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Review

Determining the Role of Urban Greenery in Soil Hydrology: A Bibliometric Analysis of Nature-Based Solutions in Urban Ecosystem

by
Muhammad Owais Khan
1,*,
Saskia D. Keesstra
2,3,
Ewa Słowik-Opoka
1,
Anna Klamerus-Iwan
1,* and
Waqas Liaqat
4
1
Department of Ecological Engineering and Forest Hydrology, University of Agriculture in Krakow, 31-120 Kraków, Poland
2
Climate-Kic Holding B.V., 1018 Amsterdam, The Netherlands
3
Departamento de Análisis Geográfico Regional y Geografía Física, Facultad de Filosofía y Letras, Campus Universitario de Cartuja, University of Granada, 18071 Granada, Spain
4
Department of Field Crops, Faculty of Agriculture, Institute of Natural and Applied Sciences, Çukurova University, Adana 01330, Turkey
*
Authors to whom correspondence should be addressed.
Water 2025, 17(3), 322; https://doi.org/10.3390/w17030322
Submission received: 5 December 2024 / Revised: 16 January 2025 / Accepted: 21 January 2025 / Published: 23 January 2025
(This article belongs to the Special Issue Rainfall and Water Flow-Induced Soil Erosion-Volume 2.0)
Browse Figures
Versions Notes

Abstract

:
Nature-based solutions play an essential role in enhancing urban soil hydrology by improving water retention properties, reducing surface runoff, and improving water infiltration. This bibliometric analysis study reviewed the literature and identified the current trends in research related to nature-based solutions in urban soil hydrology. The study has the potential to highlight current research areas and future hot topics in this specific field. The research used the Scopus database to collect published articles from 1973 to 2023. The keywords (“trees” OR “vegetation” OR “green infrastructure” OR “blue green infrastructure” OR “greenery” OR “nature-based solutions” AND “hydrolog*” AND “urban” OR “city” OR “soil”) were searched in the Scopus database, and 13,276 articles were retrieved. The obtained publications were analyzed for bibliometric analysis by using Bibliometrix (v4.3.0) and VOSviewer (v1.6.20) software. The maximum number of publications (970) related to nature-based solutions and urban soil hydrology was published in 2023. Additionally, countries such as the United States and China published 54.2% of articles of the global research in the field of nature-based solutions and urban soil hydrology, with 36% from the USA and 18.2% of articles from China. The bibliometric analysis depicted that Beijing Normal University led this specific research field with 540 articles. The top country in terms of collaboration was the USA, with 26.17% as compared to the global countries. The most productive researcher identified was Jackson, T.J., as he had the highest number of publications, showing his considerable contribution to the field. Furthermore, the most frequent keywords used in this research area were hydrology, ecosystem services, urban hydrology, remote sensing, nature-based solutions, climate change, runoff, stormwater management, water quality, vegetation, green roof, bioretention, and land use. The early research trending topics in this field from 2015 to 2023 were remote sensing, soil moisture, climate change, drought, green infrastructure, machine learning, and nature-based solutions. The bibliometric analysis identified limited interdisciplinary research integrations, not using well-significant and standardized methodologies for the evaluation of urban soil hydrology, and under-representation of research from developing countries as current research gaps. Future research directions highlight advanced methods such as combining data-driven technologies with traditional hydrological approaches, and increasing international collaboration, specifically in developing nations, to address urban soil hydrological problems properly.

1. Introduction

Urbanization is an essential measurement for evaluating a country’s developmental level [1,2]. More than 50% of the global population currently lives in urban regions, and it is expected to rise worldwide [3]. According to a United Nations [4] report, it is estimated that by 2050, approximately 70% of the world’s population will live in cities. The growing urban population, along with increasing global temperatures and more frequent heat waves [5], is expected to increase the intensity of the urban heat island effect. This phenomenon, which has been studied by [6,7], could have adverse effects on urban ecology, energy demand for cooling systems, and outdoor thermal comfort [8,9,10,11]. Several human health risks, including stroke, irritation, distress, and fatigue, are due to high temperatures in city centers, caused by the increased heat island effect, which influences the population’s well-being and seriously leads to suicidal tendencies [12]. The urban environment’s vital role in providing livable spaces and supporting resilient ecosystems becomes increasingly significant as city populations increase. In [13,14], the authors stated that the influence of the increased urbanization level and the rapid development of economic construction on hydrological processes could not be ignored. On one hand, climate change will significantly affect hydrological processes in the face of increasing extreme weather situations [15]. Multiple research investigations have confirmed that the changing climate has transformed regional hydrology, and urbanization has increased the changes in natural watersheds [16]. On the other hand, a large area of non-urban land or agricultural land is changed into impervious land in the process of urbanization, and therefore land-use change entirely changes natural hydrological processes [17,18]. Changes in the runoff generation process, runoff depth, infiltration, and evapotranspiration will result from changes in urban land cover [19,20]. Consequently, urban hydrological impacts are crucial to evaluate qualitatively and quantitively. They play an essential role in urban and water resources management and planning and flood warning [21,22]. These fluctuations are difficult to explain. However, in urbanization, the complex relationship between land-use change and the hydrological process impacts every facet of the runoff process [2]. Furthermore, urban resources, including impervious areas, green spaces, building density, population, etc., are unequally distributed in cities. Hence, the rainfall-runoff distribution process becomes more complex and greatly depends upon the land-use changes and spatial and temporal distribution [14,23].
Amidst these challenges caused by urbanization, urban soils play a vital role in providing several urban ecosystem services, such as support for plant and vegetation growth, soil microorganisms, fertility maintenance, soil water retention, and removal of contaminants [24,25,26,27]. The soil science community is progressively recognizing the significance of soils in delivering ecosystem services in urban environments [28,29]. However, anthropogenic activities have destroyed urban soils’ ecological and health functions, and urbanization has altered urban soil properties such as increased soil pH, high EC, and soil water deficits [30,31]. Urban soil has a crucial role in providing many ecosystem services that are vital for the wellness of humans and the resilience of urban areas [32,33,34]. On a local level, these ecosystem services consist of flood mitigation, reducing the urban heat island effects, absorbing air pollution, supporting physical infrastructure, growing food in cities, and providing access to green spaces for physical and mental health. Urban soil supports carbon storage and nutrient cycling at global and local scales. The effective management of urban soils can provide several ecosystem services, such as improving soil productivity, carbon storage, water flow regulation, mitigating climate change, and recreational benefits [35]. In contrast, non-urban soils support higher levels of ecosystem services, such as food production, etc.
To restore and enhance ecosystem services in urban environments, nature-based solutions, such as urban trees, green roofs, and urban vegetation, can be used. Targeted ecosystem services include rainwater management, mitigating urban heat islands, and reducing runoff, which all play a vital part in sustainable urban development [36,37]. Vegetation influences ecosystem services by using different vegetation types and conditions across various landscapes, therefore impacting soil and water properties important for ecosystem support and regulation. In [38,39], the authors stated that vegetation was essential to regulate energy balance via transpiration, respiration, photosynthesis, and other crucial processes. Concurrently, it also plays a pivotal role in climate change mitigation, regulating the water cycle, and changing soil structure [40,41,42]. Changes in vegetation influence the water cycle through changes in soil water infiltration, root water absorption, canopy transpiration, rainfall interception and redistribution, and the energy distribution process [43]. Hence, vegetation is considered necessary in the energy exchange, biogeochemical, and hydrological cycle process on the surface of land. Trees in cities offer shade and evaporative cooling to pedestrians [44]. Moreover, an improvement in ground vegetation can potentially improve stormwater retention, as [45] suggested. Hence, numerous policymakers advocate for the augmentation of urban greenery [37].
The process of urban centers’ densification and infilling has resulted in a significant rise in impervious surface cover in several urban areas. This has resulted in a scenario where the quantity and speed of runoff water can exceed the drainage system capacity, causing localized urban floods and ecological damage to city streams [46]. The intensity and frequency of rainstorms have increased due to climate change, which may worsen this issue in cities globally [47]. The percentage of impermeable soil can be reduced by enhancing the vegetative cover. The addition of trees, shrubs, and lawn spaces has an instantaneous impact on reducing the influence of rainwater. This is achieved via direct intercepting, which reduces the flow of rainwater [48]. Plant leaves and natural mulching above the soil surface help to mitigate the adverse effects of heavy rains, hence minimizing soil erosion and maintaining fertility [45].
The bibliometric analysis has attained fame in the quantitative literature review method; it utilizes data mining, statistical analysis, and mathematical methods to reveal evolving patterns in the scientific research of a specific field [35,49,50]. This investigation evaluates the research literature, classifies the publication’s output by year, and highlights the collaboration among authors, institutions, and countries at national and international levels. Additionally, it indicates potential directions for future study in global organic and inorganic carbon [51]. Databases, including Scopus and Web of Science, can be used to collect data for a bibliometric analysis. A bibliometric analysis is conducted from 1973 to 2023 to identify the research gap, authors’ keywords, trending topics, annual number of publications, source country, institutions, journals, collaboration among countries, institutions, and authors. We aim to identify the patterns and trends in research related to nature-based solutions and urban soil hydrology by conducting a bibliometric analysis. This study does not attempt to provide a comprehensive review of empirical findings but instead highlights areas of growing interest.

2. Material and Methods

2.1. Data Source, Search, and Collection

Databases, including Scopus and Web of Science, are widely used for bibliometric analyses. Each database has its benefits and restrictions. The Scopus database provides broader coverage and a higher number of search document results [52]. Therefore, Scopus was used in this bibliometric analysis to review the role of nature-based solutions in urban soil hydrology. The bibliometric literature search was performed on Scopus on 13 November 2024. The literature search was carried out in the English language by selecting the “Topic” section, which contains “Article title, Abstract, Keywords” by using the following keywords: (“trees” OR “vegetation” OR “green infrastructure” OR “blue green infrastructure” OR “greenery” OR “nature-based solutions” AND “hydrolog*” AND “urban” OR “city” OR “soil”). In Scopus’ online interface, there are several filters to narrow down and specify the literature search. First, we applied the filter “Range” from early 1973 to 2023, excluding the 2024 publications. The filters “Author name” and “Subject area” were left as they were because the authors did not want to exclude any author and subject area from the literature research. The selection process of document type in the Scopus database focused on research articles, conference papers, and review papers, because these are considered as original research/work done by scientists and researchers in their scientific fields. Other document types, such as conference review, book, book chapters, and editorial notes were excluded using the filters available in the Scopus database interface. The remaining filters were left unchanged because the authors were interested in a metrics analysis.
Furthermore, the search filter was narrowed down by selecting the English language for the published documents. After applying those filters, the remaining publication records were exported from the Scopus database in CSV format. After that, the duplicates and missing data were removed from the data. A total of 13,276 published articles were reviewed for the bibliometric analysis.

2.2. Bibliometric Analysis and Visualization

The initial data were analyzed using the tool “Analyze Results” from Scopus. A bibliometric analysis contains different statistical and mathematical methods. These bibliometric approaches evaluate research based on the available sample data (i.e., authors, keywords, citations, titles, journals, countries, institutions, etc.) [53]. Additionally, the main focus of a bibliometric analysis is to measure the quality and scientific impact of the scientific production [54]. It also deals with bibliographic networks (co-citation, co-keywords, co-authors, etc.) by understanding the social, intellectual, and conceptual structure [55]. The free online software “VOSviewer (v1.6.20)” was used to make bibliometric maps [56]. These maps provide an overview of the network collaboration among countries, authors, and institutions. VOSviewer also identifies research topics or fields used mainly by the researchers (e.g., most frequently used keywords by the authors) [57]. Biblioshiny (v4.3.0) software produces a user-friendly and interactive interface for bibliometric analysis offered by the R package “Bibliometrix”. The main summary information was generated by the R software (v4.2.2) using the Bibliometrix package. The number of publications per country with their GDP map was generated in Python using the package Plotly [58]. The World GDP data were downloaded from the World Bank website (https://data.worldbank.org/indicator/ (accessed on 16 November 2024)). Aksnes et al. [59] used Biblioshiny software to determine the citation pattern, publication trends, and research theme in their study. Likewise, Chen et al. [60] used VOSviewer to visualize collaboration networks and map the research landscape in their research. Another study conducted by [51] utilized VOSviewer to identify and evaluate research topics and network collaboration (authors, countries, and academic institutions) and Biblioshiny for analyzing and visualizing bibliometric data. In this review study, we used VOSviewer and Biblioshiny software, which work with the R package “Bibliometrix” for our bibliometric analysis. These tools are broadly used for the same objective in various disciplines.
The main focus of our review was to find the research gap and collaboration among countries, institutions, and authors in this research area. Furthermore, the research collaboration among different countries, the relationship among research fields/topics, the main research area, trending topics, and thematic keywords evolution were also determined. The overall publication number and annual publications for nature-based solutions and urban soil hydrology were determined by summing the number of articles across all years and each year, correspondingly. The institutions and countries’ research productivity was examined based on the author’s affiliation with the published papers.

3. Results

3.1. General Information, Publications over Time, and Temporal Trend

The main summary information of this bibliometric analysis is presented in (Table 1). A total number of 13,276 documents were produced from 1923 sources, with a 10.71% annual growth rate. The average age per document was 11.4, whereas the average citation per document was 39.49. The document types published from 1973 to 2023 include 11,205 research articles, 1589 conference papers, and 482 review papers. The total number of authors was 33,351, of which the number of authors of single-authored documents was 770, and the number of single-authored documents was 859. Furthermore, the number of co-authored documents was 4.54, although the percentage of international co-authorship was 28.42%. Additionally, the analysis showed that the total number of keywords plus used in this bibliometric study was 36,589, and the number of author’s keywords was 23,155.

3.2. Number of Publications over Time

A detailed analysis of the literature showed that a large number of research articles, review articles, and conference papers were published from different sources, including books and journals. The bibliometric analysis produced a total number of 13,276 papers published from 1973 to 2023, which were related to the role of nature-based solutions in urban soil hydrology (Figure 1). The early period from 1973 to 1990 showed a very low number of publications per year and the average number of publications per year was under 50 articles. The middle acceleration period (1990–2000) showed a significant increase in the number of publications per year, which suggested high research activity in the field of nature-based solutions and urban soil hydrology. The number of publications showed a peak growth after 2010 with the highest number of articles of 900 per year by 2023. That showed significant enhancement in this research field which may be due to the higher funding, collaboration among countries, and technological advancement increasing the research output.

3.3. Global Contribution Map by Countries with GDP and Affiliations

Nature-based solutions in urban hydrology were studied in 159 countries across the globe, and 97 countries published more than five papers in this research area. The United States and China combined published 54.2% of the worldwide research relating to the application of nature-based solutions in urban soil hydrology, with 36% of the articles from the USA and 18.2% of publications from China. Germany (7.6%), the United Kingdom (7.1%), Australia (7%), Canada (5.5%), France (5%), Italy (4.6%), Spain (4.5%), and the Netherlands (4.5%) were secondary significant contributors in this research area. The geographical map (Figure 2) shows the top 10 high economic nations in the world, in which the USA, China, and Germany dominate the world economy, and they also contributed heavily in this research area in terms of research publications. The economic power of countries directly correlates with their research output, because the higher GDP enables those countries to invest more in education, technology, and infrastructure.
A bibliometric analysis is essential for gaining information about potential institutions’ collaboration in a specific research area. The graph (Figure 3) depicts the top 10 affiliations in research on the role of nature-based solutions in urban soil hydrology. This can be helpful for researchers in this specific field for collaboration among important institutions. The leading Beijing Normal University published 540 articles in China, showing their historical and current efforts in scientific research. Next, the Tsinghua University Beijing produced 410 articles, while the University of California published 389 articles as well. A total of 271 articles were recorded as non-reported in this analysis.

3.4. Corresponding Author’s Countries and Collaboration Among Countries

The corresponding authors with single- and multiple-country publications (SCPs and MCPs) are presented in Figure 4A. The corresponding authors are typically responsible for overseeing the research, managing the manuscript submission process, and representing the study’s institutional or geographical origins. This role makes them a key indicator of a country’s scientific contributions. Although first authorship also holds significance, we focused on corresponding authors as they are often seen as the primary investigators or points of contact, particularly in multi-country collaborations. The top contributing country was the United States with a total of 2833 articles, 2293 SCPs, and 540 MCPs, followed by the Republic of China with 1935 published articles in total, 1346 SCPs, and 589 MCPs, and Germany with a total number of articles 508, 294 SCPs, and 214 MCPs. Australia and Canada came in fourth and fifth position in terms of publication numbers, SCPs, and MCPs. The findings indicated that these leading countries made more significant investments in the scientific domain of nature-based solutions (i.e., vegetation, trees, green infrastructure, blue-green infrastructure, and greenery in urban soil hydrology). However, our results indicated that Sudan, Nigeria, Mali, and Lebanon produced a smaller number of articles, and more research is needed in these countries to combat urban hydrology problems.
The top country in terms of collaboration was the USA, with 26.17% as compared to other countries (Figure 4B). Germany was the second most collaborating country in terms of research with other countries on the role of nature-based solutions in urban soil hydrology. The results proved that Germany performed well in this research area on the European continent. The People’s Republic of China came in third place in terms of collaboration percentage (10.19%).

3.5. Sources and Citation Analysis

Table 2 depicts the top 10 articles with the highest global citations on the Scopus database relating to nature-based solutions and urban soil hydrology. The articles cited in high numbers were primarily original and review articles. These studies illustrated the diverse impacts of urbanization on environmental systems, demonstrating the importance of integrated models and data platforms to manage future urban expansion and its environmental effects. Gill et al. [61] examined the role of green infrastructure in mitigating the effects of climate change in Greater Manchester. They highlighted how changes in urban surfaces, including less vegetation and high surface sealing, induced problems like urban heat islands and high surface runoff especially in future climate change. The research used energy exchange and hydrological models to assess how the city green infrastructure could assist in decreasing these harmful effects. They concluded that green infrastructure was essential in urban planning to adapt to climate change, where green spaces play a significant role in the regulation of temperature and runoff management. Another study conducted by [62] presented the latest dynamic global vegetation model to simulate key processes in the biosphere that affect the global carbon cycle, including respiration, photosynthesis, fire, and energy exchanges at the soil plant surface. They concluded that their model was useful to study the feedback between vegetation cover and climate changes across global scales. Xu et al. [63] modified the normalized difference water index (NDWI) to improve open-water features in remotely sensed imagery. The goal of that study was to address the limitations of the NDWI, which often mixes the water features with built-up land noise, by replacing the NIR (near-infrared) band with an MIR (middle infrared) one to generate a modified NDWI (MNDWI). These changes improved the accuracy and clarity of water feature extraction, especially in areas dominated by land backgrounds. This enhancement provided a more reliable tool for water resource evaluation particularly in urban complex environments. Niu et al. [64] introduced the Community Noah Land Surface Model with multiple parameterization options, which was designed to enhance land surface models by enabling the flexible parameterization of biophysical and hydrological processes. The main objective of that study was to address limitations in simulating soil moisture, snow, vegetation, and runoff processes while offering numerous options for specific physical processes modeling. The results showed that Noah-MP significantly improved the surface fluxes simulations, snow water, and runoff dynamics compared to early versions. Similarly, another model such as the Global Land Evaporation Amsterdam Model was introduced by [65], which estimated root zone soil moisture and terrestrial evaporation by using satellite data. The primary goal of that research was to improve the model representation of physical processes and to improve its use of newly available geophysical variables derived from satellite. The updated model demonstrated considerable improvement in its accuracy and application, which provided a more accurate and precise soil moisture and evaporation estimation at global scales.
Mu et al. [66] aimed to enhance the MODIS global evapotranspiration (ET) method, first formulated by [67], by augmenting several aspects of its calculation and precision. The improvements included the simplification of vegetation cover fraction calculations, the computation of evapotranspiration as a sum of daytime and nighttime components, the incorporation of soil heat flux calculations, and the refinement of estimations for stomatal conductance. The results specified that the new algorithm yielded a worldwide annual total evapotranspiration estimate of 62.8 × 103 km3, which was more consistent with other reported estimates compared to the prior algorithm’s estimate of 45.8 × 103 km3. Sandholt et al. [68] presented a simplified Temperature-Vegetation Dryness Index (TVDI) to evaluate the surface moisture conditions using satellite data such as surface temperature and the vegetation index. The primary aim was to provide a straightforward method to monitor soil moisture specifically in areas with less resources. The results demonstrated that the TVDI could capture the spatial variations in soil moisture more efficiently than conventional hydrological models. Chen et al. [69] improved simulations of surface heat fluxes and seasonal soil moisture conditions by using an integrated advanced land surface-hydrology model (LSM). The aim of that study was to provide accurate and precise boundary conditions for atmospheric models by incorporating high resolution characteristics and improving soil moisture. The study investigated how vegetation and soil texture maps influenced surface energy fluxes and land atmosphere feedback.
A total number of 154 journals published 13,276 articles related to (“trees” OR “vegetation” OR “green infrastructure” OR “blue green infrastructure” OR “greenery” OR “nature-based solutions” AND “hydrolog*” AND “urban” OR “city” OR “soil”). The top 110 journals published more than 20 articles. Furthermore, the top 10 most relevant sources published 3198 articles in total (Figure 5). Additionally, the highest number of articles, 783, were published in the Journal of Hydrology, followed by the Hydrological Processes and Science of the Total Environment, with 434 and 404 articles. The lowest number of articles were published in the Journal of Ecological Engineering. The local impact of various journals based on total citations is presented in Figure 6. The Journal of Hydrology stands out among other journals based on the highest number of total citations (48,457) on nature-based solutions and urban hydrology. The Journal of Water Resources Research and Hydrological Processes obtained second and third positions with total citations of 21,615 and 18,363. After the first top 10 journals, there was a significant decrease in the total citations, which showed that there were less significant journals in this research area, followed by a considerable number of journals with fewer citations. This analysis enabled researchers to identify the most important and influential journals in this research area (nature-based solutions and urban hydrology) to publish their work and find suitable collaborators.

3.6. Authors

The investigation of the most significant authors in the research area of nature-based solutions and urban hydrology delivered essential insights into the most influential authors (Figure 7).
The Sankey graphs (Figure 8A,B) show the collaboration and contributions of different institutions, sources (journals), and countries in specific research domains, such as soil moisture, climate change, hydrology, evapotranspiration, and vegetation. The People’s Republic of China showed the most driven institutions, whereas the United States showed diverse representation across various topics and journals. The research theme soil moisture was the main focus of different institutions and countries, demonstrating its importance in the field of hydrology and climate related research. The keywords, including soil moisture, hydrology, evapotranspiration, vegetation, remote sensing, and runoff showed maximum incoming inflow from the affiliations and countries’ direction, which depicted the maximum number of affiliations and journals in different countries working on these research topics.

3.7. Keywords Analysis and Conceptual Structure Map of Trending Topics

The analysis of co-occurring author keywords provides an insightful way to show the relation among trending research topics within a specific research area based on their co-occurrence (Figure 9). The size of each node represents the frequency of used author keywords in the literature. Moreover, the lines between nodes show the occurrence of keywords used by the authors in the same publications, and the thickness of the lines represents the strength of the keyword’s co-occurrence. The most frequently used keywords in this research area were hydrology, climate change, water quality, soil properties, surface runoff, restoration, drainage, ecosystem services, soil moisture, evapotranspiration, ecohydrology, forest hydrology, soil water, throughfall, hydrological modelling, streamflow, urban hydrology, nature-based solutions, green infrastructure, low impact development, stormwater management, and infiltration. Keywords form different clusters, which are more likely to show specific research themes. For instance, the keywords “urban hydrology”, “stormwater management”, “nature-based solutions”, “low impact development”, “urbanization”, and “green infrastructure” formed a cluster that concentrated mainly on the anthropogenic factor such as urbanization and the nature-based solutions that reduced the urban hydrological issues due to extensive urbanization. This research theme generally explains how nature-based solutions (such as green infrastructure and low impact development) and different processes can be combined with urban development to properly manage water resources, minimize the impact of flooding, and adapt to climate changes in global warming situations. Furthermore, keywords including “hydrology”, “land use change”, “climate change”, “wetlands”, “ecosystem services”, “restoration”, “drainage”, and “surface runoff” formed a cluster that showed how various land practices significantly affect the hydrological processes causing high surface and altered water retention. Restoration and proper drainage can reduce the negative impacts by enhancing water retention properties and decrease surface runoff.
The conceptual structure map of the keywords shows the closeness of terms/keywords’ relationship among each other in the literature (Figure 10). The x-axis (Dim 1, showing 38.55% of the variance) demonstrates the thematic gradient from urbanization, urban hydrology, low-impact development, and stormwater management on the right side to natural ecosystem services and processes on the left. The y-axis of the graph represents (Dim 2, accounting for 20.81% of the variance) the ecological modeling and hydrological research on the bottom, and nutrient dynamics on the top. The red color cluster shows a connection with the nature-based solutions (i.e., green infrastructure and low impact development) that play an important role in stormwater management in a changing climate in urban areas and that can also retain sustainable ecosystem services. These keywords are closely associated with the sustainable management practices of urban ecosystems and their integration into urban environments for the management of stormwater and improvement of the urban ecosystem. The blue cluster signifies research topics related to natural ecosystem services and watershed, such as “soil erosion”, wetland restoration”, “hydrology”, “vegetation”, and “water quality”. These research themes are interconnected through their relevance to soil and water conservation, urban hydrology, and ecological modeling. Further, the green cluster consists of keywords/terms such as nitrogen and phosphorus, which show environmental nutrient dynamics.

3.8. Hot Trending Topics in Nature-Based Solutions and Urban Hydrology with Respect to Time

The trending topics about the role of nature-based solutions (e.g., vegetation, green infrastructure, blue-green infrastructure, greenery, and trees) in urban soil hydrology, with respect to time is presented in Figure 11. The trending keywords of urban greenery, nature-based solutions, and urban hydrology varied strongly over time. The top research topics used in the literature from 2005 to 2015 were acidification, nutrient cycling, simulation, drainage, productivity, nitrogen, species richness, erosion, hydrology, vegetation, and evapotranspiration. The early research trending keywords from 2015 to 2023 were remote sensing, soil moisture, climate change, drought, green infrastructure, machine learning, and nature-based solutions.

4. Discussion

4.1. Publications Output over Time and Global Contributions by Countries and Institutions

Our results showed significant enhancement in the number of publications after 2010, highlighting the importance of collaboration between countries, and technological advancement and funding from the institutions increased the research outputs in this research area. This trend aligns with earlier research by [70], who reported a growing focus on ecological studies in urban environments. A bibliometric study by [71] also noted a surge in the number of publications after 2020, demonstrating escalating interest in NBS for stormwater management in urban areas.
Furthermore, our analysis suggests that the knowledge exchange network could help identify under-researched areas, especially when linked to international collaboration metrics. Urban policy plays a crucial role here, as integrating vegetation or green infrastructure or blue-green infrastructure into city planning can mitigate urban heat island effects and improve stormwater management.
The United States and China together contributed highly to the global research on NBS in urban soil hydrology. This demonstrated the research capacity and commitment of both countries in addressing challenges related to rapid urbanization and climate change. The high research contributions of USA and China were due to their high GDP, which made them able to invest more money in the field of nature-based solutions to combat future climate changes issues, including urban heat islands, reduced vegetation, less available water, and high pollution. The top two most productive institutions belonged to the People’s Republic of China. The University of California was in third position in terms of the number of publications in the field of nature-based solutions and urban soil hydrology.
China and the USA dominated research related to NBS and urban hydrology (including stormwater management, flooding, and runoff). However, a majority of the institutions from China made notable contributions. Interestingly, although Germany, the United Kingdom, and Australia were secondary significant contributors in this research area, none of the institutions from these nations were ranked among the top publishing universities/institutions. This may be due to the fact UK and German researchers collaborated more internationally, producing co-authored papers with affiliations outside their own countries.
This outcome highlights the leading nations in NBS research and underscores the research productivity in these countries, offering a comprehensive understanding of NBS and urban hydrology on a global scale.

4.2. Top Reputed Journals Based on Article Number and Citations in the Field of Natured-Based Solutions and Urban Hydrology

The prominence of journals like the Journal of Hydrology, Hydrological Processes, and Science of the Total Environment in publishing research on nature-based solutions and urban soil hydrology reflects the increasing academic focus on this field. The Journal of Hydrology led this research area based on the highest number of articles and citations as compared to other journals; its dominance was not only due to the volume of publications, but also its consistent ability to attract highly impactful research. This trend shows the focus of scientific researchers on these research journals for publishing their work in this emerging research field. These results highlight the need for researchers to target journals with high impact and relevance to maximize the dissemination and recognition of their research work. Journals like Hydrological Processes and Science of the Total Environment, though less productive as compared to Journal of Hydrology, played complementary roles in advancing the field by providing researchers within nature-based solutions and urban soil hydrology. These differences among the journals allowed a diversity of research directions and publication platforms in this domain. By identifying these high impact journals, future researchers can strategically select prominent academic journals that not only increase the search visibility of their findings but also contribute meaningfully to the broader research on nature-based solutions and urban soil hydrology. Furthermore, experts in this specific field can utilize these data to publish their findings in prominent academic journals and to identify potential collaborators.

4.3. Most Productive Authors in the Field of Nature-Based Solutions and Urban Hydrology

The contributions of leading researchers, such as Jackson, T. J., with a high number of publications among top researchers in this field, represent a significant dedication to advance the understanding of nature-based solutions in urban soil hydrology. Jackson’s extensive research work underscores his role as a top researcher in this specific field, impacting research directions and setting proper standards for quality and impact. In addition, collaborative networks among authors showed key dynamics in the global research landscape. Strong co-authorship links between researchers in the United States, China, and Germany highlighted that cross-institutional and cross-country collaborations were important for research innovations. These connections not only strengthen the scope of individuals studies but also increase the exchange of methodologies and perspectives, enhancing this specific field. These patterns highlight that impactful research arises from interdisciplinary and international collaborations. This analysis could provide proper guidance for early-career researchers to identify potential researchers and collaborators in the emerging field of nature-based solutions for urban hydrology management.

4.4. Global Collaboration Among Countries

China is the leading country in terms of international collaboration (multiple-country publications) among developing nations globally. This demonstrates its ability to enhance research and improve quality in developing nations. China is investing more resources in research related to urban water management. Li et al. [72] stated that urban water management was a significant problem around the globe due to climate change and rapid urbanization and developed the concepts of sustainable water management during the last decade. Further, they explained that nature-based solutions (sponge city, blue, green, gray infrastructure) were initiated in the European Union in 2015, and it started in China in 2013, showcasing its proactive stance on sustainable urban hydrology. It plays an important role in the issues related to water management in urban areas. The lower number of publishing research articles in this research area in developing countries does not necessarily show a lack of research motivation or ability, as these nations also face the same urbanization problems as the rest of the globe. Moreover, highly productive nations like China are significantly impacted by rising urbanization and climate change. As a result, there has been an increased focus on investing in research relating to nature-based solutions to combat these emerging issues [73].
International collaboration among countries is necessary to expand the area of nature-based solutions and their role in urban soil hydrology. The top country in terms of collaboration was the USA, compared to other countries, while China was the third most collaborating country in terms of research with other countries on the role of nature-based solutions (vegetation, greenery, trees, green infrastructure, or blue-green infrastructure) in urban soil hydrology. The results proved that China was performing well in this research area in Asia. The result proved that the USA was the main collaborating country in the world in the field of nature-based solutions i.e., vegetation, trees, green infrastructure, etc., and urban hydrology. This may be due to the advancement of the concept of nature-based solutions in the region and their strong commitment to tackle climate change by using multi-sustainable approaches. However, it is essential to understand that limited research collaboration between less developed countries can have a detrimental effect on their research capabilities and their ability to tackle issues related to climate change and urbanization. Hence, it is imperative for developing nations to collaborate with developed countries in this specific field of study to expand their research capabilities and deepen their comprehension of the significance of nature-based solutions for urban hydrology. This highlights the considerable international collaboration among the United States and other less developed countries on natured-based solutions and urban hydrology. This can further create more operative and advanced solutions, benefiting not only the United States but other countries facing the same issues and challenges.

4.5. Keyword Analysis for Nature-Based Solution and Urban Hydrology

The analysis of co-occurring author keywords provided significant research trends and clustering themes within the research field of nature-based solutions and urban hydrology. The keywords around topics such as “urban hydrology”, “stormwater management”, “nature-based solutions”, “climate change”, and “ecosystem services”, “sustainability”, and “flooding” formed a cluster that showed increasing focus on implementing natural-solution processes into urban water management systems. This research theme generally explains how natural landscapes and different processes can be combined with urban development to properly manage water resources, minimize the impact of flooding, and adapt to climate changes in global warming situations. Nature-based solutions and sponge cities are considered as pioneered methods for the management of urban water. Nature-based solutions, such as permeable pavements and green roofs decrease the amount of runoff and improve stormwater management [74,75]. Furthermore, keywords including “hydrology”, “land cover”, “land use”, “climate”, “watershed”, conservation”, “surface runoff”, and “water resources” formed a cluster which showed how various land practices affect water behavior and availability in a changing climate [71,73,76]. The “runoff”, “stormwater”, “low impact development”, “green roof”, “infiltration”, and “modelling” keyword cluster largely examined the significance of nature-based solutions, like low impact development techniques and their efficiency in the management of runoff resulting from stormwater [31,77,78]. The keyword “hydrology” showed a strong connection with other key topics like natured-based solutions, climate change, ecosystem services, urban hydrology, and remote sensing. These five highlighted keywords are potential trending topics that were not directly covered in our study; nevertheless, they have been utilized by other researchers in the literature review [79,80,81].

4.6. Current and Future Topics and Their Evolution Based on Trending Topics

The analysis of trending topics showed evolving research focus areas in urban soil hydrology and nature-based solutions over time. The prominent keyword “hydrology” was frequently used in the literature for the first time in 2013, reflecting the central role of urban water management in urban ecosystems and showing the increasing focus on integrating ecological solutions into urban development. The terms “vegetation”, “green infrastructure”, and “nature-based solutions” were crucial keywords in the literature, showing the importance of the nature-based solutions’ (vegetation and green infrastructure) role in mitigating the adverse consequences of rapid urbanization such as the loss of biodiversity, climate change, drought, and increased runoff. Furthermore, keywords “natured-based solutions”, “soil moisture”, “green infrastructure”, “runoff”, and “remote sensing” were also important keywords in the literature and have been used by researchers in recent times. The application of nature-based solutions (e.g., green infrastructure, vegetation, urban forestry, etc.) are now widely acknowledged for their important role in stormwater management and runoff, reducing urban heat, and enhancing air quality in the cities. The use of remote sensing techniques could be helpful to enhance the effectiveness of nature-based solutions in urban soil hydrology. The ability to observe extensive environmental changes, including vegetation cover, water quality, and land-use changes, using satellite images and other remote sensing technologies provides an important tool for evaluating the performance of nature-based solutions across time. Utilizing this technology, researchers and policymakers could improve the implementation of nature-based solutions and gain a better understanding of their long-term effects on urban water management.
Future research could cover the integration of nature-based solutions (vegetation, green infrastructure, wetlands, urban forestry) in cities and their impact on stormwater management and runoff, biodiversity enhancement, reducing the urban heat island impact, and improving urban ecology and biodiversity. Palermo et al. [75] stated the importance of nature-based solutions in stormwater management in cities and their capacity to decrease surface runoff and improve infiltration rates and evapotranspiration. These nature-based solutions, such as green walls, green roofs, vegetation, and permeable pavements, play an essential part in restoring the urban hydrological cycles. Zhao and Yue, [74] illustrated that climate change caused waterlogging issues in China. They suggested that nature-based solutions could mitigate the impacts of climate-induced waterlogging. Another study [82] concluded that sponge-city systems in urban areas enhanced tree growth by providing appropriate conditions for root development and also mitigated urban heat island effects. Our results and the scale of research conducted worldwide clearly show that the role of urban greenery in soil hydrology is extremely important.
By examining the volume of publications, collaborations, and trends, our study highlights the growing global recognition of the importance of nature-based solutions (NBS) in urban hydrology.
Recommendations for stakeholders:
  • Integration of nature-based solutions (NBS) in urban planning: Stakeholders, including urban planners, policymakers, and municipal authorities, should prioritize the integration of nature-based solutions in urban development projects. These solutions, such as green roofs, urban forests, and permeable pavements, have demonstrated significant benefits in improving urban soil hydrology, managing stormwater, and mitigating the urban heat island effect. By incorporating NBS, cities can enhance their resilience to climate change and promote sustainable urban ecosystems.
  • Promotion of collaborative research: The study highlights the importance of international collaboration in advancing research on nature-based solutions in urban hydrology. Stakeholders should encourage and facilitate partnerships between universities, research institutions, and governments across different countries. Collaborative efforts will enable the sharing of knowledge, resources, and best practices, leading to more effective and innovative solutions to urban hydrological challenges.
  • Focus on under-researched regions: While countries like the United States and China lead in publications related to nature-based solutions, there is a need to focus research efforts on under-researched regions, particularly in developing countries. Stakeholders should allocate funding and resources to support research and the implementation of NBS in these regions, addressing local urbanization challenges and enhancing global knowledge.

5. Conclusions

The study presented a comprehensive bibliometric analysis from 1973 to 2023, highlighting the dynamic research growth in the research area of nature-based solutions (e.g., vegetation, trees, green infrastructure, blue-green infrastructure, and greenery) in urban soil hydrology. The bibliometric analysis showed considerable growth in scientific literature, with a yearly 10.71% growth rate in global research interest. It emphasized the importance of integrating ecological solutions, such as nature-based solutions, into urban regions to address hydrological challenges.
Furthermore, our analysis revealed that the USA and China were leading contributors, together accounting for half of the publications in this field. The steady increase in publications after 2010, with the highest number of articles in 2023, reflected growing academic and authors’ personal interests in sustainable water management in cities worldwide.
Future research should focus on the implementation of nature-based solutions in less developed countries to enhance their understanding and capacity to solve urban hydrological issues. The citation and publications analysis also identified prominent journals for researchers to publish their work and collaborate internationally in this specific field. Moreover, methods focusing on long-term impacts of nature-based solutions on urban water systems will help us make our cities more sustainable and resilient anywhere around the globe.

Author Contributions

Conceptualization, M.O.K. and A.K.-I.; methodology, M.O.K.; software, M.O.K., W.L., E.S.-O. and S.D.K.; validation, A.K.-I., M.O.K., W.L., E.S.-O. and S.D.K.; formal analysis, M.O.K.; investigation, M.O.K. and A.K.-I.; resources, M.O.K.; data curation, M.O.K.; writing original draft preparation, M.O.K.; writing review and editing, M.O.K., A.K.-I., S.D.K., E.S.-O. and W.L.; visualization, M.O.K.; supervision, M.O.K. and A.K.-I.; project administration, A.K.-I. and M.O.K.; funding acquisition, A.K.-I. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Ministry of Science and Higher Education of the Republic of Poland, with support specifically provided by the Department of Ecological Engineering and Forest Hydrology, University of Agriculture in Krakow.

Data Availability Statement

The data supporting the results and findings of this study are openly available in the Scopus database.

Acknowledgments

The authors express their sincere gratitude to the editors and reviewers for their valuable feedback and thorough review, which greatly improved the quality of this paper.

Conflicts of Interest

Author Saskia D. Keesstra was employed by the company Climate-Kic Holding B.V. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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Figure 1. Trends in annual publication output from 1972 to 2023, highlighting the growing research interest in nature-based solutions and urban hydrology. Data were collected from the major academic database Scopus.
Figure 1. Trends in annual publication output from 1972 to 2023, highlighting the growing research interest in nature-based solutions and urban hydrology. Data were collected from the major academic database Scopus.
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Figure 2. Top 10 countries producing a high number of publications on nature-based solutions and urban hydrology.
Figure 2. Top 10 countries producing a high number of publications on nature-based solutions and urban hydrology.
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Figure 3. The top ten most relevant affiliations with the maximum number of articles.
Figure 3. The top ten most relevant affiliations with the maximum number of articles.
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Figure 4. Corresponding authors’ countries (A) and global countries’ collaboration map (B), SCPs and MCPs: single- and multiple-country publications.
Figure 4. Corresponding authors’ countries (A) and global countries’ collaboration map (B), SCPs and MCPs: single- and multiple-country publications.
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Figure 5. The top ten most relevant journals with the maximum number of articles.
Figure 5. The top ten most relevant journals with the maximum number of articles.
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Figure 6. Top ten most relevant journals with the highest total number of citations.
Figure 6. Top ten most relevant journals with the highest total number of citations.
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Figure 7. Top 10 most relevant authors with the highest number of publications.
Figure 7. Top 10 most relevant authors with the highest number of publications.
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Figure 8. Three-field plot shows connections among (A) countries, universities, and keywords (B) countries, journals, and keywords.
Figure 8. Three-field plot shows connections among (A) countries, universities, and keywords (B) countries, journals, and keywords.
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Figure 9. Bibliometric analysis of author keywords’ distribution. The size of the keyword’s circles shows the frequency of keyword appearance, and the lines show the relationships among keywords.
Figure 9. Bibliometric analysis of author keywords’ distribution. The size of the keyword’s circles shows the frequency of keyword appearance, and the lines show the relationships among keywords.
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Figure 10. Conceptual structure map of the keywords with two dimensions showing the distribution of the keywords. The different color clusters represent keywords with strong relation with each other.
Figure 10. Conceptual structure map of the keywords with two dimensions showing the distribution of the keywords. The different color clusters represent keywords with strong relation with each other.
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Figure 11. Heatmap of research trending topics in nature-based solutions and urban soil hydrology over time from 2003 to 2023.
Figure 11. Heatmap of research trending topics in nature-based solutions and urban soil hydrology over time from 2003 to 2023.
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Table 1. Main information summary of the bibliometric analysis.
Table 1. Main information summary of the bibliometric analysis.
DescriptionResults
Timespan1973–2023
Books2
Journals1592
Conferences329
Documents13,276
Annual growth rate %10.71
Document average age11.4
Average citations per doc39.49
Research article11,205
Conference paper1589
Review482
Authors33,351
Authors of single-authored docs770
Single-authored docs859
Co-authors per doc4.54
International co-authorships %28.42
Keywords plus (ID)36,589
Author’s keywords (DE)23,155
References600,702
Table 2. The top 10 articles with the highest number of global citations on Scopus.
Table 2. The top 10 articles with the highest number of global citations on Scopus.
Document TitleJournal TitleDocument TypeCitationsPublication Year
  • Coupling and advanced land surface-hydrology model with the Penn State-NCAR MM5 modeling system. Part I: Model implementation and sensitivity
Monthly Weather ReviewResearch Article47462001
2.
Modification of normalised difference water index (NDWI) to enhance open water features in remotely sensed imagery
International Journal of Remote SensingResearch Article38652006
3.
Improvements to a MODIS global terrestrial evapotranspiration algorithm
Remote Sensing of EnvironmentResearch Article21462011
4.
The community Noah land surface model with multiparameterization options (Noah-MP): 1. Model description and evaluation with local-scale measurements
Journal of Geophysical Research AtmospheresResearch Article18502011
5.
A simple interpretation of the surface temperature/vegetation index space for assessment of surface moisture status
Remote Sensing of EnvironmentResearch Article15902002
6.
GLEAM v3: Satellite-based land evaporation and root-zone soil moisture
Geoscientific Model DevelopmentResearch Article15822017
7.
A dynamic global vegetation model for studies of the coupled atmosphere-biosphere system
Global Biogeochemical CyclesReview Article 15692005
8.
Imaging spectroscopy and the Airborne Visible/Infrared Imaging Spectrometer (AVIRIS)
Remote Sensing of EnvironmentResearch Article15601998
9.
A revised land surface parameterization (SiB2) for atmospheric GCMs. Part I: Model formulation
Journal of ClimateResearch Article15221996
10.
Adapting cities for climate change: The role of the green infrastructure
Built EnvironmentResearch Article13582007
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Khan, M.O.; D. Keesstra, S.; Słowik-Opoka, E.; Klamerus-Iwan, A.; Liaqat, W. Determining the Role of Urban Greenery in Soil Hydrology: A Bibliometric Analysis of Nature-Based Solutions in Urban Ecosystem. Water 2025, 17, 322. https://doi.org/10.3390/w17030322

AMA Style

Khan MO, D. Keesstra S, Słowik-Opoka E, Klamerus-Iwan A, Liaqat W. Determining the Role of Urban Greenery in Soil Hydrology: A Bibliometric Analysis of Nature-Based Solutions in Urban Ecosystem. Water. 2025; 17(3):322. https://doi.org/10.3390/w17030322

Chicago/Turabian Style

Khan, Muhammad Owais, Saskia D. Keesstra, Ewa Słowik-Opoka, Anna Klamerus-Iwan, and Waqas Liaqat. 2025. "Determining the Role of Urban Greenery in Soil Hydrology: A Bibliometric Analysis of Nature-Based Solutions in Urban Ecosystem" Water 17, no. 3: 322. https://doi.org/10.3390/w17030322

APA Style

Khan, M. O., D. Keesstra, S., Słowik-Opoka, E., Klamerus-Iwan, A., & Liaqat, W. (2025). Determining the Role of Urban Greenery in Soil Hydrology: A Bibliometric Analysis of Nature-Based Solutions in Urban Ecosystem. Water, 17(3), 322. https://doi.org/10.3390/w17030322

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