Local Climate Pressure on Cultural Heritage Sites—The Case of the Ancient Greek Theatre of Dodoni, Epirus, Greece †

: Climate change is an ongoing process with evident effects on local climates. Heritage management is vital for the protection of cultural heritage, with vulnerability assessment and mitigation-adaptation strategies. This research presents the pressure of local climate and the climate extremes on the ancient Greek theatre of Dodoni in North-Western Greece, which combines cultural, natural, tangible, and intangible heritage. The impact of local climate is analyzed by collecting climatological daily time series of ambient air temperature, humidity, and precipitation, acquired by the nearby meteorological station of Ioannina (Hellenic National Meteorological Service) for the period 1956–2022. This information is incorporated into heritage management for future protection.


Introduction
Cultural heritage refers to the tangible and intangible assets inherited from the past that are enriched with heritage values (historical, cultural, artistic, and scientific).The United Nations Educational, Scientific and Cultural Organization (UNESCO) plays a central role in the preservation and promotion of cultural heritage globally.Moreover, cultural heritage is also recognized as an essential component of the United Nations' 2030 Agenda for Sustainable Development.The kind of heritage that is studied in this paper is ancient Greek theatre, which is an integral part of Greek heritage.The case study is the ancient Greek theater of Dodoni.
Climate change is one of the most pressing global challenges of our time, and its impacts are being felt across various sectors, including cultural heritage.As global temperatures increase, melting glaciers and thermal expansion of seawater contribute to rising sea levels [1].Climate change intensifies the frequency and severity of extreme weather events, including hurricanes, storms, and floods.Also, both droughts and intense rainfall can have detrimental effects on cultural heritage.Moreover, there is contribution to the erosion and degradation of cultural heritage sites, particularly those located in vulnerable coastal or mountainous regions, with threats of sea-level rise and increased storm surges [2].The Intergovernmental Panel on Climate Change (IPCC) report (2019) [3] highlighted the importance of safeguarding traditional knowledge and its contribution to climate change adaptation, as the loss or damage of cultural heritage seems inevitable.The United Nations Educational, Scientific and Cultural Organization (UNESCO) [4] has been actively working to raise awareness and develop strategies for protecting vulnerable cultural heritage sites.The International Council on Monuments and Sites (ICOMOS) [5] has also been involved in research, advocacy, and policy development related to climate change and heritage.
Heritage management is a multidisciplinary field aiming to safeguarding cultural and natural heritage for its intrinsic value and as a source of identity, education, and sustainable development.It fosters a sense of place, supports local economies, and promotes cultural understanding and dialogue and it involves principles such as authenticity, integrity, sustainability, and stakeholder engagement.
Vulnerability assessment of heritage sites is a critical process that involves identifying and evaluating potential risks and threats to cultural and historical assets.Such assessments help in understanding the vulnerabilities of heritage sites and developing strategies to protect and preserve them.This tool collects information and analysis for the heritage assets regarding the following: (i) Environmental Factors: climate change and natural disasters; (ii) Physical Deterioration: aging infrastructure and pollution and industrialization; (iii) Human-Induced Threats: urbanization and development, as well as vandalism and theft; and (iv) Socio-Economic Factors: lack of funding and resources and tourism pressures.
Towards understanding the climate-related risks on the ancient Greek theatre of Dodoni, the objective of this study is to quantify the climate extremes on the ancient Greek theatre of Dodoni by means of extreme air temperature, precipitation, and humidity indices.

Ancient Greek Theater of Dodoni
The ancient Greek theater of Dodoni, located in northwestern Greece 22 km from the city of Ioannina near the modern village of Dodoni, was one of the most important theaters in ancient Greece.It follows the typical structure of ancient Greek theatres.It is semicircular in shape and consists of a seating area (koilon) for the audience, a circular orchestra for the performers, and a stage building (skené).The seating area could accommodate around 17,000 spectators, making it one of the largest ancient Greek theatres [6].The curved shape of the seating area allowed sound to be projected efficiently, enabling performers to be heard by the audience without the need for amplification.This acoustic feature was achieved by carving the seating tiers directly into the natural slope of the hill [7].The excavation process at the theatre of Dodoni started in 1874, with great evidence of the heritage [6].The monument faces problems of corrosion and structural decay.The damages of corrosion and erosion are relevant to the effects of climate change on the heritage of this theatre, which is vulnerable to the frequency of extreme weather events and the temperature and humidity variations.
The datasets used in the analysis concern 3 h observations of air temperature, relative humidity, and precipitation for Ioannina station (latitude: 39.6964 • ; longitude: 20.8225 • ; and elevation: 483 m) within the period 1955-2022 and have been provided by the Hellenic National Meteorological Service.In the process, the calculated climatic indices concern extreme air temperature and precipitation indices, defined by the joint CCl/CLIVAR/JCOMM Expert Team (ET) on Climate Change Detection and Indices [8].The air temperature indices concern tropical days, SU30 (number of days with daily maximum temperature above 30 • C); tropical nights, TR20 (number of days with daily minimum temperature above 20 • C); frost days, FDO (number of days with daily minimum temperature below 0 • C); ice days, IDO (number of days with daily maximum temperature below 0 • C); the maximum daily maximum air temperature, TXx; the minimum daily maximum air temperature, TXn; the maximum daily minimum air temperature, TNx; the minimum daily minimum air temperature, TNn; maximum diurnal air temperature range, Max DTR; and minimum diurnal air temperature range, Min TDR.The relative humidity indices concern maximum diurnal relative humidity range, Max DRH, and minimum diurnal relative humidity range, Min DRH.The precipitation indices concern dry days (number of days with precipitation below 1 mm); wet days (number of days with precipitation above 1 mm); very wet days, R95p (number of wet days with precipitation above the 95th percentile on wet days); extremely wet days, R99p (number of wet days with precipitation above the 99th percentile on wet days); the annual precipitation; the simple daily intensity index, SDII (the total daily precipitation amount on wet days divided by the number of wet days); heavy precipitation days, R10 (the number of days with daily precipitation above 10 mm); very heavy precipi-tation days, R20 (the number of days with daily precipitation above 20 mm); and extremely precipitation days, R30 (the number of days with daily precipitation above 30 mm).
The trends in the time series of the aforementioned climatic indices were estimated by the Mann-Kendall statistical method [9,10].

Results and Discussion
The climate extremes, defined in the previous section, are depicted in Figure 1 (air temperature and humidity extremes) and in Figure 2 (precipitation extremes).The statistical coefficients of the extreme climatic parameters are presented in Table 1.
simple daily intensity index, SDII (the total daily precipitation amount on wet days divided by the number of wet days); heavy precipitation days, R10 (the number of days with daily precipitation above 10 mm); very heavy precipitation days, R20 (the number of days with daily precipitation above 20 mm); and extremely precipitation days, R30 (the number of days with daily precipitation above 30 mm).
The trends in the time series of the aforementioned climatic indices were estimated by the Mann-Kendall statistical method [9,10].

Results and Discussion
The climate extremes, defined in the previous section, are depicted in Figure 1 (air temperature and humidity extremes) and in Figure 2 (precipitation extremes).The statistical coefficients of the extreme climatic parameters are presented in Table 1.More specifically, the variability and trends in the extreme indices pose significant concern in the deterioration of the historical monument.During the study period 1955-2022, the tropical days (TR30) show a statistically increasing trend resulting in more 28 days, whereas the frost days (FDO) count in more 14 days.The minimum daily minimum air temperature (TNn) has been decreased by −1.9 • C, and the maximum diurnal air temperature range (Max DTR) has been increased by +2.5 • C. Regarding relative humidity, the maximum diurnal range (Max DRH) has increased by 17.3% against decrease in minimum diurnal range by −3.2%.It is worthy to mention the statistically significant increase in precipitation extreme indices, namely, the number of very wet days (R95p) and extremely wet days (R99p) has been increased by 9 and 3 days, respectively.The annual precipitation totals count in more 853 mm within the study period, and daily intensity (SDII) shows an increase of 2.4 mm/day.Regarding heavy precipitation days (R10), very heavy precipitation days (R20), and extremely precipitation days (R30), increases of 14 days, 17 days, and 16 days appear, respectively.
The increases in tropical days and maximum diurnal air temperature range contribute synergistically with the increases in extreme precipitation in the observed deterioration of the ancient theatre of Dodoni.Additionally, the increases in the maximum relative humidity range could interpret the gradual wear of the open monument.Taking into consideration the current variability and trends in the climate extremes associated with the recorded deterioration of the ancient theatre, it is of great concern that the anticipated climate conditions will pose a high risk of the vulnerability of open historic structures in Greece, which are exposed in higher frequencies and intensities of climate extremes.

Conclusions
The interpretation of the findings can expose the crucial points of the vulnerability of the heritage landscape.As climate change dictates a process of alterations and modified environmental conditions, heritage management should be focused on mitigation and adaptation strategies in order to obtain the sustainability of culture.Thus, the ancient Greek Theatre of Dodoni is identified by the current condition of its environment, which influences the landscape and the heritage.The documentation of heritage values along with meteorological measurements show the risks and the eminent damage caused by climate change.

Figure 1 .
Figure 1.Time series of Tropical Days (TR30) and Tropical Nights (TR20) (upper left graph), Frost Days (FDO) and Ice Days (IDO) (upper right graph), Max of Tmax and Min of Tmax (middle left graph), Max of Tmin and Min of Tmin (middle right graph), Max of DTR and Min of DTR (lower left graph), and Max of DRH and Min of DRH (lower right graph) for Ioannina station, within the period 1956-2022 (the period for DRH is 1956-2004).

Figure 1 .
Figure 1.Time series of Tropical Days (TR30) and Tropical Nights (TR20) (upper left graph), Frost Days (FDO) and Ice Days (IDO) (upper right graph), Max of Tmax and Min of Tmax (middle left graph), Max of Tmin and Min of Tmin (middle right graph), Max of DTR and Min of DTR (lower left graph), and Max of DRH and Min of DRH (lower right graph) for Ioannina station, within the period 1956-2022 (the period for DRH is 1956-2004).

Figure 2 .
Figure 2. Time series of Dry Days and Wet Days (upper left graph), Very Wet Days and Extremely Wet Days (upper right graph), Annual Precipitation and Annual Simple Daily Precipitation Index (SDII) (lower left graph), Heavy Precipitation Days (R10), Very Heavy Precipitation Days (R20), and Extremely Precipitation Days (R30) (lower right graph) for Ioannina station, within the period 1956-2022.

Figure 2 .
Figure 2. Time series of Dry Days and Wet Days (upper left graph), Very Wet Days and Extremely Wet Days (upper right graph), Annual Precipitation and Annual Simple Daily Precipitation Index (SDII) (lower left graph), Heavy Precipitation Days (R10), Very Heavy Precipitation Days (R20), and Extremely Precipitation Days (R30) (lower right graph) for Ioannina station, within the period 1956-2022.

Table 1 .
Statistical Coefficients of the extreme climatic parameters for Ioannina station, within the period 1956-2022.Statistically significant B values at 95% Confidence are in bold.

Table 1 .
Statistical Coefficients of the extreme climatic parameters for Ioannina station, within the period 1956-2022.Statistically significant B values at 95% Confidence are in bold.