INTERNATIONAL JOURNAL OF CLIMATOLOGY
Int. J. Climatol. (2008)
Published online in Wiley InterScience
(www.interscience.wiley.com) DOI: 10.1002/joc.1809
Analysis of an ensemble of present day and future regional
climate simulations for Greece
P. Zanis,a * I. Kapsomenakis,b,c C. Philandras,b K. Douvis,b,c D. Nikolakis,c E. Kanellopoulou,c
C. Zerefosc,d,e and C. Repapisb
a
c
Department of Meteorology-Climatology, School of Geology, Aristotle University of Thessaloniki, Greece
b Research Centre for Atmospheric Physics and Climatology, Academy of Athens, Greece
Laboratory of Climatology and Atmospheric Environment, School of Geology and Geoenvironment, National and Kapodistrian University of
Athens, Greece
d National Observatory of Athens, Athens, Greece
e Foundation for Biomedical Research, Academy of Athens, Greece
ABSTRACT: This study investigates the simulated changes in temperature and precipitation over Greece from nine
Regional Climate Models (RCMs) for the period 2071–2100 under the A2 emission scenario and evaluates their
performance during the control period 1961–1990 using Greek gridded datasets of temperature and precipitation. In
winter, most RCMs show a bias towards warmer and dryer conditions and a bias towards higher inter-annual temperature
variability and lower inter-annual variability of precipitation than the Greek gridded datasets during the control period
1961–1990. In summer, all RCMs show a cold bias for the maritime sub-regions and generally all sub-regions show very
small biases in precipitation. Concerning the future projections of the RCMs for Greece the mean change of the nine RCMs
for the mean air temperature, T 2mean, between the future period and the control period for the integrated Greek domain
is 3.4 ° C for winter and 4.5 ° C for summer with the changes being larger in continental than in the marine sub-regions.
The inter-annual temperature variability in the future simulations generally increases in summer and decreases in winter
almost for all RCMs with these changes being larger in the continental sub-regions than in maritime sub-regions of Greece.
Almost all RCMs simulate a decrease of the precipitation for the future climate for both winter and summer with the
inter-annual variability of summer precipitation decreasing for the majority of RCMs. The reported future climatic changes
will have important impacts for the region of Greece in vital sectors such as water resources, agriculture, tourism, forest
fire risk and energy demand. Copyright  2008 Royal Meteorological Society
KEY WORDS
Greece; regional climate; regional climate models (RCMs); future simulations
Received 4 July 2007; Revised 9 October 2008; Accepted 11 October 2008
1.
Introduction
In recent decades there is growing interest in the past,
present and projected in future climate variability and climate change related to the study of the global warming
as a consequence of the anthropogenic enhancement of
the greenhouse effect (IPCC, 2007). Decision makers in
governments, non-governmental organizations and industry as well as the general public need detailed information
on future regional climate in order to evaluate the risks
of climate change. Coupled Atmospheric-Ocean General
Circulation Models (AOGCMs) and General Circulation
Models (GCMs) are the modelling tools traditionally
used for generating projections of climatic changes as
a result of anthropogenic forcing. However, because of
limited computational resources, the horizontal resolution
of present day coupled AOGCMs are still of the order of
* Correspondence to: P. Zanis, Department of MeteorologyClimatology, School of Geology, Aristotle University of Thessaloniki,
University Campus, Thessaloniki 54124, Greece.
E-mail: zanis@auth.gr
Copyright  2008 Royal Meteorological Society
a few hundred kilometres (Mearns et al., 2001). At this
resolution, the effects of local and regional topographic
characteristics are not fully captured. Regional climate
models (RCMs) have been developed for the application of dynamical downscaling methods to enhance the
regional information provided by (GCMs) or by the largescale reanalysis fields (NCEP/ERA-40) (Dickinson et al.,
1989; Giorgi et al., 1990). RCMs represent in more detail
surface features, such as complex mountain topographies
and coastlines as well as small islands and peninsulas,
which in a global model could not even appear because
of their smaller size relative to the GCM gridbox. When
comparing the RCMs with their driving GCM, they generally reproduce the large-scale circulation of the GCM
though in some cases there are substantial differences
between regional biases in surface temperature and precipitation (Jacob et al., 2007).
Greece is situated at the southern part of the Balkan
Peninsula in a region characterized by complex topography and steep orography of a land stripe embedded
into the Mediterranean Sea and hence regionalization
P. ZANIS ET AL.
techniques to enhance the regional climatic information
are necessary. The assessment of potential effects and
adaptations for climate change in the area of Greece
has so far been drawn from available published material,
typically based on GCM scenario simulations in which
Greece is represented by only two grid-boxes (Parry,
2000; Mitchell et al., 2002).
Furthermore Mediterranean is recognized among the
most responsive regions to climate change (Giorgi, 2006).
There are a number of studies which have investigated
changes in temperature and precipitation since the middle of the 20th century for eastern Mediterranean and
Greece. Repapis and Philandras (1988) showed that eastern Mediterranean air temperature time series follow the
Northern Hemisphere secular trend from late 19th Century to 1970s. Nevertheless the warming trend of the last
30 years that is well documented for the Northern Hemisphere and the global average appears only since early
1990s in the eastern Mediterranean region and Greece in
particular (Saaroni et al., 2003; Feidas et al., 2004; Repapis et al., 2007). Feidas et al. (2004) showed an overall
cooling trend in winter for the period 1955–2001 for
Greece. Xoplaki et al. (2003) reported that variations of
a mode related to a more meridional circulation at the
upper tropospheric levels are found to be responsible
for the occurrence of extreme events and decadal trends
in summer air temperature over Greece, the latter being
characterized by a cooling in the early 1960s and a warming in the early 1990s. Recent studies of 20th century
Mediterranean precipitation trends show large precipitation decreases in the region starting in the 1960s (e.g.
Giorgi, 2002; Dünkeloh and Jacobeit, 2003; Maheras
et al., 2004; Xoplaki et al., 2004; Krichak and Alpert,
2005; Feidas et al., 2007).
As far as the future climate projections in Mediterranean are concerned, several studies based on GCMs
and RCMs predict mainly a warming and drying of
the Mediterranean region for the last decades of the
21st century for various emission scenarios (Gibelin
and Déqué, 2003; Pal et al., 2004; Giorgi and Bi,
2005; Giorgi and Lionello, 2008). Gao et al. (2006),
based on high-resolution climate change simulations with
RegCM3, showed that in winter the mean precipitation change is positive in the northern Mediterranean
and negative in the southern Mediterranean, while in
the other seasons precipitation mostly decreases. Hertig
and Jacobeit (2007), using statistical downscaling methods to assess Mediterranean precipitation changes for the
period 1990–2100, indicated that the eastern and southern parts of the Mediterranean area will exhibit mainly
negative precipitation changes from October to May.
Other recent studies have focused on future changes in the
extremes of temperature and precipitation. Diffenbaugh
et al. (2007), on the basis of a high-resolution simulation with RegCM3, reported that elevated greenhouse gas
concentrations dramatically increased the heat stress risk
in the Mediterranean region, with the occurrence of hot
extremes increasing by 200–500% throughout the region.
Goubanova and Li (2007) assessed the potential future
Copyright  2008 Royal Meteorological Society
changes in climate extremes around the Mediterranean in
an ensemble of future climate scenario simulations and
they concluded that the Mediterranean basin will experience in general a warmer and dryer climate. As far as the
near future projections are concerned, multi-model GCM
experiments show a global warming trend of 0.2 ° C per
decade for the period 2011–2030 with a mean annual
near surface air temperature increase of 0.5–1 ° C for the
Mediterranean region which is insensitive to the choice
among Special Report on Emission Scenarios (SRES)
(IPCC, 2007). Even if all greenhouse gases and aerosols
were held constant at year 2000 levels, a global warming
trend of about 0.1 ° C per decade would occur as a result
of the thermal inertia of the oceans and ice sheets and
their long time scales for adjustment (IPCC, 2007).
For Greece in particular there are only a few studies
so far on future climate change, and these are mainly
based on data from GCMs. Tolika et al. (2006) demonstrated that the spatial distribution of winter precipitation
in Greece is not well reproduced by the Hadley Center
atmospheric GCM (HadAM3P) with the model underestimating also the rainfall amounts. In another study Anagnostopoulou et al. (2006) found that HadAM3P model
underestimates the frequency of severe cyclones in the
Mediterranean region.
The European project Prediction of Regional Scenarios
and Uncertainties for Defining European Climate change
risks and Effects (PRUDENCE) provided a series of highresolution climate change scenarios for Europe at the
end of the 21st century using dynamical downscaling
methods with 10 different RCMs. Regional multi-model
ensembles are valuable because not only they increase the
spatial resolution of the global simulations, but also they
moderate the uncertainties arising from different parameterisations and dynamical cores in different RCMs. The
aim of this work is to contribute to the few studies so
far on the projected climate changes in the region of
Greece, by including detailed regional information from
these state-of-the-art RCMs for different climatic subregions of Greece.
2.
Data and methods
The model performance of the nine RCMs was investigated during the control period 1961–1990 using gridded
temperature and precipitation data interpolated from a
network of about 74 stations covering Greece and neighbouring countries. All the data from the Greek stations
have been officially provided by the Hellenic Meteorological Service where they follow standard quality control
procedures except for four stations with precipitation data
provided by another governmental organisation. Furthermore the homogeneity of the temperature and precipitation data in a large number of our stations have also been
studied in previous publications and they are considered
homogeneous (Peterson et al., 1998; Xoplaki et al., 2000,
2003, 2004; Feidas et al., 2004, 2007). Among the stations with temperature data, 40 stations had no gaps, 16
Int. J. Climatol. (2008)
DOI: 10.1002/joc
ENSEMBLE OF PRESENT AND FUTURE REGIONAL CLIMATE SIMULATIONS FOR GREECE
stations had gaps of less than 5% and only 4 stations had
gaps between 5 and 15%. As far as the precipitation data
availability is concerned, 46 stations had no gaps, 9 stations had gaps of less than 5% and only 2 stations had
gaps between 5 and 10%. These gaps in monthly values
were filled using recorded monthly values in neighbouring stations with high correlation following procedures
similar to those suggested by Feidas et al. (2004) and
Feidas et al. (2007) for temperature and precipitation,
respectively.
These Geek gridded temperature and precipitation
data were compiled as yearly and seasonal means for
the period 1961–1990 on the RCM’s model grid. The
methodology applied for the interpolation from irregularly distributed surface station data at coordinates xi, yi,
zi (where xi = lon, yi = lat and zi = alt from mean sea
level of the i station) to surface gridded points Xj,Yj,Zj
(where Xj = lon, Yj = lat and Zj = alt from mean sea
level of the j grid) was based on 2-D kriging procedure in association with a back fitting loop to estimate
the elevation component. The kriging calculations were
done with the statistical package R-project (http://www.rproject.org/).
In the first part of this study, the mean and the
inter-annual variability of the Greek gridded temperature and precipitation data (shown in Table I) were
compared with temperature and precipitation for each
one of the nine RCMs for winter, summer and the
whole year for individual sub-regions of Greece and
the integrated Greek domain. For clarity reasons the
Greek gridded temperature and precipitation data were
also compared with the Climatic Research Unit (CRU)
TS 2.0 dataset supplied on a 0.5° grid (Mitchell and
Jones, 2005) in a similar way. The Greek domain
and the selected sub-regions are shown in Figure 1.
The sub-regions selected mainly with geographical criteria but climatic information was also considered taking into account the regional division followed by the
Hellenic Meteorological Service and previous studies
(Balafoutis and Arseni-Papadimitriou, 1992; Anagnostopoulou, 2003).
In the second part of this study we have investigated
the simulated changes for each one of the nine RCMs
between the future period 2071–2100 and the control
period 1961–1990 in the mean and the inter-annual
variance of (1) mean air temperature at 2 m above the
ground (T 2mean), (2) maximum air temperature at 2 m
(T 2max), (3) minimum air Temperature at 2 m (T 2min)
and precipitation (Prec) for each individual season and
the whole year for the individual sub-regions of Greece
as well as for the intergraded Greek domain.
The RCMs used within this paper are introduced in
alphabetical order together with their main references and
the Institute of their origin in Table II. All nine RCMs
cover Europe with a 50 × 50 km resolution, they have
been forced with six hourly lateral boundary conditions
provided from the same global model HadAM3H of the
Hadley Center (Buonomo et al., 2007) and run for both a
control period and a future scenario period following the
Copyright  2008 Royal Meteorological Society
A2 emission scenario from IPCC (the only scenario used
consistently from the full list of PRUDENCE RCMs).
Hence the differences among these RCM simulations
originate from differences in the dynamical core, the
physical parameterizations of sub-grid processes and
solving techniques among the different RCMs. The A2
scenario is among the worse IPCC future emission
scenarios characterized by an independently operating
world with continuously increasing population, regionally
oriented economic development and slower and more
fragmented technological changes and improvements to
per capita income. The emission scenarios are described
in the IPCC (SRES) (Nakićenović et al., 2000). It should
be noted that the use of one GCM (e.g. HadAM3H)
and one emission scenario (e.g. A2) for driving the
different RCMs is a dominant factor for the RCM results.
In a study assessing the uncertainties in PRUDENCE
RCM projections it was found that the uncertainty
introduced by the choice of the driving GCM is generally
larger than those introduced by choice of the RCM,
by the choice of the scenario and the choice of the
member of the ensemble (Déqué et al., 2007). More
details for the overall experiment set-up that was utilized
within PRUDENCE are described by Christensen and
Christensen (2007).
3. Results
3.1. Comparison between Greek gridded data and
CRU
The Greek gridded data of temperature and precipitation
were compared first with the respective values from the
CRU TS 2.0 dataset for clarity reason and because the
evaluation of the PRUDENCE RCMs has been done in
previous studies with respect to the CRU data-set. As it is
shown in Table III, the yearly averages of the CRU data
are in general colder than our gridded Greek database for
all sub-regions in a range of 0.3–1.1 ° C. The integrated
Greek domain show that the CRU data are colder than
our Greek gridded dataset by 0.7 ° C for the whole year,
0.6 ° C for winter and 0.9 ° C for summer. In winter season
the CRU data are colder than our gridded Greek database
for all maritime influenced regions (except Crete) in a
range of 1.4–2.1 ° C while for the continental regions the
temperature bias is smaller and ranges between −0.5 and
0.4 ° C. In summer season the CRU data are colder than
our gridded Greek database for the continental regions
in a range of 1.1–1.7 ° C while the maritime influenced
regions (except Crete) show a much smaller temperature
bias ranging between −0.3 and 0.3 ° C. As far as the interannual temperature variability is concerned both datasets
show similar values.
The yearly averages of the CRU precipitation data
show lower values than the Greek gridded precipitation for most of the sub-regions, ranging from 2.6%
in Dodekannese to 37.2% in West Greece, except in
Cyclades and East Aegean where CRU data show more
precipitation. This behaviour is also observed for the winter season. In summer season the precipitation of the
Int. J. Climatol. (2008)
DOI: 10.1002/joc
Copyright  2008 Royal Meteorological Society
18.0
0.7
2.0
0.9
11.5
0.7
4.2
1.4
25.1
0.6
0.2
0.2
Year
T 2m (° C)
T 2m-stdev (° C)
Prec (mm/day)
Prec-stdev (mm/day)
DJF
T 2m (° C)
T 2m-stdev (° C)
Prec (mm/day)
Prec-stdev (mm/day)
JJA
T 2m (° C)
T 2m-stdev (° C)
Prec (mm/day)
Prec-stdev (mm/day)
Crete
26.3
0.5
0.0
0.1
13.1
0.7
3.8
1.3
19.4
0.6
1.6
0.8
Dodekannese
24.3
0.7
0.4
0.3
9.4
0.8
4.0
1.1
16.4
0.7
2.2
0.7
Peloponnese
25.1
0.5
0.1
0.1
12.2
0.7
2.5
0.9
18.3
0.6
1.2
0.5
Cyclades
25.2
0.5
0.2
0.2
10.2
0.8
3.6
1.2
17.4
0.7
1.7
0.7
E. Aegean
24.7
0.3
0.5
0.2
8.1
0.5
2.7
0.5
16.0
0.5
1.5
0.4
N. Aegean
25.2
0.4
0.3
0.1
11.7
0.3
4.5
0.9
18.1
0.4
2.5
0.6
Ionian
23.8
0.8
0.8
0.4
6.6
0.8
5.4
1.7
14.9
0.9
3.2
1.2
W. Greece
Greek gridded dataset
24.4
0.7
0.7
0.3
6.7
0.9
3.3
1.0
15.1
0.9
2.0
0.8
CE Greece
23.6
0.8
1.0
0.5
4.1
1.0
2.7
0.9
13.7
1.0
2.0
0.7
W-C Macedonia
23.1
0.7
1.1
0.4
4.2
1.0
3.0
1.2
13.5
0.9
2.0
0.8
E. Maced./Thrace
24.5
0.7
0.5
0.3
8.2
0.9
3.5
1.2
16.0
0.8
1.9
0.8
Greece
Table I. Mean and the inter-annual variance of temperature and precipitation of the reference period 1961–1990 for winter, summer and the whole year for individual sub-regions of
Greece and the integrated Greek domain based on the Greek gridded temperature and precipitation.
P. ZANIS ET AL.
Int. J. Climatol. (2008)
DOI: 10.1002/joc
ENSEMBLE OF PRESENT AND FUTURE REGIONAL CLIMATE SIMULATIONS FOR GREECE
Figure 1. Map with the selected Greek sub-regions indicated with boxes while with points is indicated the station with precipitation and temperature
data used to produce the gridded Greek datasets. Specifically, circles indicate stations with both temperature and precipitation data, triangles
indicate stations with only precipitation data and asterisks indicate stations with only temperature data. The sub-regions include continental
regions such as a) West Greece (WG), b) Central-eastern Greece (CEG), c) West-central Macedonia (WCM), d) Eastern Macedonia/Thrace
(EMT) and e) Peloponnese (P) as well as maritime influenced regions such as f) Crete (C), g) Dodekannese (D), h) Cyclades (CY), i) East
Aegean (EA), j) North Aegean (NA) and Ionian (I). This figure is available in colour online at www.interscience.wiley.com/ijoc
Table II. Regional Climate Model acronyms, main references and institute of their origin.
Acronym
Institute of their origin
Main references
CHRM
CLM
HadRM3H
HIRHAM
RACMO
RCAO
RegCM2
REMO
PROMES
Swiss Federal Institute of Technology, Zurich, Switzerland (ETHZ)
GKSS Research Center, Geesthacht GmbH, Germany (GKSS)
Hadley Centre for Climate Prediction and Research, UK (HC)
Danish Meteorological Institute, Denmark (DMI)
Royal Netherlands Meteorological Institute, the Netherlands (KNMI)
Swedish Meteorological and Hydrological Institute, Sweden (SMHI)
The Abdus Salam International Centre for Theoretical Physics, Italy (ICTP)
Max-Planck-Institute for Meteorology, Germany (MPI)
Universidad Complutense de Madrid, Spain (UCM)
Vidale et al. (2003)
Steppeler et al. (2003)
Buonomo et al. (2007)
Christensen et al. (1998)
Lenderink et al. (2003)
Döscher et al. (2002)
Giorgi and Mearns, (1999)
Jacob, (2001)
Castro et al. (1993)
CRU dataset is similar to our Greek gridded dataset,
although the percentage differences can be very high
because of the dry summer conditions in Greece with
low amounts of precipitation. For the integrated Greek
domain the CRU data show less precipitation than our
Greek gridded dataset by 8.3% for the whole year and
11% for winter while for summer the CRU data show
more precipitation by only 2.0%. Finally, the inter-annual
variability in precipitation is smaller in CRU data than in
our Greek gridded dataset for almost all sub-regions for
the whole year and for both winter and summer except
for Cyclades and East Aegean. In conclusion, apart from
a few regional differences the comparison of the two
datasets can be considered satisfactory. However, in some
sub-regions such as West Greece, significant differences
between Greek gridded dataset and CRU are observed for
both the absolute and the percentage amount of precipitation, particularly during winter. It should be highlighted
that for these sub-regions the total precipitation, especially in the winter season, increases with altitude as the
westerly flow passing over the Adriatic Sea and Ionian
Sea is forced to orographic uplift over the Pindos mountain range at West Greece (Xoplaki et al., 2000). The
network of meteorological stations, on which the Greek
Copyright  2008 Royal Meteorological Society
gridded dataset is based, is denser than the network of
the CRU database for the area of Greece (with only a few
Greek stations), and additionally it includes high-altitude
stations. Therefore, we anticipate that the Greek gridded dataset represents the total amount of precipitation at
West Greece more realistically.
3.2. Validation of the control simulations
3.2.1. Near surface air temperature
The differences in temperature and inter-annual temperature variability between the nine RCMs and the Greek
gridded dataset for the winter and summer seasons during
the control period 1961–1990 for the individual Greek
sub-regions are shown in Figures 2 and 3, respectively.
In the winter season the air temperature biases for most
RCMs range between −1 and 2 ° C for most of the subregions and for the integrated Greek domain except the
CLM model which shows colder biases. In general the
majority of RCMs are warmer than the observed values
in winter (Figure 2). An outstanding regional feature in
winter season is the North Aegean where all RCMs show
Int. J. Climatol. (2008)
DOI: 10.1002/joc
Copyright  2008 Royal Meteorological Society
0.0
0.1
5.4
14.3
0.9
0.1
65.7
116.2
DJF
T 2m (° C)
T 2m-stdev (° C)
Prec (%)
Prec-stdev (%)
JJA
T 2m (° C)
T 2m-stdev (° C)
Prec (%)
Prec-stdev (%)
0.1
0.0
−74.8
−40.5
2.1
−0.1
13.2
16.8
1.1
−0.1
2.6
21.2
Dodekannese
1.5
0.1
23.1
31.0
0.4
0.1
12.1
−1.1
0.9
0.0
14.4
3.4
Peloponnese
−0.3
0.0
−52.3
−31.3
1.7
0.0
−29.6
−28.2
0.7
0.0
−32.2
−29.8
Cyclades
0.3
0.0
−34.9
−29.4
1.4
−0.1
2.1
−0.3
0.8
−0.1
−6.6
−4.7
E. Aegean
Because of lack of CRU data there are no values given for North Aegean and Ionian.
0.3
0.1
8.4
19.8
Year
T 2m (° C)
T 2m-stdev (° C)
Prec (%)
Prec-stdev (%)
Crete
N. Aegean
Ionian
Differences
1.3
0.2
28.3
19.7
−0.5
0.0
42.6
29.4
0.3
0.1
37.2
25.7
W. Greece
1.1
0.1
29.3
15.9
−0.4
0.1
21.6
18.3
0.3
0.1
22.3
12.2
CE Greece
1.7
0.2
2.4
5.6
0.1
0.1
24.2
6.1
0.8
0.1
18.0
9.5
W-C Macedonia
1.3
0.1
−4.6
−3.3
0.3
0.0
27.1
38.1
0.7
0.0
17.9
23.4
E. Maced./Thrace
0.9
0.1
−2.0
0.5
0.6
0.0
11.0
9.2
0.7
0.0
8.3
8.1
Greece
Table III. Differences in the mean and the inter-annual variance of temperature and precipitation between the Greek gridded dataset and the CRU TS 2.0 dataset for winter, summer and
the whole year of the reference period 1961–1990 for the individual sub-regions of Greece and the integrated Greek domain.
P. ZANIS ET AL.
Int. J. Climatol. (2008)
DOI: 10.1002/joc
ENSEMBLE OF PRESENT AND FUTURE REGIONAL CLIMATE SIMULATIONS FOR GREECE
Figure 2. Differences in mean temperature at 2 m in winter and summer seasons between each one of the nine RCMs and the Greek gridded
dataset during the control period 1961–1990 for the individual Greek sub-regions and the integrated Greek domain. This figure is available in
colour online at www.interscience.wiley.com/ijoc
warm biases between 2 and 3.5 ° C except RegCM2 which
shows a warm bias of only 0.5 ° C (Figure 2). It should be
noted that REMO model shows consistently the warmest
bias, whereas CLM model shows the coldest bias among
the nine RCMs. As far as the inter-annual variability of
air temperature in winter is concerned most of the RCMs
show higher variability than the Greek gridded dataset
(Figure 3). We also detect a tendency of the continental
sub-regions towards a larger positive bias in the interannual variability of air temperature compared with the
maritime sub-regions.
In summer, all RCMs show a cold bias for the maritime
sub-regions and the intergraded Greek domain ranging
from 0 to −2.5 ° C (Figure 2), whereas in the continental
sub-regions there are models showing a small warm
bias (e.g. HadRM3P, RCAO and REMO) and other
models showing a cold bias (e.g. CLM and PROMES).
In summer the most RCMs under-predict the inter-annual
air temperature variability in the maritime sub-regions
and over-predict it in continental sub-regions. The CLM
model shows the largest underestimation of the interannual air temperature variability while HadRM3P shows
Copyright  2008 Royal Meteorological Society
the highest overestimation among the nine RCMs. In
general the range of the temperature changes of the
nine RCMs is smaller in winter than in summer and
it is also smaller at the marine than at the continental
sub-regions of Greece for both winter and summer
seasons.
The temperature trend for the nine RCMs, the Greek
gridded dataset and the CRU dataset during the control
period 1961–1990, for the winter and summer seasons, of
the individual Greek sub-regions and Greece as a whole
are shown in Figure 4. During winter the majority of
PRUDENCE RCMs reproduce well the negative temperature trends observed in the Greek gridded dataset
and in CRU dataset. The observed summer temperature
trends in the Greek gridded and CRU datasets are relatively smaller than in winter. The summer temperature
trend is also reproduced reasonably by the PRUDENCE
RCMs. The only exception is PROMES, which continuously reproduces a warming temperature trend for all
Greek sub-regions for both the winter and summer seasons. However, the majority of the trend calculations for
summer and winter over the period 1961–1990 from both
Int. J. Climatol. (2008)
DOI: 10.1002/joc
P. ZANIS ET AL.
Figure 3. Differences in inter-annual temperature variability in winter and summer seasons between each one of the nine RCMs and the Greek
gridded dataset during the control period 1961–1990 for the individual Greek sub-regions and the integrated Greek domain. This figure is
available in colour online at www.interscience.wiley.com/ijoc
observed and modelled temperature data are not significant in the 95% significance level.
The residual mean square error (RMSE) of the differences in temperature between each one of the nine RCMs
and the Greek gridded dataset during the control period
1961–1990 for the individual Greek sub-regions and the
integrated Greek domain was also calculated. In winter,
the RMSE for the integrated Greek domain ranges from
1.1 to 1.9 ° C for the different RCMs with a mean RMSE
value of 1.3 ° C. In summer, the RMSE for the integrated
Greek domain ranges from 0.5 to 2.2 ° C for the different
RCMs with a mean RMSE value of 1.1 ° C. The RMSE at
the continental sub-regions is slightly higher (by 0.1 ° C)
than at the maritime sub-regions in winter while in summer no differences are seen.
3.2.2. Precipitation
As it can be noted from Figure 5, all RCMs in winter
underestimate the precipitation by 25 to 55% for the
integrated Greek domain with the smallest biases from
REMO and RegCM2. For the individual sub-regions, the
smallest biases are noted for the Aegean Sea, whereas
Copyright  2008 Royal Meteorological Society
the largest underestimation is observed for Crete except
for the REMO model. In summer, all RCMs give very
small differences from the observed gridded data in
absolute amounts of precipitation, but the percentage
precipitation biases are very large especially for the
maritime influenced sub-regions and the Southern Greece
sub-regions because of the fact that the precipitation in
South Greece in summer is very low. Practically the
models RACMO, RCAO and CLM simulate almost zero
amount of precipitation.
All RCMs underestimate the inter-annual variability
of precipitation compared with the Greek gridded dataset
in winter (Figure 6). The largest underestimation is seen
at the most southern Greek sub-domains at Crete and
Dodecanese. For the integrated Greek domain the bias of
the inter-annual variability of precipitation ranges from 5
to −42%. The smallest biases in winter for the integrated
Greek domain are observed for the models REMO and
RegCM2. In summer, the nine RCMs show discrepancies
concerning the inter-annual variability of precipitation but
this can also be attributed to the fact of the low amounts
of precipitation at this time of the year.
Int. J. Climatol. (2008)
DOI: 10.1002/joc
ENSEMBLE OF PRESENT AND FUTURE REGIONAL CLIMATE SIMULATIONS FOR GREECE
Figure 4. Temperature trend for each one of the nine RCMs, the Greek gridded dataset and CRU dataset in winter and summer seasons during
the control period 1961–1990 for the individual Greek sub-regions and the integrated Greek domain. This figure is available in colour online at
www.interscience.wiley.com/ijoc
As far as the precipitation trend for the control period
1961–1990 is concerned, both the Greek gridded dataset
and the CRU dataset show a negative precipitation trend
for all Greek sub-regions during winter (Figure 7). The
nine RCMs also reproduce the negative trend for all subregions but with smaller (absolute) values. In summer,
the observed precipitation trends in the Greek gridded
and CRU datasets are close to zero and the same feature
is also reproduced by the majority of RCMs for most
sub-regions.
The RMSE of the differences in precipitation between
each one of the nine RCMs and the Greek gridded dataset
during the control period 1961–1990 for the individual
Greek sub-regions and the integrated Greek domain was
also calculated. In winter, the RMSE for the integrated
Greek domain ranges from 1.5 to 2.1 mm/day for the
different RCMs with a mean RMSE value of 1.7 mm/day.
In summer, the RMSE for the integrated Greek domain
ranges only from 0.2 to 0.3 mm/day for the different
RCMs. The RMSE at the continental sub-regions is
greater than at the maritime sub-regions in both winter
and summer by 0.2 and 0.3 mm/day, respectively.
Copyright  2008 Royal Meteorological Society
3.3. Future projections
3.3.1. Future projections of near surface air
temperature
As it can be inferred from Table IV the mean change
of the nine RCMs for the mean temperature at 2 m
(T 2mean) between the future period 2071–2100 for
scenario SRES A2 and the control period 1961–1990
for the integrated Greek domain for the whole year is
3.7 ° C, for winter 3.4 ° C and for summer 4.5 ° C. As far
as the individual Greek sub-regions are concerned, there
are regional differences within Greece for the simulated
increase of air temperature at 2 m for A2 scenario with
respect to the control run. The main difference is between
the continental and the marine parts of Greece with the
marine sub-regions showing temperature changes lower
by 0.5–1 ° C compared with the continental sub-regions.
This feature is seen in all seasons but is more distinct for
summer.
The differences in mean air temperature at 2 m and
in the inter-annual temperature variability in winter and
summer seasons between future period 2071–2100 for
scenario SRES A2 and the control period 1961–1990 for
Int. J. Climatol. (2008)
DOI: 10.1002/joc
P. ZANIS ET AL.
Figure 5. Percentage differences in total precipitation in winter and summer seasons between each one of the nine RCMs and the Greek gridded
dataset during the control period 1961–1990 for the individual Greek sub-regions and the integrated Greek domain. This figure is available in
colour online at www.interscience.wiley.com/ijoc
each one of the nine RCMs for the individual Greek subregions and the integrated Greek domain are shown in
Figures 8 and 9. Figure 8 indicates that the range of the
nine RCMs is smaller in winter than in summer, and it
is also smaller at the marine than at the continental subregions of Greece for both winter and summer seasons.
In winter the T 2mean becomes largest in North Greece
(West-central Macedonia and eastern Macedonia/Thrace)
ranging from 3.3 to 4.5 ° C from the nine RCMs. The
lowest values are seen at Ionian See and Aegean See
(Cyclades and Crete) ranging from 2.8 to 3.5 ° C. Integration for the whole Greek domain shows a T 2mean
increase ranging from 3 to 3.6 ° C from the nine RCMs. In
summer the T 2mean is clearly larger in continental subregions compared with marine sub-regions ranging from
4 to 6.5 ° C for the continental sub-regions and from 3.5
to 5 ° C for the maritime sub-regions. Integration for the
whole Greek domain shows a T 2mean increase ranging
from 4 to 5° from the nine RCMs.
In order to examine if the future projected temperatures are significantly different from the present time
values, the two-sample Welch t-test was applied. The
Copyright  2008 Royal Meteorological Society
results of the Welch’s t-test indicated that the changes in
temperature are statistically significant at the 95% significance level for winter, summer and the whole year, for
all RCMs, and for all Greek sub-regions.
Temperature trends during the future period 2071–
2100 have also been calculated for each one of the
nine RCMs for all Greek sub-regions and the integrated
Greek domain. In all cases there is a warming trend for
both winter and summer seasons. In winter the RCMs
predict a positive temperature trend ranging from 0.01
to 0.08 ° C/year for the different sub-regions with a mean
positive trend of 0.04 ° C/year for the integrated Greek
domain. In summer the RCMs predict a stronger positive
temperature trend ranging from 0.03 to 0.14 ° C/year for
the different sub-regions with a mean positive trend
of 0.07 ° C/year for the integrated Greek domain. In
general during this season the RCMs predict higher
trends for the continental than for the marine subregions.
The inter-annual temperature variability generally
increases in summer in the future simulations almost
for all RCMs (Figure 9). The increase in inter-annual
Int. J. Climatol. (2008)
DOI: 10.1002/joc
ENSEMBLE OF PRESENT AND FUTURE REGIONAL CLIMATE SIMULATIONS FOR GREECE
Figure 6. Percentage differences in inter-annual precipitation variability for winter and summer seasons between each one of the nine RCMs
and the Greek gridded dataset during the control period 1961–1990 for the individual Greek sub-regions and the integrated Greek domain. This
figure is available in colour online at www.interscience.wiley.com/ijoc
temperature variability in summer between the A2 scenario and the control run is larger in the continental sub-regions than in maritime sub-regions of Greece
(Figure 9). In contrast, in winter, the standard deviation
of T 2mean between the A2 scenario and the control run
shows a decrease for almost all RCMs except HadRM3P
(Figure 9). This decrease is largest and is clearly seen in
continental sub-regions of Greece, but it is also evident
for the integrated Greek domain.
Concerning the mean changes in T 2max and T 2min
of the nine individual RCMs between the future period
2071–2100 for scenario SRES A2 and the control
period 1961–1990, we get qualitatively similar results
to T 2mean but in general the T 2max is slightly
higher than T 2mean and T 2min is slightly lower
than T 2mean especially over the continental parts
of Greece for summer season when we notice the
biggest differences among T 2mean, T 2max and
T 2min. For example Table IV indicates that T 2mean,
T 2max and T 2min in summer are 4.5, 4.7 and
4.5 ° C, respectively, for the integrated Greek domain
while for the continental sub-regions such as West-central
Copyright  2008 Royal Meteorological Society
Macedonia and eastern Macedonia/Thrace the respective
values are 5.2, 5.5 and 5.0 ° C. In maritime sub-regions we
notice negligible differences among T 2mean, T 2max
and T 2m for both winter and summer seasons.
3.3.2. Future projections of precipitation
Almost all nine RCMs simulate a decrease of the
precipitation for the future climate for both summer
and winter and for all sub-regions of Greece. For
the integrated Greek domain in winter we calculated
an overall precipitation decrease of −15.8% (about
−0.20 mm/day) for the whole year, −14.2% (about
−0.30 mm/day) for winter and −57.3% for summer
(about −0.18 mm/day) from the nine RCMs (Table IV).
More specifically, in winter the precipitation change
between A2 scenario and control run shows a percentage
decrease for all Greek sub-regions up to 40% for the
majority of the nine RCMs. Especially at the southern
sub-regions of Greece (Crete, Peloponesse Dodekannese
and Cyclades) we note the largest percentage decreases
of precipitation ranging from −10 to −35% (Figure 10).
Int. J. Climatol. (2008)
DOI: 10.1002/joc
P. ZANIS ET AL.
Figure 7. Precipitation trend for each one of the nine RCMs, the Greek gridded dataset and CRU dataset in winter and summer seasons during
the control period 1961–1990 for the individual Greek sub-regions and the integrated Greek domain. This figure is available in colour online at
www.interscience.wiley.com/ijoc
Interestingly, at the eastern Macedonia and Thrace subregion we note that some RCMs (HIRHAM, CHRM,
RACMO and PROMES) demonstrate an increase of
winter precipitation up to 4%. The inter-annual variability
of winter precipitation generally increases in the future
climate for the majority of RCMs at maritime sub-regions
while in the continental sub-regions there is no robust
tension from the various RCMs as a few of them show
an increase and others a decrease.
In summer the precipitation change between A2 and
control run shows a percentage decrease for all nine
RCMs. This percentage decrease is similar for the individual Greek sub-regions ranging from −20 to −80%
(Figure 10). However, in absolute values there is larger
decrease of summer precipitation at the northern parts of
Greece since at the southern parts there is small amount of
total precipitation both in present and future simulations.
The inter-annual variability of summer total precipitation
generally decreases in the future climate for all Greek
sub-regions almost for all RCMs (Figure 11).
The Welch’s t-test was used to examine if the future
projected precipitation (2071–2100) is significantly different from the present time values (1961–1990). It was
Copyright  2008 Royal Meteorological Society
found that for the majority of the nine RCMs the changes
in precipitation for winter season are not statistically significant at the 95% significance level for almost all Greek
sub-regions and the integrated Greek domain which is
related to large variability in precipiatation. The main
exceptions are Crete for the majority of RCMs and other
southern Greek sub-regions (Peloponnese, Dodekannese,
Cyclades) for HadRM3P and RegCM2 showing statistical significant changes in future winter precipitation.
On the contrary, the changes in future summer precipitation are statistically significant at the 95% significance
level for the majority of the nine RCMs for all Greek
sub-regions.
Precipitation trends during the future period 2071–
2100 have also been calculated for each one of the
nine RCMs and for all Greek sub-regions. All RCMs
predict a positive precipitation trend for the winter
season, where the intra-model variability is high. For
the summer season all RCMs except PROMES predict
a negative precipitation trend for all the sub-regions of
Greece except for the south maritime sub-regions where
the future projected summer precipitation is close to
zero.
Int. J. Climatol. (2008)
DOI: 10.1002/joc
4.5
4.5
4.7
−57.3
5.2
5.0
5.5
−54.9
5.2
5.0
5.5
−49.7
5.0
4.9
5.1
−54.2
5.3
5.1
5.6
−58.9
4.1
4.1
4.2
−59.7
4.1
4.0
4.1
−58.2
4.2
4.2
4.3
−64.6
4.0
3.9
4.0
−62.9
4.8
4.7
4.9
−65.2
4.2
4.3
4.3
−56.1
JJA
T 2mean (° C)
T 2min (° C)
T 2max (° C)
prec (%)
4.1
4.1
4.1
−68.2
3.4
3.4
3.5
−14.2
4.0
3.9
4.3
−2.1
3.9
3.8
4.2
−11.2
3.7
3.5
4.0
−20.3
3.6
3.5
3.8
−8.0
3.1
3.2
3.0
−12.1
3.7
3.7
3.6
−5.9
3.5
3.6
3.6
−8.4
3.2
3.3
3.1
−20.4
3.3
3.2
3.4
−19.4
3.1
3.1
3.3
−26.9
DJF
T 2mean (° C)
T 2min (° C)
T 2max (° C)
prec (%)
3.2
3.3
3.1
−18.0
3.7
3.7
3.8
−15.8
4.2
4.1
4.4
−16.8
4.2
4.1
4.4
−14.2
4.0
3.9
4.1
−15.5
4.1
4.0
4.3
−19.1
3.5
3.5
3.4
−15.0
3.6
3.7
3.6
−9.5
3.7
3.7
3.7
−14.2
3.4
3.4
3.4
−16.1
3.8
3.7
3.9
−20.6
3.5
3.5
3.5
−16.3
3.5
3.5
3.6
−19.4
Year
T 2mean (° C)
T 2min (° C)
T 2max (° C)
prec (%)
Greece
E. Maced./Thrace
W-C Macedonia
CE Greece
W. Greece
Ionian
N. Aegean
E. Aegean
Cyclades
Peloponnese
Dodekannese
Crete
Table IV. Mean changes for mean temperature (T 2mean), minimum temperature (T 2min), maximum temperature (T 2max) and total precipitation (Prec) from nine RCMs between
the future period 2071–2100 and the control period 1961–1990 for the integrated Greek domain and the Greek sub-regions for the whole year as well as for winter and summer seasons.
ENSEMBLE OF PRESENT AND FUTURE REGIONAL CLIMATE SIMULATIONS FOR GREECE
Copyright  2008 Royal Meteorological Society
4.
Discussion and conclusions
The PRUDENCE dataset of high-resolution simulations
from nine RCMs gave us the opportunity to evaluate
their model performance for the Greek area during the
control period 1961–1990 against gridded observations
of temperature and precipitation interpolated from a
network of 74 stations covering Greece and neighbouring
countries and to investigate the regional characteristics of
their projected future climate for Greece.
Regarding the mean near surface air temperature, apart
from a few regional differences the comparison between
Greek gridded and CRU datasets can be considered
satisfactory. However, in most Greek sub-regions where
the differences between the two datasets are notable, the
RCM results are closer to the Greek gridded dataset.
The majority of RCMs are warmer than the observational gridded data for all Greek sub-regions during
winter season which is in line with a general tendency
of the PRUDENCE ensemble for warm bias in the European area during winter in an intercomparison study with
respect to CRU data (Jacob et al., 2007). In the summer season, all RCMs show a cold bias for the maritime
sub-regions. The tendency of RCMs in the maritime subregions for a warm bias in winter and a cold bias in
summer, might be partially attributed to the fact that
maritime observations originate from island stations in
the Aegean Sea where the air could be warmer in summer and colder in winter than the surrounding air above
the sea while the models consider the Aegean islands
mainly as sea. Despite the bias of the RCMs’ results the
temperature pattern that they produce is similar to that
of the observational gridded datasets. In this respect the
RCMs largely improve the results of the GCM because
of their higher analysis which allows them to better represent the smaller-scale effects as well as the land–sea
and orographic characteristics.
The CRU and Greek gridded dataset show similar values of the inter-annual temperature variability with their
differences being small for all seasons and sub-regions. In
contrast most of the RCMs show higher inter-annual temperature variability than both gridded datasets for winter
and summer seasons in the continental sub-regions. The
overestimation of inter-annual temperature variability in
summer by most of the RCMs in the Greek continental sub-regions has been also reported in other studies
for the European domain with respect to the CRU TS 2.0
observational dataset (Jacob et al., 2007; Lenderink et al.,
2007). This was linked to the behaviour of the different
RCMs in the partitioning of the different terms to the surface energy budget. It appeared that the overestimation
of the temperature variability has no unique cause but the
effect of short-wave radiation dominates in some RCMs,
whereas in others the effect of evaporation dominates
(Lenderink et al., 2007). In the maritime sub-regions of
Greece most RCMs overestimate the inter-annual temperature variability for winter while underestimate it for
summer. We also note a tendency that the continental
sub-regions show a larger positive bias in the inter-annual
Int. J. Climatol. (2008)
DOI: 10.1002/joc
P. ZANIS ET AL.
Figure 8. Differences in mean temperature at 2 m in winter and summer seasons between future period 2071–2100 for scenario SRES A2 and
the control period 1961–1990 for each one of the nine RCMs for the individual Greek sub-regions and the integrated Greek domain. This figure
is available in colour online at www.interscience.wiley.com/ijoc
variability of air temperature compared with the maritime
sub-regions which can be attributed to the fact that the
variability is higher over the continents than over the sea.
The summer and winter temperature trends observed
in the Greek gridded dataset and in CRU dataset are
also reproduced reasonably by the PRUDENCE RCMs.
The winter cooling trend for Greece in the observed
datasets and in the PRUDENCE RCMs is in line with
several observational studies (Repapis and Philandras,
1988; Proedrou et al., 1997; Feidas et al., 2004).
Regarding the precipitation, both the CRU dataset and
the nine RCMs used in this study underestimate the
winter rainfall amounts and the inter-annual variability
of precipitation in comparison with the Greek gridded
dataset. In summer, all RCMs and the CRU dataset
show small differences from the Greek gridded dataset
in precipitation and its inter-annual variability that can
be attributed to the low amounts of precipitation at this
time of the year.
The Greek gridded dataset represents more realistically
than CRU the total amount of precipitation at West
Greece during winter where the presence of the Pindos
Copyright  2008 Royal Meteorological Society
mountain range enforces the prevalent westerly flow
to uplift and produce the larger portion of the winter
precipitation. We anticipate that the underestimation of
winter precipitation in the CRU data can be explained by
the lack of high-altitude station data, whereas the Greek
gridded dataset includes.
The causes responsible for the precipitation underestimation by the RCMs are more complex. One possible reason is that the RCMs underestimate the rainfall
amounts during winter season mainly because the driving GCM HadAM3H also underestimates it. HadAM3H
exhibits a stronger pressure gradient across a large part
of central to northern Europe than the ERA-40 reanalysis
which is caused by too high pressure over the Mediterranean region and too deep Icelandic low (Jacob et al.,
2007). The consequence is too high precipitation rates
over northern Europe and too low precipitation rates over
southern Europe. Another possible reason is that although
the PRUDENCE RCMs reproduce better, the general features of the spatial distribution of precipitation for Greece
than the course resolution driving GCM, even finer spatial resolution is needed to simulate more adequately the
Int. J. Climatol. (2008)
DOI: 10.1002/joc
ENSEMBLE OF PRESENT AND FUTURE REGIONAL CLIMATE SIMULATIONS FOR GREECE
Figure 9. Differences in the inter-annual temperature variability in winter and summer seasons between future period 2071–2100 for scenario
SRES A2 and the control period 1961–1990 for each one of the nine RCMs for the individual Greek sub-regions and the integrated Greek
domain. This figure is available in colour online at www.interscience.wiley.com/ijoc
effects of the complex orography of the Greek terrain on
the precipitation.
The summer and winter precipitation trends for the
control period 1961–1990 observed in the Greek gridded dataset and in CRU dataset (negative trend in
winter and close to zero trend in summer) are reproduced reasonably by the PRUDENCE RCMs. The negative precipitation trend is in line with a number of
recent studies showing large precipitation decreases in
the region starting in the 1960s associated with circulation patterns or with climatic indices such as the
North Atlantic Oscillation (NAO) Index (Dünkeloh and
Jacobeit, 2003; Maheras et al., 2004; Xoplaki et al.,
2004; Krichak and Alpert, 2005; Feidas et al., 2007).
It is well established that positive NAO phase is associated with less precipitation in the Mediterranean as
storm tracks from the Atlantic shift to Northwest (Hurrell and Van Loon, 1997) even though the impact
of the winter NAO on the Mediterranean precipitation regime is not homogeneously distributed (Xoplaki,
2002).
After the investigation of the biases in the various
RCMs used in this study against the Greek gridded and
Copyright  2008 Royal Meteorological Society
CRU datasets for the present day climate of Greece and
taking into account the results from similar studies for the
whole European domain (Jacob et al., 2007; Lenderink
et al., 2007), we consider that the models’ performance
is reasonable in representing the main climatic features
of the overall mean, inter-annual variability and trend
of temperature and precipitation. Hence their future
simulation is a valid tool to investigate the future
simulated changes in temperature and precipitation for
different sub-regions of Greece.
All nine RCMs predict a dramatic increase of the
mean near surface air temperature for the future climate
(SRES A2) during winter, summer and the whole year for
all sub-regions of Greece. These air temperature future
changes are higher during summer than during winter as
well as for the continental regions than for the maritime
ones. The mean temperature change of the nine RCMs
(T 2mean) between the future period 2071–2100 and
the control period 1961–1990 for the integrated Greek
domain for the whole year is 3.7 ° C, for winter 3.4 ° C and
for summer 4.5 ° C. Almost all RCMs predict an increase
of the inter-annual temperature variability in summer and
decrease in winter.
Int. J. Climatol. (2008)
DOI: 10.1002/joc
P. ZANIS ET AL.
Figure 10. Percentage differences in total precipitation in winter and summer seasons between future period 2071–2100 for scenario SRES A2
and the control period 1961–1990 for each one of the nine RCMs for the individual Greek sub-regions and the integrated Greek domain. This
figure is available in colour online at www.interscience.wiley.com/ijoc
The estimated temperature increase results form the
increase of the greenhouse gases (GHGs), which affect
the earth’s radiative balance. Furthermore, the changes
in the radiative balance lead to changes in the general circulation thus redistributing synoptic patterns and
associated temperature anomalies. In winter, the regional
models closely follow the circulation changes simulated
by the driving global model HadAM3H with a weak
enhancement of southerly flows and a clear enhancement of the strength of westerly flows (van Ulden et al.,
2007) which in turn can be associated with a shift to
the north of the sub-tropical jet stream. The IPCC models predict a strengthening and a poleward shift of the
tropospheric zonal jets in response to global warming
(Lorenz and DeWeaver, 2007). This winter circulation
change is also revealed by the future mean sea level
pressure (SLP) fields (Figure 12(a)) and the differences
between the future and the present mean SLP of RCM
HIRHAM (Figure 12(c)). SLP decreases largely over
northern Europe with maximum decrease over Northwest
Europe. The HIRHAM SLP anomalies resemble the SLP
anomalies of the driving GCM (HadAM3H). Furthermore
Copyright  2008 Royal Meteorological Society
we also note a decrease in the SLP inter-annual variability
over Europe indicating, in association with Figure 12(a)
and (c), a more zonal westerly flow with less dynamical
instabilities in the future climate. As a consequence of
the more stable circulation (more zonal) and the weak
enhancement of southerly flows (also seen in the Balkan
Peninsula) the frequency of cold air penetrations from the
north in Greece will decrease leading to enhanced warming and smaller inter-annual temperature variability.
The increase of the inter-annual temperature variability in summer for almost all RCMs and sub-regions of
Greece is a common finding for the whole European
domain. Climate models consistently predict an increase
in the variability of summer temperatures in European
mid-latitudes, but the underlying mechanisms responsible
for this increase remain uncertain. Inter-annual temperature variability can be affected by large-scale circulation changes. In summer the most prominent circulation
response in the RCMs is a weakening of westerlies or an
enhancement of the frequency of the easterly flows even
though this feature is less pronounced in some RCMs
(van Ulden et al., 2007). This weakening of westerly flow
Int. J. Climatol. (2008)
DOI: 10.1002/joc
ENSEMBLE OF PRESENT AND FUTURE REGIONAL CLIMATE SIMULATIONS FOR GREECE
Figure 11. Percentage differences in the inter-annual precipitation variability in winter and summer seasons between future period 2071–2100
for scenario SRES A2 and the control period 1961–1990 for each one of the nine RCMs for the individual Greek sub-regions and the integrated
Greek domain. This figure is available in colour online at www.interscience.wiley.com/ijoc
is also revealed by the differences between the future
and the present mean SLP as SLP increases over the
British Isles (Figure 12(d)). This SLP increase is associated with a ridging over the British Isles and Western
Europe (Figure 12(b)). Many climate change simulations
show such a ridging over Western Europe, which suggests
an increase in the incidence of warm summers and more
frequent heat waves in the future climate (Meehl and
Tebaldi, 2004; Schär et al., 2004). van Ulden et al. (2007)
suggested that depending on the sensitivity of a RCM
to soil-moisture depletion, a positive feedback between
future circulation changes (e.g. enhancement of the frequency of the easterly flows) and soil-moisture depletion
may result in higher frequency of warm extreme events
and very warm months. This may lead to an increase
in the future inter-annual temperature variability. Vidale
et al. (2007) also provided evidence that the increase of
inter-annual temperature variability in future climate may
be linked to the dynamics of soil-moisture storage and
the associated feedbacks on the surface energy balance
and precipitation. In a another recent study it was suggested that especially for Central and Eastern Europe the
Copyright  2008 Royal Meteorological Society
predicted increase in summer temperature variability is
mainly due to feedback between the land surface and the
atmosphere (Seneviratne et al., 2006).
Almost all nine RCMs simulate a decrease of the
precipitation for the future climate (SRES A2) during
all seasons and for all sub-regions of Greece. For
the integrated Greek domain in winter we calculated
an overall precipitation decrease of −15.8% (about
−0.20 mm/day) for the whole year, −14.2% (about
−0.30 mm/day) for winter and −57.3% for summer
(about −0.18 mm/day) from the nine RCMs. An overall
decrease of mean precipitation was also noted in most of
the Mediterranean regions for future climate (Pal et al.,
2004; Tapiador et al., 2007). The reliability of the future
projections of precipitation for Mediterranean can be
assessed by the fact that the majority of the AOGCMs
participated in IPCC AR4 show consistently strong
precipitation decreases in the Mediterranean region for
both winter and summer for the 21st century (Tselioudis
et al., 2006).
The decrease in precipitation in winter is linked with
a clear enhancement of the strength of westerly flows
Int. J. Climatol. (2008)
DOI: 10.1002/joc
P. ZANIS ET AL.
Figure 12. Upper panel: Mean sea level pressure (SLP) fields (hPa) for the future period 2071–2100 under scenario SRES A2 in (a) winter and
(b) summer. Lower panel: Difference (hPa) of sea level pressure (SLP) between future period 2071–2100 and the control period 1961–1990 in
(c) winter and (d) summer. The data are from the regional climate model HIRHAM.
in the future simulation (van Ulden et al., 2007), which
is linked with the intensification of the Icelandic low
(Figure 12(c)). This is a common feature of the PRUDENCE RCMs resembling the driving GCM HadAM3H,
which causes an increase in the pressure gradient between
the Azores high and the Icelandic low, thus resulting in
an intensified zonal circulation over Europe that brings
more storms into Northwestern Europe following the
North Atlantic storm tracks (Figure 12(a)). The spatial
characteristics of the winter SLP changes (Figure 12(c))
in future climate indicate a more intense NAO-positive
phase and show similarities with the first canonical patterns (geopotential height at 1000 hPa or SLP vs precipitation) leading to present time winter precipitation
anomalies obtained by Dünkeloh and Jacobeit (2003) as
well as by Xoplaki et al. (2004) even though the future
SLP anomalies are rather extending to the east. A study
on the ability of the global circulation model HadAM3P
to generate the frequency and intensity of severe cyclones
in the Mediterranean region showed that the frequencies
of the cyclones will decrease during the future period
2071–2100 as a result of this northward shift of the
location of the storm tracks (Anagnostopoulou et al.,
2006).
The various RCMs show a non-robust behaviour for
the future changes in the inter-annual variability of
winter precipitation for continental Greece. Goubanova
and Li (2007) reported that the future winter extreme
precipitation will increase around the Mediterranean over
Copyright  2008 Royal Meteorological Society
the areas where mean precipitation decreases, except in
Greece with decreasing extremes.
The future decrease in precipitation and its interannual variability in summer might be associated with
the ridging over British Isles and Western Europe [SLP
increases over the British Isles and Western Europe in
Figure 12(d)] and the enhancement of the frequency of
the easterly flows (or weakening of westerly flow). As it
was also mentioned earlier in the text, this ridging situation (Figure 12(b)) and a positive feedback between
future circulation changes and soil-moisture depletion
may result in warmer and dryer conditions for Greece
with more frequent heat waves and less frequent precipitation events. Giorgi et al. (2004) associate the decrease
in mean precipitation over southern Europe with a more
frequent anticyclonic circulation in this region in future
climate. Concerning the decrease of the inter-annual precipitation variability, a recent study shows that Greece
is an area where in the future the probability for the
occurrence of extreme precipitation events will decrease
(Goubanova and Li, 2007). Presumably we have also to
consider that in future climate soil-moisture drying would
also cause a less significant soil-moisture-precipitation
feedback associated with a weaker land–atmosphere coupling (Seneviratne et al., 2006).
The summer and winter temperature and precipitation future projections of the ensemble of nine
RCMs for the integrated Greek domain lie within the
range of respective calculations from various GCMs
Int. J. Climatol. (2008)
DOI: 10.1002/joc
ENSEMBLE OF PRESENT AND FUTURE REGIONAL CLIMATE SIMULATIONS FOR GREECE
reported for Greece (Mitchell et al., 2002; see also
http://www.cru.uea.ac.uk/∼timm/climate/scatter/TYN C
Y 2 0.html). The reported future winter and summer temperature and precipitation changes will have important
impacts for the region of Greece in vital sectors such as
water resources, agriculture, tourism, forest fire risk and
energy demand.
From the above-mentioned discussion concerning the
comparison of the nine RCMs against the Greek gridded dataset during the control period 1961–1990 and the
future projections (period 2071–2100 for scenario SRES
A2) of the nine RCMs for Greece, the following concluding remarks could be highlighted:
• The majority of RCMs are warmer and show higher
inter-annual temperature variability than the Greek
gridded dataset in winter, while in summer all RCMs
show a cold bias for the maritime sub-regions and the
intergraded Greek domain.
• All nine RCMs underestimate the precipitation and
its inter-annual variability in winter for the integrated
Greek domain, while in summer all RCMs have very
small absolute differences from the Greek gridded
dataset.
• The future mean air temperature change (T 2mean)
of the nine RCMs over Greece is 3.4 ° C in winter,
4.5 ° C in summer and 3.7 ° C for the whole year with the
marine sub-regions showing lower future temperature
changes by 0.5–1 ° C compared with the continental
sub-regions.
• The future mean changes in T 2max and T 2min of the
nine individual RCMs are similar to T 2mean, but in
general the T 2max is slightly higher than T 2mean
and T 2min is slightly lower than T 2mean especially over the continental parts of Greece in summer.
• Generally, almost all nine RCMs simulate a decrease in
the precipitation for the future climate for both seasons
for all sub-regions of Greece. The mean precipitation
change (prec) of the nine RCMs over Greece is
−14.2% for winter, −57.3% for summer and −15.8%
for the whole year.
• The inter-annual temperature variability generally
increases in summer, but decreases in winter in the
future simulations almost for all RCMs, whereas
the inter-annual variability of precipitation shows the
opposite behaviour.
Acknowledgements
This study is part of work funded by the programme,
PENED 2003, General Secretariat for Research and
Technology (GSRT), Ministry of Development, Greece.
Data have been provided through the PRUDENCE data
archive, funded by the EU through contract EVK2CT2001-00132. The authors would like also to thank the
two reviewers for their constructive comments.
Copyright  2008 Royal Meteorological Society
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