Having established the empirical basis for the underrepresentation of the spatial system in urban SES research and proposed the SESS framework in response, we now position it within the broader landscape of SES extensions. As discussed in the Introduction, frontier SES scholarship has increasingly accommodated spatial complexity through ecological concepts such as heterogeneity and patch dynamics, demonstrating that the nested hierarchical structure of SES can in principle incorporate spatial concerns as sub-theories within existing domains. However, our review suggests that in practice this accommodation has been uneven: when the spatial system remains nested beneath the social or ecological domain, its ontological properties tend to be subordinated to the analytical priorities of the host domain, a pattern reflected in the persistent marginality of Deep Attributes (11.9%) even at the analytical frontier. The three properties outlined in our theoretical case (configurational causality, material inertia, and historical continuity) are not characteristics of either social behavior or ecological processes; they are properties of the spatial system itself. Subsuming them under either domain is not merely a practical difficulty but an ontological misattribution, comparable to treating ecological dynamics as a subdomain of social institutions. This motivates our choice to elevate the spatial system to co-equal status, not as a rejection of nested hierarchy, but as a strategic means to ensure that configurational, material, and historical properties receive sustained analytical attention.
A structurally parallel choice has been made by the SETS framework, making a direct comparison particularly instructive. Since its early formulations15,52, SETS has developed into a substantial body of work spanning theoretical foundations16,17, empirical applications53,54,55, governance18, and comprehensive reviews19,56. SETS and SESS share a common diagnosis: the binary SES framework lacks sufficient conceptual space for the material, constructed dimensions of urban systems, and both respond by elevating a third domain to co-equal status, recognizing multi-scalar dynamics, path dependency, and cross-system interactions. Yet the two frameworks diverge in their intellectual lineage, their conception of the third domain, and consequently in the types of questions they are best equipped to address. We articulate these differences below along three dimensions that correspond to the ontological structure of the spatial system proposed above.
The most immediate divergence is in spatial organization. SETS approaches the built environment primarily as a network of interconnected infrastructural systems, analyzing how water, energy, transportation, and communication networks interact with social and ecological systems16,18. The emphasis is on functional interdependence and cascading vulnerabilities. SESS, drawing on the tradition of urban morphology20,57,58, approaches the built environment as a configurational system whose spatial arrangement possesses causal properties of its own. A street network, in this view, is not only transportation infrastructure but a spatial configuration that shapes movement probabilities, encounter patterns, and the distribution of social activity through its topology28. Recent studies have reinforced the significance of this configurational perspective, demonstrating that urban morphological features exert nonlinear effects on ecological resilience59 and that spatial configuration constitutes a key variable in urban sustainability assessment60. This distinction matters analytically: the same physical object is understood through different causal logics, yielding different research questions and policy implications.
A related distinction emerges around materiality. SETS engages with the material properties of infrastructure in terms of condition, capacity, age, and interdependency61,62. Materiality in this context is primarily functional: material degradation signals vulnerability, and material capacity determines service levels. SESS engages with materiality in a broader sense, drawing on urban metabolism studies30,31 and material stock analysis41,63. In this view, the material stock of the built environment is not only a functional asset but a repository of embodied energy, a record of construction history, and a determinant of future adaptation pathways through its sheer physical inertia. The analytical object here is not the biogeochemical flows themselves, which remain within the ecological domain, but the ways in which the physical stock and configuration of the built environment govern, constrain, and lock in the pathways through which such flows move. Recent research has quantified the scale of this challenge: Zhang et al. show that China’s building material stock accounted for 19% of the country’s total carbon emissions64, while Heisel et al. demonstrate the potential of high-resolution material stock mapping for evaluating whole-life carbon emissions at the urban scale65. These findings underscore that the material composition of cities constitutes a critical but often overlooked dimension of urban sustainability, one that SESS is designed to foreground.
The third dimension, and the one where the analytical distance is greatest, concerns historicity. SETS addresses temporal dynamics through the lens of infrastructure lock-in and life-cycle management16. Time, in this framework, is primarily operational: it marks the aging of systems and the accumulation of sunk costs that constrain future decisions. SESS draws on a different conception of time, rooted in the morphological tradition of historical layering20 and in the growing body of scholarship on the tensions between climate adaptation and heritage preservation66. In this framework, the historicity of the built environment is not merely a constraint but a carrier of meaning: the accumulated layers of urban form encode collective memory, cultural identity, and symbolic value. This is the theoretical basis for the variable SP6 (Cultural Heritage and Place Identity), which has no direct counterpart in the SETS framework. The urgency of this dimension is underscored by recent findings that 80% of UNESCO World Heritage sites already face climate stress, yet the analytical tools for navigating the tension between adaptation and preservation remain underdeveloped.
These differences are not deficiencies in either framework but reflections of their distinct disciplinary roots and analytical purposes. SETS is well-suited to questions about infrastructure resilience, functional interdependence, and adaptive capacity under stress. SESS is oriented toward questions about morphological agency, material continuity, and the temporal tensions between heritage and adaptation. The two are complementary, and future work could explore how the functional focus of SETS and the ontological focus of SESS might be integrated into a more encompassing analytical architecture for urban sustainability science.
Illustrating SESS: the Venice MOSE case
To demonstrate how these conceptual differences translate into distinct analytical perspectives in practice, we return to the Venice MOSE case. Rather than offering a full empirical application, we use the Venice MOSE case as a diagnostic illustration to show how the same urban challenge is refracted differently through SES, SETS, and SESS (Table 1; Fig. 3).
The three panels depict how the same climate adaptation challenge is refracted through SES (a), SETS (b), and SESS (c). Each panel maps the key variables, interactions, and trade-offs foregrounded by the respective framework onto the spatial context of Venice, its lagoon, and the MOSE flood barrier system. Variable codes correspond to those defined in Table 2. The comparison demonstrates the complementary relationship among the three perspectives.
An SES analysis (Fig. 3a) would frame this as a trade-off between social values (heritage appreciation, economic dependence on tourism, resident well-being) and ecological functions (lagoon ecosystem health, tidal dynamics, sediment transport). The governance challenge would center on how institutions mediate between these two domains. The built environment enters the analysis primarily as a passive object of protection or as context for social-ecological interactions.
A SETS analysis (Fig. 3b) would add a valuable layer by foregrounding MOSE as an infrastructural system embedded in a network of interdependencies. It would examine how MOSE interacts with Venice’s water management infrastructure, transportation systems, and energy supply. The analysis would attend to infrastructure lock-in: the multi-billion-euro investment constrains future adaptation options and creates path dependencies in flood management strategy. It would also consider cascading risks: if the barrier system proves insufficient under accelerated sea-level rise, what are the consequences for interconnected urban systems? This perspective foregrounds dimensions that a standard SES analysis is not designed to prioritize.
A SESS analysis (Fig. 3c), while sharing the recognition that MOSE must be understood as more than a social-ecological trade-off, foregrounds a different set of questions organized around the three ontological dimensions of the spatial system. In terms of Morphology and Configuration (SP1), the project’s 1.6 km of mobile barriers comprising 78 steel gates, together with concrete caissons, breakwaters, artificial islands housing control systems, and navigation locks that maintain selective vessel transit during closures, collectively constitute a configurational intervention in a spatial system whose urban morphology has remained broadly continuous since the Middle Ages. Venice’s Outstanding Universal Value rests on the integrity of the morphological relationship between city, lagoon, and sea, a relationship co-produced over more than a millennium67. The MOSE infrastructure reorganizes the spatial configuration of the three inlets that have historically mediated this relationship, replacing the historically continuous permeability of these thresholds with a managed, intermittent connectivity, altering the morphological legibility of the lagoon boundary at landscape scale, disrupting the seasonal migration pathways of fish species that depend on uninterrupted lagoon-sea exchange (I2)68, and reconfiguring the accessibility patterns of island fishing communities whose livelihoods have been organized around these tidal thresholds for centuries (I1)69.
In terms of Materiality and Metabolism (SP3, SP4), the consequences of this configurational change become visible when traced through the lagoon’s material flows. Under normal tidal conditions, ~60% of the lagoon’s water volume is exchanged with the Adriatic Sea during each tidal cycle70, and peak discharge through the inlets can reach 20,000 m³/s during spring tides71. Each MOSE closure temporarily halts this exchange. As sea levels rise, closures are becoming more frequent: the barriers have been activated with increasing regularity since becoming operational in 2020, and modeling studies project that under high-emission scenarios, MOSE closures during autumn months may exceed 20% of the time, substantially reducing water exchange with the open sea and exacerbating eutrophication risks in confined areas of the lagoon72. Meanwhile, analysis of recent storm events reveals that each major surge results in a net sediment loss of ~14,000 tons from the lagoon, with barrier operations affecting the spatial distribution of sediment import and export across the three inlets73. Reduced sedimentation also threatens the vertical accretion of salt marshes, compromising habitats that support the lagoon’s biodiversity (I2)74. These metabolic flows are thus governed by the physical operation of a spatial structure whose design thresholds embed specific climate projections into the material fabric of the city, and whose load-bearing limits define the upper boundary of the system’s adaptive capacity. The causal chain extends further into the social domain: the same hydrodynamic changes that alter ecological processes also condition the productivity of clam aquaculture and artisanal fisheries that have sustained lagoon communities for centuries (I3)69.
Most distinctively, in terms of Historicity and Memory (SP5, SP6), the case brings into focus a conflict between two temporal orders operating in the same physical space. MOSE embodies a logic of future-oriented engineering designed for projected climate scenarios on a decadal timescale, yet its long-term efficacy is uncertain: studies suggest that accelerating sea-level rise may require increasingly frequent closures that progressively transform the lagoon from an open tidal system into a periodically enclosed basin71. Venice’s built environment, by contrast, embodies an accumulated heritage whose value derives from historical continuity across centuries. The spatial entanglement of these two temporal orders is rendered most tangible in the Venice Arsenal, where the MOSE command center and lagoon management functions have been housed since 2011 within a historic complex that symbolized the maritime power of the Serenissima for centuries before falling into decades of decay. The restoration of the Arsenal to accommodate MOSE operations simultaneously safeguards a heritage of extraordinary architectural value and repurposes it as a hub for climate-adaptation engineering, condensing within the same physical structures the very temporal collision between accumulated identity and future-oriented intervention that characterizes the broader case. UNESCO has repeatedly assessed the combined effects of climate change and human interventions on the property’s built fabric and landscape attributes, warning that unresolved threats could warrant inscription on the List of World Heritage in Danger67. Such warnings carry force precisely because the accumulated morphological and material identity of the city constitutes the basis upon which heritage governance frameworks (SO1) and community attachment (SO6) are organized; any spatial reconfiguration therefore simultaneously destabilizes the social structures built upon it (I1). The Climate Heritage Paradox is thus not merely a social preference conflict but a temporal collision traversing all three domains of the SESS framework. The infrastructure built to protect heritage simultaneously transforms the very spatial conditions that constitute it: the open relationship between city and sea, the tidal rhythms embedded in Venetian architectural fabric, and the morphological character of a lagoon landscape co-produced over a millennium.
The comparison is not intended to establish a hierarchy. Each framework illuminates dimensions that the others leave in the background. The purpose is to demonstrate that SESS generates a distinct and complementary perspective, one particularly valuable for challenges where the morphological, material, and historical properties of the spatial system mediate the interactions between social and ecological processes, and where rendering these mediating properties analytically visible is a precondition for adequate diagnosis.
Analytical implications and future directions of SESS
Table 3 illustrates how the SESS framework reframes the analysis of key urban challenges by rendering the configurational, material, and historical properties of the spatial system analytically visible.
By grounding abstract trade-offs in the configuration, materiality, and history of the built environment60, the SESS framework opens a rich research agenda that will further integrate urban sustainability science into a more interdisciplinary realm. One major direction is the modeling of the temporal complexity of urban evolution. Future studies should explore the relationship between the slow spatial system with its inertia and lock-in and fast-moving social and ecological variables. It necessitates the creation of new methodologies that couple high-resolution urban form analysis with life-cycle analysis of the built environment and dynamic ecosystem service modeling. Recent advances in high-resolution material stock mapping63 and urban morphology-sustainability assessment60 provide promising methodological foundations for such integration. In addition, the framework promotes research aimed at measuring the constraining influence of the path dependency of the spatial system on future adaptation pathways, determining critical thresholds of urban transformation.
The implications of the SESS framework for urban governance are also considerable, as it calls for a more spatially aware approach to policymaking. It reminds policymakers that any intervention is not simply an input into a social or ecological system but a reconfiguration of a spatial system with enormous inertia and long-term effects. Sustainable urban futures thus necessitate the breaking of sectoral silos. It requires merging urban planning, environmental management, and cultural heritage conservation within an integrated analytical framework to develop holistic and adaptive policies. The SESS framework, together with the complementary perspectives offered by SETS and frontier SES scholarship, provides a conceptual foundation for such integration.
Limitations
A number of methodological limitations should be acknowledged. Our systematic review was restricted to peer-reviewed journal articles in English indexed in Web of Science Core Collection and Scopus75. This inevitably introduces publication bias, as pertinent gray literature and non-English research are excluded. Furthermore, the search strategy was designed around SES-specific terminology, which means that scholarship engaging with urban spatiality through other conceptual vocabularies, including the SETS literature, socio-technical systems research, urban metabolism studies, and spatially advanced work in urban ecology, was not captured in the quantitative review. In particular, spatially rich concepts such as heterogeneity, patch dynamics, and place, which appear frequently in ecologically and geographically oriented SES research, were not included as search terms; a complementary review organized around such vocabulary would likely reveal additional dimensions of the field’s engagement with space. Our findings therefore characterize a specific body of literature rather than the full breadth of urban sustainability scholarship. We have sought to address this limitation through the qualitative comparison with SETS presented in Discussion, but a future review mapping spatial treatment across multiple frameworks would be a valuable complement. In addition, the review was limited to journal articles, excluding book chapters and monographs. Some of the most integrative spatial thinking in the SES tradition has been developed in longer-form publications (e.g., ref. 12.13), which permit the kind of extended, exploratory synthesis that journal articles often cannot accommodate.
The four-level coding system though strictly implemented and tested with near-perfect inter-rater reliability, inherently reduces sophisticated theoretical treatment to ordinal categories, entailing a degree of interpretation. In our qualitative analysis, we have strategically analyzed the Level 4 studies to explore the analytical frontier. As a result, quantitative analysis of the broader literature (Levels 1-3) was conducted to determine the degree of spatial engagement and not the quality of content. This approach, while necessary to map the macro-structure of the field, can miss emergent spatial conceptualizations within the literature. Lastly, the SESS framework is presented as a conceptual contribution. While its analytical capacity has been illustrated through the Venice MOSE case, the framework requires rigorous empirical testing and operationalization across diverse urban contexts to fully validate its utility.