Bibliometric analysis of rice and climate change publications based on Web of Science

To clarify the current situation, hotspots, and development trends in the field of rice and climate change topic research, a massive literature dataset were analyzed from the Web of Science database by bibliometric method. The research theme was chosen given the continuous increase of studies related to climatic changes and their consequences to rice. Based on the Web of Science core database, this study analyzed 4170 papers in the field of rice and climate change topic research from 1990 to July 2022, which include 86 highly cited papers and 3 hot papers. Papers were mainly written in English (4157, 99.688%), from 16,363 authors, 4017 organizations, and 129 countries/territories, published in 841 journals and seven book series. The top five Journals are Science of the Total Environment (136, 3.261%), Sustainability (89, 2.134%), Agronomy Basel (81, 1.942%), Agricultural and Forest Meteorology (77, 1.847%), and Climatic Change (74, 1.775%), each published more than 74 papers. Top five countries and regions of People’s Republic of China, the USA, India, Australia, and Japan were the major article contributors, each published more than 360 papers. Top five organizations of Chinese Acad Sci, Nanjing Agr Univ, Univ Chinese Acad Sci, Chinese Acad Agr Sci, and Int Rice Res Inst (IRRI) were popular based on contribution of articles more than 133 papers each. Among the all authors, top five authors were Tao Fulu, Pan Genxing, Zhang Zhao, Hasegawa Toshihiro, and Iizumi Toshichika, each published more than thirty papers. All keywords were separated into eight clusters for different research topics. Visualizations offer exploratory information on the current state in a scientific field or discipline as well as indicate possible developments in the future. The results will help researchers clarify the current situation in rice and climate change adaptation science but also provide guidance for future research. This work is also useful for student identifying graduate schools and researchers selecting journals.


Introduction
In recent years, climate change has had a more significant impact on earth's ecosystem and its human socio-economic system. In response to climate change, countries all over the world have enacted various policy measures to reduce greenhouse gas emissions to reduce the further rise in global average temperatures and reduce the risks and losses of climate change. Climate change adversely impacts our agriculture and will force agricultural production to adapt to the altered environmental conditions. Increase in climatic variations and extreme weather events in the recent past have exerted significant effect on crop productivity over different regions on earth. The consequences of climate change are drastically impacting field crop production; it is an immense prerequisite to attribute resilience through crop improvement. Rice (Oryza sativa L.) is the staple food for half the world's population. Climate change has been an increasingly significant factor behind fluctuations in the yield and quality of rice (Murphy et al. 2013;Morita et al. 2016;Zafar et al. 2018;Kingra et al. 2019;Schneider and Asch, 2020;Senguttuvel et al. 2020). In the recent years, increased interests in climate change research by scholars have been witnessed. These interests are accompanied by spectacular rise in the amount of scientific output in this topic of research.
Bibliometric analysis, as an important quantitative analysis tool, can effectively describe the overall trend of the development of a subject or field, and it has been widely used in various fields. In recent years, the bibliometric method is more and more frequently used in climate change research. Li et al. (2011) used it to evaluate the academic output, trends, features, and research methods in climate change literature from 1992 to 2009 and proposed a key innovative clustering analysis method. Wang et al. (2014) explored the development trend of the literature in the cognate area of climate change vulnerability through quantitative analysis, pointing out that health problems in the socio-economic system, food safety problems in agriculture, and water resources management problem were the most frequently discussed in the field of vulnerability research at present. Based on Science Citation Index-Expanded (SCI-E) and Social Science Citation Index (SSCI) database, Wei et al. (2015) reviewed research hotspots and model methods used in the field of climate policy modelling with a bibliometric method. A bibliometric analysis of climate change adaptation was completed based on massive research literature data (Wang et al. 2018). There are others bibliometric analysis publications, such as peer-reviewed literature on climate change and human health with an emphasis on infectious diseases (Sweileh 2020), scientific production on coastal communities' social vulnerability to climate change (Lima & Bonetti, 2020), bioenergy research under climate change (Zhang et al. 2021), carbon capture technologies for climate change mitigation (Omoregbe et al. 2020), climate change and carbon sink (Huang et al. 2020), disaster and climate change resilience (Rana, 2020), soil and water conservation in the Loess Tableland-Gully Region of China (Wang et al. 2019), advances in water use efficiency in agriculture, and sustainable water use in agriculture (Velasco-Muñoz et al. 2018a, 2018b. Bibliometric analysis technique has been adopted related with agronomy or crop research such as perennial staple crops (Kane et al. 2016), Japanese rice (Morooka et al. 2014), rice physiology and management in China (Peng, 2017), global rice research during 1985-2014 (Liu et al. 2017), genetically modified maize (Santillán-Fernández et al. 2021), transgenic maize (Li et al. 2018), fiber crops (Bartol and Mackiewicz-Talarczyk, 2015), climate change in agriculture (Aleixandre-Benavent et al. 2017), plant defense against biotic stresses as improvement for sustainable agriculture (Gimenez et al. 2018), soil nutrient research between 1992 and 2020 (Pan et al. 2021), planthopper (Hu and Cao, 2018), etc. Sun and Yuan have analyzed rice with fertilizer based on Citespace , rice with irrigation (Sun and Yuan, 2020a), the top papers in world rice research (Sun and Yuan, 2020b), Library and Information Science (Sun and Yuan, 2020c), water Resources (Sun and Yuan, 2020d), Agronomy category , green and sustainable science and technology , scientific research on maize or corn Sun, 2020a, 2020b), muskmelon , strawberry (Fragaria × ananassa Duch.) research publications from Horticulture category (Yuan and Sun, 2021a), and cotton research from Plant Sciences category based on Web of Science (Yuan and Sun, 2021b). However, no bibliometric research papers were published on climate change and rice topic research.
The purpose of this paper was to use bibliometric methods to analyze the publications of rice and "climate change" topic research through publication year, category, author, affiliations, country, journals, all keywords and other key features, according to the Clarivate Analytics Web of Science (WoS) core database. Co-authorship network visualization of author, organizations and countries, and co-occurrence network visualization of all keywords were done by VOSviewer.

Web of science
Clarivate Analytics WoS is the world's leading scientific citation search and analytical information platform, and one of the world's largest and most comprehensive academic information resources covering more than 12,000 core academic journals. The publication counts from the WoS Core Collection were derived from the following databases: The Science Citation Index-Expanded (SCIE), 1900-present; Social Science Citation Index (SSCI), 1900-present; Conference Proceeding Citation Index-Science (CPCI-S), 2015-present; Conference Proceedings Citation Index-Social Science & Humanities (CPCI-SSH), 2015-present; Current Chemical Reactions (CCR-EXPANDED), 1985-present; and Index Chemicus (IC), 1993-present.

Data collection
This study surveyed papers in WoS Core Collection (1900-present), and the data collection was completed on the single day on July 9, 2022, to avoid the bias. We used the keywords as "rice" and "climate change" in the topic (TS). The query as following: TS= "rice" and "climate change." Then, the results were refined by document types of Article or Review article. So, there are 4170 papers on "rice" and "climate change" topic research from WoS core collection. The records were downloaded and saved as plain text format by selecting the export format "full records and cited references," and then imported into VOSviewer (version 1.6.18, 2022, Leiden University, Leiden, Netherlands) for further citation analysis. The impact factors (IF 2021 and IF 5 year) were taken from the Journal Citation Report (JCR 2021) published in June 2022, which had the latest data available (Clarivate, Journal Citation Reports ™ 2021, 2022a. The Journal Citation Reports™ includes journals from the SCIE and SSCI.

VOSviewer
Visualizations (network and overlay) using program VOSviewer are conducted on WoS data in order to determine co-occurrence and clusters of connected publications, country input and author collaboration (co-authorship), as well as clusters of interrelated research topics (text data). VOSviewer (1.6.18 version, 2022) is a free bibliometric visualizer with an intuitive and user-friendly interface. It was chosen because it can work with large sets of data and offer a range of analysis and investigation options, creating intuitive images that aid in evaluating data (Van Eck and Waltman, 2010). In this work, we used VOSviewer to show the international collaboration between the authors, organizations, countries, and the research trends through all keywords. VOSviewer (version 1.6.18; van Eck and Waltman, 2022) were used to conduct bibliometric analysis, network analysis, and cluster analysis. In this paper, default parameter values of the VOSviewer are usually used in the analysis. Items are represented by a label and a circle. The size of circles reflects the weight of an item. Some items are not displayed in avoidance of overlapping. The colors in network visualization (text maps) represent clusters of similar items as calculated by the program. Distance between the items indicates the strength of relationships.
Among the 4170 papers, there are 88 top papers of 86 highly cited papers and 3 hot papers based on Clarivate Analytics Essential Science Indicators (ESI) database covering over a 10-year 2-month period: January 1, 2012-February 28, 2022 (Clarivate, 2022a, b. Essential Science Indicators Help). All of the papers were almost published in English (4157, 99.688%), and then others were Portuguese (4, 0.096%), Spanish (4, 0.096%), French (3, 0.072%), German (1, 0.024%), and Japanese (1, 0.024%). The English was dominating language from the WoS, and scholars tend to publish their articles in English as they want them to be widely accepted. Moreover, most of the published documents were in the form of original research articles written in English language (Khan, et al. 2020).

Publication output
The number of published academic papers is an important indicator to measure the development trend of certain scientific research. Figure 1 shows the publications of "rice" and "climate change" topic research between 1990 and 2022. The highest publication value was 671 in 2021. In general, the quantity of rice and climate change topic research publications presents a fast growth tendency after 2008. There are 62, 213, 2322, and 1573 papers during the period of 1990-1999, 2000-2009, 2010-2019, and 2020-2022,  respectively. These trends reflect the increasing attention devoted to this area during the past decade. Publications were exponential growth during period from 1990 to 2022 (R 2 =0.948).
The number of citations to a paper is considered a good quantitative measure of a paper's impact. The quality of publications was measured by the number of citations and h-index. The h-index was initially proposed as a measure of a researcher's scientific output based on counting the number of publications (N) by that researcher cited N or more times (Hirsch, 2005). For the total 4170 papers, the h-index is 139, the total number of citations was 117,016 over the period, and the average citation per item is 28.06. Based on WoS core database, the first paper on the rice and climate change topic titled of "Potential rice yields in future weather conditions in different parts of Asia" written by Jansen DM was published in 1990 in the Netherlands Journal of Agricultural Science (38(4):661-680).

Web of Science categories and research areas
There are total 117 WoS subject categories and 79 research areas for rice and climate change topic research. Table 1 showed the top 20 WoS categories and research areas for rice and climate change topic research during 1990-2022. Among these, the top five categories include Environmental Sciences (1335 papers, 32.014% of 4170 papers), Agronomy (703, 16.859%), Meteorology Atmospheric Sciences (548, 13.141%), Plant Sciences (538, 12.902%), and Agriculture Multidisciplinary (341, 8.177%). The top five research areas include Environmental Sciences Ecology (1582 papers, 37.938% of 4170 papers), Agriculture (1261, 30.24%), Meteorology Atmospheric Sciences (548, 13.141%), Plant Sciences (538, 12.902%), and Science Technology Other Topics (481, 11.535%). Journals or papers may be classified into two or more categories in the WoS, showing the multidisciplinary character of this research field (Elango & Ho, 2018). Documents are also mapped to one or several research areas in WoS. In WoS, publications are mapped to WoS categories which are more detailed than research areas (Stopar et al. 2021).

Core journals
All the 4170 publications were published in 841 journals and seven book series. The seven book series titles are Advances in Agronomy (18), Annual Review of Phytopathology (2), Advances in Biochemical Engineering Biotechnology (1), Advances in Ecological Research (1), Advances in Parasitology (1), Biotechnology Genetic Engineering Reviews (1), and World Review of Nutrition and Dietetics (1). The top 20 core journals were displayed in the Table 2 with total articles Journal co-citation analysis refers to the phenomenon that occurs when two journals are cited by the same document. Co-citation of journals reflects correlations between various journals and disciplines. The intellectual base of a research field can also be obtained through journal citation analysis. According to the publication data in the citation of 841 journals, there were 186 journals that met the thresholds of five publications, of which 186 journals were connected to each other. The network of citation in the field of rice and climate change topic research based on WoS has shown twelve clusters with different colors in Figure 2; the size of circles reflects a total number of journal publication records. Journals in the same color cluster usually suggested that they published the similar content papers and had close relations with each other. The first cluster (red) had thirty-eight journals and centered as Sustainability and Climatic Change, the second cluster (green) had thirty-five journals and centered as Frontiers in Plant Science and PloS One, the third cluster (blue) had thirty-three journals and centered as Science of the Total Environment and Global Change Biology, the fourth cluster (yellow) had twenty journals and centered as Journal of Cleaner Production and Agricultural Water Management, the fifth cluster (violet) had fifteen journals and centered as Agricultural and Forest Meteorology and European Journal of Agronomy, the sixth cluster (light blue) had thirteen journals and centered as Environmental Research Letters, the seventh cluster (orange) had thirteen journals and centered as Remote Sensing, the eighth cluster (brown) had seven journals and centered as Field Crops Research, the ninth cluster (pink) had six journals and centered as Agronomy-Basel, the tenth cluster had only three journal

Authors co-authorship analysis
Authors and their social relationships are the core elements of a research field, as well as an important embodiment of the research power of the field. Those researchers with high academic productivity usually dominate the development tendencies of research field. A total of 16,363 authors have 4170 publications, and among these, 409 authors met the thresholds of five publications, but only 354 authors were connected with each other. The network map has a large number of participants as well as a wide range of collaborations. The network map of authorship in the field of rice and climate change topic research based on WoS represented in Figure 3, the size of circles reflects a total number of records. Authors in the same cluster usually suggested that they studied in a similar field or worked at same institute or had close cooperation with each other. Table 3 provides the top twenty-one author information published articles in the field of rice and climate change topic research from 1990 to 2022 along with citation, average citations, organization-enhanced and countries, and published more than eighteen papers. Among the all authors, top five authors were Tao Fulu, Pan Genxing, Zhang Zhao, Hasegawa Toshihiro, and Iizumi Toshichika, each published more than thirty papers.
The organization of the author is the latest institute based on the latest publications. Among the twenty-one authors, there were thirteen authors from China, the organizations were Chinese Acad Sci, Nanjing Agr Univ, Beijing Normal Univ, and Chinese Acad Agr Sci; three authors are from DNDC Applicat Res & Training, Ohio State Univ, and Univ Florida of USA; two authors are from Natl Agr & Food Res Org NARO of Japan; one author is from Int Maize & Wheat Improvement Ctr CIMMYT of India; one author is from Univ Aberdeen of Scotland; one author is from Leibniz Assoc, Potsdam Inst Climate Impact Res PIK of Germany. The five authors with the higher average citations per paper were Smith Pete, Mueller Christoph, Pan Genxing, Li Tao, and Zhu Yan, and the average citations per paper was more than 60.20 times.

Countries/regions co-authorship analysis
There were 129 countries or regions that contributed 4170 papers in the field of rice and climate change topic research from 1990 to 2022. Table 4 represents the list of the top 20 countries or regions that published more than 70 papers, and also shows the cluster, total link strength, citations, and average citations. Among the top 20 countries or regions, People's Republic of China, the USA, India, Australia, and Japan were the five major article contributors, each published more than 360 papers. In case of average citations, Canada, the USA, the Philippines, Germany, and the Netherlands showed the higher citations per paper more than 47.5 times. The strength of international research collaboration was presented as Total Link Strength (TLS) which is We developed the co-authorship network map using VOSviewer (Figure 4). There are 76 countries or regions that met the requirement threshold as five. The size of circles in Figure 4 reflects a total number of records and the distance    (Tang et al. 2018).
Comparison of the growth trends of the top five countries is displayed in Figure 5. China, the first on the list ranked by total papers, has published 1347 (32.3%) articles with the fastest growing trend after 2012 year. This could be due to a series of positive policies motivated the rapid development of research in China. China is one of the most attractive countries in terms of scientific performance today. It has experienced a sustained and remarkable increase in scientific production and became the global second largest producer of scientific publications since 2006, particularly taking a world-leading position in special fields (Fu et al. 2011). The past decades have witnessed a rapid rise of China in economic development, with a GDP averaging about a 10% annual growth rate since 2000, and China overtook Japan as the second largest economy in 2010 (Liu et al. 2015). Now, the GDP of China is the second after the USA in the world.

Organizations co-authorship analysis
The analysis of research institution will give us the information that which organizations stand on the frontier of this research. According to the publication data, it was revealed that a total of 4017 organizations have 4170 publications. Table 5 represents the top 20 organizations and institutions ranked by the number of total publications (more than 43 papers), the total link strength, citations, average citations, and country. These 21 organizations were mainly based in China (ten organizations), the USA (three organizations), Japan (three organizations), the Philippines (one organization), Mexico (one organization), Australia (one organization), the Netherlands (one organization), and India (one organization). Furthermore, top five organizations of Chinese Acad Sci, Nanjing Agr Univ, Univ Chinese Acad Sci, Chinese Acad Agr Sci, and Int Rice Res Inst (IRRI) were popular based on contribution of articles more than 133 papers each. Similarly in case of citation, the top five organizations of Univ Calif Davis, Natl Inst Agroenvironm Sci, Kansas State Univ, Int Rice Res Inst (IRRI), and Wageningen Univ showed the higher average citations more than 55.5 times per paper.
Among the 4017 organizations, there were 497 organizations that met the minimum thresholds of five, and 495 organizations were connected to each other ( Figure 6). The VOSviewer software divided these 495 institutes into thirteen clusters with different colors. Geographical localization is an important factor for partnership and joint venture.

All keywords co-occurrence analysis
For a specific scientific field study, keyword plays a large role as it can reflect the root contents of articles and compilation of keywords can reveal the pattern and trends of specific academic research (Badaluddin et al. 2021). To analyze the co-occurrence of the keywords, author keywords, keywords plus, and all keywords as unit were chosen and analyzed.
For the author keywords by full counting method for cooccurrence analysis, there were a total of 9175 author keywords, and 511 keywords met the threshold level of more than five times and were separated into fourteen clusters in   Fig. 6 The organizations co-authorship network map of rice and climate change topic research related publications from 1990 to 2022. The institutions co-authorship network map with 495 nodes and 13 clusters; the bigger nodes represented the more influential institution in this field. The distance and thickness of links represented the degree of cooperation among organizations. network visualization. The top twenty co-occurrence author keywords were climate change, rice, agriculture, food security, adaptation, China, yield, drought, wheat, global warming, Oryza Sativa, irrigation, temperature, Bangladesh, rice production, heat stress, rice yield, methane, biochar, and crop model; each keywords co-occurred more than 58 times. For the keywords plus by full counting method for cooccurrence analysis, there were a total of 7471 keywords plus, and 1060 keywords met the threshold level of more than five times and were separated into nine clusters in network visualization. The top twenty co-occurrence keywords plus were climate-change, rice, temperature, yield, impacts, growth, management, impact, agriculture, model, responses, variability, wheat, productivity, adaptation, food security, trends, soil, carbon-dioxide, and China; each keywords plus co-occurred more than 177 times.
For the all keywords by full counting method for cooccurrence analysis, there were a total of 15,029 all keywords, and 1494, 1249, 1053, and 920 all keywords met the threshold level of five, six, seven, and eight times. There are eight main clusters for 920; all keywords met the threshold level of eight times in network visualization map (Figure 7). Figure 7 shows the network map that links the all keywords to the entire sample of the articles analyzed. There are eight main clusters that represent different viewpoints on rice and climate change topic research. Each node in the figure represents a keyword. The larger the node, the higher the frequency of keyword occurrence; the more lines, the higher the frequency of keyword co-occurrence; additionally, the thickness of the connecting line is proportional to the closeness of the connection. 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 (Leal et al. 2022). The top twenty co-occurrence all keywords were climate-change, climate change,rice,yield,temperature,agriculture,impacts,growth,food security,adaptation,impact,management,wheat,model,China,responses,productivity,variability,elevated CO 2 , and maize; each all keywords occurred more than 206 times.
The same data in Figure 7 were then arranged by a period of rice and climate change topic research as overlay map (Figure 8). Blue color indicates earlier research topics, whereas yellow and green colors indicate the more recent topics of interest. The blue colored topics do not indicate no longer research work on that topics; it usually indicates that, on average, this topic was intensely investigated earlier and now more attention has shifted towards other topics. Perhaps, these terms are now so general, therefore no longer extensively used as keywords. Yellow and green circles present those research fronts. For example, the keywords of carbon-dioxide in Figure 8 can be observed with blue Of the all 15,029 keywords, there were only 920 keywords that met the threshold more than 8 times included in the map. After all keywords analysis, there are eight main clusters that represent eight different viewpoints on rice and climate change topic. Nodes with similar color represent a cluster of related terms circles showing the older topic research; the keywords of adoption, famers, footprint, sustainability, climate change, and management in Figure 8 can be observed with yellow or shallow green circles showing the front research. Blue colors indicated earlier research topics, whereas yellow and green colors indicated more recent topics of interest. Yellow and green circles present those research fronts.
Visualizations conducted on large datasets (big data) offer exploratory information on the current state in a scientific field or discipline as well as indicate possible developments in the future. Here, the twenty keywords or so were list and ranked in each cluster based on Figure 7. Nodes with similar color represent a cluster of related terms. Here, the eight clusters for different topics on the climate change and rice were given, such as rice growth and yield responses to elevated CO 2 , soil management and greenhouse gas emissions, climate change impacts agriculture and food security, crop yield models under climate change, crop yields response to temperature and water, weather sensitivity and air pollution, crop yields under tropical environments, and modelling for crops or climate.
The first cluster (red) is focused on rice growth and yield responses to elevated CO 2 and includes keywords as rice, growth, responses, elevated CO 2 , drought, carbon dioxide, grain yield, photosynthesis, stress, tolerance, plants, Oryza-Sativa L., high temperature, global warming, Oryza Sativa, atmospheric CO 2 , cultivars, heat stress, heat-stress, and night temperature; each all keywords occurred more than 65 times.
The second cluster (green) represents the soil management and greenhouse gas emissions and including keywords as management, soil, nitrogen, greenhouse-gas emissions, systems, CO 2 , dynamics, nitrous-oxide emissions, methane, emissions, carbon, use efficiency, N 2 O emissions, carbon sequestration, performance, biomass, mitigation, methane emission, methane emissions, and cropping systems; each all keywords occurred more than 74 times.
The third cluster (blue) is focused on climate change impacts agriculture and food security and include keywords as climate-change, agriculture, impacts, food security, adaptation, impact, China, variability, water, rice production, vulnerability, precipitation, India, sustainability, climate, food, Bangladesh, land use, risk, and strategies; each all keywords occurred more than 68 times.
The fourth cluster (yellow) represents crop yield models under climate change, and keywords include as climate change, yield, wheat, model, productivity, simulation, irrigation, crop yield, rice yield, crop production, yields, system, uncertainty, quality, resources, crop model, models, change impacts, river-basin, and evapotranspiration; each all keywords occurred more than 60 times.
The fifth cluster (violet) is focused on crop yield response to temperature and water, and keywords include Fig. 8 VOSviewer co-occurrence overlay visualization mapping of most frequent all keywords (minimum of eight occurrences) on rice and climate change topic research from 1990 to 2022. The years in which specific keywords frequently occur are shown by different colors. Importance of all keywords is represented by their centrality in the network. More occurrences of all keywords are shown with bigger circles. More co-occurrences of keywords are shown with thicker lines as temperature, maize, trends, winter-wheat, phenology, rice yields, crop, irrigated rice, water-use, wheat yield, decline, Northeast China, scales, challenges, crop management, growth duration, radiation, winter wheat, cultivar, and maize yield; each all keywords occurred more than 22 times.
The sixth cluster (shallow blue) is focused on weather sensitivity and air pollution, and keywords include as sensitivity, weather, United-States, metaanalysis, wheat yields, exposure, tropospheric ozone, cotton, ozone, surface ozone, integrated assessment, yield variability, climate impacts, pollution, potential impact, aerosols, benefits, economicimpacts, air pollution, air-pollution, and regression; each all keywords occurred more than 11 times.
The seventh cluster (orange) is focused on crop yields under tropical environments, and keywords include as crop yields, crop productivity, climate change impacts, cereswheat, pests, agroecosystems, assimilation, losses, infocrop, dynamic simulation-model, and tropical environments; each all keywords occurred more than 8 times.
The eighth cluster (brown) is only one keywords of modelling.

The most frequently cited articles
Although a great many articles have been published, a relatively small number of individuals account for a large proportion of the citations within the period. The annual citations of the eight papers showed an increasing trend after year of publication ( Figure 9). The eight papers were written by Lobell et al (2011), Peng et al (2004, Smith et al (2008), Challinor et al (2014), Ruddiman (2003), Weaver and Reisen (2010), Ray et al (2012), and Ray et al (2015). Here, the total citations for the most frequently cited articles were more than 741 times. The time dependence of a single paper is called its history. In the beginning year (zero year here), generally the articles have lower citation because of same year of publication. From the publication year to 2022, the average citation per year of the most citation eight papers were 171, 71.79, 89.93, 106.67, 44.1, 64.62, 71.09, and 92.63 times. From Figure 9, it can be found that the citation per year of the papers increased until 2021, but the increase rate was different each year. Among eight articles, the highest average citation per year (171, blue color) was observed for article of Lobell et al (2011) published in Science (Figure 9).