Mapping the Research Landscape of Stormwater Quality Improvement Devices: Trends, Influencers, and Thematic Evolution (1992–2024)

Abstract

This study presents a comprehensive bibliometric analysis of the research landscape on Stormwater Quality Improvement Devices (SQIDs) covering 1992–2024. Using data from the Web of Science (WoS) and utilizing Bibliometrix R-package 5.1.0 and VOSviewer 1.6.20, this study identifies key trends, influential contributors, and the thematic evolution within SQIDs research. The findings reveal distinct growth phases driven by policy shifts, scientific advancements, and an increasing global emphasis on sustainability. Keyword analysis highlights a significant thematic transition post-2015, with terms like performance, runoff, and management (Keyword Plus), and stormwater management, green infrastructure, and stormwater (Author Keywords) indicating a strong shift toward sustainable, nature-based solutions. Bioretention system has emerged as the most researched SQIDs, reflecting widespread academic and practical interest. The most prolific countries in SQIDs research are the USA, China, and Australia, while prominent thought leaders include Fletcher (Monash University), Wang (Guangzhou University), Shuster (US EPA), and Deletic (UNSW). Leading publication outlets include the Journal of Environmental Management, Science of the Total Environment, Journal of Hydrology, and Water. Overall, this study underscores the field’s maturation toward policy-relevant and interdisciplinary innovations, long-term performances and smart SQIDs using artificial intelligence positioning SQIDs as vital tools in addressing urban stormwater management challenges globally.

1. Introduction

Stormwater management is an important aspect of sustainable urban development, particularly in addressing the increasing volumes of runoff caused by rapid urbanization and the proliferation of impervious surfaces. These changes hinder natural hydrological cycles, leading to heightened risks of flooding, erosion, and degradation of water quality in receiving water bodies [1,2,3,4]. In recent years, there has been a growing shift toward integrating nature-based solutions (NbS) into urban stormwater systems. Among these, Stormwater Quality Improvement Devices (SQIDs) have gained attention as practical, decentralized systems that aim to treat and manage stormwater at the source [5,6]. SQIDs include a diverse set of green infrastructure technologies such as bioretention systems, constructed wetlands, vegetated swales, infiltration trenches, and permeable pavements [5,7,8,9,10].

Concurrently, scholarly interest in sustainable stormwater management has grown significantly. Researchers are increasingly applying bibliometric methods to evaluate the evolution of knowledge in this field. Bibliometric analysis allows for the systematic assessment of the scientific literature, providing insights into publication trends, dominant research themes, author collaborations, and geographic distributions of research studies [6,11,12,13,14,15,16,17,18]. For example, Wang et al. [19] highlighted a global transition toward hybrid grey–green infrastructure approaches and low-impact development strategies, reflecting an interdisciplinary response to urban water challenges.

Bibliometric studies offer significant value by identifying research hotspots, knowledge gaps, and influential works that have shaped the trajectory of the field [10,12]. In the realm of SQIDs, these analyses can support the strategic planning of future studies, funding allocations, and evidence-based policymaking. Foundational studies, such as Fletcher et al. [14], have played a pivotal role in defining terminology and advancing the conceptual understanding of a decentralized stormwater infrastructure. Furthermore, countries like the United States, China, and Australia have emerged as global leaders in stormwater research, contributing substantially to knowledge production and international collaboration networks [18,19].

Nature-based solutions such as SQIDs are known for their multifunctionality. In addition to stormwater control, they offer co-benefits including pollutant removal, biodiversity enhancement, and recreational and aesthetic values [6,20,21,22,23,24,25]. Su et al. [18] emphasized the broader sustainability contributions of these systems, while Zhang et al. [20] observed a shift in research from engineering-dominated paradigms to integrated socio-ecological frameworks. Similarly, Bhargavan et al. [26] identified urban stormwater harvesting as a complementary strategy, particularly important for enhancing flood resilience and urban water security. Xie et al. [27] argued that deep learning can enhance performances of SQIDs. Silveira et al. [28] presented a review of studies on SQIDs to present a global overview of this theme.

Despite the increasing body of the literature on stormwater management and green infrastructure, there is a notable absence of focused bibliometric reviews specifically addressing SQIDs. Given the growing significance of these technologies in urban water management, a dedicated analysis is warranted. Therefore, this study conducts a comprehensive bibliometric analysis of the SQID-related literature published between 1992 and 2024. The objective is to examine the evolution of research themes, identify leading contributors and institutions, assess global collaboration patterns, and uncover emerging trends that shape the current and future landscape of SQID research.

2. Materials and Methods

Figure 1 illustrates the methodological framework adopted in this study. The process follows a structured bibliometric approach [29], beginning with data retrieval from the Web of Science (WoS) database, followed by a series of steps including article screening, data cleaning, and bibliometric analysis utilizing Bibliometrix [30] and VOSviewer [31].

In the initial phase, data were extracted from the WoS database, selected for its comprehensive coverage of high-quality, peer-reviewed publications and its suitability for bibliometric research. The choice of WoS was motivated by its reliability, accessibility, and compatibility with the analytical tools used in this study.

To ensure a robust and inclusive dataset, a detailed search query was constructed using Boolean operators. Keywords were strategically selected to encompass a wide range of themes associated with stormwater management, including green infrastructure, urban runoff, and pollutant removal technologies. The full search string used is provided in

Table 1. Search string used in this study to identify relevant articles.

Groups	Query Terms
1	“sustainable stormwater management” AND “stormwater quality improvement devices”
2	“green infrastructure” AND “stormwater management”
3	“best management practices” OR “BMPs” AND “stormwater treatment”
4	“low impact development” OR “LID” AND “urban runoff”
5	“urban runoff management” AND “stormwater pollutants”
6	“stormwater treatment technologies” AND “stormwater filtration systems”
7	“water-sensitive urban design” OR “WSUD” AND “stormwater quality”
8	“bioretention” OR “rain gardens” AND “stormwater management”
9	“constructed wetlands” AND “stormwater treatment”
10	“permeable pavements” AND “stormwater infiltration”
11	“gross pollutant traps” OR “hydrodynamic separators”
12	“infiltration trenches” AND “stormwater runoff”
13	“sustainable urban drainage systems” OR “SUDS” AND “catchment management”
14	“decentralized stormwater management” AND “urban water quality”
15	“stormwater pollutant removal” OR “stormwater filtration”
16	“sponge city” AND “urban stormwater management”

Note: Each group is connected with OR.

.

The search results found 1703 different sources. Once the initial dataset was retrieved, a screening process was conducted to refine the results. The objective of this step was to remove irrelevant or low-quality records, ensuring that only high-quality peer-reviewed journal articles were considered. The filtering criteria included:

• Date range: All available years included to ensure a comprehensive analysis of historical and recent trends.
• Document type: Excluded editorial materials, meeting abstracts, corrections, reprints, and retracted publications.
• Source type: Only peer-reviewed journal articles were retained to maintain academic integrity.
• Language: Non-English publications were excluded to ensure accessibility and consistency.

The number of articles remaining after screening and filtering were 1685. After filtering, the dataset was subjected to a rigorous data cleaning process to correct inconsistencies and ensure data accuracy. Common issues encountered included duplicate author names, inconsistent author name formats, and variations in initials. These issues were manually reviewed and corrected. Few examples of data corrections:

• Merging duplicate author records such as “Shuster W” and “Shuster WD”.
• Standardizing names, e.g., “Geronimo F.K.F” was corrected to “Geronimo F.K”.
• Correcting variations in author initials, such as “Montalto F.” standardized to “Montalto F.A”.

Following data cleaning, bibliometric analysis was conducted using two specialized tools: Bibliometrix and VOSviewer. These tools allowed for statistical evaluation, citation analysis, and visualization of research trends.

The key analytical steps performed were:

• Descriptive Analysis: Evaluating the distribution of publications across years and journals.
• Co-occurrence Analysis: Identifying frequent keywords and thematic trends in the literature.
• Citation Analysis: Measuring the impact of key publications through citation frequency.
• Network Analysis: Visualizing collaborations among authors, institutions, and countries.

Bibliometrix, an R-based bibliometric analysis package, was employed for statistical analysis, including citation metrics and keyword trends. VOSviewer was used for visualizing co-authorship networks, keyword clustering, and collaborative relationships within the research domain.

To quantitatively assess the academic output and influence of a researcher, metrics such as the h-index, g-index, and m-index are commonly employed. The h-index introduced by Hirsch [32] serves as a key metric in bibliometric evaluations for assessing both the volume and significance of academic contributions [33,34]. Hence, a higher h-index implies a stronger academic influence. The g-index, developed as a measure to enhance the h-index, focuses on the overall citation impact of a set of publications [35]. Additionally, the g-index is more sensitive than the h-index and complements it well [35,36]. The m-index offers an alternative way of assessing academic performance over time by dividing a researcher’s h-index by the number of years since their first publication [36].

3. Results

The bibliometric analysis of the SQIDs literature, spanning from 1992 to 2024, distinctly highlights three periods defined by clear changes in publication rates (Figure 2). The two breakpoints, identified in the years 2008 (Pettitt’s test) and 2014 (SNHT test), signal shifts in research dynamics, driven by various scientific, technological, and policy developments. The foundational period (1992–2008) is characterized by limited research outputs, averaging 5.6 articles per year. Publications were sporadic with modest citation counts, reflecting initial explorations and emerging conceptual frameworks within SQIDs. Key research in this phase focused primarily on early experimental evaluations, basic technological developments, and the formulation of preliminary best management practices (BMPs). The modest increase in publications around 2004–2006 aligns with heightened environmental policy awareness and the increased recognition of urban stormwater impacts, particularly driven by influential reports and environmental regulations implemented during this time frame.

The second period (2009–2014) marks a notable shift in productivity, with the average annual publication count increasing substantially to 32.2. The growth starting around 2009 corresponds with global shifts towards sustainable urban water management practices, including increased adoption of green infrastructure (GI), low impact development (LID), and water-sensitive urban design (WSUD) methodologies. Policy initiatives worldwide, particularly those emphasizing climate change adaptation and urban resilience, significantly contributed to this rise. This phase also saw steady citation rates, around 3 citations per article annually, indicating a stable and recognized scholarly engagement with established methods and emerging solutions.

The third and most recent period (2015–2024) is characterized by a dramatic rise in scholarly output, averaging 126.5 articles per year. This accelerated growth began around 2015, strongly influenced by global policy actions such as the Sustainable Development Goals (SDGs), heightened concerns about climate-induced urban flooding, and increased advocacy for nature-based solutions and hybrid grey–green infrastructure. This surge in research corresponds to intensified governmental and international focus on urban sustainability, resilience frameworks, and infrastructural innovation to mitigate urban stormwater impacts effectively. Notably, this period also experienced the highest mean annual citations per article (peaking at 5.18 citations in 2017), indicating influential studies addressing novel, practical, and innovative solutions. However, subsequent years (particularly after 2020) saw a decline in mean citations per article, likely due to the rapid growth of the literature volume, diversification of topics, and the inherent citation lag common in recent publications.

The most cited documents (

Table 2. The most cited documents.

Rank	Author	Country	Paper Main Theme	GTC	GTCPY	LTC
1	Fletcher TD, 2015 [14]	Australia	Evolution of urban stormwater management terminologies and the importance of having a uniform set of terminologies to describe urban stormwater principles and practices.	1000	90.91	236.00
2	Meerow S, 2017 [37]	USA	The use of Green Infrastructure Spatial Planning (GISP) model to strategically site green infrastructure in order to maximize social and ecological resilience of urban area.	544	60.44	61.00
3	Eckart K, 2017 [38]	Canada	A comprehensive evaluation of low impact development (LID) practices, summarizing their effectiveness in mitigating stormwater impacts, while also identifying barriers to implementation and areas for future research.	434	48.22	117.00
4	Hunt WF, 2006 [39]	USA	The evaluation of bioretention systems in North Carolina for their effectiveness in reducing stormwater volume and removing pollutants under varying field conditions.	375	18.75	117.00
5	Hatt B, 2009 [16]	Australia	The evaluation of the hydrologic performance and pollutant removal effectiveness of field-scale stormwater biofiltration systems.	365	21.47	0.00
6	Davis AP, 2001 [40]	USA	The laboratory evaluation of bioretention systems for urban stormwater management, focusing on their effectiveness in removing heavy metals and nutrients through soil, mulch, and plant-based treatment processes.	332	13.28	58.00
7	He, M, 2022 [41]	China	Discussion of the potential of engineered biochar as a sustainable, multifunctional solution for wastewater treatment and stormwater management.	324	81.00	0.00
8	Berland A, 2017 [42]	USA	Discussion of the vital role urban trees can play in managing stormwater and the need to integrate them into green infrastructure strategies for better urban stormwater management.	323	35.89	33.00
9	Persson J, 1999 [43]	Sweden	Discussion of the hydraulics efficiency of constructed wetlands and ponds and their importance in urban stormwater management.	316	11.70	16.00
10	Keeler BL, 2019 [44]	USA	Provides a comprehensive review value and effectiveness of urban nature-based solutions and how they are strongly influenced by social, ecological, and technological factors.	316	45.14	16.00

Note: Country refers to the country where the institution of the first author’s paper is, GTC is global total citations, GTCPY is global total citations per year, LTC is local total citation.

) reveal pivotal research trends and critical developments within the SQIDs literature. The leading paper, authored by Fletcher (2015) [14] from Australia, received a total of 1000 citations, emphasizing a crucial shift towards standardizing terminologies within urban stormwater management. Its remarkably high local total citation (LTC) count of 236 underscores its substantial relevance within the specific SQID-focused scholarly community. Meerow’s influential work (2017) [37], from the USA, has attracted 544 citations globally, focusing on innovative spatial planning through green infrastructure to enhance both ecological and social resilience in urban areas. However, its relatively low LTC of 61 suggests its broad global impact contrasts with a more moderate influence within the specialized SQID research community. Eckart’s 2017 [38] Canadian study, which garnered 434 global citations, rigorously assessed low impact development (LID) methodologies, their practical effectiveness, barriers to adoption, and future research directions, with a notably high LTC of 117. This indicates significant resonance within the specialized SQID academic community. Collectively, the comparison highlights that while all these works have significant global influence, Fletcher [14] and Eckart [38] have been particularly impactful within the SQIDs-focused literature, indicating their foundational and extensively utilized contributions to the field.

Co-occurrence network analysis of keywords (Figure 3) reveals the thematic landscape and evolving research directions [45]. The analysis shows that among the 194 keywords that met the threshold of at least 15 occurrences, several terms emerged as central and frequently co-occurring, notably “stormwater management”, “green infrastructure”, and “low impact development”, each demonstrating both high occurrence and strong link strength across the network. These keywords occupy central positions in the visualization, indicating their foundational and cross-cutting role in the literature. The spatial clustering of terms shows distinct thematic groupings. One prominent cluster centers around policy, resilience, and ecosystem services, represented by terms such as “climate change”, “nature-based solutions”, and “governance”, reflecting a growing academic focus on sustainable planning and adaptation frameworks. Another cluster, marked by terms like “low impact development”, “SWMM”, and “simulation”, indicates a strong focus on hydraulic modeling, system design, and performance assessment of stormwater infrastructure. A third, more technically oriented cluster includes keywords such as “pollutant removal”, “heavy metals”, “biochar”, and “constructed wetlands”, suggesting detailed process-based and treatment-focused research on contaminant dynamics and media performance.

The network also includes transitionary nodes like “performance”, “runoff”, and “design” which link various thematic areas and demonstrate the interdisciplinary nature of SQID research. Temporal data embedded in the network further highlights shifting priorities over time. While earlier research tended to emphasize pollutant removal and technical aspects (e.g., “stormwater”, “removal”), more recent studies, with average publication years around 2019–2020, increasingly emphasize sustainability, adaptation, and decentralized solutions, as seen in the rise in terms such as “green infrastructure” and “low impact development”. Notably, keywords like “low impact development” and “removal” also exhibit high average citation rates, indicating that both innovative planning approaches and traditional treatment practices continue to attract substantial scholarly attention. The integration of governance and policy-related keywords, although slightly peripheral, shows a strengthening connection with core infrastructure terms, signaling the rising importance of institutional and socio-political considerations in the design and implementation of effective stormwater management strategies.

The analysis of the most frequently used Keyword Plus terms over the three designated time periods provides insight into the evolving focus and priorities within SQIDs research. In the earliest period (1995–2008), keywords such as “removal” (8 occurrences) and “runoff” (7 occurrences) were relatively common, reflecting an initial emphasis on basic functional aspects like pollutant removal and runoff control. From 2009 to 2014, a notable rise in the frequency of terms like “performance”, “runoff”, and “removal” indicates intensified attention on evaluating and quantifying the effectiveness of stormwater systems, likely driven by the need for practical validation and evidence-based decision-making in stormwater management strategies.

The most significant keyword usage surge is observed in the most recent period (2015–2024), with “performance”, “green infrastructure”, “stormwater management”, and “low impact development” showing dramatic increases in frequency. Specifically, “green infrastructure” transitioned from almost negligible usage to becoming one of the top keywords, highlighting a paradigm shift toward sustainable and nature-based approaches. Similarly, the notable rise in “climate change” occurrences—from negligible to 131—underscores heightened global concern regarding climate impacts on urban flooding and the urgency for adaptive, resilient stormwater solutions. These trends strongly suggest that contemporary research is increasingly guided by sustainability objectives (e.g., UN SDGs), policy shifts toward resilience and adaptive infrastructure, and enhanced integration of ecological considerations into urban stormwater management practices. The rise of the themes such as “stormwater management” and “climate change” are linked to the rising awareness and actions to fulfil UN SDGs and to tackle climate change and policies/guidelines adopted by many governments/institutions on SDGs and climate change.

Table 3. The most used Keyword Plus and authors’ keywords over time.

Rank	Keyword Plus	Total Frequency	1995–2008	2009–2014	2015–2024
1	Performance	300	1	22	227
2	Runoff	242	7	25	210
3	Management	190	1	17	172
4	Green Infrastructure	178	0	1	177
5	Water	168	6	20	142
6	Stormwater Management	166	0	5	161
7	Removal	154	8	25	121
8	Low Impact Development	147	0	3	144
9	Quality	146	1	16	129
10	Climate Change	133	0	2	131
Rank	Author’s Keywords	Total Frequency	1995–2008	2009–2014	2015–2024
1	Stormwater Management	388	15	52	321
2	Green Infrastructure	352	0	24	328
3	Stormwater	192	18	32	142
4	Low Impact Development	187	2	23	162
5	Bioretention	127	6	18	103
6	Water Quality	78	7	13	58
7	Climate Change	76	0	0	76
8	SWMM	75	0	3	72
9	Best Management Practices	68	6	17	45
10	Sponge City	67	0	0	67

presents an analysis of author-selected keywords over the three defined time intervals, demonstrating significant shifts in research emphasis and thematic evolution within SQIDs studies. Initially (1995–2008), authors primarily employed broad foundational terms such as “stormwater”, “stormwater management”, “water quality”, “best management practices”, and “bioretention”, indicating a strong focus on general conceptual understanding, fundamental processes, and early technical approaches to managing urban stormwater issues. Between 2009 and 2014, there was a noticeable diversification and intensification in keyword usage, particularly with increasing appearances of terms like “green infrastructure”, “stormwater management”, and “low impact development” (LID). This reflects growing research interest in practical, innovative, and sustainable approaches to urban water management, driven by increasing regulatory requirements and the need for sustainable urban planning strategies. In the most recent period (2015–2024), there was a substantial rise in the selection of keywords emphasizing sustainability, resilience, and adaptive management approaches.

The dramatic increase in the usage of “green infrastructure”, “stormwater management”, and “low impact development” demonstrates authors’ heightened focus on integrating nature-based solutions within stormwater frameworks, aligning with global sustainability agendas and climate resilience goals. Moreover, the emergence and frequent use of new terminologies like “climate change” and “Sponge City” clearly indicate growing awareness and incorporation of climate adaptation strategies in stormwater management, directly responding to intensifying urban flooding and climate-related impacts. Additionally, the frequent selection of modelling-related keywords such as “SWMM” (Storm Water Management Model) underscores an increasing emphasis on advanced analytical techniques and computational modelling to evaluate and enhance stormwater infrastructure performance. Collectively, these shifts highlight a progressive refinement of research priorities from fundamental and conventional methods towards more holistic, adaptive, and innovative stormwater management strategies, strongly influenced by global climate change discourse, technological advancements, and policy-driven sustainability frameworks.

Table 4. The most productive countries.

Rank	Country	Articles	SCP	MCP	MCP Ratio
1	USA	653	573	80	0.12
2	China	279	176	103	0.37
3	Australia	139	105	34	0.24
4	Canada	90	69	21	0.23
5	Korea	45	35	10	0.22
6	Germany	35	27	8	0.23
7	Iran	31	18	13	0.42
8	United Kingdom	31	22	9	0.29
9	Malaysia	26	18	8	0.31
10	Italy	23	15	8	0.35

Note: SCP is single country publication; MCP is multiple country publication; MCP Ratio is MCP/articles.

shows the top 10 most productive countries in the field of SQIDs, based on corresponding author data, and reveals a clear distinction between high-output countries and those leading through international collaboration. The United States stands out as the dominant country, contributing 653 articles, which accounts for 38.8% of the total publications. A significant majority of these publications (573) are single country publications (SCPs), suggesting that the USA maintains a strong internal research base with relatively fewer international collaborations (MCP share of 12.3%). This reflects both the depth of expertise and robust national funding and infrastructure supporting SQIDs research. China follows as the second most productive nation, with 279 publications (16.6%). However, unlike the USA, China exhibits a much higher proportion of multi-country publications (MCPs) at 36.9%, indicating that Chinese researchers are deeply engaged in international collaboration. This pattern highlights China’s growing integration into global research networks and its strategic efforts to build capacity and influence in stormwater and environmental engineering disciplines through cross-border partnerships.

Australia, with 139 articles (8.3%), also plays a significant role in SQIDs research. While its total output is lower than that of the USA and China, its MCP rate (24.5%) is relatively high, reflecting a well-established international research profile, especially within the Asia-Pacific region and through collaborations with leading Western institutions. Other notable contributors include Canada (90 articles, 5.4%) and Korea (45 articles, 2.7%), both of which exhibit balanced SCP and MCP distributions, indicating steady domestic productivity alongside moderate international engagement. Countries like Iran, Malaysia, and the United Kingdom—though lower in total output—show relatively high MCP percentages (41.9%, 30.8%, and 29.0%, respectively), suggesting that their contributions are strongly driven by international collaboration rather than internal research scale.

The United States clearly leads with 1753 author appearances, reflecting not only its high domestic productivity but also its widespread involvement in collaborative international research. This dominance is visually represented by dark green on the map (Figure 4), marking the highest range of productivity (231–1753). Following the USA, China (734 appearances) and Australia (311 appearances) also appear as major contributors, both shaded in green, indicating their strong and growing presence in the field, with China’s output supported by both high national funding and extensive collaboration networks. Canada (230), the United Kingdom (120), and South Korea (91) also stand out for their moderate to high author appearances, reflected in blue and purple shades on the map. This shows that while they may publish fewer total articles than the USA or China, they are active participants in international collaborations. Notably, countries like Germany, Malaysia, and Iran also appear prominently in the dataset (86, 73, and 68 appearances, respectively), indicating their emerging roles as contributors to global research efforts in stormwater management. The red-shaded countries on the map (1–20 appearances) represent emerging or occasionally contributing nations. Although their research output is limited in volume, their participation reflects the expanding global interest in SQIDs and the potential for future growth in collaboration and capacity building. For instance, countries in Latin America, Eastern Europe, and parts of Africa and Southeast Asia fall into this group, showing nascent engagement in the field.

Figure 5 illustrates the countries co-authorship analysis and reveals patterns of international collaboration, scholarly impact, and research recency in the field of SQIDs, based on 29 countries that have each contributed to at least 10 co-authored documents. The United States stands as the most connected and collaborative country, with the highest number of co-authorship links (27) and total link strength (201), demonstrating its central role in facilitating global research partnerships. Its average publication year (2017.4) suggests a long-standing and continuous contribution to the field. While its normalized citation impact is moderate, it reflects consistent and widespread collaboration across both established and emerging research nations. China also exhibits strong international connectivity, with 21 links and a total link strength of 184, placing it as a prominent collaborative hub. Its average publication year (2020.4) indicates that China’s contributions are more recent, aligning with its rapid rise in global research influence. Despite its newer engagement, China has maintained a solid normalized citation score, reflecting growing recognition of its research outputs. Australia follows closely with 19 links and a total link strength of 95, reinforcing its role as an influential and well-networked research country. Its average publication year (2017.6) and high normalized citation score demonstrate both long-term involvement and sustained impact in the field. Countries such as England, Germany, and Sweden are also notable for their collaborative ties and exceptional citation impact. Germany, for example, shows a very recent average publication year (2020.1) and the highest normalized citation impact among the leading nations, suggesting that its recent outputs are particularly influential. Similarly, Sweden, with an average publication year of 2018.6, exhibits one of the highest average citations per document and a strong normalized citation rate, highlighting the quality and resonance of its contributions. Emerging players like Iran and Malaysia are increasingly active, with growing collaborative linkages and more recent average publication years (2020.3 and 2019.1, respectively). Iran, in particular, displays a strong normalized citation impact, indicating that its collaborative work is gaining traction and scholarly visibility.

Wang M of Guangzhou University leads in publication count with 23 papers since 2016, indicating a high level of recent productivity (

Table 5. The most productive authors.

Rank	Author	Institution	Country	TC	NP	H-Index	FIY
1	Wang M	Guangzhou University	China	439	23	10	2016
2	Fletcher TD	Monash University	Australia	2046	22	15	2006
3	Deletic A	UNSW	Australia	1205	20	17	2006
4	Jia HF	Suzhou University of Science and Technology	China	1151	20	13	2012
5	Shuster WD	U.S. Environmental Protection Agency	USA	2145	18	15	2004
6	Zhang DQ	Guangdong University of Petrochemical Technology	China	429	17	10	2016
7	Hunt WF	North Carolina State University	USA	1813	16	13	2006
8	Chui TFM	The University of Hong Kong	China	728	16	12	2015
9	Wiston RJ	The Ohio State University	USA	355	16	10	2010
10	Wadzuk BM	Villanova University	USA	308	15	8	2009

Note: Country refers to the country where the institution of the author’s latest paper is located, TC is total citations, NP is number of publications, CPP is citation per publication, FIY is first issue year.

). However, Fletcher TD from Monash University stands out as one of the most impactful authors, with 22 publications and a remarkable 2046 total citations, giving him a strong h-index of 15. His early contributions (since 2006) and consistent influence underscore his foundational role in shaping the field, particularly through widely cited works on stormwater terminology and green infrastructure. Similarly, Shuster WD of the USA Environmental Protection Agency demonstrates exceptional impact with the highest total citation count (2145) from 18 publications and an h-index of 15. His work, beginning in 2004, suggests long-standing and influential contributions, particularly likely in applied, policy-oriented, and field-based stormwater management. Deletic A from UNSW is also highly impactful with 1205 citations across 20 publications and an impressive h-index of 17, the highest among all listed authors. This indicates that a substantial portion of their work is consistently well-cited, reflecting both productivity and enduring influence across topics like low impact development (LID) and urban runoff modeling. Authors such as Jia HF and Hunt WF also present strong dual profiles in both productivity and citation impact, with over 1100 and 1800 citations, respectively. In contrast, while Zhang DQ, Chui TFM, and Wiston RJ have comparable productivity (16–17 publications), their total citations are notably lower (355–728), suggesting their influence, while growing, may be more recent or focused on narrower subfields.

US EPA (United States Environmental Protection Agency) and Monash University appear as dominant nodes in the network—both centrally located and strongly connected to many institutions (Figure 6). This is corroborated by their high total link strengths (noted in the full table, US EPA with one of the highest) and extensive collaborative links across countries and disciplines. The US EPA, in particular, has served as a longstanding leader in field-based stormwater research and national-scale management practices, with earlier average publication years (typically pre-2018), reflecting its long-term involvement. Institutions such as the University of Florida and South Florida Water Management District, while slightly isolated from the central cluster, form a distinct and tightly interconnected subgroup, focusing more on regional water management and utility-based implementation. Their relatively newer average publication years (post-2018) suggest recent and possibly more applied or field-based contributions that are expanding the applied edge of SQIDs research. Other major contributors, like Beijing University of Civil Engineering and Architecture, Tsinghua University, Guangzhou University, and Tongji University, illustrate China’s strong academic presence in this space. These universities are highly interconnected and exhibit recent average publication years (~2020), indicating a rapidly expanding and currently active research footprint. Their collaboration patterns also highlight tight domestic and Asia-Pacific regional networks. Notably, Arizona State University and the University of Maryland show strong total link strength and relatively high average citations per paper, with publication averages around 2019, suggesting both collaborative breadth and scholarly impact. Similarly, Colorado State University and the University of Illinois act as important hubs in the USA network, connected with government agencies, consulting firms, and academic institutions. In terms of collaboration recency, many East Asian and European institutions—such as Wuhan University, Nanyang Technological University, and the University of Copenhagen—display brighter yellow tones, indicating average publication years post-2019, consistent with growing international engagement and investment in stormwater sustainability.

Table 6. The most productive sources.

Rank	Source	h-Index	g-Index	m-Index	TC	NP	FIY
1	Journal of Environmental Management	33	54	1.83	3112	75	2008
2	Science of the Total Environment	31	56	1.55	3226	64	2006
3	Journal of Hydrology	29	52	1.53	2753	57	2007
4	Water	26	42	2.00	2298	139	2013
5	Ecological Engineering	24	46	0.86	2291	74	1998
6	Sustainability	18	28	1.29	1004	79	2012
7	Water Science and Technology	17	31	0.53	1057	61	1994
8	Hydrological Processes	16	22	0.73	838	22	2004
9	Journal of Cleaner Production	16	29	1.46	896	33	2015
10	Landscape and Urban Planning	16	22	1.07	1703	22	2011

Note: TC is total citations, NP is number of publications, FIY is first issue year.

provides the most productive sources in the field. Leading the list is the Journal of Environmental Management, which holds the highest h-index (33) and m-index (1.83) among the sources, reflecting both sustained scholarly impact and consistent productivity since its entry into this research area in 2008. Closely following is Science of the Total Environment, with an impressive g-index (56) and the highest total citations (3226), showcasing its prominence as a multidisciplinary outlet for high-impact environmental research. The Journal of Hydrology and Water also stand out for their performance. The Journal of Hydrology demonstrates a strong h-index (29) and citation influence, whereas Water, despite being a more recent entrant (since 2013), exhibits a high m-index (2.00) and the highest number of publications (139), indicating rapid and intensive engagement with SQID-related topics. Ecological Engineering, one of the earliest contributors (since 1998), maintains a robust profile with an h-index of 24, indicating long-term relevance. In contrast, Sustainability and Water Science and Technology show differing profiles: Sustainability has a more recent focus with a higher publication count but a slightly lower h-index, while Water Science and Technology reflects longevity in the field (since 1994) but a more modest m-index (0.53), suggesting lower publication frequency or citation growth over time. Other journals such as Hydrological Processes, Journal of Cleaner Production, and Landscape and Urban Planning offer specialized contributions. Notably, Journal of Cleaner Production and Landscape and Urban Planning demonstrate high m-indices (1.46 and 1.07, respectively), despite fewer publications, highlighting their efficiency in generating impactful studies within a shorter time frame.

4. Discussion and AI Based SQIDs

The research landscape surrounding SQIDs has evolved dynamically between 1992 and 2024, shaped by scientific progress, technological development, and significant policy transformations. This bibliometric analysis provides a comprehensive overview of the current state of the art, synthesizing trends in publication volume, citation patterns, and thematic focus across three distinct phases: the foundational period (1992–2008), a phase of methodological expansion (2009–2014), and a more recent era of accelerated innovation and global alignment (2015–2024). This progression underscores the increasing academic and practical relevance of SQIDs in the context of urban water management.

A consistent rise in both publication output and citation frequency reflects growing scholarly engagement, alongside heightened societal and regulatory urgency to address stormwater pollution and urban flood resilience. Global policy initiatives—particularly the Sustainable Development Goals (SDGs) and climate adaptation frameworks—appear to have significantly influenced research trends, especially after 2015. Statistical analyses using Pettitt’s and SNHT tests identified key breakpoints in citation activity that align with major policy milestones and technological advances, affirming the field’s responsiveness to external drivers.

Keyword and thematic analyses reveal a clear evolution in research focus over time. Earlier studies concentrated on pollutant removal and runoff control, whereas recent investigations increasingly incorporate themes of sustainability, resilience, and a decentralized infrastructure. The co-occurrence network analysis highlights a shift from core technical terms such as “removal” and “bioretention” to broader interdisciplinary concepts including “governance”, “climate change”, and “nature-based solutions”. This thematic transition reflects a maturing research domain that draws not only on engineering but also on ecology, urban planning, and socio-political perspectives. Temporal keyword trends and Keyword Plus analyses further support this evolution, with the emergence of terms such as “Sponge City” and “SWMM” signaling increased regional engagement and technical sophistication through advanced modelling tools.

Patterns in authorship and international collaboration indicate a transition from nationally focused efforts to a well-connected global research community. The United States and China lead in research output; however, China demonstrates a higher level of international collaboration, while the United States maintains a strong, primarily domestic research base. Other leading countries, such as Australia, Canada, and the United Kingdom, display a balanced profile of domestic productivity and international cooperation. Meanwhile, countries such as Iran, Malaysia, and several in Latin America and Africa are emerging as important contributors, reflecting growing global engagement with SQIDs and the potential for future capacity building in underrepresented regions.

Several researchers have made foundational contributions to the field. In particular, Fletcher, Shuster, and Deletic are recognised for their work in standardizing terminology, promoting green infrastructure, and advancing low impact development (LID) methodologies. Key institutions such as the United States Environmental Protection Agency (EPA) and Monash University have played central roles in shaping and disseminating applied knowledge, as evidenced by their strong citation performance and extensive collaborative networks. In terms of publication venues, the Journal of Hydrology and Ecological Engineering continue to demonstrate sustained impact, while journals such as Water and Sustainability have emerged as rapidly growing outlets for SQID-related research.

Collectively, this analysis shows that SQIDs research has progressed from a niche technical domain into a globally relevant, interdisciplinary, and policy-oriented field. The integration of hydrological modelling, ecosystem-based design, and governance frameworks highlights the field’s growing potential to contribute meaningfully to sustainable and climate-resilient urban development. However, challenges remain in balancing technical precision with socio-political feasibility, scaling up innovative practices, and fostering inclusive international collaboration—particularly with researchers and institutions in underrepresented regions. Addressing these issues will be critical in advancing the field and realizing the potential of SQIDs as a key component of integrated urban water management strategies.

The future research scopes on SQIDs are summarized below:

(i)

Climate Change Adaptation: While sustainability and nature-based solutions have gained attention, limited research has been undertaken on how SQIDs perform under future climate scenarios. Research should assess the resilience and adaptability of SQIDs to changing rainfall characteristics, urban heat, and extreme weather events.

(ii)

Long-Term Performance: Most previous studies focus on short-term performance metrics. To fill this knowledge gap, longitudinal studies are needed to evaluate the durability, clogging potential, pollutant retention capacity, and cost-effectiveness of different SQIDs over time, especially bioretention systems.

(iii)

Smart SQID Systems: Emerging technologies, including IoT, AI, and real-time monitoring, offer opportunities to enhance the effectiveness of SQIDs. Future research should explore the development of “smart” SQIDs that can self-monitor, adapt, and optimize operations using AI.

(iv)

Policy Aspects: More interdisciplinary research is needed on the institutional and governance aspects of SQID implementation. Studies should assess policy functionalities, funding mechanisms, stakeholder engagement, and public acceptance of SQIDs.

(v)

Application to Developing Countries: The concentration of SQID research in high-income countries (e.g., USA, China, Australia) points to a gap in this research in low- and middle-income countries. Investigating context-specific challenges, design adaptations, and knowledge transfer in regions like South Asia, Middle east, Africa, and Latin America is warranted.

(vi)

Emerging Contaminants: Future work should expand beyond traditional pollutants (e.g., sediment, nutrients) to address emerging contaminants such as microplastics, PFAS, and pharmaceuticals, and explore the efficacy of different SQIDs in treating these from urban runoff.

(vii)

Decision Support Tools: It is important to develop integrated models and decision-support systems that couple hydrologic performance, pollutant removal efficiency, lifecycle cost, and environmental co-benefits for optimal SQID design and implementation.

In practice, a biofilter is composed of level/soil-moisture sensors and a controllable underdrain (e.g., valve). Control rules hold water in an internal water storage zone, pre-drain before large storms, and manage drying/wetting cycles to favor target processes (e.g., nitrification/denitrification or pathogen die-off). Shen et al. [46] evaluated the application of real time control (RTC) methods to stormwater biofilters to enhance microbial removal performance with mixed results. In a subsequent study, Shen et al. [47] introduced the BioRTC model, which allowed the effective application of the RTC applications. Mullapudi et al. [48] evaluated an RTC approach using reinforcement learning to achieve real-time control of urban stormwater systems. An algorithm was developed to train a reinforcement learning agent to operate valves in a distributed stormwater management system. In a recent study, Zhang et al. [49] tested RTC of stormwater biofilters. They examined five RTC strategies: (a) dynamic soil moisture control; (b) infiltration rate control; (c) pre-drain; (d) fully unsaturated; and (e) fully saturated. They found that dynamic soil moisture control, infiltration rate control, and pre-drain were the top three methods.

5. Conclusions

This study presents a comprehensive bibliometric analysis of the research landscape on SQIDs between 1992 and 2024. This study, through data collection from WoS, rigorous screening, and use of advanced analytical tools—such as Bibliometrix and VOSviewer, revealed crucial trends, influential authors, countries and institutions, and the evolving thematic priorities. The evolution in the field has been highlighted through the distinct phases of growth, compelled by policy shifts, scientific advances, and the increasing global concern for urban water resilience and sustainability.

The top Keyword Plus words identified were performance, runoff, management while for authors, the top keywords were stormwater management, green infrastructure and stormwater, with all the keywords having a noticeable surge starting from 2015. This noticeable shift highlights a paradigm shift towards sustainable and nature-based approaches. Additionally, the analysis revealed that bioretention systems are the most extensively researched SQIDs in the field, highlighting a strong interest from authors and researchers in this field.

The analysis shows that geographically, the top three most productive countries in the field are the USA, China, and Australia, respectively. Through high impact publications and thought leadership, influential authors and institutions—such as Fletcher (Monash University), Wang (Guangzhou University), Shuster (US EPA), and Deletic (UNSW)—have significantly shaped the field of SQID research. Additionally, journals like Journal of Environmental Management, Science of the Total Environment, Journal of Hydrology, and Water have emerged as prominent publication venues.

In conclusion, the findings on the SQID research demonstrates how the field have progressed towards policy-relevant, interdisciplinary, and innovation-driven approaches hence, positioning SQIDs as a pivotal instrument to tackle the global urban stormwater management challenges. The future research potentials on SQIDs include long-term performances under changing climate, the development of decision support system and the application of AI to enhance monitoring, and the optimization of performances.