26 (1.8)
Precipitation 836 22 (1.7) 34 (1.2) 33 (1.2) 22 (1.8) 20 (2.1)
Growth 831 23 (1.7) 14 (2.0) 19 (1.7) 21 (1.8) 33 (1.6)
River 828 24 (1.7) 70 (0.75) 28 (1.4) 22 (1.8) 18 (2.1)
Aquifer 786 25 (1.6) 23 (1.6) 22 (1.5) 28 (1.6) 30 (1.7)
TA: total number of articles; R (%): rank and percentage of KeyWords Plus in total articles.
13 cosmetic and pharmaceutical compounds belonging
to different groups (musks, anti-infl ammatories, anti-
epileptics, tranquillizers, antibiotics, natural and syn-
thetic estrogens, and contrast media), and the removal
effi ciency from the water phase of each substance in
each particular unit was determined [67]. “Runoff” was
one of the key parameters in hydrological models [68,
69]. As in the analysis of author keywords, “model” and
“adsorption” were the most popular techniques in the
KeyWords Plus analysis.
4.4. Most cited articles
The time-dependence of citations might be infor-
mative for tracking the impact of an article. The most
highly cited papers appear to be pioneers in the fi eld
with papers departing signifi cantly from what has come
before and to be effective in creating similar, follow-on
papers [22]. The number of citations per year versus
time was presented for article life. Article history has
been investigated by the percentage of cited papers [54]
and the citations per article [70] versus time. From 1993
to 2008, the most frequently cited article was “occur-

M.-H. Wang et al. / Desalination and Water Treatment 28 (2011) 353–365
362
Table 7
Most frequently cited articles every year during 1993–2004
Year Article/Journal Authors TC C/Y Country
1993 Prophecy, reality and uncertainty in distributed
hydrological modeling
Advances in Water Resources
Beven, K 300 19 UK
1994 Enhanced degradation of halogenated aliphatics
by zero-valent iron
Ground Water
Gillham, RW; Ohannesin, SF 451 30 Canada
1995 Artifi cial neural-network modeling of the rainfall-
runoff process
Water Resources Research
Hsu, KL; Gupta, HV; Sorooshian, S 314 22 USA
1996 Extraction of extracellular polymers from
activated sludge using a cation exchange resin
Water Research
Frolund, B; Palmgren, R; Keiding,
K; Nielsen, PH
300 23 Denmark
1997 A new method for the determination of fl ow
directions and upslope areas in grid digital
elevation models
Water Resources Research
Tarboton, DG 273 23 USA
1998 Occurrence of drugs in German sewage treatment
plants and rivers
Water Research
Ternes, TA 630 57 Germany
1999 Evaluating the use of “goodness-of-fi t” measures
in hydrologic and hydroclimatic model validation
Water Resources Research
Legates, DR; McCabe, GJ 289 29 USA
2000 The kinetics of sorption of divalent metal ions
onto sphagnum moss peat
Water Research
Ho, YS; McKay, Gs 367 41 Hong
Kong
2001 Equifi nality, data assimilation, and uncertainty
estimation in mechanistic modelling of complex
environmental systems using the GLUE
methodology
Journal of Hydrology
Beven, K; Freer, J 207 26 UK
2002 Tracking persistent pharmaceutical residues from
municipal sewage to drinking water
Journal of Hydrology
Heberer, T 150 21 Germany
2003 Removal of copper ions from aqueous solution by
tree fern
Water Research
Ho, YS 132 22 Taiwan
2004 Behavior of pharmaceuticals, cosmetics and
hormones in a sewage treatment plant
Water Research
Carballa, M; Omil, F; Lema, JM;
Llompart, M; Garcia-Jares, C;
Rodriguez, I; Gomez, M; Ternes, T
153 31 Spain,
Germany
TC: total times cited of articles from publication until 2008; C/Y: times cited per year.
rence of drugs in German sewage treatment plants and
rivers”, which was published in Water Research by Ternes
from Germany in 1998 and had been cited 630 times by
2008. The most frequently cited articles every year that
was cited more than 100 times up to 2008 are listed in
Table 7. Five were published in Water Research, which
ranked fi rst in the category of water resources with an
impact factor of 3.427. Three originated in the USA and
Germany, two in the UK, and one each in Canada, Den-
mark, Hong Kong, Taiwan, and Spain. Five articles were
published by a single author. The citation history of the
most frequently cited articles listed in Table 7 are shown
in Fig. 5. The citation times of the most frequently cited
article [71] continued increasing and even reached 108
in 2006 and then decreased in the following years. The
most frequently cited article in 2008 was published in
2000 by Ho and McKay with 99 citations. This paper is
still in a high enough position to impact current water
resources research. Moreover, Beven and Ho published
two fi rst author articles (Table 7).

M.-H. Wang et al. / Desalination and Water Treatment 28 (2011) 353–365
363
Fig. 5. Citation history of the most frequently cited articles
each year during 1993–2004.
5. Conclusions
In this study on the articles in the category of water
resources journals listed in SCI-Expanded, signifi cant
points on worldwide research performance from 1993
to 2008 were revealed. The effort provided a system-
atic structural picture, as well as clues to the impact of
research on water resources. Even though English was
the dominant language, eight other languages were
also used, which indicated global concern about water
resources. Apparently more authors, institutes, and
countries were engaged in this research over the 16
years. The United States Geological Survey was the pio-
neer in the fi eld of water resources, with the most inde-
pendent, inter-institutionally collaborative, fi rst author,
and corresponding author articles. Furthermore, the
h-index (64) of the United Stated Geological Survey was
the highest. The G7 along with China, India, Australia,
and Spain had a long research history in this fi eld. China
showed a rapidly ascending trend in the number of arti-
cles during the last 6 years. Not only did they have the
absolute ascendancy of articles, but were also the most-
frequent research partners and had higher h-in dices.
The number of journals published in three zones of
articles approximately followed Bradford’s law. We cal-
culated the coeffi cients of determination of the impact
factor and the h-indices, and found that the journals in
the second group had a weaker relationship than that
in the fi rst group. In terms of the distributions of words
in the paper titles, “river” and “groundwater” were the
most concerned “water bodies”. In the author keywords
analysis, the two most frequently used keywords were
“groundwater” and “water quality”. The topics, “run-
off”, “wastewater”, “irrigation”, and “evapotranspira-
tion” had become new foci. The top four most frequently
used KeyWords Plus were “water”, “model”, “fl ow”, and
“transport”. “Management”, “waste-water”, “runoff”,
and “variability” were active research areas. In addition,
“modeling” and “adsorption” were the most popular
techniques. The most frequently cited paper each year
was a backstage pioneer in the research fi eld. The article
published in Water Research by Ternes in 1998 had been
cited 630 times up to 2008. But its citation rate decreased
in the past two years. Another paper published in 2000
by Ho and McKay still has a great impact on current
water resources research. This study provided research-
ers with a panorama of global water resources research
and established further research directions.
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