An Evaluation of Sponge City Construction and a Zoning Construction Strategy from the Perspective of New Quality Productive Forces: A Case Study of Suzhou, China

Abstract

With the acceleration in urbanization, surface hardening has increased, urban flooding and soil erosion problems are frequent, and urban water resource management faces great challenges. Sponge city construction can effectively alleviate these problems by simulating the natural water cycle and constructing blue–green infrastructure. In this study, the analytic hierarchy process (AHP) and the ArcGIS weighted overlay tool were used to construct a framework for assessing the suitability of sponge city construction in Suzhou from the three dimensions of Geo-Smart spatial productive forces, Eco-Dynamic green productive forces, and Resilio-Tech responsive productive forces. A zoning strategy based on new quality productive forces is also proposed. The results show that Suzhou can be divided into three types of construction zones according to the suitability level: key construction zones, secondary key construction zones, and general construction zones. The key construction zones account for about 28.01% of the total land area, mainly covering the built-up areas of Suzhou, covering the developed urban areas such as Gusu District, Xiangcheng, Suzhou Industrial Park, and other key zones such as Northern Kunshan. The secondary key construction area and general construction area, on the other hand, account for 61.94% and 10.05% of the total area, respectively. From the new quality productive forces, this study proposes the following construction guidelines for sponge city zones: (1) enhance the coordinated development of urban planning and sponge city construction; (2) promote blue–green infrastructure development, strengthen inter-departmental cooperation, and ensure ecological and economic co-development; and (3) encourage public participation in governance. This research offers theoretical and practical guidance for sponge city construction in Suzhou and other cities from the perspective of new quality productive forces.

1. Introduction

Globally, the acceleration in urbanization has made cities the core driving force for economic growth and social development. However, this rapid development has also triggered a series of environmental issues, particularly unprecedented pressure on urban water resources and ecosystems. Urbanization has not only changed the original land use patterns but also led to severe a host of problems such as overexploitation of water resources, increased stormwater runoff, water pollution, and ecosystem degradation, all of which constitute serious threats to the sustainable development of cities (Lin et al., 2018; Chen et al., 2014) [1,2].

To effectively address these challenges, countries around the world have begun actively exploring new paths for sustainable urban development, among which the concept of sponge cities has gradually emerged. In China, ever since ecological protection was incorporated into the basic national policy in 1983, the importance of environmental protection has become increasingly prominent. Since the 18th National Congress of the Communist Party of China, the concept of ecological civilization construction and harmonious coexistence between man and nature has been elevated to an unprecedented height (Zhang et al., 2023) [3]. The Sponge City Construction (SCC) initiative was proposed and rapidly adopted nationwide (Sun et al., 2018; Wang et al., 2017) [4,5].

The concept of sponge cities represents a new urban development paradigm with Chinese characteristics, aiming to achieve sustainable rainwater management in urban areas to meet multiple objectives such as local flood control, reduction in rainwater disasters, control of non-point source pollution, and rainwater utilization, which can effectively mitigate the urban heat island effect (Zhang et al., 2023; Buchholz, 2013; Onmura et al., 2001; Qin et al., 2013) [3,6,7,8]. In recent years, the concept has received widespread attention and has become the cornerstone of China’s pursuit of high-quality development. Developing new quality productive forces means driving the transformation of production modes through technological innovation, cultivating emerging industries, and digitizing traditional industries. This transformation is crucial for addressing the major contradictions facing Chinese society in the new era, especially in urban environments (Xie et al., 2024; Li et al., 2024) [9,10]. In the field of urban planning and design, combining the concept of new quality productive forces with sponge city construction represents a forward-thinking approach. New quality productive forces represent an advanced form of productivity characterized by innovation-led, high-tech, high-efficiency, and high-quality measures. Their rapid development requires urban and rural planning to provide flexible spaces that support innovative activities, considering increased technological complexity and diversified user needs. This approach emphasizes communication, collaboration, and systemic support to facilitate the flow and allocation of innovative elements (Wang et al., 2024) [11]. Effective urban planning and design, supported by intelligent technologies and networked production organizations, promote sustainable urban and rural development. As conceived, sponge cities require innovative technologies and practices to ensure effective water resource management and urban resilience (Zhang et al., 2019; Xu et al., 2022; Wang et al., 2023) [12,13,14].

Furthermore, research highlights the potential revolutionary impact of the development of new quality productive forces on production relations, especially under the influence of the Fourth Industrial Revolution (Liu, 2024) [15]. The reshaping of ownership relations, corporate organization, and distribution models presents challenges and opportunities for urban planners. As cities like Suzhou face challenges such as rapid urbanization and increasing environmental pressures, they must adapt to these changes and embrace sponge city construction to ensure that development strategies align with the changing economic and social environments. While the aforementioned research focuses on the broader aspects of new quality productive forces and their impact on development, research on the promoting effects and mechanisms of new quality productive forces on green development is directly related to sponge city construction (Xu et al., 2024) [16]. This research shows that new quality productive forces significantly promote green development by improving technology and optimizing industrial structures. The spatial spillover effect further enhances this positive impact, indicating that sponge city construction can benefit from regional cooperation and the sharing of innovative practices. Additionally, research on the spatial pattern and evolutionary characteristics of new quality productive forces at the provincial level in China provides valuable insights into the regional differences and trends in their development, emphasizing the importance of formulating sponge city construction strategies tailored to different urban regions (Li et al., 2024) [10].

As a key technical support for territorial spatial planning, land suitability evaluation analyzes the spatial fit of land resources in a specific area for target functions, offering scientific bases for spatial resource allocation. The AHP is widely used for its structured decision-making advantages in weight determination and multi-criterion decision-making (Chandio et al., 2013; Rahmati et al., 2015; Xiang & Jia, 2018) [17,18,19]. Current research shows that while sponge city studies have rich empirical results, they are biased, mostly focusing on post-construction effect evaluation (Xiang & Jia, 2018; Zhou et al., 2018) [19,20], with insufficient attention to pre-construction suitability evaluation and system resilience analysis (Fan et al., 2019) [21]. Few scholars have studied sponge city construction suitability. Xu and Jiang (2022) built a sponge city construction potential evaluation index system, using a variable fuzzy recognition model to score and rank the suitability of 13 prefecture-level cities in Jiangsu Province [13]. Wang, Zhou et al. (2018) created an index system from four aspects—rainfall, water pollution, flood disasters, and ecological green spaces—and used the gray relational analysis method to assess the sponge city construction potential in Tianfu New District [22].

Despite the abundant research on sponge city construction, especially in the application of information technology, such as smart sponges (Zhang et al., 2019; Ma et al., 2023; Luo et al., 2021; Shao et al., 2016) [12,23,24,25] and digital landscape-based sponge cities (Sun et al., 2022; Pavesi et al.) [26,27], research is still lacking in terms of a suitability quantitative evaluation system, especially concerning the question of how to integrate the concept of new quality productive forces into the comprehensive consideration of water resource utilization and social factors. Moreover, the question of how to ensure the coordinated development of sponge city construction with existing water resource management systems is also an important challenge currently faced. Suzhou became a pilot city for sponge city construction in Jiangsu Province in 2016 and has accumulated extensive experience in this field. This study aims to identify spatial advantages and implementation barriers in sponge city construction under new quality productive forces, providing a scientific basis for optimizing the construction path by systematically evaluating its suitability. As a strategic initiative proposed by the Chinese government, new quality productive forces emphasize technological innovation, coordinated development, open cooperation, and shared development, which align with the core principles of high-quality urban development. By combining this concept with sponge city construction, we aim to explore innovative paths for urban planning and design that promote ecological protection and economic and social progress.

2. Methodology

2.1. Study Area

The study area is located in Suzhou City, Jiangsu Province, China (31°30′ N, 120°62′ E), which is one of the first pilot cities for sponge city construction in Jiangsu Province. Suzhou is situated in the southeastern part of Jiangsu Province, in the middle of the Yangtze River Delta. The city is bordered by Shanghai to the east, Zhejiang Province to the south, Taihu Lake to the west, and the Yangtze River to the north, with a total area of 8657.32 square kilometers. Suzhou has a low-lying terrain, with a dense network of rivers and numerous lakes. The majority of Taihu Lake’s surface area lies within Suzhou, and the combined area of rivers, lakes, and tidal flats accounts for 36.6% of the city’s total land area, making it a well-known water town in the Jiangnan region. With the rapid urbanization of Suzhou, issues such as increased surface imperviousness and the reduction in natural water systems have emerged, exacerbating urban waterlogging risks and water environment pressures. It is essential to properly evaluate the suitability of sponge city construction in Suzhou, providing a scientific basis for the rational use and protection of water resources and technical support for the city’s overall planning.

Since 2016, Suzhou has initiated sponge city pilots in Gusu District and Xiangcheng District, achieving remarkable results, with water quality improving to Class IV standards. After 2018, the construction was accelerated to cover the entire city. By 2023, a total of 308.73 square kilometers of the city had been developed into sponge city areas, accounting for 40.02% of the urban built-up area. Its exploration serves as a demonstration for other similar Jiangnan water town cities. Additionally, Suzhou, with its developed economy and profound water culture, faces both the impact of high-density development on the water ecosystem and the dual need to protect the ancient city’s water system while modernizing. This “interweaving of tradition and modernity” makes it an ideal case for studying the suitability of sponge city construction. Therefore, the entire region of Suzhou City was selected as the specific study area in this study (Figure 1).

2.2. Data Source

This study employs two types of key data: Natural Environment Data and Socioeconomic Data. Natural Environment Data, which are used to evaluate terrain, hydrology, vegetation, and other related factors, are crucial for assessing the natural foundation for sponge city construction. Socioeconomic Data, on the other hand, are utilized to analyze population distribution, economic development levels, infrastructure construction, and other aspects, aiding in our understanding of the socioeconomic demands of sponge city construction. All data are sourced from reliable open-source platforms or specialized databases and have been appropriately processed and spatialized according to research requirements to ensure data accuracy and practicality (

Table 1. Data sources and descriptions.

Data Type	Data Name	Data Resource	Resolution
Natural environment data	Elevation data	From the USGS EarthExplorer open source platform (https://earthexplorer.usgs.gov), derived from Landsat-8 satellite imagery and corrected based on the UTM-WGS84 coordinate system	30 m × 30 m
	Slope data	Derived from Landsat-8 satellite imagery data	30 m × 30 m
	Land use data	Chinese Multi-Period Land Use/Land Cover Remote Sensing Monitoring Dataset (CNLUCC)	30 m × 30 m
	Surface runoff data	Derived from Landsat-8 satellite imagery data	30 m × 30 m
	Water system distance data	https://www.openstreetmap.org/ (accessed on 30 October 2024)	Vector file
	Normalized Difference Vegetation Index (NDVI)	http://www.gscloud.cn (accessed on 30 October 2024)	30 m × 30 m
	Groundwater level data	Annual Report on Groundwater Level Monitoring in China 2021	Vector file
	Soil clay content data	https://www.isric.org/explore/soilgrids (accessed on 30 October 2024)	30 m × 30 m
Socioeconomic data	Population density data	https://www.worldpop.org (accessed on 27 October 2024)	100 m × 100 m
	Building density data	http://www.rivermap.cn/ (accessed on 28 October 2024)	10 m × 10 m
	Road network density data	https://www.openstreetmap.org/ (accessed on 30 October 2024)	Vector file

).

2.3. Research Method

The analytic hierarchy process (AHP) is a decision-making method that divides elements related to decision-making into multiple levels, such as the goal level, criterion level, and measure level, and then conducts a comprehensive qualitative and quantitative assessment based on these levels. This method facilitates the consideration of multiple factors influencing sponge city construction comprehensively, thereby avoiding the one-sidedness inherent in single-factor evaluations. The method of using AHP to determine weights and subsequently establishing a corresponding indicator system framework has demonstrated broad applicability in the field of sponge cities (Ding et al., 2021; Jiao et al., 2017; Li et al., 2019) [28,29,30].

The Suitability Evaluation Method is a comprehensive methodology employed in the fields of resource science and physical geography, which employs weighted factor analysis to assess factors such as geological and environmental conditions and ecological sensitivity. The method plays a significant role in sponge city construction. It determines construction areas, optimizes design schemes, assesses actual effectiveness and sustainability, and provides a scientific basis for decision-making. (Luo et al., 2021; Wang et al., 2022; Li, N. et al., 2019) [24,31,32].

In this study, key factors for sponge city construction were extracted through a literature review and field investigation. Important evaluation factors were determined through expert consultation to construct a comprehensive evaluation index system. A quantitative evaluation was then conducted to determine the suitability levels. The raster model was assessed using the ArcGIS weighted overlay tool, and the suitability of sponge city construction was divided according to the suitability index. Construction guidelines were proposed based on the perspective of new quality productive forces (Figure 2).

3. Suitability Evaluation

3.1. Current Distribution of Sponge Bodies

In the realm of urban sponge construction, based on the origins of sponge bodies, we can distinguish between ecological and artificial categories. When constructing the urban sponge ecosystem, it is essential to pinpoint five key ecological sponge components: mountains, water bodies, forests, farmland, and lakes. These elements are vital components of the urban sponge ecological foundation, offering direct retention and regulation capabilities for urban rainfall.

Suzhou, characterized by its relatively low-lying terrain and predominant plains, still boasts some hills and mountains, such as Qionglong Mountain and Tianping Mountain. The city’s water system is highly developed, featuring major rivers like the Beijing–Hangzhou Grand Canal, Suzhou Creek, Loujiang River, and Zhangjiagang River. Larger lakes and ponds, such as Taihu Lake, Yangcheng Lake, Jinji Lake, and Shi Lake, dot the landscape. Suzhou also possesses abundant forest resources, including Dayangshan National Forest Park and Dongshan Forest Park, with a forest coverage rate of 20.56%. The city is rich in farmland, especially paddy fields. Ecological sponge bodies in Suzhou are primarily concentrated around Taihu Lake, the waterways circling the city, and hilly areas, while natural water bodies like paddy fields, rivers, and ponds are prevalent throughout the city. However, in the urban core, due to dense development, the coverage of ecological sponge bodies is relatively limited.

3.2. Construction of Evaluation Indicator System

3.2.1. Determination of Evaluation Indicators

This study comprehensively considers multiple dimensions such as topography, hydrology, ecology, and human activities. Through expert assessments, an evaluation system centered on the suitability for sponge construction is constructed, encompassing three aspects: topographic factors, environmental factors, and resilience factors. This system includes 11 indicators such as elevation, slope, and land use type, as detailed in

Table 2. Appropriateness of sponge city construction evaluation system.

Target Level	Factor Level	Indicator Level	Impact of Indicators
Suitability for sponge city construction	Geo-Smart spatial productive forces	Elevation [33]	Impacts urban rainwater flow direction and vegetation cover.
		Slope [33]	Areas with higher slopes are more susceptible to soil erosion, increasing the difficulty of soil and water conservation.
		Land use type [34]	The proportion of green spaces and permeable pavements reflects rainwater drainage and purification effectiveness.
		Surface runoff density [35]	Reflects the urban flood discharge capacity.
	Eco-Dynamic green productive forces	Water system distance [36]	Closer proximity to water systems enhances the effectiveness of using them for flood regulation and ecological restoration.
		Normalized Difference Vegetation Index (NDVI) [36]	Higher vegetation coverage strengthens urban soil and water conservation and purification capabilities.
		Groundwater level [37]	Influences the performance of sponge facilities.
		Soil clay content [38,39]	Impacts rainwater infiltration and retention effectiveness of sponge facilities.
	Resilio-Tech responsive productive forces	Population density [40]	Indicates population concentration and determines the urgency of sponge city transformation.
		Building density [40]	Reflects the proportion of impermeable areas.
		Road network density [40,41]	Reflects the layout and connectivity of the road network, influencing rainwater drainage and green space planning and construction.

.

Slope has a significant impact on the growth environment of plants and the difficulty and cost of constructing sponge green spaces. Meanwhile, soil clay content, groundwater levels, and water system distance as key indicators for measuring the development of water systems, also exert important influences on the retrofitting of sponge cities. With the acceleration of urbanization, areas with dense buildings, complex road networks, and large populations have an increasingly urgent need for water resource security and comprehensive water environment management. From the perspective of new quality productive forces, this analysis delves into the construction conditions and actual demands of sponge cities and conducts a comprehensive evaluation of their suitability, striving to enhance the overall benefits of sponge city construction.

3.2.2. Evaluation Grade Division and Weight Assignment

In this study, by referring to relevant studies and expert opinions, and based on the characteristics of the indicators and their contribution to sponge city construction, each evaluation indicator was quantitatively classified into multiple grades to make them more specific and objective.

Table 3. Quantitative grading of sponge city construction suitability evaluation indicators.

Classification Categories	Suitable	Relatively Suitable	Moderately Suitable	Less Suitable	Unsuitable
Elevation (m)	<160	160–180	180–200	200–300	300
Slope (°)	0–2	2–5	5–15	15–35	35–75
Land use type	Construction Land	Farmland	Grassland–Shrubland	Wetland–Forestland	Water Body
Surface runoff density (km/km2)	2.64–5.08	1.45–2.64	1.03–1.45	0.52–1.03	0–0.52
Water system distance (m)	0–100	100–300	300–600	600–1000	1000–2500
Normalized Difference Vegetation Index (NDVI)	0.4	0.3–0.4	0.2–0.3	0.1–0.2	<0.1
Groundwater level (m)	−18.56–12.14	−12.14–7.67	−7.67–4.54	−4.54–2.36	−2.36–0.84
Soil clay content (%)	42–47	1–42	0.3–1	0.1–0.3	0–0.1
Population density (people/km2)	683.41–2000	265.79–683.41	113.92–265.79	30.40–113.92	0–30.40
Building density (%)	0.62–1	0.38–0.62	0.21–0.38	0.07–0.21	0–0.07
Road network density (km/km2)	12.47–19.71	8.39–12.47	5.31–8.39	2.31–5.31	0–2.31

presents the detailed classification results, where a higher score indicates stronger suitability of the indicator for sponge city construction.

Gentle slopes in low-elevation areas are prone to waterlogging and resulting flooding (Tehrany et al., 2019) [33]. Based on DEM raster data analysis, elevation and slope were classified, with lower-value areas being more suitable for development (Tehrany et al., 2019) [33]. Impervious surfaces were divided into five categories based on land use types (Li J et al., 2022) [34]. Poor soil permeability reduces the runoff absorbed. While high permeability, although conducive to absorption, increases the risk of groundwater contamination and subsequently raises the demand for water purification. The higher the density of surface runoff, the higher the degree of surface hardening, necessitating sponge city construction (Li H et al., 2024) [35]. Areas closer to river systems face a greater risk of pollutants being directly discharged into rivers, thereby enhancing the purification demand of water systems (Tran et al., 2020) [36]. Regions with high vegetation coverage exhibit better soil and water conservation and purification capabilities, rendering them more suitable for construction (Tran et al., 2020) [36]. Areas with lower groundwater levels rely more on rainwater infiltration and recharge to promote groundwater replenishment and elevate groundwater levels (Sun et al., 2020) [37]. Clay, an important component of soil, consists of fine particles with strong adsorption and water retention capabilities. In Suzhou, clay has low permeability but typically high fertility, higher clay content necessitates enhancing the rainwater infiltration and retention capabilities of sponge facilities (Zhang et al., 2005; Zhao et al., 2018) [38,39]. The greater the density of population, buildings, and urban road networks, the more severe the losses during disasters, thereby making the need for sponge city construction more urgent (Huang et al., 2024; Du et al., 2022) [40,41].

As a multi-dimensional decision-making tool, AHP is particularly crucial in quantitative analysis. The opinions of 10 experts in the fields of urban planning and water engineering were collected through a rating scale to quantitatively assess the importance of each indicator factor (Appendix A). Based on a comprehensive consideration of expert opinions, this method is adopted to allocate weights to each evaluation indicator, aiming to reduce redundancy and subjectivity in the decision-making process. YAAHP V10.3 is software specifically designed for the method, capable of efficiently processing and judging matrices as well as verifying consistency (Appendix B). The consistency ratio (CR) of all judgment matrices is less than 0.1, indicating good consistency in expert scoring. The final weights are shown in

Table 4. Weights of evaluation factors.

Primary Indicator	Weight W1	Secondary Indicator	Weight W2
Geo-Smart spatial productive forces	0.411	Elevation	0.044
		Slope	0.097
		Land use type	0.188
		Surface runoff density	0.082
Eco-Dynamic green productive forces	0.240	Water system distance	0.073
		Normalized Difference Vegetation Index (NDVI)	0.075
		Groundwater level	0.057
		Soil clay content	0.035
Resilio-Tech responsive productive forces	0.349	Population density	0.101
		Building density	0.182
		Road network density	0.066

.

4. Results

4.1. Analysis of Indicator Level Results

4.1.1. Analysis of Geo-Smart Spatial Productive Forces

Elevation data of Suzhou was processed using ArcGIS 10.8 software to generate suitability assessment maps for elevation and slope, as shown in Figure 3a,b. The results indicate that Suzhou has a low and flat terrain, mainly consisting of plains, with minimal variations in overall elevation and slope, which is conducive to the development and construction of sponge cities.

The urban stormwater absorption capacity is constrained by land use types and surface runoff density. Soils with high permeability can accelerate rainwater infiltration, replenish groundwater reserves, and effectively reduce the formation of surface runoff. However, impermeable construction land can hinder rainwater infiltration, leading to the formation of surface runoff. By analyzing land use types, impermeable areas and their permeability can be identified. Among them, ecological sponge elements such as woodlands and grasslands have strong permeability, while construction land has weaker permeability, as shown in Figure 3c,d. To promote the construction of sponge cities, areas with weak soil permeability and high runoff density should be prioritized for renovation.

4.1.2. Analysis of Eco-Dynamic Green Productive Forces

Water buffer zones play a crucial role in protecting the ecological functions of water bodies and mitigating non-point source pollution. Generally, the closer an area is to water bodies, the easier and more cost-effective it is to implement sponge city construction. The Normalized Difference Vegetation Index (NDVI) is a metric used to measure vegetation cover, with higher values indicating denser vegetation and stronger rainwater purification capabilities. As shown in Figure 4a, the study area features a well-developed river network, with approximately 63.2% of the region having water bodies within 600 m for rainwater absorption. However, areas around rivers are at high risk of flooding, necessitating enhanced risk management. Figure 4b, compiled using Landsat remote sensing data, reveals that areas with high NDVI values correspond to the distribution of water systems. These regions have well-grown vegetation, which aids in soil and water conservation and purification. Areas with low groundwater levels should promote recharge to raise water levels, whereas caution should be exercised in constructing sponge cities in areas with high groundwater levels to prevent excessive water infiltration that could lead to rising water levels, as illustrated in Figure 4c. The distribution of clay content in the soil of the study area exhibits relatively little variation, largely falling within a generally suitable range, as shown in Figure 4d.

4.1.3. Analysis of Resilio-Tech Responsive Productive Forces

The degree to which a city is affected by flood disasters and its suitability for renovation are directly related to the city’s resilience characteristics. An assessment of the suitability for sponge city construction has been conducted from the aspects of urban population density, building density, and road density. Populated and built-up areas suffer more severe damage during waterlogging events, making the need for sponge city construction an urgent priority.

Suzhou exhibits incoordination and imbalance in the spatial distribution of population, building, and road densities, with concentrations in the historical core area of Gusu District, which serves as the core and expands outward. The Industrial Park follows closely behind the city center in terms of building and road density. Given that Gusu District has become a high-risk area for waterlogging due to its large areas of impervious surfaces and high population density, while also demonstrating high suitability in terms of urban construction indicators, it should be prioritized in planning for sponge city construction, as detailed in Figure 5.

4.2. Analysis of Suitability Results for Sponge City Construction

The construction of a sponge city is a process that requires multi-dimensional consideration. By utilizing the weighted overlay analysis function of the ArcGIS platform, a zoning classification table for the suitability of sponge city construction in Suzhou was derived based on the comprehensive weight evaluation of Geo-Smart spatial productive forces (0.411), Eco-Dynamic green productive forces (0.240), and Resilio-Tech responsive productive forces (0.349), as shown in

Table 5. Zoning classification table for sponge city construction in Suzhou.

Zone Classification	Key Construction Zone	Secondary Key Construction Zone	General Construction Zone
Scores	0–1.4001	1.4001–2.98753	2.98753–28.3985

. Furthermore, using the natural breaks classification method and based on detailed evaluation results, the sponge city construction areas in Suzhou were scientifically divided into key, secondary key, and general construction zones, as illustrated in Figure 6.

4.2.1. Distribution Pattern

The results of the construction suitability evaluation indicate that areas with higher suitability are primarily concentrated in the urban core. This distribution is influenced by key factors such as land use type, building density, population density, and slope, with suitability gradually decreasing from the center to the periphery. In the comprehensive evaluation, the suitability of Wuzhong District, central Wujiang District, central Huqiu District, northern Xiangcheng District, Zhangjiagang, Taicang, and the outer areas of Changshu is significantly lower than that of Gusu District, southern Xiangcheng District, the northern and southern sides of Wujiang District, the outer areas of Huqiu District, southern Xiangcheng District, the Industrial Park, and Kunshan.

4.2.2. Zoning Characteristics

The total area of the study region for sponge city construction in Suzhou is 8657.32 square kilometers, of which the key construction zones cover 2424.86 square kilometers, accounting for approximately 28.01% of the total area. These zones are primarily located in the central areas with high-density construction land, a slope of less than 5 m, and a surface runoff density of less than 1.03 km per square kilometer, urgently requiring sponge transformation. The secondary key construction zones are dominated by plains with dense runoff, a surface runoff density of more than 1.45 km per square kilometer, and a high degree of vegetation cover. They cover an area of 5362.58 square kilometers, accounting for up to 61.94% of the total. The general construction zones, mainly within the Taihu Blue Line and along rivers, cover an area of 869.88 square kilometers, accounting for approximately 10.05% of the total. These zones are interspersed with woodland, nature reserves, and rural settlements.

4.3. Suitability Results for Sponge City Construction

Based on the results of suitability assessments and the patterns and characteristics they reveal, combined with ecological and construction conditions, different regions were classified according to the natural breakpoint method, and the characteristics of sponge city zoning construction in Suzhou were extracted, as shown in

Table 6. Suitability zoning for sponge city construction in Suzhou.

Construction Category	Area (km2)	Proportion (%)	Construction Characteristics
Key construction zone	2424.86	28.01	Features large impervious areas, fragmented urban green spaces, and low per capita green space area. It has high ecological and aesthetic demands and exhibits good suitability for construction.
Secondary key construction zone	5362.58	61.94	Dominated by agricultural land with relatively small construction land areas. Limited and underutilized developable areas, with generally suitable construction conditions.
General construction zone	869.88	10.05	Contains a large proportion of water source protection areas and waterway corridors, with high ecological sensitivity. Poor suitability for construction and not suitable for development and construction.

. Furthermore, guidelines for the zoning construction of Suzhou’s sponge city from the perspective of new quality productive forces are proposed.

Specifically, the urban-built areas (Gusu, Xiangcheng, Suzhou Industrial Park, Eastern Huqiu, Southern Zhangjiagang, Western Changshu, Southern Taicang, Northern Kunshan) are key construction zones and should be high-density sponge resilience pilot area. Due to high urbanization and ecological pressure, smart technologies like GIS and big data analysis should be used to optimize land use, promote mixed-use modes, integrate sponge facilities with urban functions (transportation, commerce, residence), and improve facility efficiency. Ecological corridors and blue–green networks should be upgraded and inland rivers and lakes restored to enhance flood storage and purification.

The Lake Yangcheng Basin (Eastern Wujiang, Southern Kunshan), as a secondary construction zone, is a sponge collaborative extension corridor with important ecological functions. It needs to balance ecological protection and urban development. An intelligent rainwater management system should be built to efficiently manage and utilize rainwater resources through intelligent means. Internet of Things (IoT) sensors should be deployed to monitor rainfall, water levels, and quality in real-time, analyze flood patterns, and optimize storage strategies. A smart platform for the joint scheduling of reservoirs, rivers, and wetlands should be established.

The Yangtze River Basin (Northern Zhangjiagang, Eastern Changshu, Northern Taicang) and the Taihu Basin (Wujiang, Western Huqiu, Western Wujiang) are general construction zones, as detailed in Figure 7. With concentrated green patches and high biodiversity, they suit low-impact development (LID). Ecological redlines should be established to strictly protect sensitive zones such as wetlands and forests along Taihu Lake and the Yangtze River, prohibiting urban development. LID techniques can be integrated into these protected corridors to mitigate hydrological disruptions from urbanization, enhancing natural rainwater infiltration and retention. Regional coordination should be prioritized, fostering integrated development around Taihu Lake, the Yangtze River, and adjacent areas.

5. Discussion

5.1. Reassessing the Evaluation System: Moving Towards Dynamic Adaptation

When collecting expert opinions, the sponge city suitability evaluation system based on AHP is established under the guidance of new quality productive forces, integrates scientific rigor with practical adaptability. By assigning different weights to criteria like Geo-Smart spatial productive forces and Resilio-Tech responsive productive forces, it transcends traditional one-size-fits-all approaches. Crucially, experts’ strong consensus on land use type and building density highlights the dual necessity of ecological sustainability and social equity in sponge city development. However, there is an inherent contradiction between groundwater-level-driven infiltration design and rainwater retention strategies that rely on clay content. This contradiction indicates that under different climatic conditions, it is necessary to dynamically adjust the weights of each indicator in the evaluation system according to specific contexts.

5.2. Sponge Cities Driven by New Quality Productive Forces: Catalyzing the Transformation of Green Society and Economy

The integration of new productivity concepts, especially AI-aided drainage simulation and IoT-based sponge facility monitoring, is reshaping urban economic models, the schematic diagram of the measures is shown in Figure 8. Our analysis has identified three transformation pathways.

(1)

Enhanced natural resource efficiency: Sponge city projects boost rainwater efficiency, reducing tap water use. In Xiamen, the rainwater utilization rate rose from 0.5% in 2014 to 2% in 2020, saving about 14.016 million cubic meters of rainwater and cutting carbon emissions by 2719.1 tons annually (Shao et al., 2018) [42]. This improves resource efficiency, reduces carbon footprints, lessens reliance on conventional water sources, and promotes sustainable water use.

(2)

Increased social investment returns: In Xi’an and Guyuan, the benefit-to-cost (B/C) ratios were 3.86 and 0.93, respectively. A ratio above 1 means benefits outweigh costs, indicating economic viability. For urban benefits, the static payback periods in Xi’an and Guyuan were about 3.7 years and 15.3 years; for regional benefits, they were 4.0 years and 16.2 years. Xi’an’s higher B/C ratio and shorter payback period show greater economic benefits, while Guyuan’s lower ratio and longer payback period suggest the need for project optimization or alternative financing (Jia et al., 2023) [43].

(3)

Increased property values: Sponge cities enhance ecological livability, boosting property values. Studies show that sponge city pilots, especially in water-scarce cities, significantly improve ecological livability, with a statistically significant coefficient of 0.006 at the 1% level (Wang Q et al., 2024) [44]. In Wuhan, in 2016 and the first half of 2017, the average unit housing transaction price was higher in sponge city areas than in non-sponge city areas (Zhang S et al., 2018) [45]. This improvement attracts investment and talent, driving property market prosperity.

Sponge city construction promotes a green socioeconomic transition by boosting natural resource efficiency, social investment returns, and property values. These impacts align with the UN Sustainable Development Goals (SDGs 11 and 13), positioning sponge cities as engines for circular urban economies. Through case studies and synergy analysis, it not only tackles environmental issues but also delivers significant economic and social benefits, offering valuable experience for global sustainable urban development.

5.3. Limitations and Future Horizons: Bridging Technological, Social, and Ecological Gaps

This study has three primary limitations that reveal critical research frontiers. (1) Insufficient technological integration and innovation: although new quality productive forces like smart monitoring, big data, and ecological modeling were noted, this study did not explore how they can further advance sponge city construction. (2) Overlooking life-cycle costs of sponge facilities and insufficient social factor assessment: community participation, crucial for project sustainability and social acceptance in sponge city construction, was not adequately considered. (3) Static weights are inadequate for climate change, and there is a lack of comprehensive consideration for the Taihu Lake ecosystem. The basin spans multiple cities, yet this study only focuses on Suzhou, ignoring its overall functions and impacts.

To address these gaps, future research should prioritize the following: (1) Explore synergies among these technologies and how innovation can optimize the construction process for sustainable development. Investigate the application of block chain in sponge infrastructure financing and maintenance responsibilities. (2) Incorporate social factors by gathering residents’ opinions through surveys and public participation to formulate more comprehensive policies. (3) Establish trans-boundary governance for basin-scale sponge city networks. View Taihu Lake as a complete ecosystem in the future, exploring its impacts and feedback mechanisms on sponge city construction. Cross-regional cooperation should be initiated to achieve comprehensive protection and sustainable development.

6. Conclusions

The research findings are as follows: (1) using AHP, weights were assigned to various factors based on their importance, with land use type having the highest weight, followed by building density, population density, slope, surface runoff density, Normalized Difference Vegetation Index (NDVI), water system distance, road network density, groundwater level, elevation, and soil clay content. (2) Based on the indicators and weights, the suitability for constructing sponge cities oriented towards new quality productive forces in Suzhou was evaluated using ArcGIS software, and the results were visualized to provide a scientific basis for site selection and timing arrangements for the planning and construction of sponge cities in the study area. (3) The analysis revealed that the key construction area accounts for approximately 28.01% of the total study area, mainly concentrated in the central part of the study area, where construction needs are relatively urgent. The secondary key construction area and the general construction area account for 61.94% and 10.05% of the total area, respectively.

To further enhance Suzhou’s sponge city construction, the following recommendations are proposed based on the above conclusions. (1) Staged implementation for different zones: From the perspective of new quality productive forces, sponge city construction and promotion should be implemented in stages, using new technologies and concepts, and tailored to local conditions. In key construction areas, intelligent technologies like GIS and big data analysis should be used to optimize land use and improve sponge facility efficiency. In secondary key areas, a smart rain–flood joint-regulation system should be installed to balance ecological protection and urban development, considering storm water storage capacity and ecological corridor connection. In general construction areas, prioritize ecological protection and use LID technology to maintain the natural hydrological cycle. (2) Encourage public participation: Promote sponge city knowledge and significance through community lectures, media publicity, and school education. Raise public awareness and support, fostering a good atmosphere of joint construction, management, and sharing. (3) Strengthen cross-departmental cooperation and technical support: Set up a dedicated sponge city construction management department to coordinate the work of various departments. Introduce IoT, big data, and remote-sensing technologies to establish a unified data monitoring and sharing platform for real-time updates and efficient scheduling.