Constructing Sustainable Shelters to Safeguard Monuments from Climate Change ^†

Abstract

Aiming to address climate change, management plans for monuments and archaeological sites should be upgraded in order to increase the resilience of historical sites. Adaptation to the SDG 11.4 and SDG 13 (Sustainable Development Goals 11.4 and 13) is necessary to mitigate climate change impacts on heritage structures. Proper protection against climate change may be achieved by adjusting the microclimatic conditions of the archaeological site by using shelters that perform as regulators. Artificially created environments depend on the construction of shelters that will be capable of performing as intermediate barriers between the outer climate and the interior, having different temperature and humidity conditions. The shelter determines the interior climate and also interacts with the surrounding environment.

1. Introduction

In order for the Sustainable Development Goals (SDGs) to be achieved, scientific research should provide the knowledge required for designing, implementing and monitoring the SDGs, but it should also, at a practical level, provide standards and solutions [1].

Proper protection of heritage structures against climate change may be achieved by adjusting the microclimatic conditions on the site by using shelters, which perform as regulators. Artificially created environments depend on the construction of proper shells.

Since the shelter determines the interior climate and also interacts with the surrounding environment, it is crucial to define what we want to protect (type of findings and materials), whether or not human presence will be on the site, and take into account the climate and the morphology of the surrounding area.

Considering the protective shelter, recommendations should be given according to the size required, the architectural concept and shape to be integrated in the landscape, and the properties of the construction materials. An important issue is how to achieve energy efficiency, the cost of the construction and the possible funding sources. New challenges, such as energy autonomy, renewable systems, smart systems and Information and Communications Technology (ICT), have to be addressed.

Aiming at evaluating the construction of shelters in archaeological sites as well as their contribution to a stable microclimate on the site, the present paper includes comparative diagrams of temperature and humidity in underground heritage structures and proposes a methodology that can be used in similar cases [2]. In addition, this paper defines criteria and specifications regarding the construction of shelters for monuments and archaeological sites.

With respect to the SDGs, this work is at the nexus between SDG 11.4 and SDG 13. The target SDG 11.4 has a more prominent place as it aims to “strengthen efforts to protect and safeguard the world’s cultural and natural heritage”, while the target SDG 13 aims to “take urgent action to combat climate change and its impacts”.

2. Built Heritage and the Concept of Sustainability and Climate Change Adaptation

Sustainability in tangible heritage can be described as the action of preserving heritage assets as adequately as possible, while at the same time providing the best possible access to the site, given limited resources. The National Park Service (NPS) Climate Change Response Strategy sets out four primary pillars for the management of protected areas: science, adaptation, mitigation and communication [3]. In this scheme, the science pillar collects all work undertaken to gather climate-relevant data (i.e., measurements, modeling and related techniques). Adaptation combines efforts to determine what to do about climate change, including policy, guidance and approaches to planning and decision making. Mitigation refers to efforts aiming at reducing greenhouse gas emissions [4].

Regarding adaptation, it should be mentioned that there are two types of it. First, there is adaptation of management approaches to address the impacts of climate change in cultural heritage. Additionally, there is learning from cultural heritage in order to assist in adapting resource management and society to climate change.

Strategies need to be developed in order to reduce the negative consequences of climate change in sites of historical value and also to mitigate climate change by reducing greenhouse gas (GHG) emissions. The tangible cultural heritage is threatened by the gradually shifting of weather patterns and by extreme events. An increase in temperature, together with changes in precipitation, relative humidity and wind, can negatively impact the materials comprising a built heritage. This takes place because a change in average climatic conditions as well as changes in the frequency and intensity of severe weather events can affect the biological, chemical and physical mechanisms, leading to the degradation of the heritage structures [5].

Sabbioni et al. [4] developed guidelines for adapting the European cultural heritage to climate change impacts; these guidelines were later adopted by the Italian Strategic Agenda. Those included strategies for both physical adaptation and adjusting management practices. Cassar [6] investigated the impacts of climate change in archaeological sites and suggested adopting solutions that are sensibly designed to the specific conditions of the site after a long-term program of monitoring and maintenance. Additionally, Cassar [7] summarized the adaptation measures suggested by the UN Educational, Scientific and Cultural Organization (UNESCO) and by the International Council on Monuments and Sites (ICOMOS), who recommend increasing research, knowledge, education and engagement and also the upgrading of management plans including risk assessments and monitoring procedures to increase the resilience of the sites.

Climate change adaptation is thus a relatively new challenge, and this is the case in particular in the field of cultural heritage.

3. Why Is a Sustainable Shelter Important?

In the case of underground heritage structures, the external structural components, especially the external layers which often support wall paintings, are the most vulnerable to cyclic changes of the microclimatic conditions. The hygrothermal behavior of the walls depends on the boundary conditions of temperature and relative humidity inside the chamber and in the protective shelter. The water content in the mass changes during the year. Moisture fluxes change from negative to positive during the spring, and they switch again to negative during the fall. Positive fluxes mean that water is moving from the inside to the outer facades and evaporating, causing exfoliation of the external plaster. Negative fluxes mean that water is moving from the exterior layers to the interior of the chamber, which is getting wet again. Thus, an annual deterioration cycle is taking place.

Therefore, by stabilizing the conditions in the shelter, water movement is no longer taking place, and an equilibrium in the walls is achieved.

4. Shelters for Underground Heritage Structures. Case Studies Worldwide

Ancient tombs are underground structures, and as such they need specific protection measures on the site during the excavation procedure. They mainly need a proper shelter that will operate as a regulator for the microclimate.

Case studies worldwide show that the main issue to address when constructing shelters on the site is the stabilization of the temperature and humidity, thus reducing and minimizing the fluctuations of the exterior climate [8].

4.1. Royal Macedonian Tombs in Vergina-Greece

A tumulus-shaped shelter with a soil embankment was constructed over the Royal Macedonian Tombs in Vergina, including mechanical equipment to regulate the interior conditions of temperature and relative humidity (Figure 1, [9,10]).

4.2. Etruscan Tombs. Tarquinia and Cerveteri, Italy

In Tarquinia, Etruscan tombs dated from the 7th to the 2nd century B.C. were found, all carved out of bedrock. Problems of humidity were addressed. Once frescoes were repaired, transparent barriers, low-heat lighting and climatic monitoring systems were installed (Figure 2, [11,12]).

4.3. Tombs of the Emperors in Japan

The Takamatsuzuka tumulus, in the Asuka Historical National Park, is a site with great historic value, and its murals are considered to be national treasures. The burial is a stone chamber. Murals are painted on the walls and on the ceiling. The microclimate is being controlled. The original murals are not available for public viewing; replicas are displayed in the Takarazuka Mural Hall next to the burial tumulus (Figure 3, [13,14,15]).

4.4. Thracian Tombs in Bulgaria

The tomb in Kazanluk dates to around the end of the 4th century B.C., and it was inscribed in the World Heritage List. The burial chamber is decorated with murals. The tomb was secured under a permanent protective building with air conditioning to ensure a stable temperature. The negative impact of visitors is limited by constructing a nearby museum that contains a copy of the tomb and its decoration (Figure 4, [16]).

4.5. The Tombs of Egypt. Valley of the Kings and Queens

The tomb of Queen Nefertari, the favorite wife of King Ramses II (13th century B.C.), was discovered in the Valley of the Queens in 1904. In 1986, the Getty Conservation Institute in collaboration with the Egyptian Antiquities Organization created a multidisciplinary international group of experts who conducted an intensive six-year campaign. The works included microclimate conditions’ assessment, analysis, emergency treatment and conservation of the extraordinary wall paintings (Figure 5, [17,18]).

5. Evaluation Methodology

An evaluation methodology based on a computer simulation for a hygrothermal analysis will be crucial for decision making. In particular, a full understanding of the monument’s hydrothermal behavior and the contribution of each individual factor to the deterioration processes are given by the simulation program. In this way, decision making for the strategic management and control of the microclimate in the shelter will be based on the results of the evaluation.

Through the data collection, analysis, simulation and interpretation of the results, research aiming at protecting Macedonian tombs has provided an assessment methodology for microclimate control strategies.

This methodology has the following steps [2,19,20,21]:

• Investigation of the microclimatic conditions with recordings using digital recorders with sensors, evaluation of the recordings and conclusions;
• Simulation in the computer and visualization of the deterioration processes using the simulation program WUFI©, based on the recordings. The simulation program provides data concerning the hygrothermal performance of the tombs’ structural elements;
• Assessment of strategies to control the microclimate. As input, there are used set-points for the museum microclimate proposed by the international guidelines and standards;
• The interpretation of the results leads to conclusions about the effect of the applied microclimate on the hygrothermal performance of the tomb and, consequently, on the resulting deterioration processes;
• The general principles that come out can be applied to similar monuments.

6. Results Concerning the Construction of the Shelters of Macedonian Tombs

The variations of temperature and relative humidity have been recorded for three years inside three Macedonian tombs, two of them having been excavated in the area of Pella and the other near the village Agios Athanasios. After the excavation, protection shelters were constructed on the site, as follows:

The construction of a closed shelter on the Macedonian tomb of Agios Athanasios aimed at reducing the air exchange with the environment. It did not fully protect due to the lack of thermal insulation. The addition of styrofoam plates has improved the insulation inside the shelter.

The construction of an open metal roof on the two tombs of Pella was mainly intended to enhance the aesthetics of the monument, without contributing to the protection from the external climate (Figure 6, [2]).

The annual records of temperature and relative humidity show the following:

• The closed shelter of the tomb of Agios Athanasios seems to have protected the ancient structure to a certain degree. After its construction, the interior microclimate fluctuations were reduced but still remained quite intense. A wooden protective enclosure with a sheet of nylon was constructed. This was later reinforced with a double inlet and foam insulation, with noticeable results in reducing the range of fluctuations;
• The fluctuations were intense in the Ionic tomb C′, since no substantial intervention was made in order to reduce the effect of external climate changes, except for a sheet of nylon on the facade. The open metal shelter made no contribution;
• The fluctuations in the Doric tomb D′ were considerably reduced, as the closed shelter (a wooden enclosure with a sheet of nylon) has positively performed to isolate the interior from the outer environment and remained for a long time after the construction of the open metallic shelter.

The daily records of the contribution of the shelters to the interior microclimate show the following:

• Fluctuations in the external environment have been reduced in the tomb chambers. The shelter did not achieve the stabilization of the internal conditions, but only the minimization of the daily fluctuations;
• The shelter eliminated periodic fluctuations on a daily basis, but not on a weekly basis;
• Absolute moisture values were reduced internally, relatively to the environment;
• Fluctuations were caused by the entrance of people during the working hours of the day.

We must note that the reduction of the range of fluctuations inside depends additionally on the visitation hours and number of visitors, the dimensions and the volume of the interior chamber, the size of the tumulus, the degree of the excavation and the exposure of the structural body to the environment (Figure 7, [2]).

7. In Search for the Best Solution—Recommendations

The managerial and decisional adaptations to climate change suggested by the Intergovernmental Panel on Climate Change (IPPC) [22] included the following:

• Knowledge of climate change impacts on cultural heritage;
• Dissemination of information;
• Engagement with stakeholders (e.g., communities and decision-makers);
• Monitoring and maintenance;
• Inclusion of climate change in management plans;
• Preservation of values;
• Regulations and guidelines for adaptation;
• Mitigation strategies;
• Financial resources.

The IPPC also suggested practical adaptations, which included the following:

• Avoiding the inappropriate use of certain building materials and developing new materials compatible with the historic environment;
• Improving or strengthening monitoring;
• Digital recording of cultural heritage.

7.1. Minimum Requirements That the Shelter Must Provide

The shelter must provide the following minimum requirements [23]:

• Thermal insulation;
• Protection from overheating in the summer;
• Thermal capacity of the material of the components;
• Resistance to water vapor diffusion;
• Protection from external noise;
• Fire safety (non-flammable materials);
• Expansion properties control, thermal conductivity and water vapor permeability.

From a construction point of view, all of the above conditions are more easily met by an outer shell consisting of two layers. The exterior layer protects against rain, sun and winds, while the interior protects against heat and moisture. Possible air moisture can be treated with a slight ventilation of the space between the two layers of the wall. Such a construction solution also favors sound insulation.

7.2. Recommended Actions to Control the Microclimate

The following actions are recommended [24]:

• A shelter must ensure the control of microclimate conditions and possibly their correct setting to provide protection from humidity, temperature, solar radiation, micro-organisms, dust, atmospheric pollution, protection from indirect threats, i.e., those that act at an unseen level but are perceived only by their effects;
• Thermal insulation in the shelter is needed to protect the enclosure from overheating in the summer and frost in the winter;
• A sufficient heat capacity of the shelter components to avoid condensation and water formation internally during winter nights and to delay the temperature rise during peak hours;
• The possibility of receiving and removing the moisture generated in the interior (resistance to water vapor diffusion, water vapor barrier, dehydration);
• Double entrance to the shelter, so that one door will be closed when the other opens, in order to minimize the air exchange;
• In the case of mechanical systems operating in order to regulate the variations of temperature and relative humidity, energy consumption should be taken into account. Additionally, constant maintenance and good functioning must be ensured. The type of the shelter predetermines to a significant extent the internal climate and the cost of support systems;
• A mechanical system will manage the temperature and humidity in the shelter. Even if it cannot achieve a constant temperature and relative humidity throughout the year, it could minimize the heat and water flows through the tomb’s walls;
• The energy consumption for maintaining a stable indoor climate can also be affected by interventions in the surrounding area which can modify the microclimate, using artificial barriers and proper plantations for shading and for changing the direction and speed of the winds [2].

8. Conclusions

This paper emphasizes the need for more research, identification and dissemination of practical solutions and tools for the incorporation of climate change adaptation in the preservation and management of cultural heritage. With reference to the SDGs, this work connects SDG 11.4 and SDG 13, as was analyzed in Section 2.

Management plans for monuments and archaeological sites should be upgraded in order to increase the resilience of historical sites. This research provides standards and solutions in a practical way, in order for the Sustainable Development Goals (SDGs) to be achieved.

There is a great difficulty in generalizing adaptation solutions due to the diversity of typologies of built heritage, the different geographical locations of heritage sites, the surrounding context in which they are located and the local climatic conditions to which they are exposed, as well as the state of decay and the different materials, geometries, and ageing of the heritage structures.

In the case of the Macedonian tombs presented in this paper, the assessment methodology that is proposed and the obtained results reveal the importance of applying simulation tools, which can capture the particularities of the microclimate and improve the accuracy of the performance simulations’ results.

Climate change adaptation requires a case-by-case approach. Nevertheless, there are some types of adaptation practices that can be generalized, such as, for example, strengthening monitoring, using assessment methodologies based on simulation tools, protecting archaeological sites by constructing sustainable shelters in situ and of course increasing awareness of climate change impacts.