Climate change impact: Mapping thermal stress on Carrara marble ...

Science of the Total Environment 407 (2009) 4506–4512
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Science of the Total Environment
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<strong>Climate</strong> <strong>change</strong> <strong>impact</strong>: <strong>Mapping</strong> <strong>thermal</strong> <strong>stress</strong> on Carrara marble in Europe
A. Bonazza ⁎, C. Sabbioni, P. Messina, C. Guaraldi, P. De Nuntiis
Institute of Atmospheric Sciences and <strong>Climate</strong>, National Research Council, Bologna, Italy
article
info
abstract
Article history:
Received 14 October 2008
Received in revised form 3 April 2009
Accepted 7 April 2009
Available online 8 May 2009
Keywords:
<strong>Climate</strong> <strong>change</strong>
Thermal <strong>stress</strong>
Marble
Risk
Europe
The <strong>impact</strong> of climate <strong>change</strong> on monuments and historic buildings is addressed for the first time, in terms of
modelling and predicting <strong>thermal</strong> <strong>stress</strong> on stone in Europe over the next century. While the effect of
changing climate on frost in porous materials and on surface recession of carbonate stone, has recently been
treated, prediction of the future evolution of <strong>thermal</strong> <strong>stress</strong> on stones still requires elucidation. The present
paper provides maps showing future scenarios of <strong>thermal</strong> <strong>stress</strong> on Carrara marble for the 21st century, using
the output data from the Hadley general and regional climate models in the European window.
The work carried out made it possible to forecast in the near and far futures (i.e. 2010–2039, 2070–2099) the
number of events per year of <strong>thermal</strong> <strong>stress</strong> in marble greater than 20 MPa, the latter being adopted as the
maximum sustainable load for this specific material. The data demonstrate that the Mediterranean area will
continue to experience the highest level of risk from <strong>thermal</strong> <strong>stress</strong>, with more than 300 events/year
predicted in the 2070–2099 period. In addition, Central Europe will be more affected by <strong>thermal</strong> <strong>stress</strong> during
the present century compared to the baseline period, 1961–1990, taken as reference.
© 2009 Elsevier B.V. All rights reserved.
1. Introduction
Observations of climate <strong>change</strong> over the past hundred years have
induced the research sector to invest greater resources in forecasting
its future evolution and ensuing <strong>impact</strong>s. So far, efforts have focused
on improving knowledge of future climate effects on water resources,
marine systems, agriculture, biodiversity, energy supplies and human
health. Only within the EC Noah's Ark Project (2004–2007, http://
noahsark.isac.cnr.it/), was cultural heritage finally considered among
the sectors threatened by climate <strong>change</strong> (Sabbioni et al., 2007). Apart
from contrasting an intellectual approach that does not attribute
priority status to cultural heritage, the main difficulty linked to such
issues arises from the remaining uncertainty involved in modelling
the damage processes acting on materials, both individually and
simultaneously, due to the <strong>impact</strong> of climate parameters.
In that sense Grossi et al. (2007) were pioneers in addressing the
future evolution of freezing processes on porous stones induced by
temperature variations. Adopting the notion that freezing and
thawing take place below and above 0 °C, the authors evidenced
that freezing in the future will decrease significantly in temperate
Europe, implying a reduction of frost damage on the porous stones
typically used in the monuments located in this area.
Moreover, papers predicting carbonate stone surface recession for
chemical dissolution, induced by <strong>change</strong>s in precipitation amount and
atmospheric CO 2 concentration, have recently been submitted to the
⁎ Corresponding author. Tel.: +39 0516399571; fax: +39 0516399649.
E-mail address: a.bonazza@isac.cnr.it (A. Bonazza).
attention of the scientific community (Bonazza et al., 2009; Grossi
et al., 2008). In particular, these works highlighted the increasing
importance that climate parameters will have in the future compared
to air pollution, in the decay and conservation of built heritage.
Prediction of future stone weathering due to heating and cooling
cycles for temperature variations has still not been faced. The present
paper provides for the first time Europe-wide maps charting the risk
of Carrara marble towards <strong>thermal</strong> <strong>stress</strong> as a result of climate <strong>change</strong>
for three 30-year periods from 1961 to 2099.
1.1. Thermal <strong>stress</strong> on stone
Thermoclastism results in granular disaggregation and material
exfoliation due to the differential <strong>thermal</strong> expansion and contraction
of mineral grains and surface–subsurface stone in response to shortand
long-term temperature fluctuations, caused by the <strong>impact</strong> of solar
radiation on materials. Debate still exists concerning its efficacy,
magnitude and scale of action, since weathering agents act synergistically,
making it impossible to assess the effect produced by any single
variable (Blackwelder, 1933; Cooke and Warren, 1973; Camuffo, 1998;
Gómez-Heras et al., 2006). Furthermore this damage process depends
on the <strong>thermal</strong> conductivity of materials, which differs in relation to
their mineralogical composition and texture (Goudie et al., 1992;
McGreevy et al., 2000; Doulos et al., 2004).
In geomorphological terms, rock weathering by <strong>thermal</strong> <strong>stress</strong>
has been dealt with in depth for the Antarctic environment by
Hall (1997, 1998,1999) and Hall and André (2001, 2003). In addition to
advancing interesting arguments in support of the significant role
that <strong>thermal</strong> <strong>stress</strong> may play in cold and dry regimes, these authors
0048-9697/$ – see front matter © 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.scitotenv.2009.04.008

A. Bonazza et al. / Science of the Total Environment 407 (2009) 4506–4512
4507
highlighted the importance of high frequency measurements of rock
temperature <strong>change</strong>s in order to identify meaningfully the ΔT/t rates
producing damage, ΔT/t≥2 °C min − 1 being said to cause <strong>thermal</strong>
<strong>stress</strong> according to Yatsu (1988).
Marble and granite are demonstrated to be the stones most
affected by thermoclastism (Gómez-Heras et al., 2006; Malaga-
Starzec et al., 2002; Schouenburg et al., 2003; Siegesmund et al.,
2007, 2008). However, field tests performed by Viles (2005) aimed at
monitoring weathering on marble and granite blocks in the Central
Namib Desert, found evidence of a greater resistance of granites with
respect to marbles under natural conditions.
The susceptibility of marbles derives from the anisotropy in the
<strong>thermal</strong> response of calcite, which expands parallel to the c-axis
and contracts normal to the c-axis. Consequently, the polycrystalline
<strong>thermal</strong> expansion behaviour of marbles can vary from almost
isotropic, for a marble with weak texture, to strongly anisotropic,
for a marble with a strong texture with or without residual strain
(Siegesmund et al., 2000; Weiss et al., 2003). In addition even if in
the case of metamorphic rocks exhaustive explanation on residual
locked-in <strong>stress</strong>es (e.g. residual <strong>stress</strong> generated during the stone
geological history) is still lacking, Winkler (1994) had already
highlighted that pre<strong>stress</strong>ed crystalline marble tends to expand
more during the first cycle of heating as the locked-in <strong>stress</strong>es are
released.
The size of the stones undergoing <strong>thermal</strong> cycles must also be
considered, as in large rock masses, temperature gradients can give
rise to <strong>thermal</strong> <strong>stress</strong>es as a result of temperature not being a linear
function of size: the value ΔT necessary to induce cracking decreases
as the rock increases in volume. Thus, large rock bodies do not require
a ΔT value as high as that used in laboratory experiments. Moreover,
laboratory samples are generally not confined, while it is known that
greater damage occurs when a stone block is not free to expand as a
consequence of <strong>thermal</strong> <strong>stress</strong> (Lazzarini and Tabasso, 1986; Hall,
1999).
In terms of heritage management, even though the efficacy of
<strong>thermal</strong> <strong>stress</strong> acting alone has still to be demonstrated in a natural
environment, the possible consequences of <strong>change</strong>s in temperature
distribution within materials on other decay mechanisms must also
be taken into account. For example, temperature controls the
distribution and pressure of salt crystallization in the stone pores.
Moreover the higher <strong>thermal</strong> expansion of salts in the pores with
respect to the stone may eventually led to microfracture development
(Winkler, 1994). Gómez-Heras (2006) demonstrated that in
the case of sodium chloride, radiative heating favours the formation
of sub-efflorescences, implying a greater tendency to spalling in
areas of a building exposed to insolation. In addition, he underlined
that in soft freezing environments (−10–0 °C) high insolation can
inhibit freeze–thaw weathering on porous stones, even when the air
temperature is below 0 °C.
2. Experimental section
2.1. <strong>Climate</strong> <strong>change</strong> model
For future projections, the outputs of two widely used models of
the Hadley Centre (UK) —HadCM3 and HadRM3 — were employed:
HadCM3 is a general model with a grid resolution of 2.5×3.75°
(295×278 km at 45 N latitude), while HadRM3 is a regional climate
model that encompasses Europe at a higher resolution (a grid of
equal-area cells, 50×50 km), but spans only the years from 2070 to
2099 (Gordon et al., 2000). The model outputs were based on the A2
scenario (Nakicenovic and Swart, 2000).
The selected geographical area centres on Europe, covering a
region of 80°N–25°N latitude and 33.75°W–67.50°E longitude for the
general model, and 72°N–35°N latitude and 30°W–55°E longitude for
the regional one.
The research utilised daily air maximum and minimum temperature
values extracted from HadCM3 and HadRM3 and processed
for use in the estimation of the risk towards <strong>thermal</strong> <strong>stress</strong> in marble
for three 30-year periods: 1961–1990 (baseline), 2010–2039 (near
future) and 2070–2099 (far future).
2.2. Damage function
A review was made of previously published works on the damage
functions relating temperature to stone damage processes. Although
numerous studies on <strong>thermal</strong> <strong>stress</strong> have been performed on the basis
of laboratory and field exposure tests (Blackwelder, 1933; Griggs,
1936; McGreevy et al., 2000; Zhu et al., 2003; Gómez-Heras et al.,
2006), the papers proposing its modelling by functions remain few
(Timoshenko and Goodier 1970; Mutluturk et al., 2004). By contrast
several models exist for freeze–thaw cycles (Walder and Hallet, 1985;
Nelson and Outcalt, 1987; Matsuoka, 1990; López and Mesones, 2001;
Mutluturk et al., 2004).
According to Timoshenko and Goodier (1970) and Turcotte and
Schubert (2002), the maximum <strong>thermal</strong> <strong>stress</strong> (σ T [MPa]) for a
uniform elastic medium confined in the horizontal directions and
unconstrained in the vertical direction can be calculated by:
σ T = E·α · Δ T = ð1− mÞ ð1Þ
where:
E Young's modulus (GPa)
α Thermal expansion coefficient (K − 1 )
ΔT Actual amplitude of the periodic surface temperature
variation
ν Poisson's ratio
This function, valid for an isotropic body, has already been used by
Scheffzϋk etal.(2004), who calculated a maximum horizontal thermoelastic
<strong>stress</strong> of around 42 MPa for a marble with α=7×10 −6 K −1 ,
E = 30 GPa and ν = 0.25, subjected to a cooling of 150 K. Lazzarini
and Tabasso (1986) and Dal Prà (1987) previously evidenced that
the risk of damage for a given material is evaluated through the
comparison between the <strong>thermal</strong> <strong>stress</strong> σ T caused and the maximum
sustainable load specific to that material. The maximum sustainable
load is calculated by dividing the material's compressive strength by
its safety coefficient, which depends both on the type of material and
its structural role. For concrete a safety coefficient of 3 is generally
assumed, while higher values are adopted for stone (Dal Prà, 1987;
Blanco, 1991).
The comparison of the <strong>thermal</strong> <strong>stress</strong> σ T obtained using Eq. (1)
with the maximum sustainable load allows an estimation of the risk of
damage for a material undergoing a temperature surface variation.
Surface temperatures may be obtained from field measurements
and laboratory simulations. However, Eq. (1) cannot be used for future
projections, because outputs of climate models generally provide
mean monthly/seasonal/yearly data of the air temperature. Therefore,
work was also done to find a correlation between the daily
air temperature variations extracted from the general and regional
Hadley climate models and daily surface temperatures, in an attempt
to make Eq. (1) suitable for producing future scenarios of <strong>thermal</strong>
<strong>stress</strong>.
2.3. Environmental monitoring
Experimental results from the environmental monitoring campaign
at the UNESCO listed Hagar Qim and Mnajdra Temples on the
island of Malta from June 2005 to August 2006, carried out by ISAC-
CNR, were processed along with the few data available from the

4508 A. Bonazza et al. / Science of the Total Environment 407 (2009) 4506–4512
literature, in order to correlate daily ΔT of the air (ΔT air ) and daily ΔT of
the stone surface (ΔT surface ). The megalithic temples are built mainly
in large blocks of globigerina limestone. Research carried out on
damage affecting Maltese Cultural Heritage indicates that salt crystallization
is the main deterioration process affecting the conservation
of the temples, and that it acts synergistically with <strong>thermal</strong> <strong>stress</strong> and
wind erosion in causing alveolization, a phenomenon leading to a
complete powdering of the material (Vannucci et al., 1994; Cassar and
Vannucci, 2001). While the present paper addresses projections of
<strong>thermal</strong> <strong>stress</strong> on Carrara marble, the Malta campaign was taken into
account because it represents a rare case of monitoring assessment
for the purpose of correlating meteorological data with damage processes
at an outdoor heritage site. With particular reference to our
work, it should be underlined that in the literature, data of both air
and stone surface temperatures for long-term periods (one year) on a
large scale (monoliths) are very scarce (Viles, 2005). Additionally,
little information is available on monitoring campaigns carried out
directly on monuments and archaeological sites (Mandrioli et al.,
2006), providing both air temperature measured in their proximity
and temperatures at the material surface. Malta is characterised by a
Mediterranean climate with low precipitation during most of the year
(maximum mean monthly rainfall of about 110 mm from November to
January) and mean monthly temperature ranging from 13 to 28 °C.
Data recorded over the last 20 years show hot and dry summers, with
maximum temperatures as high as 43 °C in July and August, while the
lowest temperature recorded during winter is 3 °C. Throughout the
year the island is exposed to wind influence, with maximum velocity
ranging between 13 and 20 m/s.
During the one-year campaign, the following meteorological
parameters were measured every 15 min by microclimatic stations
equipped with sensors: air temperature, relative humidity, rainfall,
solar radiation and barometric pressure. Wind speed and direction
were measured by two 5 m wind poles installed in proximity of the
temples. The continuous monitoring was carried out through a local
wireless network connected by GSM modem to the Data Management
Centre (DMC) of the ISAC-CNR Institute, Bologna, Italy. All the data
from the remote sites were daily transmitted and uploaded into the
DMC database.
In addition, four seasonal campaigns took place to study the stone
surface temperature performing <strong>thermal</strong> infrared measurements
on the south and south-east facing surfaces of both temples, using
an infrared <strong>thermal</strong> camera (NEC THERMO TRACER TH5104). The surfaces
were monitored continuously for 24 h (one thermography every
30 min) in each season (Figs. 1 and 2). Nearly all the measurements
Fig. 2. Thermography (02/02/2006,10:00 am) relating to the monument area in Fig. 1.
were performed in clear sky conditions, in order to ensure the maximum
effect of solar radiation on monument surfaces. The <strong>thermal</strong>
camera measures and images the emitted infrared radiation from the
object investigated, which is a function of the object's emissivity and
corresponding surface temperature (following Planck's equation). It
allows the acquisition of a thermographic image with a matrix of
255×223 pixels and temperature resolution of 0.1 °C. The database of
air and surface temperatures has been utilised in the present work.
3. Results and discussion
3.1. Stone surface temperature
In Eq. (1) Young's modulus E, <strong>thermal</strong> expansion coefficient α
and Poisson's ratio ν have specific values for each material, most of
which can be obtained from data in the literature (Dal Prà, 1987;
Blanco, 1991; Fiori et al., 1998; Nicholson and Nicholson, 2000).
However, to enable the use of Hadley climate model outputs in producing
future scenarios of <strong>thermal</strong> <strong>stress</strong> on marble using Eq. (1), a
correlation between air temperature and stone surface temperature
is needed.
Lazzarini and Tabasso (1986) found that marble monoliths in the
Mediterranean area can undergo <strong>thermal</strong> cycles of 40–50 °C, causing
deformation of some tenths of a millimetre for each meter of length.
Winkler (1994) stated that the maximum surface temperature can
be almost double the maximum air temperature, while the minimum
values of air and surface temperature are comparable, pointing out
that the surface temperatures of black stones are very much higher
(in desert areas, black basalt and dark sandstone recorded almost
80 °C) than those of white rocks in the same climate conditions. Viles
(2005) performed continuous measurements of surface temperature
on marble and granite every 3 h, and hourly air temperature readings
Table 1
Maximum and minimum daily air and surface temperatures measured during the
environmental monitoring at the megalithic temples of Malta.
Site Date T air Max
(°C)
T air Min
(°C)
T surface Max
(°C)
T surface Min
(°C)
ΔT surface −
ΔT air
a
Hagar Qim 29/06/2005 28.2 b 24.3 b 40.4 23.4 13.2
Mnajdra 01/07/2005 32.3 24.7 41.7 25.0 9.1
Mnajdra 27/09/2005 26.3 19.4 35.7 15.6 13.2
Hagar Qim 29/09/2005 26.9 18.5 27.7 15.9 3.5
Hagar Qim 02/02/2006 16.2 9.1 35.1 2.5 25.5
Hagar Qim 03/05/2006 21.4 15.3 42.2 10.5 25.6
Mnajdra 06/05/2006 20.9 13.1 29.3 12.5 9.1
Fig. 1. View of the south-facing monoliths of Hagar Qim Temple, Malta Island.
a
[T surface Max−T surface Min] −[T air Max−T air Min].
b Air temperature data from the monitoring station close to Hagar Qim Temple, other
data are from ISAC monitoring campaign.

A. Bonazza et al. / Science of the Total Environment 407 (2009) 4506–4512
4509
in February and August for three years at four sites in the Central
Namib Desert, showing that in February the daily ΔT surface of marble
blocks can be 11–20 °C higher than the daily ΔT air . In August the range
can be between 8 and 19 °C. Maximum stone surface temperatures
were found to exceed maximum air temperatures in February by up
to 18 °C and in August by up to 13 °C. Concerning minimum surface
temperatures in February, rock temperatures were generally the same
as air temperatures, or below them by as much as 1.5–2 °C, whereas in
August, rock surface temperature minima were 1 to 4.5 °C below air
temperature minima.
The data obtained during the environmental monitoring at Hagar
Qim and Manjdra Temples in Malta are summarized in Table 1.
Fig. 3. a. Estimated <strong>thermal</strong> <strong>stress</strong> risk on Carrara marble for 1961–1990 under the A2 scenario derived from HadCM3 output. b. The period 2070–2099. c. The difference map from
baseline to the far future representing the <strong>change</strong>s in number of events per year of maximum <strong>thermal</strong> <strong>stress</strong> higher than 20 MPa.

4510 A. Bonazza et al. / Science of the Total Environment 407 (2009) 4506–4512
Maximum and minimum daily surface temperatures are reported
with the air temperatures measured on the days when the surface
<strong>thermal</strong> monitoring was performed. The maximum and minimum
surface temperatures are the mean values of the temperature maxima
and minima, respectively, given by a horizontal temperature profile on
the thermographic image in correspondence to 1 m above ground
level at both sites.
The results show that the difference between daily ΔT surface and
daily ΔT air ranges from 9 to 26 °C. The lowest value identified, i.e. 3 °C,
can be explained by the partially cloudy conditions on 29 September
2005. The greatest differences (up to 26 °C) between daily ΔT surface
and daily ΔT air were identified in February and May.
It should be emphasised that the surface temperatures in Table 1
are not the absolute maximum and minimum values measured at the
temples. In February 2006, for example, some points at Hagar Qim
experienced a daily ΔT surface equal to 42 °C, while in May 2006 a range
of 38 °C was reached. These values are to be compared with the
corresponding daily ΔT air equal to 5 °C for both periods, meaning a
difference between daily ΔT surface and daily ΔT air ranging from 33 to
37 °C.
Following the processing of the data from the Malta monitoring,
supported by the scarce data reported in the literature, the setting of
daily ΔT surface =daily ΔT air +20 °C was considered reasonable for
predicting the maximum daily cycle of surface temperature to be used
in the present research. Therefore, substituting in Eq. (1), the
maximum <strong>thermal</strong> <strong>stress</strong> can be calculated by:
σ T = E·α · ðdaily ΔT air + 20 -CÞ= ð1 − mÞ ð2Þ
Eq. (2) was applied in combination with the outputs of the general
and regional Hadley models for future scenario production.
3.2. <strong>Mapping</strong> <strong>thermal</strong> <strong>stress</strong>
Europe-wide maps representing the risk towards thermoclastism
on marbles for the 21st century were produced utilising Eq. (2),
assuming: E=70 GPa, α=8 10 − 6 K − 1 , ν=0.25 and a compressive
strength of 100 MPa. The adopted values refer to Carrara marble
(Blanco, 1991; Fiori et al., 1998). It has to be underlined that marbles
from different geometrical and structural positions within the
Alpi Apuane metamorphic complex, among them the variety called
“Cararra marble”, present a large variability in microfabric types.
Carrara marble itself can show a nearly homogeneous fabric, with no
or weak grain-shape, or preferred crystallographic orientation. Within
the present work the annealed microfabric (type-A) distinguished
by Molli et al. (2000) was considered. This type of microfabric is
characterized by equant polygonal grains (granoblastic or “foam”
microstructure), with straight to slightly curved grain boundaries that
meet in triple points at angles of nearly 120°. c-Axis orientations show
a random distribution or a weak preferred crystallographic orientation.
This allowed the use of Eq. (2), which is valid for an isotropic
body. The use of a safety coefficient of 5 was considered reasonable,
leading to a maximum sustainable load of 20 MPa, which is close to
the maximum compressive load admissible for a marble monolith;
thereupon the number of events per year of maximum <strong>thermal</strong> <strong>stress</strong>
higher than 20 MPa were mapped. With regard to surface temperatures,
as illustrated above, daily ΔT surface was taken to be 20 °C higher
than daily ΔT air , which allowed the utilisation of the daily maximum
and minimum air temperatures provided by the Hadley climate
models, for each HadCM3 and HadRM3 grid point for three 30-year
periods: 1961–1990 (baseline), 2010–2039 (near future) and 2070–
2099 (far future).
The maps relate to Carrara marble with weak, almost non-existent,
calcite texture and polycrystalline isotropic <strong>thermal</strong> expansion
behaviour without residual strain. An ideal situation of dry conditions,
absence of wind and maximum surface exposure to sunlight (south
facing vertical surfaces in winter clear sky conditions) is considered. It
is also to be underlined that no estimation is done of the locked-in
<strong>stress</strong>es. Nevertheless, it should be borne in mind that for stone
constructions, a safety coefficient lower than 5 is never adopted, in
order to take in consideration possible hidden defects and weakness
(such as locked-in <strong>stress</strong>).
Fig. 3a–b maps the number of events per year of maximum <strong>thermal</strong>
<strong>stress</strong> higher than 20 MPa obtained with the general climate model
HadCM3 for the two 30-year periods, from 1961 to 1990 (baseline),
and from 2070 to 2099 (far future), respectively. The maps report
absolute values, distinguishing the geographical areas according to the
different number of events experienced per year. Fig. 3c shows the
difference between the two periods, far future and baseline. It does
not report absolute values, but highlights the <strong>change</strong>s in the number
of events occurring in the far future with respect to the baseline
(period assumed as reference).
Fig. 4 illustrates the number of events for the far future obtained
with the regional climate model HadRM3, which provides higher
resolution outputs.
Fig. 4. Estimated <strong>thermal</strong> <strong>stress</strong> risk on Carrara marble for 2070–2099 under the A2 scenario derived from HadRM3 output.

A. Bonazza et al. / Science of the Total Environment 407 (2009) 4506–4512
4511
The results obtained evidence on how the Mediterranean Basin
will generally continue to experience the highest level of risk, in some
cases with more than 300 events per year, meaning almost one event
per day. In addition, Central Europe and the south of England will be
increasingly affected in the future, while a decreasing risk is predicted
for northern Europe and some areas of the European landmass.
The most marked <strong>change</strong> in <strong>thermal</strong> <strong>stress</strong> risk across the century is
the general increase throughout the Mediterranean Basin and Europe—
particularly Spain, France, Italy, and the Balkan Peninsula–Turkey and
North Africa, with a maximum increase of 50 events per year.
4. Conclusions
The work presented represents the first attempt to predict the risk
of <strong>thermal</strong> <strong>stress</strong> on Carrara marble over the next century, by mapping
the number of events per year with maximum <strong>stress</strong> higher than
20 MPa. It is important to underline that the function utilised allowed a
good combination of stone-related variables with the output extracted
from climate models, this being a necessary step towards providing
future projections of damage processes. Furthermore the approach
adopted may be extended to mapping the risk on other stone typologies,
upon proper selection of Young's modulus and <strong>thermal</strong>
expansion coefficient. The determination of the difference between
daily ΔT surface and daily ΔT air in different environments and for different
materials remains an existing gap in knowledge that needs to be
filled through specific monitoring campaigns. Moreover, it has to be
underlined that <strong>change</strong>s in microclimate conditions, conditioned by
factors such as aspect, shading, wetting, and stone <strong>thermal</strong> properties,
can influence <strong>thermal</strong> <strong>stress</strong>es. Thus, further research is undoubtedly
required in order to account for the effects of cloud shading and wind in
the heating/cooling cycles on stone surfaces. Additionally, in dealing
with monuments, a comprehensive spatial understanding of sunlight
exposure on architectural elements is necessary. Another effect to be
considered is the <strong>thermal</strong> shock occurring when a heated surface is
wetted or affected by sudden rainfall.
Work should proceed in two main directions: the development of
more realistic damage functions, including the critical climate
parameters (intensity and declination of solar radiation in this specific
case), and the improvement of the spatial and temporal resolution
of existing climate models for future projections. The last point is of
fundamental importance, the downscaling of climate models being
necessary for an understanding of climate <strong>change</strong> <strong>impact</strong> on cultural
heritage assets. For such purposes, environmental monitoring campaigns
carried out in proximity of monuments and archaeological
remains, are fundamental prerequisites for the determination of
strategies of preventive conservation.
In terms of heritage management, the maps presented indicate
that monuments built in marble will undergo an increasing risk of
<strong>thermal</strong> <strong>stress</strong> in the future, especially in those areas in which their
density (number of monuments/area) is highest, such as Italy, Greece,
Turkey.
For preventive management, it is urgent to consider the <strong>impact</strong> of
climate <strong>change</strong> on cultural heritage on the basis of the existing
knowledge on both material damage and climate predictions.
Scientifically valid mitigation and adaptation strategies may only be
developed if the scientific community directs its research results
within the future perspective.
Acknowledgments
This work forms part of the EC Project “Global climate <strong>change</strong>
<strong>impact</strong> on built heritage and cultural landscapes — NOAH'S ARK”,
supported by the European Commission, within the 6th Framework
Program on research (Contract nr. SSPI-CT-2003-501837-NOAH'S
ARK). It also benefits from the project “Environmental Monitoring at
Hagar Qim and Manjdra Temples”, funded by Heritage Malta.
The authors gratefully acknowledge Dr. Paolo Mandrioli, Prof.
Giacomo Moriconi and Prof. Giovanni Santarato for the stimulating
and fruitful discussions.
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