Beyond hydrologic benefits: post-occupancy evaluation of the Sponge City Construction in China, a case study of the Quyuan Park, Changde

The worldwide urbanization process has resulted in increased impervious surfaces and disruption of natural hydrological processes (Goonetilleke et al. 2005; Burns et al. 2012; Fryd et al. 2013; Fletcher et al. 2014). These city syndromes have gradually emerged in Chinese urbanization in recent decades (Xia et al. 2017). Rapid urbanization in China has boosted the national economy and also increased risks of flooding, water pollution, water resource shortages, and water ecology deterioration, causing negative impacts on resident assets and the urban environment (Lyu et al. 2016; Chan et al. 2018; Wang 2018).

In order to alleviate water-environmental problems and explore a contemporary urban stormwater management paradigm, the Chinese government launched the Sponge City policy in 2013 (Yin et al. 2022). The Sponge City Construction (SCC) program was promoted by the Ministry of Housing and UrbanRural Development, the Ministry of Finance and the Ministry of Water Resource, with a series of top-down policies, local regulations, and implementation standards (MoHURD 2014a). Thirty cities were selected as the first-round pilot cities in 2015 and 2016, with an average construction area of 31.3 km² (MoHURD 2014b; Xia et al. 2017). In the second round, an additional 15 pilot cities were selected for SCC in 2022 (Yin et al. 2022). The SCC initiative has been promoted for a decade, resulting in extensive practical experience and knowledge from numerous implementations.

SCC was originally proposed to address water-environmental problems, with the philosophy of building a nature-based solution of ‘infiltration, detention, retention, purification, utilization and discharge’ (MoHURD 2014b; Chan et al. 2018; Yin et al. 2021). In the current national-provincial-municipal guidelines and manuals for SCC, the breakdown and threshold of hydrological indicators (e.g. volume capture ratio of annual rainfall) have become a substantive focus (Li et al. 2017; Yin et al. 2021). Therefore, hydrological benefits were largely investigated to measure the effectiveness of cases based on various hydrological and hydraulic modeling (Li et al. 2020a, 2020b; Zhai et al. 2021). However, the wide-ranging influence of SCC projects is complex due to the interaction between public perception, civil infrastructure and urban-built environment. Examining SCC solely from a hydrological perspective is incomplete as it overlooks diverse ecological, social, and economic impacts. At the same time, regulations at all hierarchies require comprehensive feedback from multiple sources to be supplemented and improved rather than rigid hydrological monitoring results. Thus, a comprehensive evaluation for assessing landscape and human well-being factors of implementation, which is lacking in current multi-level SCC guidelines, remains to be explored.

SCC practices are largely implemented in green spaces (so-called spongy green space (SGS)) which are public and multi-functional. SGS, firstly, has the ‘sponge’ impact due to its facilities or techniques with rainwater infiltration and retention capacity. Secondly, SGS retains its function as a green space with ecological and recreational benefits (Chen et al. 2019; Zhou & Tan 2024). SGSs mostly serve a broad citizen group, high usage frequency, and are directly managed by the local government, thereby becoming the focus subject of this study. We posit that users perceive the space as being improved due to its ‘sponge’ functions or they may see the changes as a negative effect or might have gone largely unnoticed by them. Although numerous studies have been conducted in recent decades focusing on SGS effects by practical evidence and modeling (Liang et al. 2020a, 2020b; Yang et al. 2021; Hou et al. 2022; Xu & Cheng 2023), the impact on citizens' daily experience of these spaces has been rarely explored under this ‘sponge-green space’ hybrid model.

The objective of this study is to evaluate the public perception of SGS in a selected SCC project. Experts, who have diverse education and industry backgrounds, were invited to gain insights into indicators’ selection. We then evaluated the public feedback from questionnaire participants and interviewees based on a post-occupancy evaluation (POE) research framework.

The rest of this paper is organized as follows: Section 2 collects the literature review, Section 3 introduces the study area and methodology, Section 4 presents the results, Section 5 discusses the implication contribution, reflection, and limitations, and Section 6 presents the conclusions.

The initial vision and current regulation alignment for SCC centered on the hydrological benefits have received significant attention. Existing literature on SCC primarily focuses on hydrological and hydraulic performance, measured through indicators such as runoff volume reduction, peak flow control, and water quality improvements (Xu et al. 2017; Randall et al. 2019; Hou et al. 2022; Xie et al. 2022; Chikhi et al. 2023; Xu & Cheng 2023). These studies provide robust quantitative data but largely overlook the socio-ecological dimensions of SCC projects, particularly their impact on community well-being and public perception (Qi et al. 2021a, 2021b). Under the combined themes of ‘SCC’, ‘Public Perception’, and ‘POE’, the author identified only a limited number of studies. Some studies have focused on the public perception of willingness to pay for the SCC brand (Wu et al. 2023; Zhang et al. 2023). Some studies have taken a broader approach by considering the public perception of green spaces in general rather than specifically targeting SGS (Chen et al. 2019; Chen et al. 2020; Zhao et al. 2022; Zhou & Tan 2024). For instance, while studies like Zhou & Tan (2024) and Zhao et al. (2022) discuss what the attributes of public perception toward urban green spaces are and how they perceive them, they do not narrow to a specific evaluation of SGS or the particular socio-ecological implications of SCC interventions. Therefore, the application of POE to SCC projects remains scarce, particularly in the context of SGS. Addressing this gap, our study focuses on developing a tentative POE framework that incorporates both quantitative and qualitative dimensions, thus bridging technical performance metrics and user-centered evaluations. Previous research on POE offers references for the selection of indicators and the determination of their weights that can be adapted to case studies (Zhang et al. 2019; Qi et al. 2021a, 2021b).

To address the multidimensional nature of POE in SCC projects, we adopt the analytic hierarchy process (AHP) and fuzzy comprehensive evaluation (FCE) as our primary analytical methods. Both approaches have been successfully applied in previous studies to evaluate complex decision-making scenarios involving multiple criteria and stakeholders. The AHP is a measurement method that uses ratio scale factors for pairwise comparison, enabling the making of a judgment or priority decision after weighting several criteria (Saaty 1987, 2001). It is widely used in various fields which require decision-making and index weighting in evaluation processes (Xu et al. 2019; Colak et al. 2020; Du et al. 2020; Ruiz et al. 2020). In the context of green spaces, AHP has been employed to prioritize factors such as ecological benefits, recreational value, and user satisfaction. For example, Li et al. (2020a, 2020b) utilized AHP to assess the relative weights of various indicators to identify priority areas for green infrastructure planning. Ding & Zhang (2021) used AHP and life cycle costing to evaluate the environmental and economic benefits of various types of SCC projects. By applying AHP in this study, we aim to systematically determine the weights of five aspects: (1) water management; (2) ecological environment; (3) service management; (4) space design; and (5) user perception. This ensures a balanced and objective assessment of the diverse factors influencing the public perception of SGS. FCE is an evaluation method based on the fuzzy set theory, which is an ideal complement to AHP for handling situations where there is uncertainty or vagueness (Van Laarhoven & Pedrycz 1983). Studies such as Chen et al. (2023) have applied FCE to evaluate urban infrastructure projects, incorporating both expert opinions and public feedback. In this study, FCE allows us to aggregate public feedback and expert evaluations into one POE framework, addressing the qualitative aspects of user perception that are often overlooked in technical assessments.

The Quyuan Park was selected to conduct the POE for three reasons: (1) Changde is a pilot city in the first-round SCC promotion, which provides a possible knowledge foundation for citizen awareness and our investigation of the Quyuan Park; (2) the Quyuan Park ranks high in terms of local popularity and usage frequency, which raised good opportunities for questionnaires and face-to-face interviews (Ye 2017); (3) the SCC retrofit of the Quyuan Park was completed early as a local pilot project and the site conditions have remained stable since then.

Assigning criteria factor layers and corresponding weights within an AHP model is somehow a subjective process as this strictly depends on the objectives of the researchers, the knowledge bias from experts and the surveying of related literature (Saaty 2001). Therefore, we reviewed existing criteria-related studies and considered the diversity of the experts' backgrounds as possible (Kuller et al. 2018a, 2018b; Li et al. 2018; Xu et al. 2019; Xiang et al. 2022; Yang et al. 2022; Lacroix et al. 2024). In this study, a three-layer hierarchy was applied (Table 1). Five sub-criteria and 33 indicators were extracted based on SCC documents or other SGS evaluation research, which considered official principles and proved effective indicators (MoHURD 2018; Li et al. 2019; Qi et al. 2021a, 2021b; Viti et al. 2022; Xiang et al. 2022; Yang et al. 2022; Xu et al. 2023). Seven experts were invited to score (Supplementary material 1.1, 1.2), including five researchers and two landscape architects, in order to obtain the weights of the indicators. The researchers, two Chinese and three international, focus on stormwater management and Sponge City (SC) research with diverse backgrounds in landscape architecture, hydrology, and environment engineering. The two landscape architects from China have front-line experience in the SCC project design and construction (Supplementary material, Table S1).

FCE quantifies various evaluation factors into fuzzy sets and then uses fuzzy operations to obtain a comprehensive evaluation result (Shariat et al. 2019; Park et al. 2020; White et al. 2021). The questionnaire was designed based on the positive description of indicators (Supplementary material S2.1 and S2.2). Each question offers five response options on a 5-point Likert scale: ‘Strongly agree,’ ‘Agree,’ ‘Neutral,’ ‘Disagree,’ and ‘Strongly disagree,’ corresponding to scores from 5 to 1, respectively. Demographic questions and two open-ended questions were integrated into the questionnaire. After questionnaire collection, the weights of indicators determined by AHP are applied to obtain the FCE calculation result.

The population size of 50,000 for the residential community surrounding the study area was estimated using census data and demographic reports from the local planning authority, forming the basis for calculating representative sample size. Following standard sampling formulas (with z = 1.44, p = 0.5, and c = 0.05), a theoretical sample size of 207 was determined. The return rate is another important factor influencing validity. Generally, a 70% return rate is the baseline for a successful survey, while a 75% return rate is preferred. In this study, all questionnaires were distributed on-site on a case-by-case basis on the acceptance of respondents, the recovery rate was around 95%. To ensure the randomness and validity of the respondents, the questionnaires were distributed at different areas within the park, from 10:00 to 16:00 on different days of 2 weeks in December 2023 and January 2024. The time span, however, excluded early morning and late evening visitors, which may have limited the representation of users with different park usage patterns and introduced a degree of sampling bias. Considering the convenience of questionnaire collection, the digital questionnaire was uploaded to the Wenjuanxing platform and the QR code was generated. Respondents could directly scan the QR code via mobile phones and fill in the questionnaire on-site. In order to prevent the QR code from spreading incorrectly, we set restrictions for the questionnaire in terms of time and equipment location to ensure the validity of the respondents. In total, 210 questionnaires were distributed, the valid rate was 95% with 204 valid surveys returned.

Generally, classic interview methods include structured interviews, semi-structured interviews, unstructured interviews, and focus group discussions (Bolderston 2012; Galletta & Cross 2013). The SSI is an intermediate form between a rigorous fully-prepared question style and no question list ‘freestyle’ (Bolderston 2012; Qi et al. 2021a, 2021b). The guideline for SSI partly provides an indicative orientation for interviewees so that interviewers gather key information in relatively relaxed circumstances. In this study, we set up the last question in the questionnaire to ask respondents if they would like to join an SSI and leave contact information. After a second confirmation, interviews were conducted both face-to-face at the site or by telephone afterward, given the reference of the SSI question list (Table 2). Our expectation is to delve deeper into respondents' detailed descriptions of the Quyuan Park and their personal understanding and perceptions of SCC following the completion of the questionnaire. All participants also agreed on the conduction of the research. All data were used anonymously.

In the service management category, facility maintenance had the highest weight (0.0669) and commercial facilities (0.0099) had the lowest among all indicators. In water management, water drainage (0.0382) and water retention and detention (0.0372) were the most significant, while water purification had the lowest weight (0.0138). For the ecological environment, waterbody protection (0.0463) and plant growth (0.0436) ranked highest. The space design category showed the least variation between indicators, with elevation design (0.0404) and facility layout (0.0380) scoring relatively higher. In the user perception category, the education effect (0.0437) and the livability of surrounding places (0.0424) were identified as the most important.

According to the open-ended question answers, 11 expressed willingness to participate in the SSI. Overall, participants were satisfied with the design and planning of the Quyuan Park, viewing it as a public space that provides the possibility of daily contact with green space to the respondents. Local people from Changde are bonded with this park due to its history, as one interviewee noted:

The Quyuan Park is regarded as a park for all as it serves as a space for all age groups, given its multi-functionality. Many functions were mentioned by the respondents, such as walking the dog, social interaction, and also playing with their children.

The way people use the Quyuan Park does not link to the SC concept. During the interview, there was only one respondent who was aware that this park is one of the pilot projects in the SCC program. Despite the Quyuan Park being designed as a pilot project in the SCC program, locals are not aware of specific hydrological benefits when using the park. One reason is that people lack knowledge and perception of the SC concept. One respondent mentioned that whether the park is designed as an SGS would not influence the way how he uses it:

However, it has been discovered that people use this park as a recreational green space and is not perceived as an SGS:

People also show interest in the SCC. One respondent said:

The Quyuan Park invites people from all age groups, but this park is particularly popular with housewives retired staff, and their children. Children-friendly facilities should be more focused in future. One respondent mentioned:

This study evaluated the public perception of an SGS, the Quyuan Park, within the POE framework. The park was positively rated by most respondents, in terms of different aspects including stormwater management functions, such as water infiltration, retention, and detention. The sponge facilities in the Quyuan Park reflect the early stages of exploration in the SC initiative, where improving hydrological benefits – such as reducing runoff volume and peak flow – was the primary design goal. However, the POE results of this park indicate that public satisfaction with water management indicators was generally lower than other aspects. In addition, in terms of demand feedback, the respondent public emphasized a strong demand for service facilities, especially for children's activity, which contrasts with the lower weights assigned to such aspects by experts. These mismatches revealed a gap between the technical goals of SCC implementations and public expectations. As all know, the core aim of SCC is to improve water quality and flooding control, but these functions in the Quyuan Park are often less visible and difficult for the public to perceive. In contrast, the public tends to focus more on everyday experiences, such as park amenities, cleanliness, and recreational opportunities, and are less aware of the long-term benefits of improved stormwater management. The two possible reasons we hypothesize to be the cause of the gap are (1) Flaws in the SCC implementation mechanism. It is reflected in the government's strong top-down governance structure, the ineffectiveness of feedback mechanisms, and the constraints of time and resources. Efforts to gather input from local communities during decision-making and post-project surveys, are usually superficial. Meanwhile, SCC projects often prioritize efficiency over inclusivity due to tight schedules and resource limitations. (2) Social ideology of group consciousness. It contributes to a passive acceptance of government actions, as many citizens tend to trust that state-led programs will adequately address public interests. This trust might stem from a historical and cultural association of the government with competence and authority in managing public affairs (Wang 2018). The mentioned mechanism has reinforced societal attitudes where the public plays a minimal role in urban planning or policy discussions. Cultural norms of deference and a preference for avoiding conflict further discourage active participation in SCC projects.

The Quyuan Park attracts recreational use across different age groups and supports a wide range of activities, presenting its characteristic of being multi-functional. However, the SC concept is less recognized or noticed in this park, which is most likely due to a lack of knowledge of branding and communication. In fact, SGS can serve as a living lab for users to learn about the SC concept and its environmental and social benefits. The case of the Quyuan Park shows that POE is valued to better understand how people perceive the project and whether the concept of SC is well-communicated in society. With more awareness and knowledge of the SC concept, the public can contribute to the process and co-design the SGS.

Current research on the POE of SGS is limited, with few studies offering comprehensive evaluation models or frameworks. This research contributes to this gap by proposing a POE framework, combining the AHP and FCE, to assess both functional and perceptual aspects of SGS. We have used the FCE method to minimize the subjectivity inherent in the AHP process. The framework was well proved for its feasibility, implementation difficulty, and credibility of results in the social context of the case cities. However, biases from respondents and differences in their understanding of the questions still influence the evaluation result. Therefore, it is a feasible framework but requires adjustments based on different regions, cases, or themes.

In the case of the Quyuan Park, the objective of retrofit in 2016 was mainly to enhance its water environments and stormwater management functionality. The driving forces behind the objectives arise from (1) the dual political and economic imperatives associated with brand building in SCC pilot cities and (2) the engagement opportunity and benefits game among various stakeholders within this context. Retrofit is primarily tasked with balancing cost and performance, while also facing uncertainties inherent in undertaking designs of this nature for the first time. Generally, the concept of Sponge Cities was a relatively unfamiliar innovation for both professional designers and the general public a decade ago. This could explain why the case of the Quyuan Park highlights a gap between the technical goals of SGS implementations and public expectations. The nearby residents' focus tends to lean more toward recreational and social aspects rather than hydrological benefits. To bridge this gap, stakeholders and park managers could enhance public understanding of SGS functions through interpretive signage or interactive installations. Notably, the ‘invisibility’ of SCC infrastructure needs to be discussed, because it may also be viewed as a design benefit as it allows a green infrastructure to integrate harmoniously with the park's natural features. When public awareness and technical objectives gradually complement each other and form a comprehensive evaluation system, creating a positive feedback loop becomes possible for future projects, contributing to improved multi-criteria decision analysis and full life cycle practices (Kuller et al. 2018a, 2018b; Lienert et al. 2022). Also, responding to public demands for better infrastructure and services could further enhance public engagement.

SCC, beyond providing solutions to immediate challenges like stormwater management, also enhances the spatial quality of surrounding areas in direct and indirect ways, such as increasing green spaces, improving air quality, and providing more recreational opportunities. These benefits align with current popular concepts such as nature-based solutions (NBS) and green infrastructure. However, the widespread application of SC projects seems limited, partly due to concerns over high operational and maintenance costs (Jia et al. 2017). While some people are willing to accept high investments if matched by substantial returns, there is a need for more holistic evaluations that account for both the advantages and limitations of these projects (Wang et al. 2017).

Lastly, this study has limitations in terms of the number of case studies and the size of the respondent group. The Quyuan Park has undoubtedly brought multiple benefits beyond hydrological improvements, but these specific benefits need further clarification. Future research should aim to include a broader range of cases and a more diverse population to strengthen the generalizability of the findings. Furthermore, longitudinal studies that assess public perception over a longer time span would provide more insights into how opinions evolve as the SCC become more popular. These longitudinal studies could help further understand the lasting impacts of SC projects and whether initial concerns about facilities, hydrological benefits, and costs remain relevant over time.

Despite nearly a decade of the SCC in China, there is little knowledge about how users perceive SGS and different local needs. POE of the SCC is rarely explored, a striking contrast to the rapid expansion of SCC implementations and the ‘prosperity’ of its hydrological studies. This study presents a comprehensive POE of the Quyuan Park, using a framework that combines the AHP-FCE-based quantitative and SSI-focused qualitative evaluation, offering insights into the public perception of the park. Key findings of the study are the following: (1) The SCC retrofit of the Quyuan Park was qualified and the POE showed overall positive feedback, yet the public mostly remains unaware of hydrological benefits, reflecting a gap between technical outcomes and public awareness; (2) the public shows a greater emphasis on the park's recreational and esthetic features, with notable dissatisfaction regarding commercial and children's play facilities; (3) there is a clear need for post maintenance and sustainable management of SGS, but the prospects are not promising due to the SCC implementation mechanism and social group consciousness.

While the overall public satisfaction with the Quyuan Park is positive, these findings suggest that future SCC projects should not only prioritize hydrological improvements but also address user needs and enhance the recreational and educational value of such public spaces. By bridging the gap between technical objectives and public perception, SGS can foster multi-functional daily usage and improve overall effectiveness. The single sample size may lower the generalizability of the findings. Future research should expand to multiple cases and adopt longitudinal approaches to better understand the evolving perception of SCC implementations. Finally, the Quyuan Park illustrates the potential for SGS to provide both hydrological and socio-ecological benefits and public feedback is helpful for policymakers, designers, and stakeholders to promote future projects and construct a better urban water environment.

All relevant data are included in the paper or its Supplementary Information.

The authors declare there is no conflict.