SWOT-Based Evaluation of Nature-Based Solutions for Stormwater Resilience in Historic Urban Landscapes

Abstract

Urban flooding increasingly threatens the resilience of historic urban landscapes (HULs), where conventional gray infrastructure often fails to balance flood protection with cultural preservation. This study systematically evaluates five stormwater management models—conventional drainage, direct surface infiltration, subterranean infiltration, surface infiltration with retention at source, and stormwater retention—within the context of HULs. Using a structured SWOT (Strengths, Weaknesses, Opportunities, and Threats) analysis, combined with Internal Factor Evaluation (IFE) and External Factor Evaluation (EFE) matrices, we identify key implementation factors, performance trade-offs, and context-specific constraints. Expert surveys (n = 20) were conducted to assess the relative importance and uncertainty of SWOT elements, further visualized through an impact–uncertainty grid. The results highlight that while conventional systems offer proven reliability and regulatory alignment, they lack adaptability to climate change and ecological functions. In contrast, infiltration- and retention-based models enhance resilience, water quality, and multifunctional urban benefits but face challenges of space limitations, cost, and integration with heritage preservation requirements. The analysis underscores the need for interdisciplinary, participatory, and policy-supported approaches to embed Nature-Based Solutions into HULs. The findings provide evidence-based guidance for urban planners and policymakers seeking to reconcile stormwater management with cultural heritage protection, offering strategic pathways for sustainable and climate-resilient heritage cities.

1. Introduction

Urban flooding has become a major global concern, threatening public safety, economic stability, and urban infrastructure systems [1,2]. The risks are intensified by the interaction between climate-driven precipitation extremes and extensive hydrological modification in cities, which produces compound impacts that require urgent attention. These risks are particularly critical for historic urban landscapes (HULs), where irreplaceable buildings, streets, and cultural assets are highly vulnerable to water-related deterioration [3,4]. Protecting heritage districts from flooding thus requires approaches that address both contemporary urban pressures and the preservation of cultural identity [5].

Conventional stormwater management, based on rapid drainage through pipes and channels, was developed to quickly remove surface runoff from impervious areas [6,7]. While effective for immediate flood prevention, such gray systems show clear limitations under present conditions [8]. They reduce opportunities for local water retention and reuse, for example, through groundwater recharge [9], and accelerate the transfer of pollutants to receiving waters [10]. The rapid concentration of stormflows also raises peak discharge, intensifies downstream flooding, and disturbs natural hydrological regimes [11,12]. For historic districts with fragile fabric and dense urban form, these effects pose additional risks by amplifying waterlogging, erosion, and damage to heritage assets.

In response, sustainable stormwater management promotes integrated solutions that retain, store, and utilize rainfall within the urban fabric [13]. This represents a shift away from single-purpose drainage, toward landscape-based systems that accept temporary flooding and treat stormwater as a resource [14]. Within historic cores, such Nature-Based Solutions (NBSs) provide dual benefits: they mitigate runoff and support adaptation to climate change, while also enhancing environmental quality and cultural value [15]. Modern sustainable urban drainage systems incorporate multiple functions, including pollutant removal, ecological restoration, hydrological recovery, and stormwater harvesting [16]. They also strengthen the urban environment by improving recreation, esthetics, microclimate, and overall resilience, thus extending benefits beyond flood control [17,18]. This integrated approach aligns the built environment with natural hydrological processes [19] and is particularly relevant for heritage areas, where balancing functional resilience with cultural authenticity is essential.

Implementation requires action across scales, from regional planning to site design [20]. Models such as surface infiltration systems employ permeable pavements that allow rainfall to percolate into soil, thereby restoring natural water cycles disrupted by impervious surfaces [21]. High-permeability materials—including porous asphalt, pervious concrete, and modular paving—enable distributed infiltration that reduces runoff and supports groundwater recharge [22]. Subsurface infiltration systems channel runoff into underground structures, making them suitable for space-limited historic areas where surface use must be preserved [23]. Surface infiltration with retention models combine temporary storage with infiltration, decoupling rainfall events from downstream hydrological impacts. These systems both attenuate peak flows and sustain groundwater recharge [24]. Retention systems such as detention basins, tanks, and modular storage units regulate hydrologic volume and discharge, flattening the hydrograph and lowering flood peaks [25]. It is important to note that large-scale NBSs such as floodplain reconnection and constructed wetlands, though highly effective in regional flood mitigation, fall outside the spatial and regulatory scope of this study. The analysis focuses on site- and block-scale measures that can be integrated within compact heritage districts, where extensive land modification or floodplain restoration is not feasible. These larger-scale interventions are, however, acknowledged as complementary strategies within the broader watershed framework for urban resilience.

While many studies have explored the technical performance of NBS, few have systematically compared their strategic suitability in heritage contexts where spatial, regulatory, and cultural constraints prevail. This study aims to bridge that gap by developing a SWOT-based framework integrated with IFE–EFE matrices to evaluate five stormwater management models in HULs. The specific objectives are (1) to identify internal and external factors affecting NBS implementation; (2) to quantify their relative importance and uncertainty using expert scoring; and (3) to derive strategic pathways to embed NBS within cultural heritage conservation.

2. Method

2.1. Principles of the SWOT

In this part of the paper the authors made an attempt to answer the question about factors characterizing different models of stormwater management that determine the process of their implementation within HULs. In line with the methodology of the SWOT analysis, both positive and negative aspects of the following stormwater management models were identified (Figure 1):

• Solution Baseline: Conventional stormwater management model;
• Solution I: Direct surface infiltration model;
• Solution II: Subterranean stormwater infiltration model;
• Solution III: Surface infiltration with retention model at source;
• Solution IV: Stormwater retention model.

The foundational phase of this study commenced with the delineation and categorization of factors influencing the implementation of above five alternative solutions in heritage cities. These factors were systematically grouped into four distinct categories (S, W, O, and T). From each category, nine pivotal elements were extracted, identified as crucial for the progression of NBS in these urban settings. This selection process was enriched by a comprehensive brainstorming session among subject matter experts, meticulously moderated by the authors. The representativeness of research outcomes was ensured by the inclusion of an adequate number of experts, a critical factor in maintaining research integrity. This strategic choice balanced precision, operational workload, duration of the research, and incurred costs, as discussed in Ilchenko and Bondarenko [26]. Building on the methodology proposed by [27], the requisite number of experts (N_experts) was determined based on a pre-established error rate (ε), as elucidated in Equation (1). For this study, a total of 20 participants were selected through purposive sampling to ensure adequate expertise and representativeness. Each participant had more than six years of professional experience in stormwater management, heritage conservation, or related disciplines. The sample size corresponded to an acceptable error margin (ε) of 8.6%, ensuring statistical reliability while maintaining feasibility. Researchers and engineers were primarily selected because their technical background and professional experience enabled them to assess the hydrological, spatial, and engineering implications of alternative stormwater management models. This selection ensured that each evaluation was grounded in practical feasibility and technical soundness. This multi-perspective approach strengthened the balance between technical precision and contextual relevance. The participants had an average age of 40 years (ranging from 34 to 45 years) and an average of 8.6 years of professional experience. Their high level of expertise contributed to robust outcomes regarding the potential impact and uncertainty of the evaluated factors.

$$N_{experts}=0.5 \ast ({\displaystyle \frac{3}{\epsilon }}+5)$$

(1)

The construction of the Impact/Uncertainty Grid, based on the survey results [28], was a critical step. This grid was formulated using the arithmetic means of the ratings provided by the individual experts, thereby representing the potential impact and uncertainty associated with each element. The analysis of this grid was crucial in identifying the elements most critical for the development of alternative solutions, as well as illuminating primary areas of uncertainty.

An online survey was designed and disseminated among the participants. Respondents were asked to indicate their level of agreement on a 9-point Likert scale, ranging from 1 (“strongly disagree”) to 9 (“strongly agree”), for each thematic item. The level of agreement was then quantified as a percentage between 0% and 100%, representing the proportion of respondents who either agreed (ratings of 6–9) or disagreed (ratings of 1–4) with each statement. Accordingly, the percentage values were derived from the ratio of responses within these defined ranges (1–4 = Disagree, 5 = Neutral, 6–9 = Agree). Participants were then asked to rank the perceived significance of the themes within the four SWOT categories. The “sum” represents the cumulative numerical value of all individual ratings assigned to a given theme by respondents. The total importance score was then calculated using a weighted-ranking method, in which each participant identified the three most significant themes within each SWOT category (scores per respondent: 3 = most significant, 2 = second, 1 = third). The weighted scores were summed across all respondents to yield the total importance score for each theme. The theoretical maximum of 60 would be achieved if all 20 experts unanimously ranked the same theme as the most significant.

2.2. Description of SWOT Elements for Alternative Solutions

2.2.1. Description of SWOT Elements for Conventional Stormwater Management Solution

(1)

Strengths and Weaknesses

Conventional stormwater management in HULs adeptly preserves historical esthetics while managing water flow, earning community acceptance and aligning with preservation regulations [29]. These systems integrate seamlessly with the HULs’ infrastructure, contributing to their reliability and supporting tourism by maintaining the locale’s historical charm. Despite these strengths, conventional systems face significant limitations [30]. Their inflexibility to adapt to innovative stormwater management approaches without disturbing historical integrity poses a challenge to sustainability efforts. Space limitations inherent to HULs can restrict the size and scope of potential upgrades or new implementations [31]. Aging infrastructures may not only be less efficient but can also lead to increased maintenance costs and potential damage to historical features during upkeep or system upgrades. Environmental considerations also present a conundrum, as these systems may contribute to pollution and often fall short in enhancing ecological values or improving stormwater quality [32]. The difficulty in integrating these systems with modern, more sustainable solutions, coupled with stringent regulatory frameworks that limit the scope of modifications, further compounds the issue, making it a complex endeavor to balance historical preservation with environmental innovation.

(2)

Opportunities and Threats

These systems can serve as educational tools, promoting water conservation and heritage awareness, and can be integrated with green infrastructure to maintain the area’s historic charm [33]. Funding for cultural preservation also presents an opportunity to enhance stormwater systems while protecting HULs. Collaborative planning involving key stakeholders can lead to management strategies that support tourism and respect heritage significance [34]. However, these opportunities are challenged by the growing impacts of climate change, with increased rainfall and severe weather testing the limits of traditional infrastructure [35]. Introducing modern solutions without compromising the historical ambiance of HULs is a delicate task, often hindered by restrictive regulations, spatial limitations, and financial constraints. Resistance from communities accustomed to the status quo and vulnerabilities in aging systems add to the complexity. Moreover, reconciling technological advancements with strict environmental standards requires careful strategy to uphold heritage integrity. Balancing these elements is essential for the sustainable management of stormwater in the culturally rich settings of HULs.

2.2.2. Description of SWOT Elements for Direct Surface Infiltration Solution

(1)

Strengths and Weaknesses

Direct surface infiltration solution in heritage cities offer benefits and present weaknesses that must be carefully weighed. They utilize limited subsurface space efficiently, enhancing water quality through pollutant filtration and reducing surface runoff to prevent erosion and flooding—a significant urban concern [23]. The sustainability of these systems aligns with environmental conservation efforts, with designs that minimize maintenance visibility to maintain esthetic values [36]. They also increase climate resilience by managing heavy rainfall and contribute to groundwater recharge, showcasing adaptability for various urban conditions [37]. However, these systems are not without drawbacks. Installation costs can be substantial, especially where existing infrastructure is complex [38]. The engineering requirements are intricate, considering the unique characteristics of heritage cities. Maintenance poses challenges and incurs higher costs compared to alternative systems [39]. There Is also the risk of damaging undiscovered historical artifacts during installation, potentially leading to cultural loss. Capacity limitations may be exposed during extreme weather events, resulting in overflow and damage. Additionally, stringent regulations and permitting processes can complicate implementation. System clogging requires regular inspections, increasing upkeep efforts. The long-term effects on the structural integrity of heritage sites remain uncertain. Moreover, public awareness and acceptance are critical.

(2)

Opportunities and Threats

Direct surface infiltration solution in HULs offer opportunities to innovate sustainable urban solutions that harmonize environmental needs with the preservation of historical integrity. Access to targeted funding and grants supports the incorporation of these systems into urban renewal projects, yielding benefits that span economic, cultural, and ecological domains [40]. Public–private partnerships are pivotal, harnessing technological advancements to deliver efficient systems while engaging communities in sustainability practices that could also enhance tourism [41]. Nevertheless, these systems face challenges from the intensifying impacts of climate change, increased urbanization, and the specific constraints of HULs, which put a strain on their capacity and adaptability. Budgetary constraints, shifting regulatory landscapes, and the need for public buy-in add layers of complexity. Additionally, the variability of soil and subsurface conditions [42] affects system performance, and the potential for system failure or underperformance poses risks to both heritage preservation and public trust. Restrictions from historical preservation mandates may also limit system design.

2.2.3. Description of SWOT Elements for Subterranean Stormwater Infiltration Model

(1)

Strengths and Weaknesses

Subterranean stormwater infiltration models in HULs marry ecological functionality with cultural conservation, enhancing urban esthetics and biodiversity through integrated green spaces [43]. These systems align with Low-Impact Development principles, improving water quality via natural filtration, and bolster climate resilience by mitigating urban heat and managing rainfall [42]. They also serve educational roles, fostering public engagement in sustainable urban design and maintenance [44]. Despite their advantages, these models have weaknesses in HULs, where space is a premium, and they necessitate regular maintenance to remain functional and visually appealing. Urban flooding risks, integration complexities with existing infrastructure, and strict conservation regulations present significant hurdles. Their performance can falter under extreme weather, and the potential for inadvertent damage to historical features during works is a concern [45]. High initial costs and potential public misconceptions about their effectiveness may also hinder widespread adoption.

(2)

Opportunities and Threats

Subterranean stormwater infiltration models in HULs offer a symbiotic solution for historical conservation and sustainable urban development. These models facilitate innovative designs that respect historical sites while addressing modern water management needs [43], supported by grants that bolster such environmentally and culturally sensitive projects. They not only augment the esthetic and educational appeal of HULs but also invite community and multi-agency collaboration for sustainable practices. Additionally, these systems contribute to urban heat island effect mitigation and present new research opportunities for tailored stormwater management in HULs. However, these systems face challenges from climate change, with increased rainfall testing their capacity. Urbanization adds pressure by limiting space for system expansion. The aging infrastructure in HULs may hinder the integration of new technologies, while budget constraints and shifting regulations affect long-term feasibility and maintenance. Balancing historic preservation with modern sustainable methods, overcoming public skepticism, dealing with variable soil conditions, and safeguarding against vandalism are additional hurdles. Despite these challenges, subterranean infiltration remains a crucial component in the future-proofing of HULs, requiring strategic planning to harness its benefits fully.

2.2.4. Description of SWOT Elements for Surface Infiltration with Retention Model at Source

(1)

Strengths and Weaknesses

Surface infiltration with retention models in HULs adeptly conserve historical esthetics while offering functional stormwater management. These systems reduce flood risks and improve water quality through natural filtration, enhancing urban ecosystems and biodiversity. They also provide community spaces for recreation and education, bolster climate resilience, and promote groundwater recharge. Bioretention areas constitute a representative form of surface infiltration with retention systems [46]. These installations combine engineered soil media with carefully selected native vegetation to enhance stormwater retention, filtration, and evapotranspiration [47,48]. In the context of heritage cities, planned vegetation processes—such as root-zone uptake and rhizosphere microbial activity—play a pivotal role in pollutant removal and hydrological regulation [49,50]. Vegetated bioretention cells can also serve as subtle landscape features, compatible with the visual and cultural fabric of historic districts when designed with native or context-appropriate plant palettes. Moreover, their decentralized nature allows modular deployment within courtyards, plazas, or buffer zones, aligning well with the spatial constraints typical of historic urban cores. Yet, such models are challenged by the spatial constraints of HULs, requiring substantial surface area and regular maintenance. They may struggle under extreme weather, risking overloading and runoff. Integration with existing historical infrastructure is complex, often hindered by stringent regulations and high initial costs. Moreover, potential waterlogging and mosquito breeding demand careful oversight, and public misconceptions about their efficacy could limit support. Scalability remains a concern, with adaptations for larger areas proving difficult.

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Opportunities and Threats

Surface infiltration with retention at source offers a progressive avenue for urban water management, particularly in HULs, where it can foster a harmonious blend of historical preservation and modern sustainability. This approach not only avails funding opportunities for green urban initiatives but also enriches community spaces with educational and recreational functions. It can catalyze policy shifts toward sustainable practices and seamlessly integrate with broader green infrastructure efforts, enhancing the visual and recreational allure for residents and tourists alike. Such models encourage collaborative ventures with various stakeholders and allow for the incorporation of advanced technologies for system optimization, fostering community-based environmental stewardship. Conversely, these models are not without their challenges. The increasing severity and frequency of climatic events pose a risk of overwhelming retention capabilities. Urban expansion often results in a scarcity of space, complicating the implementation of such systems. Additionally, the integration of modern infrastructure with aging urban fabric necessitates significant revisions, often constrained by financial and regulatory limitations. Public reluctance or indifference towards new installations can also impede progress. The variability in soil and subsurface conditions must be carefully considered in system design to avoid inadvertently damaging historical features, a concern that underscores the competing priorities between conservation and contemporary water management needs.

2.2.5. Description of SWOT Elements for Stormwater Retention Model

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Strengths and Weaknesses

Stormwater retention models are innovative solutions designed to align with the preservation of HULs, offering a suite of benefits while navigating certain limitations. These systems are tailored to reduce the impact on historical areas, mitigating flood risks by controlling stormwater overflow and enhancing water quality through natural sedimentation processes. Esthetically, they can be woven into the existing landscape, providing additional value through the creation of water features and green spaces that serve multiple purposes, including recreation and community gathering. Their design supports groundwater replenishment and offers increased resilience to the challenges posed by climate change, such as heightened rainfall and extreme weather conditions. Furthermore, these models foster community engagement by involving local stakeholders in sustainable urban development and contribute to mitigating the urban heat island effect. However, the practical application of stormwater retention in HULs presents several weaknesses. The systems require substantial space, which is often a scarce resource in densely populated historical centers. Ensuring their functionality and esthetic appeal necessitates regular maintenance, a task that can be resource-intensive. There is also the risk of urban flooding if the design does not adequately account for extreme weather scenarios. Integrating these systems within aged urban infrastructure demands careful planning and can encounter complexities. Stringent regulations specific to heritage conservation may limit the extent and nature of retention installations. The initial financial outlay for such models is considerable, encompassing planning, design, and construction costs. Furthermore, if standing water is not managed effectively, there is a potential for mosquito breeding, posing health concerns. Public perception and acceptance of these systems are critical and require proactive education to foster community support. Lastly, scalability is limited, with challenges in expanding these systems to meet the needs of larger or more densely populated urban areas.

(2)

Opportunities and Threats

Stormwater retention models in HULs blend environmental stewardship with the preservation of historical sites, offering innovative urban planning solutions. These systems not only support sustainable landscape resilience and augment educational and recreational offerings but also encourage public policy leadership in sustainability. They promise esthetic enhancement, potentially increasing tourism through integrated green infrastructure and smart technology applications. Collaborative efforts with stakeholders are essential, promoting community involvement in the preservation and functionality of these systems. However, these opportunities are met with substantial threats. Climate change exacerbates the risk of system overload, and urban densification limits space for new installations. Outdated infrastructure in HULs often requires significant updates to accommodate modern systems, with financial limitations further restricting their deployment and upkeep. Fluctuating environmental and heritage regulations may complicate system design and feasibility, while variability in soil conditions poses additional technical obstacles. There is also the risk of damaging historical features during construction, and potential public resistance or indifference can slow system adoption.

In addition to the above five models, green roofs represent a valuable complementary NBS typology that enhances stormwater retention, improves microclimate, and contributes to urban biodiversity [51,52,53]. Although this parameter was not included in the expert survey due to its limited feasibility within structurally sensitive heritage cores, its conceptual relevance remains significant [54,55]. In many cases, adaptive retrofitting of non-historic or restored roof structures can integrate extensive or lightweight green roof systems without affecting the visual integrity of the historic skyline [56]. These installations can act as decentralized retention and evapotranspiration units, thereby supporting the overall hydrological balance of heritage districts when implemented selectively.

2.3. IFE-EFE Matrix

The Internal Factor Evaluation (IFE) matrix is used to measure the key strengths and weaknesses that shape the internal setting of a project. The External Factor Evaluation (EFE) matrix complements this by identifying the opportunities and threats arising from the wider environment. Together, these tools provide a structured way to translate the results of the SWOT analysis into scores that reflect both internal capacity and external conditions. This combined evaluation helps to position NBS initiatives in heritage cities within a clear strategic framework, showing where internal advantages can be matched with external opportunities and where weaknesses and risks need closer attention.

In the IFE matrix, internal factors of an organization, categorized as strengths and weaknesses, are first identified and listed. Each factor is assigned a weight (W_i), reflecting its relative importance, with the sum of all weights equal to 1.0. Subsequently, these factors are rated (R_i) on a 1 to 4 scale to indicate performance levels, with 1 denoting a major weakness and 4 a major strength. The weighted score for each factor is calculated by multiplying its weight by its rating (WS_i = W_i ∗ R_i). The total IFE score is the sum of these weighted scores (Total IFE = ∑WS_i), offering a quantitative assessment of the organization’s internal strengths and weaknesses.

Similarly, in the EFE matrix, external factors, classified as opportunities and threats, are identified. Each external factor is weighted (W_j) and rated (R_j), on the same scale as in the IFE matrix, to represent the effectiveness of the organization’s strategies in responding to these factors. The weighted score for each external factor is computed (WS_j = W_j ∗ R_j), and the total EFE score (Total EFE = ∑WS_j) is obtained by summing these scores. This score provides a measure of how well the organization is positioned in relation to the external environment.

Subsequently, the Internal–External (IE) matrix is applied to identify the strategic position of each SWOT factor. This matrix links the internal and external scores along vertical and horizontal axes to highlight the most suitable strategies. On the vertical axis, the IFE score ranges from 1.0 to 4.0. Values between 1.0 and 1.99 indicate a weak internal setting, 2.0 to 2.99 represent an average condition, and 3.0 to 4.0 reflect a strong internal capacity. The midpoint is 2.5, with scores above this level showing internal strength. On the horizontal axis, the EFE score follows a similar classification: 1.0 to 1.99 signals low external support, 2.0 to 2.99 suggests a medium level, and 3.0 to 4.0 indicates a favorable external environment.

3. Results and Discussion

3.1. Breakdown of Outcomes by SWOT Category

3.1.1. Conventional Stormwater Management Solution

In an analysis of the efficacy of conventional stormwater management solutions within heritage cities (

Table 1. SWOT analysis of the conventional stormwater management model in heritage cities.

ID	Themes	Agree (%)	Neutral (%)	Disagree (%)	Sum	Total Importance Score
S1	Cultural Preservation	100	0	0	157	38
S2	Proven Reliability	100	0	0	143	11
S3	Minimal Aesthetic Impact	95	5	0	151	29
S4	Infrastructure Compatibility	95	5	0	131	5
S5	Tourism Support	95	5	0	146	18
S6	Regulatory Alignment	60	35	5	117	5
S7	Public Acceptance	55	45	0	114	0
S8	Low Visual Intrusion	100	0	0	145	8
S9	Expertise Availability	95	0	5	131	5
W1	Limited Flexibility	95	0	5	135	5
W2	Space Constraints	100	0	0	138	18
W3	Aging Infrastructure	100	0	0	164	48
W4	Environmental Concerns	100	0	0	146	28
W5	Cost of Maintenance	75	25	0	125	0
W6	Risk of Damage to Historical Features	50	30	20	113	3
W7	Water Quality Issues	95	5	0	142	13
W8	Limited Integration with Modern Techniques	85	10	5	130	5
W9	Regulatory Restrictions	30	35	35	98	0
O1	Technological Advancements	100	0	0	151	27
O2	Educational and Cultural Engagement	100	0	0	147	15
O3	Green Infrastructure Integration	100	0	0	169	48
O4	Funding for Cultural Preservation	70	25	5	113	0
O5	Collaborative Planning	95	5	0	140	7
O6	Tourism Enhancement	90	5	5	133	5
O7	Regulatory Evolution	20	70	10	103	0
O8	Community Involvement	100	0	0	136	4
O9	Research and Development	100	0	0	153	14
T1	Climate Change Impacts	100	0	0	180	60
T2	Balancing Preservation with Innovation	100	0	0	154	22
T3	Regulatory Constraints	100	0	0	127	4
T4	Limited Space for Expansion	100	0	0	139	9
T5	Financial Limitations	40	60	0	114	0
T6	Public Resistance to Change	5	40	55	90	0
T7	Aging Infrastructure Vulnerabilities	100	0	0	161	25
T8	Technological Integration Difficulties	100	0	0	132	0
T9	Environmental Regulation Compliance	75	25	0	119	0

), ‘Climate Change Impacts’ (T1) emerged as the preeminent concern, accruing a score of 60, underscoring the criticality of adaptive measures in the face of meteorological shifts. This was closely followed by concerns regarding ‘Aging Infrastructure’ (W3) and the potential for ‘Green Infrastructure Integration’ (O3), each receiving a score of 48, highlighting the juxtaposition between existing urban decay and progressive ecological adaptation. The imperative of ‘Cultural Preservation’ (S1) also featured prominently, with a score of 38, reflecting the necessity to safeguard historical veracity within urban conservation efforts.

In the realm of conventional stormwater management within heritage cities, the most pressing issues converge around the impacts of climate change, the challenges of aging infrastructure, the potential of green infrastructure integration, and the imperative for cultural preservation. Climate change looms large, bringing increased storm frequency and intensity that traditional systems, often antiquated and designed under old norms, are ill-equipped to manage. This presents a significant threat to the preservation of irreplaceable historical structures, making adaptive strategies essential for safeguarding these cultural legacies against the vagaries of extreme weather. Concurrently, the aging infrastructure of these heritage cities, with its legacy design limitations, necessitates judicious upgrades that synergize modern water management needs with the delicate historical context. The opportunity to integrate green infrastructure emerges as a compelling solution that offers both ecological benefits, like biodiversity enhancement and urban heat island effect mitigation, and esthetic improvements aligned with the historic urban fabric. This integration becomes a strategic endeavor to maintain the urban character and support the tourism that often underpins the local economy. Above all, cultural preservation stands as the cornerstone, dictating that any stormwater management intervention must be sensitive to the historical essence of these cities, ensuring that the rich past is not only commemorated but also actively protected for future generations. These interrelated issues form the crux of developing sustainable and respectful stormwater management practices in heritage city settings.

The concurrence among respondents regarding identified strengths was notably varied, ranging from a moderate 55% to unanimity at 100%. For weaknesses, the spectrum of agreement extended from a balanced 50% to full consensus. The opportunities presented elicited a wider range of assent, from a scant 20% to complete agreement, indicating divergent perceptions of potential benefits. Conversely, the acknowledgment of threats displayed a stark range of consensus from a mere 5% to totality. Notably, ‘Regulatory Restrictions’ (W9), ‘Regulatory Evolution’ (O7), and ‘Public Resistance to Change’ (T6) were met with the lowest levels of agreement, at 30%, 20%, and 5%, respectively, suggesting significant discord or skepticism regarding these factors as barriers to implementation. This lack of agreement stems from the tension between the need to preserve historical integrity, as mandated by stringent regulations, and the imperative to upgrade infrastructure in response to climate change—a dichotomy that splits stakeholder priorities. The sluggish adaptation of regulatory frameworks to the pace of environmental challenges and sustainable technology developments further fuels uncertainty, casting doubt on the capacity of legal structures to accommodate innovative yet culturally sensitive stormwater solutions. Compounding these regulatory and technological dilemmas is public resistance, often rooted in a lack of understanding of the conventional stormwater management systems’ benefits or fear of losing the historical character and identity that heritage sites embody. Such resistance is exacerbated by varying levels of community engagement and the perceived risks of implementing contemporary management practices. Collectively, these issues underscore the complexity of achieving a consensus in the deployment of conventional stormwater management solutions.

3.1.2. Direct Surface Infiltration Model

A SWOT analysis of direct surface infiltration systems (

Table 2. SWOT analysis of the direct surface infiltration model in heritage cities.

ID	Themes	Agree (%)	Neutral (%)	Disagree (%)	Sum	Total Importance Score
S1	Preservation of Historical Integrity	100	0	0	154	21
S2	Space Efficiency	100	0	0	151	10
S3	Enhanced Water Quality	100	0	0	150	22
S4	Reduced Surface Runoff	100	0	0	145	5
S5	Long-Term Sustainability	95	5	0	162	32
S6	Low Maintenance Visibility	95	5	0	125	5
S7	Resilience to Climate Change	95	5	0	159	18
S8	Groundwater Recharge	90	0	10	129	1
S9	Adaptability	100	0	0	157	6
W1	High Installation Costs	70	10	20	111	23
W2	Complex Engineering Requirements	55	30	15	117	19
W3	Maintenance Challenges	65	15	20	121	23
W4	Risk of Damage to Historical Artifacts	55	40	5	123	18
W5	Limited Capacity in Extreme Events	65	15	20	108	14
W6	Regulatory and Permitting Hurdles	55	35	10	114	8
W7	Potential for System Clogging	80	15	5	117	2
W8	Unknown Long-Term Effects	40	45	15	109	2
W9	Public Awareness and Acceptance	100	0	0	141	11
O1	Innovation in Stormwater Management	100	0	0	158	25
O2	Funding and Grants for Sustainability Projects	90	10	0	148	17
O3	Integration with Urban Renewal Projects	95	5	0	146	15
O4	Public-Private Partnerships	100	0	0	160	23
O5	Advancements in Technology	95	5	0	153	19
O6	Educational and Community Engagement	100	0	0	143	3
O7	Tourism Enhancement	65	15	20	113	0
O8	Climate Resilience Planning	100	0	0	159	13
O9	Green Infrastructure Integration	95	5	0	149	5
T1	Climate Change and Increasing Rainfall Intensity	100	0	0	173	57
T2	Urbanization Pressures	95	5	0	139	15
T3	Technological and Engineering Limitations	50	40	10	115	3
T4	Budget Constraints	75	15	10	120	3
T5	Regulatory Changes	65	30	5	122	9
T6	Public Misunderstanding or Opposition	90	5	5	135	17
T7	Soil and Subsurface Variability	70	30	0	123	2
T8	Risk of System Failure or Underperformance	75	5	20	123	4
T9	Historical Preservation Limitations	80	15	5	133	10

) has elucidated ‘Climate Change and Increasing Rainfall Intensity’ (T1) as the paramount challenge, registering a score of 57. This concern accentuates the imperative for resilient infrastructure capable of withstanding the vicissitudes of climate variability. Proximate to this is the issue of ‘Long-Term Sustainability’ (S5), which attained a score of 32, spotlighting the necessity for enduring stormwater management strategies that coalesce with the conservation imperatives of such historically rich urban fabrics.

The consensus among the study participants delineates a pronounced affirmation of the strengths of these systems, with agreement levels oscillating between a robust 90% and unanimity. In contrast, the acknowledgment of weaknesses displayed a broader divergence, with concordance ranging from 40% to complete agreement. The prospects identified as opportunities engendered a moderately optimistic agreement ranging from 65% to totality. Conversely, the recognition of potential threats exhibited a mid-range consensus, with assent varying from 50% to 100%. Remarkably, ‘Unknown Long-Term Effects’ (W8), and ‘Technological and Engineering Limitations’ (T3) elicited the most significant contention, registering minimal agreement at 40%, and 50%, respectively. This disparity underscores the exigent need for comprehensive research into the long-term implications of these infiltration systems and a concerted effort to surmount the technological constraints that currently circumscribe their efficacy.

3.1.3. Subterranean Stormwater Infiltration Model

Within the evaluative framework of a SWOT analysis detailed in

Table 3. SWOT analysis of the subterranean stormwater infiltration model in heritage cities.

ID	Themes	Agree (%)	Neutral (%)	Disagree (%)	Sum	Total Importance Score
S1	Aesthetic Enhancement	100	0	0	144	5
S2	Preservation of Historical Integrity	100	0	0	158	38
S3	Improved Water Quality	100	0	0	156	24
S4	Low Impact Development	85	15	0	122	0
S5	Public Accessibility and Education	85	15	0	124	0
S6	Increased Biodiversity	75	25	0	121	0
S7	Climate Resilience	100	0	0	166	39
S8	Community Engagement	85	10	5	125	0
S9	Reduced Runoff and Erosion	100	0	0	156	14
W1	Space Requirements	100	0	0	126	0
W2	Maintenance Needs	100	0	0	142	27
W3	Potential for Waterlogging	65	35	0	124	8
W4	Integration Challenges	80	20	0	133	6
W5	Regulatory and Permitting Hurdles	95	0	5	144	30
W6	Limited Effectiveness in Extreme Events	85	15	0	126	8
W7	Risk of Damage to Historical Features	100	0	0	147	18
W8	Initial Cost	90	10	0	146	23
W9	Public Misconception	25	45	30	101	0
O1	Innovative Design Solutions	95	5	0	157	26
O2	Funding for Sustainable Projects	100	0	0	166	42
O3	Tourism and Educational Benefits	100	0	0	139	2
O4	Partnerships for Sustainable Development	90	10	0	144	3
O5	Urban Heat Island Mitigation	95	5	0	137	2
O6	Research and Development	95	0	5	129	5
O7	Policy Influence	95	0	5	147	17
O8	Community-Based Initiatives	75	20	5	126	0
O9	Climate Change Adaptation	95	0	5	163	23
T1	Climate Change and Increasing Rainfall Intensity	100	0	0	172	53
T2	Urbanization Pressure	100	0	0	148	19
T3	Aging Infrastructure	100	0	0	136	5
T4	Budget Constraints	100	0	0	150	21
T5	Regulatory Changes	80	20	0	141	18
T6	Conflicting Priorities	80	0	20	128	4
T7	Public Resistance or Apathy	70	25	5	112	0
T8	Soil and Subsurface Conditions	100	0	0	123	0
T9	Risk of Vandalism or Neglect	55	45	0	111	0

, the ‘Subterranean stormwater infiltration model’ employed in heritage cities has been critically appraised. ‘Climate Change and Increasing Rainfall Intensity’ (T1) has emerged as the predominant threat, scoring 53, signaling the acute need to address the escalating hydrological volatility ascribed to climatic perturbations, which is similar to the direct surface infiltration model. Not far behind, with a score of 42, is ‘Funding for Sustainable Projects’ (O2), denoting the essential role of economic investment in underpinning the model’s viability.

A granular examination of stakeholder concordance reveals a spectrum of consensus on the model’s strengths, with an assent ranging from a substantial 75% to unanimity. However, a notable variability is observed in the agreement with perceived weaknesses, with a significantly broader range of 25% to full agreement, reflecting divergent perceptions of the model’s limitations. The potential opportunities yield a more cohesive viewpoint, reverting to the 75% to 100% concurrence bracket. The threats, too, exhibit a variance in consensus, stretching from 55% to 100%. Particularly, ‘Public Misconception’ (W9) and ‘Risk of Vandalism or Neglect’ (T9) registered the lowest agreement levels at 25% and 55%, respectively. This suggests a pronounced discrepancy in the perceived understanding of the model’s functions and community engagement, coupled with concerns over the physical integrity and upkeep of the infiltration systems. These figures underscore the imperative for enhanced public outreach and educational initiatives to bridge the knowledge gap and foster a communal ethos of stewardship towards the implemented infrastructure.

3.1.4. Surface Infiltration with Retention Model at Source

In the strategic assessment of the Surface infiltration with retention model at source within heritage cities, as depicted in

Table 4. SWOT analysis of the surface infiltration with retention model at source in heritage cities.

ID	Themes	Agree (%)	Neutral (%)	Disagree (%)	Sum	Total Importance Score
S1	Historical Landscape Preservation	90%	10%	0%	136	30
S2	Flood Mitigation	90%	10%	0%	137	26
S3	Water Quality Improvement	70%	20%	10%	128	11
S4	Eco-friendly Solution	75%	25%	0%	129	19
S5	Recreational and Educational Spaces	45%	25%	30%	107	0
S6	Climate Change Adaptation	75%	15%	10%	131	9
S7	Aesthetic Enhancement	85%	15%	0%	127	19
S8	Community Engagement	60%	15%	25%	117	4
S9	Groundwater Recharge	50%	15%	35%	115	2
W1	Space Requirements	85%	15%	0%	124	19
W2	Maintenance and Upkeep	100%	0%	0%	128	26
W3	Potential for Overloading	25%	60%	15%	102	0
W4	Complex Integration	85%	15%	0%	126	24
W5	Regulatory and Planning Constraints	70%	30%	0%	121	19
W6	Initial Investment	85%	15%	0%	120	8
W7	Risk of Waterlogging and Mosquito Breeding	75%	25%	0%	119	11
W8	Public Perception	75%	25%	0%	117	13
W9	Limited Scalability	40%	55%	5%	107	2
O1	Innovative Urban Solutions	100%	0%	0%	150	25
O2	Grants and Funding for Green Projects	90%	10%	0%	129	1
O3	Tourism Attraction	90%	10%	0%	128	0
O4	Multi-disciplinary Collaboration	100%	0%	0%	160	58
O5	Policy Influence and Leadership	100%	0%	0%	146	8
O6	Educational Outreach	80%	20%	0%	127	5
O7	Climate Resilience and Sustainability Planning.	100%	0%	0%	159	20
O8	Community-Based Management	100%	0%	0%	132	2
O9	Technological Integration	100%	0%	0%	141	1
T1	Climate Change and Increasing Rainfall Intensity	100%	0%	0%	147	32
T2	Urbanization Pressures	100%	0%	0%	146	26
T3	Infrastructure Compatibility	70%	30%	0%	133	11
T4	Budget Limitations	70%	30%	0%	115	0
T5	Regulatory and Policy Shifts	100%	0%	0%	133	11
T6	Public Resistance or Lack of Awareness	35%	55%	10%	105	0
T7	Soil and Subsurface Conditions	100%	0%	0%	140	22
T8	Risk of Damage to Historical Assets	100%	0%	0%	136	12
T9	Competing Urban Priorities	100%	0%	0%	133	6

, ‘Multi-disciplinary Collaboration’ (O4) has been identified as the most salient threat, scoring 58. This underscores the complexities and challenges inherent in coordinating diverse fields of expertise, essential for the successful implementation of these systems in historically sensitive urban environments. In close succession, ‘Climate Change and Increasing Rainfall Intensity’ (T1) registers a score of 32, reflecting growing concerns over the model’s capacity to withstand the escalating hydrometeorological pressures brought about by global climatic alterations. ‘Historical Landscape Preservation’ (S2) follows with a score of 30, highlighting the critical need to integrate stormwater solutions without disrupting the esthetic and cultural fabric of heritage cities.

Stakeholder consensus on the strengths of the model displays a range from moderate (45%) to complete agreement (100%), suggesting varying degrees of recognition of the model’s benefits. The accord on identified weaknesses stretches from a minimum of 25% to unanimity, indicating notable discrepancies in perceived shortcomings. Opportunities presented by the model garnered a higher level of consensus, with agreement ranging from 80% to total concurrence. However, the acknowledgement of threats diverged considerably, with a consensus spread from 35% to 100%. Particularly, ‘Potential for Overloading’ (W2) and ‘Public Resistance or Lack of Awareness’ (T6) elicited the least agreement, at 25% and 35%, respectively. This reveals significant skepticism or uncertainty regarding the model’s capacity to handle extreme weather conditions and the societal reception of such systems. It points to an exigent need for comprehensive educational outreach and community engagement strategies to enhance public understanding and acceptance.

3.1.5. Stormwater Retention Model

In a SWOT analysis of the stormwater retention model deployed within heritage city contexts, as illustrated in

Table 5. SWOT analysis of the stormwater retention model in heritage cities.

ID	Themes	Agree (%)	Neutral (%)	Disagree (%)	Sum	Total Importance Score
S1	Preservation of Historical Integrity	100%	0%	0%	142	5
S2	Flood Risk Mitigation	100%	0%	0%	164	48
S3	Water Quality Improvement	100%	0%	0%	151	8
S4	Aesthetic Enhancements	90%	10%	0%	127	0
S5	Multipurpose Use	95%	5%	0%	133	1
S6	Groundwater Recharge Support	100%	0%	0%	138	3
S7	Adaptability to Climate Change	100%	0%	0%	163	49
S8	Community Engagement Opportunities	85%	15%	0%	134	3
S9	Urban Heat Island Mitigation	100%	0%	0%	142	3
W1	Space Requirements	75%	25%	0%	123	9
W2	Maintenance and Upkeep	100%	0%	0%	139	46
W3	Potential for Waterlogging	20%	50%	30%	98	0
W4	Integration Complexity	50%	45%	5%	111	6
W5	Regulatory Constraints	80%	20%	0%	123	17
W6	Initial Investment Costs	45%	45%	10%	107	3
W7	Risk of Mosquito Breeding	0%	40%	60%	88	0
W8	Public Perception and Acceptance	100%	0%	0%	143	40
W9	Limited Scalability	45%	55%	0%	111	1
O1	Innovative Urban Solutions	0%	5%	95%	132	25
O2	Funding for Sustainable Initiatives	75%	25%	0%	126	15
O3	Educational and Recreational Enhancements	50%	40%	10%	111	0
O4	Policy Leadership in Urban Sustainability	90%	10%	0%	134	29
O5	Green Infrastructure Integration	95%	5%	0%	133	16
O6	Tourism Appeal	45%	50%	5%	110	0
O7	Collaborative Partnerships	85%	15%	0%	128	19
O8	Technological Advancements	60%	40%	0%	116	6
O9	Community-Based Environmental Stewardship	80%	20%	0%	127	10
T1	Climate Change Impacts	100%	0%	0%	151	31
T2	Urban Development Pressures	100%	0%	0%	152	33
T3	Aging Infrastructure	80%	20%	0%	123	0
T4	Financial Constraints	45%	40%	15%	108	0
T5	Regulatory and Policy Changes	100%	0%	0%	152	35
T6	Public Resistance or Indifference	40%	45%	15%	106	0
T7	Soil and Subsurface Conditions	85%	15%	0%	130	2
T8	Risk of Damage to Historical Features	95%	5%	0%	132	5
T9	Competing Priorities	100%	0%	0%	148	16

, the theme of ‘Adaptability to Climate Change’ (S7) emerged as the primary threat, achieving a score of 49. This delineates the growing exigency for these systems to be versatile in the face of evolving climatic conditions, particularly pertinent in areas steeped in historical significance. Closely trailing this concern was ‘Flood Risk Mitigation’ (S2), scoring 48, underscoring the pivotal role of these models in safeguarding heritage sites from the escalating threat of urban flooding. ‘Maintenance and Upkeep’ (W2) followed with a score of 46, highlighting the perennial challenge of sustaining the operational efficacy and esthetic integrity of these systems. Additionally, ‘Public Perception and Acceptance’ (W8) notched a score of 40, reflecting the critical influence of societal attitudes on the successful integration of these models.

For strengths, the consensus was relatively high, ranging from 85% to 100%. This suggests a general agreement on the benefits of the Stormwater retention model, such as its efficacy in flood risk mitigation and its adaptability to climate change. The high degree of accord here implies a shared understanding of the model’s intrinsic value in preserving the historical and ecological integrity of heritage cities. The near-unanimity in some strengths indicates a collective recognition of certain indisputable benefits that the model offers, reinforcing its relevance and utility in the context of urban heritage conservation. However, the spectrum of agreement diverged significantly when stakeholders assessed weaknesses and opportunities, spanning from 0% to 100%. This broad range indicates a deeply polarized perception, where some stakeholders might view certain aspects as critical weaknesses or lucrative opportunities, while others may not perceive them as significant. For instance, aspects like ‘Maintenance and Upkeep’ may be seen as a trivial concern by some but as a major challenge by others. Similarly, the potential for ‘Innovative Urban Solutions’ might be highly valued by certain stakeholders, yet seen as irrelevant or unfeasible by others. This polarization could stem from diverse backgrounds, priorities, and experiences among stakeholders, leading to varied assessments of what constitutes a weakness or an opportunity. The agreement on threats also exhibited a wide range, from 40% to 100%. This suggests a more varied perception of the risks associated with the model. While some threats like ‘Adaptability to Climate Change’ are almost unanimously recognized, others have more divided opinions. This could be due to differences in how stakeholders perceive the immediacy and impact of certain threats, or it could reflect varying levels of optimism about the model’s ability to mitigate these risks.

3.2. IFE-EFE Matrix

The Internal–External (IE) matrix (Figure 2) is used to link the internal and external factors of the study. In this case, the IFE score highlights strong technical knowledge and local support for NBS. The EFE score shows pressure from rising flood risk and policy shifts. When plotted, the matrix places the project in a zone where strengths can be used to capture new policy and funding opportunities, while also reducing limits from cost and maintenance gaps.

3.2.1. Internal Factor Evaluation (IFE)

The IFE score is 2.900 (

Table 6. Internal Factor Evaluation (IFE) and External Factor Evaluation (EFE) matrix results for NBS implementation in heritage cities.

Theme	Weight (%)	Rate	IFE	Sum-IFE	Theme	Weight (%)	Rate	IFE	Sum-IFE
S1	6.058	4	0.242	2.900	O1	6.238	4.000	0.250	2.797
S2	5.978	4.000	0.239		O2	5.606	4.000	0.224
S3	5.144	4.000	0.206		O3	6.810	4.000	0.272
S4	5.382	3.000	0.161		O4	5.902	4.000	0.236
S5	6.514	4.000	0.261		O5	5.330	3.000	0.160
S6	6.058	4.000	0.242		O6	5.902	3.000	0.177
S7	5.879	4.000	0.235		O7	6.475	4.000	0.259
S8	6.892	4.000	0.276		O8	5.942	4.000	0.238
S9	5.541	3.000	0.166		O9	5.863	4.000	0.235
W1	5.045	2.000	0.101		T1	5.606	1.000	0.056
W2	5.323	2.000	0.106		T2	5.645	1.000	0.056
W3	5.382	2.000	0.108		T3	5.053	2.000	0.101
W4	4.826	2.000	0.097		T4	5.942	1.000	0.059
W5	4.667	2.000	0.093		T5	5.073	2.000	0.101
W6	5.919	1.000	0.059		T6	4.244	2.000	0.085
W7	5.601	2.000	0.112		T7	4.619	2.000	0.092
W8	5.084	2.000	0.102		T8	5.053	2.000	0.101
W9	4.707	2.000	0.094		T9	4.698	2.000	0.094

). This value is in the “average” range but close to the “strong” level. It shows that NBS projects in historic areas have a supportive internal setting. Strengths include S5 and S8. Weaknesses are present but less dominant, such as W6.

The result suggests that internal capacity is solid. These strengths can be used to involve local communities and heritage managers, making NBS more effective and acceptable. At the same time, the known weaknesses must be reduced. A clear step is to design common indicators to measure NBS benefits. These can be adapted to historic sites with different social and physical conditions. Modern tools like GIS and remote sensing can support this work by providing data on runoff, green cover, and cultural landscape change. Pilot projects in selected streets or courtyards can test methods and show cost, flood reduction, and social gains. Results from these pilots will help refine future plans. In addition, changes in planning codes and urban policy are needed to recognize the full value of NBS services. By combining strong internal support with targeted improvements, NBS can gain more stable ground in heritage cities. This approach helps keep projects resilient, culturally sensitive, and responsive to shifting local needs.

3.2.2. External Factor Evaluation (IFE)

The EFE score is 2.797 (Table 6). This shows a moderately favorable external setting. Key opportunities include O3 and O7. At the same time, threats exist. These include T1, T2, and T4. Because the score is closer to 3.0 than to the midpoint of 2.5, the prospects for NBS are positive. To make use of this, planners can link NBS projects with public forums, workshops, and exhibitions. Partnerships with schools, heritage groups, and NGOs can build stronger awareness of stormwater risks and show how NBS can address them. Visible installations—such as rain gardens or permeable squares in historic streets—can also act as education sites and strengthen public acceptance.

At the same time, the score warns of risks. One priority is to show, through local data, that NBS reduces runoff, adds biodiversity, and protects cultural assets more effectively than alternatives. Joint research and pilot comparisons can highlight these advantages. Cross-sector alliances are also needed to reduce organizational barriers. Clear rules for cooperation and training in conflict management can improve team efficiency. Diversifying funding is essential. Beyond city grants, NBS projects can seek private sponsors, joint ventures, and international heritage or climate programs. Effective proposals and community-based campaigns can widen financial support. Finally, adopting cost-efficient design and maintenance will ensure limited resources deliver maximum benefit.

3.3. The Impact/Uncertainty Grid

The analysis of impact and uncertainty led to the development of a dependency matrix (Figure 3). This tool shows how each factor affects NBS in historic districts and how predictable it is. Several strengths (S8, S5, S1, S2, S9) and opportunities (O1, O3, O7, O6, O9, O4, O2) have strong impact but are also predictable. Because of this, they are not treated as high-risk strategic areas. Their role is important but relatively stable. By contrast, factors such as S6, S7, O8, and W7 stand out. They appear in the dark red zone of the matrix, meaning they have both high impact and high uncertainty. Expert input confirms that these elements could strongly shape NBS outcomes in heritage areas. For example, uncertainty in maintenance capacity (W7) or community acceptance (S6, S7) may shift project success in different directions.

3.3.1. Strength + Opportunity (SO) Strategy

The SO strategy focuses on S6 and S7 with O8. This integration creates a pathway for advancing NBS in historic districts where stormwater challenges are pressing. Interdisciplinary cooperation allows planners, ecologists, legal specialists, and heritage experts to jointly frame policies that guide NBS application. Within this process, the legal system can serve as a testing ground where new approaches are introduced under controlled conditions, with the results informing future adjustments to regulations.

Community engagement is equally critical. By embedding residents, cultural historians, and local organizations in the design process, NBS initiatives can better reflect cultural traditions and local needs. Social research methods, including surveys and participatory workshops, provide insight into community expectations and ensure that interventions are both technically feasible and socially acceptable. The result is not only improved stormwater performance but also stronger cultural fit and long-term stewardship.

The legal framework provides another layer of support by mandating participation and safeguarding inclusivity in decision-making. Digital platforms and interactive tools can amplify public voices, allowing feedback to be collected and integrated into urban planning and policy. This reinforces the legitimacy of NBS interventions and ensures that they respond to both community values and legal standards.

When viewed together, these elements point to an integrated approach. Cross-sector committees can oversee project development, resolve conflicts, and ensure compliance with sustainability and heritage goals. Co-design becomes a central practice, bringing interdisciplinary expertise and community knowledge into a single planning process. Policy revisions, in turn, can accommodate the adaptive character of NBS and introduce incentives such as grants or tax benefits for community-led projects. In this way, the SO strategy supports the expansion of NBS in heritage cities by linking technical strength, social inclusion, and regulatory backing into one coherent framework.

3.3.2. Weakness+ Opportunity (WO) Strategy

The WO strategy focuses on turning the weakness of high resource demand (W7) into an opportunity by leveraging supportive laws and regulations (O8). Resource intensity often limits the large-scale adoption of NBS in heritage cities, yet a sound regulatory framework can help transform this constraint into a driver of innovation and efficiency. By linking resource optimization with legal support, NBS projects can be designed to balance heritage conservation goals with sustainable stormwater management.

One pathway is to strengthen the legal framework so that resource-efficient practices are encouraged and rewarded. For example, regulations can provide tax incentives for the use of local materials, or subsidies for adopting sustainable construction methods. Streamlined approval processes can also reduce administrative costs and delays, ensuring that limited resources are used directly for implementation rather than being absorbed by bureaucracy. In this way, laws and policies not only set rules but also act as instruments for improving efficiency.

Public–private partnerships represent another key opportunity. Supportive legislation can create conditions where private investment complements public funding, while also encouraging collaboration with non-profit organizations. Such partnerships bring innovation and financial capacity that can reduce the burden of resource intensity in heritage projects. Community involvement, backed by regulatory support, can further extend this approach by fostering shared responsibility for NBS development and maintenance.

An integrated strategy requires both technical and social measures. Resource mapping at the local level can identify underutilized assets, while policies can ensure these resources are prioritized in NBS projects. Capacity building and education programs can strengthen stakeholders‘ knowledge of resource management and connect them to the legal tools available. At the same time, monitoring and reporting requirements can enforce accountability, with penalties for inefficiency and rewards for exemplary practice.

By reframing resource intensity as a challenge that can be addressed through supportive laws, heritage cities gain a clear path forward. This approach ensures that NBS initiatives are not only technically effective but also resource-efficient, legally compliant, and financially sustainable. The result is a planning environment where weaknesses are minimized and opportunities are maximized, supporting the long-term integration of NBS into historic urban landscapes.

3.4. Theoretical Integration and Practical Implications

The outcomes of this study correspond closely with a growing body of literature demonstrating the effectiveness of NBS in enhancing urban stormwater resilience while preserving socio-cultural and heritage values. Previous systematic analyses have affirmed that NBS can deliver compound hydrological, ecological, and climatic benefits. Aghaloo et al. [13] synthesized evidence that NBSs outperform single-function gray systems by coupling runoff attenuation, pollutant removal, and ecosystem recovery. Similarly, Herath and Bai [17] emphasized multifunctional green infrastructure as a critical instrument for sustainable urban transformation, highlighting co-benefits such as recreation, microclimatic regulation, and social cohesion. These findings are consistent with the present results, which indicate that infiltration- and retention-based models possess superior adaptive capacity and multifunctionality compared with conventional drainage structures.

Recent regional investigations further substantiate the integration potential of NBS in high-density and heritage-sensitive settings. Wang et al. [10] reported that strategic deployment of NBS within compact urban fabrics requires careful alignment between hydrological performance and spatial–cultural constraints. Comparable conclusions were drawn by Fu et al. [3] and Salazar et al. [4], who demonstrated that heritage assets exhibit compound vulnerabilities under climate-driven flood regimes and thus necessitate context-specific, adaptive management approaches. The current SWOT-IFE-EFE framework extends these perspectives by offering a structured quantitative tool that explicitly incorporates regulatory, spatial, and social limitations unique to historic urban landscapes.

Wang et al. [57] introduced an artificial-intelligence-driven bibliometric and semantic analysis of NBS research, revealing emerging thematic clusters in resilience assessment and adaptive planning. The current study builds upon these insights by operationalizing those conceptual trends into a decision-support framework. Liu et al. [58] proposed a decentralized coupled gray-green infrastructure model for historic districts, demonstrating that integrating infiltration, storage, and conveyance processes can achieve resilience gains with cost efficiency. The SWOT and IFE-EFE analyses presented here corroborate those results, revealing similar advantages for infiltration- and retention-based systems under constrained heritage conditions.

At the strategic level, Liu et al. [59] emphasized that successful NBS planning in heritage cities depends on cross-sector collaboration and the alignment of ecological and cultural objectives. This conclusion parallels the SO-strategy identified in the present work, which couples technical strengths with participatory governance.

From a practical and engineering standpoint, the combined SWOT-IFE-EFE approach delivers actionable guidance for planners and engineers. The framework enables identification of feasible NBS typologies that achieve hydrological efficiency without compromising heritage integrity. In engineering design, internal–external evaluation assists practitioners in prioritizing system types according to site constraints and conservation regulations. For instance, subsurface or modular retention systems with high composite scores can be prioritized for narrow alleys and courtyards where minimal surface alteration is required. The quantified scoring also supports phased implementation and cost allocation, allowing municipalities to pilot smaller interventions before district-wide replication. The impact-uncertainty grid highlights variables—such as maintenance reliability, stakeholder participation, and regulatory support—that warrant targeted technical or institutional interventions, informing the formulation of adaptive maintenance and performance-tracking mechanisms. Furthermore, the reproducible structure of the framework facilitates integration into urban drainage guidelines, GIS-based planning tools, and decision dashboards, providing an evidence-based method to reconcile resilience enhancement with heritage preservation in practice.

4. Conclusions

The comprehensive SWOT analysis of NBS in HULs, as illuminated by the IE matrix and impact/uncertainty grid, culminates in a nuanced understanding of the strategic positioning and potential pathways for the implementation of NBS. The synthesis of the Strengths, Weaknesses, Opportunities, and Threats, alongside the internal and external evaluations, has elucidated both the challenges and prospects inherent in integrating NBS into HULs.

The significant strengths identified, such as ‘Reconnecting Humanity with Nature’ and ‘Integration of Multiple Values’, highlight the profound impact NBS can have in enhancing both the ecological and cultural fabric of heritage cities. These strengths are pivotal in redefining urban spaces as conduits for environmental sustainability and cultural preservation. However, the analysis also underscores the necessity of addressing key weaknesses, notably the challenges in quantifying and understanding the full spectrum of NBS ecosystem services. These shortcomings, if unaddressed, could potentially undermine the efficacy and acceptance of NBS initiatives. In the realm of opportunities, the growing recognition and support for NBS, alignment with existing policies, and the heightened environmental awareness present fertile grounds for the expansion and deeper integration of NBS. These opportunities, coupled with a strategic approach to overcoming threats such as insufficient funding, competition with alternative approaches, and organizational challenges in interdisciplinary work, form a robust framework for the advancement of NBS in heritage cities. The strategic approaches developed through the Strength + Opportunity (SO) and Weakness + Opportunity (WO) strategies further reinforce the potential of NBS. These strategies emphasize the importance of interdisciplinary collaboration, community involvement, resource optimization, and legal support in maximizing the impact of NBS.

The SWOT analysis of NBS in heritage cities presents a dynamic and multifaceted perspective. It not only identifies the key elements that contribute to the successful implementation of NBS but also highlights the critical areas that require attention and improvement. As urban landscapes continue to evolve, the integration of NBS stands as a testament to the possibility of creating sustainable, resilient, and culturally rich urban environments. The strategic insights gained from this analysis provide a roadmap for policymakers, urban planners, and stakeholders to effectively navigate the complexities of implementing NBS in heritage cities, ensuring their longevity and relevance in the face of changing urban dynamics and environmental challenges. The future of urban development in heritage cities, therefore, lies in embracing the holistic, adaptable, and integrative nature of NBS.