Bibliometric Analysis and Literature Review of Sponge City as an Emerging Concept in Sustainable Urban Water Management

Introduction: Water resources management is a vital issue in sustainable urban development. Improper water management resulting from rainstorms in cities leads to flooding and flood flow, lack of healthy urban water, soil erosion, and pollution of water bodies. In this way, the lack of proper management and insufficient control of urban floods can cause many problems, such as the spread of infectious diseases and homelessness or the death of people. Sponge City is a comprehensive approach to sustainable urban water management, which, in recent years, has attracted the attention of researchers worldwide as a basic strategy for solving water and environmental challenges. Considering the background of the sponge city concept along with the frequency of urban floods, this concept has drawn more attention to itself in recent years, which has led to the development of the sponge city research area and turned it into a hot research topic in the field of urban water management. In this context, the sponge city is one of the concepts China has achieved regarding sustainable water management. The Sponge City combines all existing concepts and technologies and uses green-blue infrastructure to deal with water shortages and reduce flood risks. The word "sponge" symbolizes a porous structure that absorbs and releases water in line with the primary goals of the concept (rainwater management and urban flood control). In this regard, the present study was conducted to investigate the progress of research related to Sponge City using a bibliometric method.
Methodology: The present research is descriptive-analytical in nature and method, carried out by bibliometric method. Bibliometric analysis is an effective method for quantifying scientific publications using statistical methods. This method is a common tool of systematic analysis in various fields, whose purpose is to evaluate the state of research and trends of a specific subject and identify future research directions to guide researchers. Bibliographic analysis identifies scientific publications through a series of methods, such as the output of different publications, countries, institutions, authors, and citation analysis, as well as paths more focused on content analysis and research evolution. In this context, the statistical community of the research consists of all scientific documents related to the field of Sponge City, which are indexed in the WOS reference database. The WOS database is one of the most important and comprehensive academic databases. It includes numerous publications in different fields, so some consider this citation database the world's number one citation database and the most important source for conducting bibliographic studies. Thus, the term "Sponge City" was searched in the WOS reference database (and on December 8, 2023) without a time limit or document type to retrieve the current research records. Finally, the collected documents were analyzed using Vosviewer software. Vosviewer is a software for drawing and displaying bibliometric maps with an emphasis on different aspects of research components, and two general categories of analysis are performed in this method: Performance analysis and scientific map drawing. Performance analysis helps to identify the contribution of each research component (authors, institutions, countries, and journals), and the output of drawing a scientific map is to determine the relationships between the research components. In general, to answer the research questions and perform bibliometric analysis, the five-step method of Zupic and Cater (2015) was used in the present study.
Results: Based on the research findings, 614 documents were published in Sponge City between 2005 and 2023, which has continuously increased. 99.8% of the papers are in English. On the other hand, with the increase in the number of documents, the number of citations obtained by the articles has also increased, and the most cited article, with 260 citations, was published in 2018. Also, Water magazine, with the publication of 88 documents, a researcher named Jia, H.F., with the publication of 17 papers, and China, with the publication of 388 records, has the most scientific productions related to the sponge city. Based on the co-occurrence map of keywords, Sponge City, management, low-impact development, efficiency and performance, and stormwater runoff management became the most frequent keywords..
Discussion: Today, water management challenges have been noticed in many cities because with the onset of climate change, the increase in climate variability, and the growing population trend, these challenges have become more serious. So, drought and flood have created problems in the water supply field, especially in arid and semi-arid areas. In this way, guaranteeing access to clean water for all sustainable water management and moving toward making cities resilient are important aspects of the global development program, also mentioned in the United Nations Sustainable Development Goals. In this context, sustainable urban water management is the key to adapting to climate change and achieving resilient cities. This is even though currently, urban water management systems such as water supply, sewage, and rainwater drainage in most urban areas are based on the usual infrastructure of a network of underground pipes that need more flexibility and adaptability to the challenges above. In such a situation, there is a general agreement between water experts, urban managers, and planners, especially in developed cities, about the need to change the direction of urban water management towards more sustainable mechanisms based on decentralized and nature-based systems. Sustainable urban water management can be both a philosophical and a technical approach that can be included in all urban planning and development forms. Current urban water policies in different countries have begun to reflect this philosophy. One of the plans mentioned in this context is the plan of the sponge city. The sponge city is a new sustainable urban water management strategy rooted in the laws of the natural water cycle and related processes. This project was proposed to reduce urban flooding, control urban water pollution, use rainwater resources, and ecologically revitalize the urban water environment. This plan emphasizes the establishment of low-impact development facilities such as rain gardens, biological maintenance ponds, green walls and roofs, lawns, and permeable pavements, etc. Using this plan, The possibility of natural infiltration, storage, natural purification, control of surface runoff, improvement of urban hydrological conditions, and re-use of rainwater resources becomes possible. It ensures the sustainable circulation of water in the urban environment. In this context, the sponge city as a new sustainable urban water management method has attracted wide attention recently. Therefore, due to the need for a comprehensive and systematic review of previous research, the current research was conducted with the aim of a quantitative review of past studies using the method of bibliometric analysis. For this purpose, the process of scientific production of the area of Sponge City indexed in the WOS database was analyzed to draw a scientific map and understand this area's conceptual and social structure using Vosviewer software.
Conclusion: According to the present research findings, it was found that due to the novelty of the sponge city issue, not many studies have been conducted in this field, and most of the studies undertaken are in line with the feasibility of its implementation in some regions of China. However, due to the existence of water challenges such as water scarcity and drought as well as the occurrence of numerous floods as well as extensive climate changes in most countries and regions of the world, Studies related to the subject of the sponge city have expanded and are being carried out in many countries of the world. These measures are related to developed countries, and many developing countries have also moved towards using this plan in their urban planning and development. However, because China proposed the plan for a sponge city, this country is still ahead in continuing the measures related to managing its water resources, and more studies have been conducted in this country than in other countries. On the other hand, according to the results of the present research, it was found that currently, the studies related to the sponge city have moved away from the aspects of structural studies and moved more towards the studies related to governance and green laws, and in various studies, These cases must be mentioned, and these cases have been considered more important than other cases that have a structure. In some studies, the success of the sponge city project implemented in some countries and cities is possible only with the participation and accompaniment of the people. This participation depends on correct legislation and moving toward water control (rain, sewage, or city runoff). They have put the origin of these sources on their agenda. This way, flood control, rain storage, and pollution control can be done as the first step. Also, the studies conducted in the area of the sponge city are now moving towards increasing the stability and resilience of cities against all kinds of water (quantity and quality) and environmental challenges in urban environments, and these studies focus on placing ecological issues and policies on Applying innovation in new methods of water management based on more sustainable mechanisms such as; Green technologies, green infrastructure, urban green spaces, etc. are emphasized. Therefore, the current research results are important from two theoretical and managerial aspects. From a theoretical point of view, this study identified the most used and most effective authors, sources, institutions, and countries and the most effective scientific productions in Sponge City. It revealed its conceptual structure so that researchers can find a comprehensive view of the scientific structure in this field and the most important concepts. It has identified the study in this field in different time frames to familiarize the researchers with the evolution of knowledge in this field and future research paths. Regarding management, the research findings show the importance of the sponge city as a new idea for the sustainable management of urban water, which can be of interest to managers and urban planners, urban designers, urban environmental experts, water experts, and other researchers. On the other hand, the current research is one of the first studies conducted in the field of sponge cities in Iran. Thus, it is considered a beacon for other researchers in different fields to conduct more research.