Adapting Cultural Heritage to Climate Change: Advances in the Study of Hygrothermal Behavior

1. Introduction

Climate change is widely recognized as one of the most significant threats to cultural heritage worldwide [1,2,3]. Changes in temperature and relative humidity, along with the increase in precipitation and pollutants, impose additional stress on built heritage and cultural artefacts [1]. These factors accelerate deterioration processes in ways that are often difficult to predict. The challenges become even more complex when the buildings housing the artefacts are themselves cultural heritage sites, such as churches, monasteries, cathedrals, or museums, without reliable indoor climate control. Monitoring, predicting, or even slowing down damage in these places is a significant challenge. There have been significant advances in this field in recent years, including diagnostic tools, climate monitoring, and numerical modelling. These advances have significantly improved our understanding of how cultural heritage reacts to climate fluctuations. Nevertheless, substantial knowledge gaps remain. This Special Issue brings together eight research studies that reveal just how broad and complex this field is. The authors have employed a variety of techniques, including non-invasive testing, laboratory experimentation, microscale analysis, in situ climate monitoring, and numerical simulations. Furthermore, the contributions included herein cover a wide range of scales and materials, from frescoes [4] and stone materials [5,6] to wood artefacts [7], bio-based boards [8], and whole-building analyses [9,10,11]. Each study provides a new perspective, exploring how climate change drives deterioration and offering practical approaches to making conservation efforts more robust and adaptable in a changing world.

2. An Overview of Published Articles

The multifaceted nature of hygrothermal damage triggered by climate change has become increasingly evident following recent developments in cultural heritage research [4,5,6,7,8,9,10,11]. This field of research furthers our theoretical understanding and provides practical support for conservation methodologies. For example, Gallo et al. [4] demonstrated how the integration of non-invasive analytical techniques can reveal the factors driving the deterioration of fresco paintings, such as persistent transmission, saline activity, and microclimatic variability. On the other hand, Lyu et al. [5] emphasized the importance of understanding deterioration mechanisms. The study of sandstone under different dissolution conditions shows that dynamic dissolution processes accelerate surface cultivation and pore structure evolution in stone materials. This information is complemented by the experimental work of Hong et al. [6], who investigated sulfate-induced protection in heritage stone sites. Their work distinguishes between modes of damage driven by crystallization and dissolution and clarifies how environmental conditions shape the progression of a saline climate. This research field frequently considers the properties of organic materials, including wood. It is evident that there are complex, multifactorial interactions between climate change, biological influences, and the natural ageing process of wood, as reported by Ibrahim et al. [7].

Another source of hygrothermal stress is the presence of visitors affecting the indoor climate of a building. Research conducted by Galiano-Garrigós et al. [9] on the Church of San Juan del Hospital has shown that visitor flow impacts the church’s climate. Higher visitor numbers result in higher internal temperatures, changes in relative humidity, and increased the CO₂ levels. Cumulatively, the impact of visitors on sensitive wall surfaces, finishes, and artefacts is significant [9]. Bio-based materials have also entered the cultural heritage conservation discussion. Cintura et al. [8] investigated the use of bio-based boards as an alternative to conventional thermal insulation. Various formulation parameters can have a major effect on the hygroscopicity and morphological structure of bio-based boards, which, in turn, influences their ability to buffer moisture and affects the regulation of hygrothermal conditions within a building.

Understanding how indoor climate, building energy efficiency, and conservation requirements interact is very important. Silva and Henriques [10] analyzed a generic room at the National Museum of Ancient Art in Lisbon using numerical simulation. They found that the local climate in which the museum is located plays a significant role in determining energy efficiency and suitability for conservation. Therefore, to effectively balance the goals of indoor climate stability and energy performance, it is essential to develop a climate control strategy that is specific to the local climatic context [10]. In addition, Baltazar et al. [11], via the airflow modelling of a church, demonstrated how employing natural ventilation strategies can provide a means of maintaining appropriate internal temperature without compromising the building’s architectural and cultural character. This is an effective means of improving the indoor climate using passive strategies.

3. Conclusions and Future Perspectives

The studies included in this Special Issue demonstrate the diverse impacts of climate change on cultural heritage. Together, they emphasize the need for a multi-disciplinary approach to the effective conservation of cultural heritage. A major theme throughout this Special Issue is the use of new and innovative diagnostic methods that integrate recent advances in the environmental monitoring of cultural heritage, the predictive modelling of climate variability, the creation of sustainable climate control strategies, and our in-depth understanding of the unique properties of various materials. The collection highlights both progress and ongoing challenges. Advanced techniques—from non-invasive analytical methods to X-ray computed tomography [4], numerical simulations [10,11], and in situ climate monitoring [9]—have improved our understanding of the deterioration processes. The studies included herein demonstrate how different factors affect heritage materials, for example, dissolution processes in stone [5,6], biological and ageing processes in wood [7], and the impact of visitors on indoor climate [9]. Research on bio-based materials [8] and passive ventilation strategies [11] suggests promising directions for sustainable conservation approaches. By summarizing current diagnostic methods and providing a comprehensive overview of the climatic factors affecting cultural heritage, this Special Issue offers decision-makers and practitioners a broad and practical framework for developing durable and responsible heritage protection strategies in a changing climate.