Historic Buildings as Urban Sensors: Multiscale Diagnostics for Climate-Resilient Cities

1. Introduction

Heritage deterioration is a growing global concern (Bryant; Turner, 2019). Its drivers include natural causes, neglect, ignorance, temporal decay, and increasing exposure to multiple climate-related threats [1,2,3]. These threats are unevenly distributed around the world, with the Global South carrying a disproportionate burden of the consequences, aggravating risks in densely populated urban areas (Figure 1) [4]. Climate change affects physical, cultural, and social aspects of heritage, positioning it as both a cultural asset and a potential vulnerability. Its losses have long-term impacts and ultimately threaten community sustainability [5,6]. Thus, the state of conservation of historic resources and the mechanisms for their protection can be interpreted as indicators of environmental resilience and adaptive capacity. Climate risk management for heritage protection involves adaptation and mitigation actions that must be implemented in concert to support the conservation and management of cultural assets [7]. This change in perspective emphasizes the need for heritage preservation in parallel with regional development, incorporating preventive adaptation and requiring a greater understanding of the intangible values that heritage represents [8,9].

Climate change has exposed communities to multiple types of threats, which can be exacerbated by their interactions [2]. The dynamic and multidisciplinary nature of cities poses challenges for developing solutions, requiring in-depth technical knowledge and skilled teams that often have limited financial resources [10]. Given that cities can be understood as complex systems composed of multiple interconnected and interdependent layers, urban historical heritage can be regarded as a layer of the urban system [6]. It results from human-ecosystem interaction in a landscape over time, creating a sense of identity among the community and helping to boost economies through the tourism industry [11,12]. This has catalyzed the development of strategies to build resilience and adapt to climate change as an imperative for reducing vulnerabilities [13,14]. The adoption of mitigation strategies, through alternative and sustainable responses that use the connections between nature and human well-being to enable cities to withstand and recover from extreme weather events, emerged as a promising solution [15]. Therefore, a holistic and integrative perspective that considers the social, economic, and cultural co-benefits for communities is required [16,17,18,19].

The Historic Urban Landscape (HUL) approach, adopted by the Recommendation on the Historic Urban Landscape in 2011, is a robust holistic approach to addressing the problem by considering the inclusive and interdisciplinary management of heritage elements in dynamic environments, including the broader urban context, the geographical and environmental setting in which it is inserted, guiding change in historic cities through multi-criteria analyses [20]. From this perspective, the historic built fabric is no longer interpreted as isolated; rather, it functions as a multiscale diagnostic medium that reveals critical interactions among different aspects of the urban environment. To deal with the great diversity of characteristics of both the heritage and the context in which it is inserted, the HUL approach proposes a set of steps and tools that will help implement the approach, assisting managers in decision-making and facilitating the use of information by non-technical groups [21,22]. This article has two goals: to analyze HUL’s implementation, recognizing important challenges, and to evaluate the integration of climate vulnerability assessment within this framework. By examining these aspects, the study seeks to advance understanding of the approach, particularly its potential for integrating climate risk management and heritage conservation.

2. Methodology

A systematic evaluation was conducted on peer-reviewed academic articles published between 2020 and 2024 to examine how the HUL approach has been adopted and analyze the integration of climate vulnerability assessment. The term “historic urban landscape” was searched in the ScienceDirect (SD), Scopus, and Web of Science (WoS) databases. In addition to the time constraint, the search considered only English-language articles and review articles that were open access. Access restrictions were implemented to ensure the replicability of the research, while language limitations prioritized selecting higher-impact articles, given that English has been used as the academic lingua franca [23]. The database results were downloaded as CSV files and processed in Google Sheets, enabling the removal of duplicate entries. The remaining 169 unique records were assessed against five eligibility criteria (Table 1), resulting in 37 relevant studies addressing the HUL approach (Figure 2, Appendix A).

The 37 remaining publications were divided into theoretical and empirical work. In theoretical works, the HUL approach was critically analyzed and developed. The empirical studies were examined using the HUL steps and tools and then submitted to the online AI DeepSeek Chat (DeepSeek-V3.2) to assist in their identification and reduce subjectivity. To be correctly processed, two procedures were adopted: (1) the downloaded papers’ pdf were opened with the software Mozilla Firefox and saved again as pdf; (2) the saved files were opened with a pdf editor, and the abstract text was erased. This was intended to remove metadata and hidden text and to prevent the abstract from being used to justify or underpin the answers, which could misdirect the AI’s responses. The documents were uploaded, and the same two prompts - one for tools and one for strategies - were used on every one of them (Table 2), developed based on the Recommendation and on “The HUL Guidebook” [20,24]. The AI replies were then analyzed and accepted when agreed upon.

3. Climate Change and Cultural Heritage Conservation

The need to predict and prevent impacts resulting from climate change, highlighted by the First World Climate Conference by the World Meteorological Organization in 1979, was the primary catalyst for the conception of climate change as a scientific field. It was defined as changes in the characteristics and properties of the climate caused, directly or indirectly, by human interference in ecosystems [25] and, since the 1980s, has led to the development of reports, programs, agreements, and organizations by researchers and professionals. The 1987 Report of the World Commission on Environment and Development, “Our Common Future,” identified sustainable development as both an approach and a goal to address climate change. However, sustainable development is not possible without considering disaster risk reduction (DRR) [26].

Over the years, the main global DRR efforts have focused on adapting by developing frameworks and goals [3]. Their focus shifted from reducing losses and disaster-induced impacts to life and property to diminishing the vulnerability of elements and improving ecosystems’ adaptability and resilience [26,27]. Resilience refers to a system’s ability to withstand and recover from disturbances while maintaining its basic structures and functions [15]. It requires a dynamic understanding of the subsystems involved and their interactions in order to select the most appropriate strategies [26,28,29,30]. The goal of this modern approach - resilient management - is to make the community capable of resisting, absorbing, adapting, and recovering efficiently from the effects of hazards. It is especially relevant for urban environments, complex systems formed by different layers through time, where the concentration of people, economic activities, institutions, and infrastructure makes them vulnerable to the increased frequency and intensity of extreme weather events [31,32]. Studies reveal different aspects of implementing resilient management, highlighting the complexity inherent in the topic [28,33,34], requiring a series of methods and tools that enable understanding and decision-making regarding climate change risks [35,36,37].

Climate change was only formally recognized as a risk to cultural heritage in 2005 by the World Heritage Committee (despite being studied since the 1990s) [38], with its inclusion on a DRR framework as a criterion in 2015 by the Sendai Framework [39]. Recent estimates indicate that approximately 17% of cultural heritage sites are at risk from climate change [5]. Cultural heritage comprehends tangible and intangible cultural and social aspects that are valued [38] and risk is the chance of negative consequences from a climate-related hazard, a consequence of the combination of elements present in the affected areas (exposure), their likelihood of being negatively affected (vulnerability), and the possibility of an event’s occurrence (hazard) [25]. Heritage is important as a relevant factor of social cohesion and identity [6,40,41],with its loss identified as a threat that challenges the sustainability of economic dynamics, especially in locations that are still in the process of modernization [8,41]. However, Dhar and Khirfan [27] and Shirvani, Dastgerdi, and Kheyroddin [42] identified challenges related to the lack of integration among different planning approaches and the difficulty of knowledge transfer across multiple sectors, which undermine the development of DRR solutions. In addition, Figueiredo, Romão, and Paupério [43] also noted the lack of public data (both at the macro and micro levels), which compromises the adequate characterization of the location and the consistency of risk and impact estimates. In the context of heritage conservation, Zin and Ismail [3] identified a challenge to adequate heritage protection within DRR frameworks due to a knowledge gap between heritage and climate experts.

Current research indicates increasing implementation of adaptation and mitigation strategies for cultural heritage [38], primarily through various approaches to assessing heritage elements. Sevieri et al. [37] developed the Multi-Hazard Risk Prioritization Framework; Ramírez Eudave et al. [41] combined the Vulnerability Index Method (VIM) with machine learning to identify vulnerable structures to earthquakes; and Salazar, Figueiredo, and Romão [44] identified 22 proposed flood vulnerability indicators. These advancements reveal common pitfalls in vulnerability assessments: they are frequently centered on specific monuments, focused on tangible aspects, led by specialists, ignoring contextual characteristics that can influence the durability, conservation status, and management solutions.

Developing comprehensive methodologies is essential to reframing perceptions of heritage urban conservation in the context of contemporary climate challenges. An early example of this course of action is UNESCO’s resource manual “Managing Disasters for World Heritage” [45]. This manual guided the development of disaster risk management (DRM) plans in World Heritage Sites by promoting hazard protection and the reduction of underlying vulnerability factors, underscoring the need for a context-specific evaluation framework and integration of heritage DRM into larger-scale planning. The Sendai Framework also underscores the need for an approach grounded in a broader understanding of risk and inclusive decision-making, supported by the dissemination of open data [3,31,46]. In a more recent example, the Climate Risk Sourcebook incorporated findings from the IPCC’s Sixth Assessment Report to propose a flexible method for climate risk assessment [47]. It identifies and analyses risk drivers, their root causes, and potential impacts and consequences, thereby supporting climate change adaptation, mitigation, and management outcomes. This framework considers stakeholder involvement a crucial element, underscoring the importance of local communities in developing effective actions for climate risk management and adaptation planning. These examples illustrate a trend toward integrating conservation and climate risk assessment through a holistic approach that allows the incorporation of different initiatives, stimulates knowledge sharing, enables community engagement, and translates insights into actionable recommendations [5,6,38,48,49].

4. The HUL Approach

Holistic approaches have been adopted as another avenue for developing solutions that promote resilience and sustainable development [6,50,51]. In the 1960s, Ian McHarg [52] developed a method for suitability analysis in landscape design. It involved mapping and interpreting a site’s natural and artificial processes as a set of superimposed layers to recognize the potential and constraints of the territory (Figure 3). Since then, this approach improved through the incorporation of new methods and tools (i.e. Geographic Information Tools and Multi-criteria Decision Analysis) and has been applied in multiple contexts to optimize complex spatial solutions and enhance planning strategies [53,54,55].

In 2011, the 36th General Conference of UNESCO adopted the Recommendation on the Historic Urban Landscape (Recommendation), which called on its member states to integrate the protection of urban historical heritage, which represents about one-third of World Heritage properties, into their development policies (UNESCO, 2011, 2023b). The Recommendation introduced the concept of HUL as an urban area resulting from the integration of layers of information on historical, cultural, and natural values. It encompasses the broader context of heritage through a multidisciplinary, holistic interpretation that incorporates both tangible and intangible characteristics associated with the element under analysis. The central idea of HUL recognizes the dynamic nature of cities and the need to understand heritage at scales beyond the object [20,36,56].

The HUL approach emerged in response to the increasing complexity of global events and urban processes [57]. It views urban heritage as essential, redefining its role in society and in decision-making processes [36,57]. HUL’s primary goal is to create mechanisms for balancing heritage conservation and sustainable development using political, financial, regulatory, and engagement tools to manage change [58]. It is a tool that must be incorporated into current practices to help heritage management. This new understanding suggests a broader, more flexible concept, allowing multiple interpretations and adaptations across contexts, shifting attention from purely conservative practices to more democratic ones [36,59]. Cunha Ferreira et al. [60] notices three innovative points: (i) the use of a landscape approach; (ii) a multidisciplinary and collaborative perspective; and (iii) the incorporation of multiple stakeholders. Quesada-Ganuza et al. [6] also note the inclusion of climate and socioeconomic risk assessments as an important novelty.

Common criticisms of the HUL approach center on its flexibility, particularly the absence of methodological clarity and tools to allow an effective implementation [56,58]. To bridge the gap between theory and practice, six critical steps are recommended: (1) mapping of natural, cultural, and human resources; (2) collective definition of what to preserve; (3) assessment of climate and socioeconomic risks; (4) integration of protection into urban planning; (5) prioritizing actions that balance conservation and development; (6) creating partnerships and local management structures. To deal with this complexity proposed by HUL, four groups of tools are proposed: (1) understanding and planning, (2) community engagement, (3) regulation, and (4) financing, in order to incorporate all the specificities necessary for its understanding. These tools are interdisciplinary and innovative, and need to be adapted and used simultaneously to ensure successful heritage management [20,24] (Figure 4).

5. Results and Discussions

5.1. Overview

The literature reveals a clear consensus on shifting from a monument-centric conservation to a holistic, values-based paradigm. This is evidenced by 8 theoretical papers (22%) and 29 empirical studies (78%) (Figure 5). The significant concentration of publications on urban planning themes (Figure 6) demonstrates recognition that the HUL approach is valued not only as a heritage tool but also as a systemic governance framework for managing complex urban change. This new perspective facilitates linking HUL to broader agendas, such as UN Sustainable Development Goals (SDGs) [49,61], adaptive reuse [62,63,64,65] and the New Urban Agenda (NUA) [49].

The evolution of the field was characterized by a transition from early studies emphasizing the definition and promotion of HUL [56,66,67] to more recent research focused on its operationalization through the creation of tools, frameworks, and metrics [61,68,69,70,71]. The concentration of papers on the 2023-2024 period (70%) shows growing attention, moving from conceptual debate to empirical application. A key trend involves integrating established digital technologies, such as BIM and GIS [68,69], with emerging tools, including social media data [72] and participatory platforms [67]. This integration aims to improve understanding of HUL’s complexity and dynamism and to engage community participation. This latter aspect is recognized by the theoretical papers as the least implemented and most challenging, despite its central importance [39,56,67,69,73].

Findings indicate that academic discourse on the HUL approach over the last five years has been concentrated in Asia, with particular focus on China (Figure 7) [39,56]. Chinese publications predominantly employ spatial and statistical analysis and GIS [51,57,59,68,70,71,72,74,75,76], presenting a technocratic approach. In contrast, non-Chinese Asian studies apply the HUL framework in contexts of marginalization, degradation, disaster and policy failure [36,49,77,78,79,80]. European research emphasizes governance, community engagement and policy analysis [60,62,63,64,65,81,82]. Meanwhile, African studies [83,84] use HUL to redefine existing heritage paradigms and the legacies of colonialism. Notably, there is a lack of publications from Oceania and the Americas.

5.2. Steps and Tools

The analysis of the 29 empirical studies aimed to assess the use of HUL steps and tools (Figure 8 and Figure 9; Appendix B). Findings show that comprehensive survey and mapping (Step 1) is the most adopted, with a prevalence of 90% (n = 26). This is further reinforced by the predominant use of knowledge and planning tools (Tool 2), employed in 93% of the cases (n = 27), highlighting the technocratic aspect of HUL. Step 1 appears as the starting point, involving data collection and systematization to produce outputs for subsequent analysis. A notable evolution has been observed from traditional mapping and surveying by incorporating new methodologies (i.e., remote sensing, user perception, and spatial analysis) and the integration of the temporal dimension, facilitating the progressive interpretation of changes.

Step 5 (n = 18), prioritization of actions that balance preservation and development, is often an outcome of analysis that recognizes priority areas, with the prioritization often implied than actionable. It is highly influenced by Step 2 (n = 17), collective consensus on what to preserve, which is closely related to Tool 1 (n = 15) - the civic engagement tool. Together, they encompass social and political processes. It is noteworthy that, although Step 2 and Tool 1 are basic requirements of the HUL approach, their implementation is inconsistent, ranging from mere consultation to co-design of solutions with actors varying from specialists to local communities. Also, the evolution of Step 1 and Tool 2 through the use of modern technologies is reflecting on a transition of Step 5 from qualitative prioritization toward a data-driven process with the use of Multi-Criteria Decision Analysis (MCDA) models, reducing reliance on subjective perception of participants.

Despite being used in 14 of the 29 papers, the vulnerability assessment to climatic impacts and socioeconomic stresses (Step 3) represents a significant gap in the HUL approach. Its occurrence is overwhelmingly associated with socio-economic factors (n = 9), including tourism, gentrification, development pressure, policy failures, and post-disaster challenges. Indexes, criteria, and community participation were used in 3 out of 5 papers addressing climate assessment. Only two studies [60,74] conducted climate change assessments in a structured manner, highlighting the weak link between climate threats and heritage action. Step 3 should be closely integrated with Step 1 and Tool 2 to establish a robust diagnostic foundation for the HUL approach.

Steps 4 (n = 13) and 6 (n = 9) - heritage protection integration on urban planning, and establishing local partnerships and management frameworks, respectively - along with Tools 3 (n = 6) and 4 (n = 3) are the least used components. Collectively, they can be considered the action phase of the HUL approach, which should shift from planning for heritage to planning with heritage while securing resources. However, in most papers, the outcomes of Step 4, Step 6, and Tool 4 are theoretical recommendations, whereas Tool 3 is used primarily to analyze and critique existing regulatory systems, with few authors proposing new regulations. This pattern shows HUL’s difficulty in influencing mainstream urban development.

The results reveal the HUL approach’s flaw: none of the analyzed papers fully applied the proposed steps and tools (Appendix B). Most studies perform well in the diagnostic and value identification phases (Steps 1, 2, 5, Tools 1 and 2), but stall in the implementation phase (Steps 4, 6, Tools 3 and 4). The inconsistent participatory aspect can conceal a technocratic approach, in which communities are engaged to identify values but do not participate in decision-making, with proposals remaining expert-led [51,59,78]. Vulnerability assessments (Step 3), when they happen, are frequently centered on socio-economic tensions [58,62,63,75,76,77,80,81,83], while climate change ones are regularly overlooked - HUL is being used as a tool to manage heritage within a dynamic urban environment rather than actively adapting heritage to climate change.

6. Conclusion

This paper shows that the HUL approach provides a critical, scalable framework for reframing-built heritage as a diagnostic medium through which climate–urban–heritage interactions can be understood. The literature revealed its applicability in integrating heterogeneous data and stakeholder perspectives across scales. The number of publications that reported implementation cases also showed a trend toward operationalizing the approach, aligning it with more effective practices. This was evidenced using models, frameworks, and digital tools for documentation and evaluation; the integration with broader agendas (Sustainable Development Goals, Circular Economy, and Urban Resilience) that encompass dimensions beyond heritage conservation; and the expansion of the scale of analysis to incorporate the diversity of the urban environment. It was revealed that community participation remains a critical challenge, despite its positive results, as it ranged from simple consultation to complex co-creation processes, thereby compromising the sense of identity associated with cultural heritage. Additionally, an in-depth examination showed that HUL is often used as a mere checklist, overlooking the relationships and interdependencies between strategies, resulting in partial application - an antithesis of the core definition of the approach.

In the studies examined, the absence of a climate vulnerability assessment was the primary flaw in the application of the HUL approach. The current need to manage climate extremes for heritage preservation has been largely neglected, with climate vulnerability relegated to the background and treated as one of many stressors. This paradox reveals a fundamental flaw that breaks the system proposed by the approach. Given the low adoption of Steps 4 and 6 and Tools 3 and 4, it can be concluded that, despite its holistic intentions, HUL has been a sophisticated mapping exercise focused on problem recognition rather than a framework for solution development.

To move beyond a mapping exercise and become a tool for solution-building capable of facing the growing need for climate adaptation, the HUL approach must be converted into a climate adaptation framework. This would allow the integration of climate imperatives into heritage preservation planning through a values-based conservation and planning framework. Future work should focus on developing an HUL-Climate Adaptation Protocol to operationalize a holistic perspective, placing climate vulnerability assessment and adaptation strategies at the center of the approach as fundamental and non-negotiable steps. It is also suggested that new research on the topic be conducted that expands publications beyond academic articles, adopts languages other than English, and includes not only open-access, so that a more complete picture of the use of the approach can be captured and the most at-risk context can be included. Evolving the HUL into a climate adaptation tool promoting participatory, resilient, and integrated heritage preservation is not merely an academic task, but an urgent practical call to safeguard cultural heritage as a central element of resilient and sustainable urban futures.