From Storage Capacity to Differentiated Stormwater Roles: A Comparative Framework for Sustainable Assessment of Sponge City Parks in Shanghai

Public parks are increasingly expected to function not only as recreational green spaces but also as components of urban green stormwater infrastructure. In practice, however, their performance is still commonly judged by stormwater storage capacity alone, a project-level metric that tends to favor larger parks and obscure differences in how parks contribute to broader blue-green stormwater systems. Accordingly, this study aimed to develop and apply an exploratory comparative framework for assessing the differentiated stormwater roles of sponge city parks beyond storage capacity alone. Using 20 sponge city parks in Shanghai as cases, the framework integrates stormwater storage capacity, storage efficiency, flow leverage, and facility configuration. The results show that annual stormwater storage capacity varied substantially across the 20 parks, ranging from 7625.12 m3 to 132,915.24 m3, with a mean value of 47,220.80 m3. However, this capacity-based ranking was strongly associated with park area. Once storage was normalized by area, the ranking changed markedly: line-type parks showed the highest mean storage efficiency of 1.393, followed by node-type parks at 0.921, whereas patch-type parks recorded a much lower mean value of 0.059. Flow leverage scores ranged from 0 to 6, with a mean value of 2.35, indicating that parks with comparable storage performance may occupy different hydrological positions within the broader topographic flow structure. The preliminary capacity-leverage typology further showed that high storage capacity did not always coincide with high hydrological leverage, and facility configuration scores ranged from 1 to 5, suggesting additional variation in internal infrastructural organization. These findings suggest that storage capacity should be complemented by spatial efficiency, hydrological position, and facility configuration when interpreting the differentiated stormwater roles of sponge city parks. The study reframes evaluation from a single project-level storage metric toward a more differentiated understanding of sponge city parks as urban green stormwater infrastructure and supports more sustainable assessment of community-scale stormwater management within broader blue-green systems.