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Erratum published on 18 May 2021, see Climate 2021, 9(5), 85.
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Article

Climate Change and Thermal Comfort in Greece

by
Harry D. Kambezidis
1,*,
Basil E. Psiloglou
2,
Konstantinos V. Varotsos
2 and
Christos Giannakopoulos
2
1
Atmospheric Research Team, Institute of Environmental Research and Sustainable Development, National Observatory of Athens, GR-11810 Athens, Greece
2
Institute of Environmental Research and Sustainable Development, National Observatory of Athens, GR-15236 P. Penteli, Greece
*
Author to whom correspondence should be addressed.
Climate 2021, 9(1), 10; https://doi.org/10.3390/cli9010010
Submission received: 16 December 2020 / Revised: 3 January 2021 / Accepted: 4 January 2021 / Published: 8 January 2021
(This article belongs to the Special Issue Human-Induced Climate Change: Truths and Controversies)
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Abstract

:
Global warming is an environmental issue keeping all nations alert. Under this consideration, the present work investigates the future thermal sensation of the Greek population. Three periods are selected (2021–2050, 2046–2075, 2071–2100) and two Intergovernmental Panel for Climate Change (IPCC) representative concentration pathway (RCP) 4.5 and 8.5 scenarios. Use of Thom’s discomfort index (TDI) is made, which is calculated from air temperature and relative humidity included in typical meteorological years (TMYs) derived for 1985–2014 and future periods (both IPCC scenarios) for 33 locations in Greece. TDI is discriminated into 6 classes. The analysis shows that there is no significant shift from past to future annual mean TDIs in terms of its classification. The same is found for the summer TDI values. Nevertheless, a distribution of the various TDI classes is provided within the TMYs. Maps of annual TDI values are prepared for Greece by using the kriging method; higher values are found in the southern part of Greece and lower values in the northern. Best-fit regression equations derived show the intra-annual TDI variation in all periods. Also, scatter plots of annual TDIs in the future epochs in comparison with the historical period show a linear relationship.

1. Introduction

The global-warming phenomenon is impacting the surface temperature of the Earth. Indeed, the Intergovernmental Panel for Climate Change (IPCC) [1] highlights that each of the recent 3 decades has become warmer than any other period prior to 1980. Also, the National Oceanic and Atmospheric Administration (NOAA) [2] reports that the 10 warmest years on record at global scale have appeared after 1998. Therefore, it is common sense that the increase in temperature may result in more frequent heat stresses (thermal discomfort) upon people [3,4,5,6], thus affecting the quality of life. This issue has, therefore, been the subject of several studies; these studies are focused on either the thermal comfort of people indoors (within a building) or outdoors (ambient conditions). For expressing the thermal comfort (or alternatively the thermal discomfort), several indices have been developed.
Yang et al. [7] have studied the thermal comfort during winter at the city of Tianjin, N. China. Adegoke and Dombo [8] examined the human thermal comfort in Akure, Nigeria. Cohen et al. [9] investigated the thermal perception in the urban web of Tel Aviv, Israel. Epstein and Moran [10] compared indices for thermal comfort and heat stress (extreme thermal discomfort). Golasi et al. [11] compared the Mediterranean outdoor comfort index (MOCI), as well as the predicted mean vote (PMV), and the popular events tracking (PET) models in Rome and found that the most appropriate is MOCI. A similar study was performed at Chiba, Japan, by comparing the models of PET, PMV, and standard effective temperature (SET) [12]. The outdoor thermal comfort was also studied in a subarctic climate of north Sweden [13]. Yousif and Tahir [14] investigated the thermal effect on people in Khartoum, Sudan. An informative review about the thermal effect on people has been given by Djongyang et al. [15].
Specifically, for Greece there have been several studies about the effect of heat on the population. Angouridakis and Makrogiannis [16] found the environmental thermal sensation for summer in Thessaloniki by analysing air-temperature and relative-humidity data in the period 1950–1957. Giles et al. [17] studied the heat stress in Athens and Thessaloniki during the heat waves of 1987 and 1988. Paliatsos and Nastos [18] compared the thermal effect during air-pollution episodes in Athens for the summers of 1993–1995 and found that it was related to the ozone concentration. Tselepidaki et al. [19] examined the summer thermal perception in Athens for cooling purposes. Tsitoura et al. [20] performed outdoors questionnaire about the thermal-comfort effect on people in 4 cities of Crete. Stathopoulou et al. [21] calculated the thermal effect from satellite-derived meteorological data and compared it with that from in situ measurements. Pantavou et al. [22] used various thermal-comfort indices in Athens (see their Table 2). Also, Pantavou [23] estimated the thermal sensation of pedestrians in 4 locations of Athens. Katavoutas and Founda [24] examined the period of 1960–2017 and found an increasing risk of heat stress in Athens.
It is obvious from the above works that no study about the thermal comfort has been conducted worldwide for a whole region or country. Therefore, the present work aims at filling this gap in the case of Greece. A second innovation of the study is the use of typical meteorological years (TMYs); such TMYs have been developed for 33 sites in Greece [25].
The work is divided into Sections. Section 2 deploys the data collection and analysis. Section 3 gives the results of the study. Section 4 provides a discussion and Section 5 deploys the main conclusions of the study.

2. Materials and Methods

According to [25] “A TMY is a set of meteorological and irradiance parameters usually consisting of hourly values in a year for a given geographical location (https://e3p.jrc.ec.europa.eu/articles/typical-meteorological-year-tmy). Furthermore, a TMY consists of a set of typical meteorological months (TMMs) selected from individual years integrated into a complete year. A TMY reflects all the climatic information of the location for a period as long as the mean life of the system.” The aim of that study [25] was the development of TMYs for 5 different applications, i.e., TMY-meteorology-climatology (TMY-MC), TMY-bio-meteorology (TMY-BM), TMY-agro-meteorology-hydrology (TMY-AMH), TMY-PV applications (TMY-PV), and TMY-energy design of buildings (TMY-EDB); all these TMYs were generated for 33 sites in Greece in the frame of the “Development of synergistic and integrated methods and tools for monitoring, management and forecasting of environmental parameters and pressures” (KRIPIS-THESPIA-II) funded project, by using historical data of various meteorological parameters in the period 1985–2014 (30 years). During this project, TMYs-MC were also derived for future periods (2021–2050, 2046–2075, 2071–2100) for all 33 locations, not yet published. The future TMYs-MC considered two opposing IPCC scenarios, i.e., the representative concentration pathway (RCP) 4.5 (intermediate scenario with an “anthropogenic” radiative forcing of 4.5 Wm−2 in the year 2100) and the RCP 8.5 (extreme scenario with an “anthropogenic” radiative forcing of 8.5 Wm−2 in the year 2100). For the TMY-generation statistical procedure one may refer to [25]. Since TMYs-MC have been derived for both the historical and the future time periods, they are used in the present work.
The historical TMYs-MC consist of hourly mean values of dry-bulb temperature (in °C), relative humidity (in %), atmospheric pressure (in hPa), and global horizontal irradiance (in Wm−2) at the sites’ altitude, while the future TMYs contain daily mean values of these parameters. To display the thermal comforts (or discomforts) across Greece for the historical and future periods and compare them, use of Thom’s discomfort index (TDI in °C) has been made [26]. Its definition is as follows.
TDI = Td − 0.55 (1 − 0.01 RH) (Td − 14.5),
where Td is the dry-bulb temperature (in °C) and RH the relative humidity (in %). Thom defined a series of limits for TDI; these are given in Table 1.
Therefore, hourly values of TDI were calculated from the corresponding values of Td and RH in the historical TMYs-MC and daily values in the future TMYs-MC for the 33 sites in Greece. These locations cover all of Greece and are given in Table 2; a map with the location of the 33 sites is also shown in Figure 1. The meteorological data for the 33 sites in the historical period 1985–2014 have been obtained from the Hellenic National Meteorological Service (HNMS) network, while the corresponding global horizontal irradiance values have been derived through the meteorological radiation model (MRM) code [27,28]. From these 33 data bases the historical TMYs-MC have been generated. As far as the future TMYs-MC are concerned, data for the closest grid point to the HNMS station’s location were employed from a transient realisation of the regional climate model RCA4 of the Swedish Meteorological and Hydrological Institute (SMHI) ([29], and references therein) driven by the Earth system model of the Max Planck Institute for Meteorology (MPI-M) [30]; simulations were carried out in the framework of the European Coordinated Regional Climate Downscaling Experiment (EURO-CORDEX) modelling experiment (http://www.euro-cordex.net). The horizontal resolution of the RCA4 model was 0.11° (~12 × 12 km). The meteorological and global horizontal radiation data for the future periods 2021–2050, 2046–2075, and 2071–2100 were provided from ECO-CORDEX to the KRIPIS-THESPIA-II project; therefore, corresponding TMYs-MC were derived following the statistical procedure described in [25]. The presentation of these future TMYs-MC will be the subject of a separate publication, which is in preparation.

3. Results

This section is divided in sub-Sections according to the time scale encountered (annual, seasonal, monthly). As far as the seasonal analysis is concerned, this is performed for the summer time (June, July, August—JJA), as it is the one which may affect people negatively because of high ambient temperatures [19] or even heatwaves [17,33]. As mentioned in Section 2, two IPCC scenarios have been adopted in this work. The first is the IPCC RCP 4.5 (stabilisation) scenario; according to it a global temperature increase by 2100 is in the order of 1.7–3.2 °C. The second is the IPCC RCP 8.5 (high-end) scenario, which foresees a global temperature increase in the range of 3.2–5.4 °C.
As mentioned in Section 1 and Section 2, use of the derived TMYs for the 33 sites in Greece (both historical and future) has been made in this study. Under this situation, analysis of the TDI tendency during the historical and future periods cannot be done because these long periods have been substituted by a single year (a TMY). As a TMY is a representative year climate-wise for the period from which it has come, so are the TDIs derived this way. Another reason for this controversy is the fact that the TMMs that comprise a single TMY come from different years of the period considered (see Table 3 as example where 4 sites have arbitrarily been chosen). On the other hand, comparison between the historical and future TDIs cannot directly be made because the historical TDIs are hourly values, while the future ones are daily values.

3.1. Annual Thom’s Discomfort Index (TDI) Values

Figure 2 shows the annual mean TDI values for all 33 sites in Greece. It is seen, as anticipated, that the RCP 8.5 scenario produces greater spread of the annual values among the various epochs in comparison with the RCP 4.5 scenario. To show this effect in a better way, differences between the future annual mean TDI values and those in the historical period have been calculated. Figure 3 provides the annual mean differences ΔTDIs = TDIfuture epoch − TDIhistorical period. Under the RCP 4.5 scenario the increase in the absolute TDI values is of the order of 0.1–1.7 °C approximately, considering all 3 future epochs. It is interesting to see that the sites of Elliniko and Ioannina present negative differences in all 3 periods, while Kasteli and Lamia in the first future period only, and Naxos and Thira in the first 2 future epochs; this means that their population will experience a “milder” thermal sensation in the future. By contrast, the RCP 8.5 scenario demonstrates an apparent increase in the thermal sensation across Greece in the range of almost 0.4–3.5 °C. Some stations (Elliniko, Ioannina, Kasteli, Kerkyra, Lamia, Naxos, Thira), however, present a dissonance as far as the first (2021–2050) future epoch is concerned, as done in the RCP 4.5 scenario also. Anyhow, in both scenarios, the average annual increase in TDI implies even higher TDI values on the daily or even hourly scale, which can be related to persistent and more intense heat waves that may occur in the future. Table 4 shows the difference between the annual mean TDI values for all sites and periods considered.
If one considers the centres of each 30-year period in Table 4, being the years 2000, 2035, 2060, and 2085, respectively, then the corresponding increase in TDI is found to be ≈0.12 °C/decade, ≈0.11 °C/decade, ≈0.10 °C/decade for the 3 periods under the IPCC RCP 4.5 scenario, and ≈0.09 °C/decade, ≈0.24 °C/decade, ≈0.30 °C/decade for the respective periods under the IPCC RCP 8.5 scenario. Such increases are considered insignificant in terms of the thermal sensation of the Greek population because they do not shift the thermal (dis)comfort from class A to a higher one, since all average annual TDIs lie in the TDI-class A (see Table 1).

3.2. Summer TDI Variation

In a similar way to what was presented in Figure 3, Figure 4 shows the summer differences between the future TDI values and the historical ones (ΔTDI = TDIfuture epoch − TDIhistorical period). From these figures the following observations can be made: (i) many sites seem to have a better summer thermal sensation (negative ΔTDIs) mostly in the RCP 4.5 2046–2075 period and less in the RCP 4.5 2021–2050 one (Figure 4a); (ii) higher annual absolute ΔTDIs values of almost 0.5 °C are found under both IPCC scenarios than their respective annual TDI ones (cf. Figure 3); this implies an abrupt increase in the future thermal (dis)comfort at these sites.
By repeating the values of Table 4 for the summer case, Table 5 is derived.
It is understandable that the summer thermal feeling throughout Greece both in the present and the future is in class B as all mean TDI values vary in the range 21–23.99; the exception is the RCP 8.5 2071–2011 period, which shifts to TDI-class C (24–26.99 °C). Calculations of the trends of TDI during summertime as done for its annual values result in the following conclusions: an increase in TDI of ≈0.03 °C/decade, ≈0.06 °C/decade, ≈0.06 °C/decade for the 3 periods under the IPCC RCP 4.5 scenario, and ≈0.10 °C/decade, ≈0.18 °C/decade, ≈0.25 °C/decade for the respective periods under the IPCC RCP 8.5 scenario. Such increases are considered insignificant in terms of the thermal sensation of the Greek population during summertime because they do not shift the thermal (dis)comfort from class B to a higher one, except for the RCP 8.5 2071–2100 period, which is classified in TDI-class C. Nevertheless, many sites seem to experience milder thermal feeling in the future than now as their ΔTDIs are negative in both RCP scenarios as shown in Figure 4a,b. Another interesting observation from Table 5 is that the average summer TDI values of RCP 4.5 2021–2050 (22.47 °C) and RCP 8.5 2046–2075 (22.43 °C) are almost equal; the same happens to the TDI values of the periods RCP 4.5 2046–2075 (22.72 °C) and RCP 8.5 2021–2050 (22.71 °C).

3.3. Intra-Annual TDI Variation

There is always a question about the in-year variability of a meteorological quantity. The quantity in question in this study is TDI, although it is not an immediate meteorological parameter but a derivative from ambient temperature and relative humidity. Figure 5 shows this variation for all periods of the study. A best-fit curve has also been derived for each case and can be used to calculate the average monthly TDI in Greece. The monthly TDI values in Figure 5 are averages over the 33 sites.
Figure 6 repeats the information posed in Figure 3, but in this case the bars refer to the monthly mean TDI differences. In both RCP scenarios the differences are generally reduced during the summer season (JJA) in comparison to the rest of the year. This may be attributed to the fact that the future climate (i.e., the climate change) seems to have a lesser effect on the summer months in comparison to the other seasons. Nevertheless, the increase in TDI under RCP 4.5 is between 0.1 and 1.4 °C and under RCP 8.5 between 0.2 and 2.9 °C. This conclusion excludes the small negative values in January and December (for RCP 8.5 2021–2050) and August (for RCP 4.5 2021–2050); the explanation is not obvious, but it can be taken as a no-real change in the future thermal feeling of the Greek population.
Some examples of the intra-annual TDI variation for selected sites are given in Figure 7. The selection has been based on the lowest and highest annual TDI values of the site during the various periods encountered in this study. It is seen that Kastoria has always the lowest thermal feeling and its population is not, therefore, in danger in the future in this respect. By contrast, Kythira in most periods and to a lesser extent Rodos and Thira shift their thermal sensation from TDI-class A to TDI-class B in the warm season of the year (June–October).

3.4. Frequency of TDI Occurrence

Up until now, the analysis has not taken into account the various TDI classes; to the contrary all TDI values have been considered from all 33 HNMS sites. This sub-section, however, gives information about the percentage of each TDI-class occurrence in all periods encountered in the study. This is shown in Figure 8. It is remarkable to observe that the TDI-class E (everyone feels thermal discomfort) appears in the historical period and not in any of the future ones, although at a very low percentage. This observation is true as this refers to almost half of the Greek territory (15 sites out of 33, i.e., Agrinio, Alexandroupoli, Anchialos, Kalamata, Kerkyra, Kozani, Lamia, Lesvos, Limnos, Mikra, Serres, Skyros, Souda, Thira, Zakynthos). The interpretation of this finding may be related to higher ambient temperatures in the future, but less humidity (drier weather) over Greece than now. Indeed, Kambezidis et al. [34] have examined the rain data of 31 HNMS stations in the period 1962–2002 and have found that the rain intensity (in mmh−1) shows (i) higher values in western Greece and lower ones in the Aegean Sea, and (ii) positive trends over Attica, Crete, southern Aegean and negative ones in the rest of the country and especially over the western mainland and Ionian islands. This is also confirmed by [35,36]. Furthermore, a technical report from the Bank of Greece [37] about the future impacts of climate change on various aspects of the Greek economy reports an increase in Td of 3.4–5.2 °C and a decrease in RH of 1.6–6.8% by 2100.

3.5. Maps of TDI

Figure 9 contains maps of the annual mean TDI values all over Greece. It is seen that all periods examined present the same pattern, irrespective to the absolute TDI values. Higher TDI values are located in the southern part of Greece, i.e., over south Ionian Sea, the Cyclades, Crete, and Megisti complex east of Rhodes and Crete, while lower TDI values occur in northern Greece and central Peloponnese (see map in Figure 1 for locating these regions). This pattern does not seem to change even in the ultimate future period (2071–2100).

4. Discussion

One might wonder whether the relationship between a historical meteorological variable and its evolution in the future is linear or not; in other words, whether there exists such a mathematical relationship for a climatic parameter between now and the future or, to the contrary, whether the climate-change system is chaotic. As a paradigm, an attempt has been made to answer this question in this study by considering the derivative climatic parameter of TDI. A first look at Equation (1) shows that TDI has a non-linear relationship with the independent variables Td and RH; so have Td and RH between each other. Furthermore, if one solves Equation (1) for either Td or RH, he/she gets a 2nd-order polynomial of Td or RH as function of the other parameter in the form y = (ax + b)/(cx + d), considering TDI is constant.
Td = (0.7975 RH + TDI)/(0.0055 RH + 0.4500),
RH = (0.4500 Td + TDI)/(0.0055 Td − 0.7975).
From the above expressions, one would, therefore, expect the historical and future TDIs to have a non-linear connection. Nevertheless, Figure 10 shows quite the opposite; there is a fine linear relationship between the historical monthly TDI values and those in any of the other 6 future epochs. No smoothing or deseasonalisation has taken place in the TDI time series. It is worth noticing that the ±95% confidence band around the best-fit line is so narrow that it contains the fewest data points. By contrast, the ±95% prediction zone around the best-fit line includes almost all data points. The difference in interpreting this result is the following. The narrow confidence interval contains some TDI pairs in any of the 6 cases (6 future periods) with a probability of 95%. The existence, however, of the majority of the data pairs outside the confidence interval dictates the fact that the linear best-fit line does not truly represent the relationship of future TDI as function of the historical TDI in the best way. Therefore, one could come to the conclusion that the relationship is not so linear as it appears, but is pseudo-linear. On the other hand, all future TDI pairs will be contained in the prediction interval with a probability of 95%. Then, one could be convinced that the pseudo-linear relation of today will evolve into a linear one in the future. This is confirmed by the high R2 values in all 6 scatter plots, thus denoting an excellent agreement (correlation) between the historical and future TDI values.

5. Conclusions

This study investigated the future thermal sensation of the Greek population because of the global-warming effect. Three future periods (2021–2050, 2046–2075, 2071–2100) and two IPCC scenarios (RCP 4.5, RCP 8.5) were chosen for analysis. The thermal (dis)comfort was expressed by Thom’s discomfort index (TDI) for 33 sites in Greece. Historical TDI values were also estimated in the period 1985–2014.
The present work presented two innovations. It is the first worldwide (in Greece as well) to (i) compute the future thermal feeling over a country, and (ii) compare it with the past. The second innovation concerns the use of historical as well as future TMYs-MC for all 33 sites, instead of using long-time series of ambient temperature and relative humidity, two parameters that define TDI. The main conclusions of the work can be summarised as follows.
No significant shift from the lowest TDI-class A to the TDI-class B has been shown to occur in the future all over Greece as far as the annual thermal sensation is concerned. TDI was, however, found to increase by ≈0.12 °C/decade, ≈0.11 °C/decade, ≈0.10 °C/decade for the 3 periods under the IPCC RCP 4.5 scenario, and by ≈0.09 °C/decade, ≈0.24 °C/decade, ≈0.30 °C/decade under the IPCC RCP 8.5 one, in comparison with the TDI values in the historical period.
Calculations of the TDI trends during summertime showed an increase of ≈0.03 °C/decade, ≈0.06 °C/decade, ≈0.06 °C/decade for the 3 periods under the IPCC RCP 4.5 scenario, and ≈0.10 °C/decade, ≈0.18 °C/decade, ≈0.25 °C/decade for the respective periods under the IPCC RCP 8.5 scenario, in comparison with the TDI values in the historical period. Such increases were considered insignificant because they did not shift the thermal (dis)comfort from TDI-class B to a higher one, except for the RCP 8.5 2071–2100 period, which was classified in TDI-class C.
For both historical and future epochs best-fit 6th-order regression equations were derived for estimating the monthly mean values of TDI. In all cases R2 was greater than 0.99.
The decomposition of TDI into its classes and their distribution within the TMYs was performed. It was observed that the TDI-class E (everyone feels thermal discomfort) appeared in the historical period only and not in any future epoch.
Maps of annual mean TDI values were derived; they showed high values over the southern part of Greece (Crete, the Cyclades, south Ionian Sea, Megisti complex), and lower ones over northern Greece and central Peloponnese. This pattern did not seem to change over the decades, from present to future.
A pseudo-linear relationship was shown to exist between the monthly TDI values in any future period with regard to the historical ones. This pseudo-linear expression seemed to evolve into a linear one in the future.
Apart from the conclusions of the present work, it also presents another value: the historical ambient temperature records of 1985–2014 from the 33 sites intrinsically include the recent global surface-warming slowdown, also referred to as hiatus, that occurred in the period 1998–2012 [38].

Author Contributions

Conceptualization, methodology, data curation, data analysis, writing—original draft preparation, writing—review and editing, H.D.K.; future Typical Meteorological Years conceptualization and development through the KRIPIS-THESPIA-II project, software and data curation, B.E.P.; provision of future meteorological and solar radiation data through the KRIPIS-THESPIA-II project, software and data curation K.V.V. and C.G. All authors have read and agreed to the published version of the manuscript.

Funding

This research was implemented in the frame of the KRIPIS-THESPIA-II project, under the grant MIS 5002517, funded by the General Secretariat of Research and Technology in Greece.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The present study was based on meteorological data of 33 sites in Greece provided by the Hellenic National Meteorological Service upon specific request. These data were used to generate the TMYs at the 33 locations.

Acknowledgments

The authors are thankful to the Hellenic National Meteorological Service for providing meteorological data from 33 stations in the network in the period 1985–2014 with the purpose of generating the historical TMYs- MC used in this work through the KRIPIS-THESPIA-II project (WP6). They also express their gratitude to the other members of the KRIPIS-THESPIA-II WP6 team for the generation of the TMYs, both historical and future: Dimitris Kaskaoutis, Kosmas Kavadias, Kalliopi Petrinoli, Ariadne Gavriil, and Dimitris Karagiannis.

Conflicts of Interest

The authors declare no conflict of interest.

Abbreviations

amslabove mean-sea level
EURO-CORDEXEuropean Coordinated Regional Climate Downscaling Experiment (Europe)
HNMSHellenic National Meteorological Service (Greece)
IERSDInstitute of Environmental Research and Sustainable Development (NOA, Greece)
IPCCIntergovernmental Panel for Climate Change
MOCIMediterranean Outdoor Comfort Index
MPI-MMax Planck Institute for Meteorology (Germany)
MRMMeteorological Radiation Model
NOANational Observatory of Athens (Greece)
NOAANational Oceanic and Atmospheric Administration (USA)
PETPopular Events Tracking (model)
PMVPredicted Mean Vote (model)
RCARossby Centre Regional Atmospheric (model)
RCPRepresentative Concentration Pathway
RHrelative humidity
SETStandard Effective Temperature (model)
SMHISwedish Meteorological and Hydrological Institute (Sweden)
TDIThom’s Discomfort Index
KRIPIS-THESPIADevelopment of synergistic and integrated methods and tools for monitoring, management and forecasting of environmental parameters and pressures (research programme, Greece)
TMMTypical Meteorological Month
TMYTypical Meteorological Year
WMOWorld Meteorological Organisation

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Figure 1. Distribution of the 33 selected HNMS stations (red circles) over Greece. The numbers within the circles refer to their names in column 1 of Table 2. The regions of south Ionian Sea, Peloponnese, the Cyclades (islands), Crete, and Megisti complex (of islands) are also shown; the Megisti complex is also known as the Kastellorizo complex, a complex of 14 small islands/rocky islets.
Figure 1. Distribution of the 33 selected HNMS stations (red circles) over Greece. The numbers within the circles refer to their names in column 1 of Table 2. The regions of south Ionian Sea, Peloponnese, the Cyclades (islands), Crete, and Megisti complex (of islands) are also shown; the Megisti complex is also known as the Kastellorizo complex, a complex of 14 small islands/rocky islets.
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Climate 09 00010 g002 550
Figure 2. Annual mean TDI values for all HNMS sites (in alphabetical order) as derived from the typical meteorological years -meteorology-climatology (TMYs-MC) during the historical period of 1985–2014 and the future epochs of 2021–2050, 2046–2075, 2071–2100 under the (a) representative concentration pathway (RCP) 4.5 and (b) RCP 8.5 Intergovernmental Panel for Climate Change (IPCC) scenarios.
Figure 2. Annual mean TDI values for all HNMS sites (in alphabetical order) as derived from the typical meteorological years -meteorology-climatology (TMYs-MC) during the historical period of 1985–2014 and the future epochs of 2021–2050, 2046–2075, 2071–2100 under the (a) representative concentration pathway (RCP) 4.5 and (b) RCP 8.5 Intergovernmental Panel for Climate Change (IPCC) scenarios.
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Climate 09 00010 g003a 550Climate 09 00010 g003b 550
Figure 3. Annual mean ΔTDIs for all HNMS sites (in alphabetical order) as derived from the TMYs-MC during the historical period of 1985–2014 and the future epochs of 2021–2050, 2046–2075, 2071–2100 under the (a) RCP 4.5 and (b) RCP 8.5 IPCC scenarios. The definition of ΔTDI is given in the text.
Figure 3. Annual mean ΔTDIs for all HNMS sites (in alphabetical order) as derived from the TMYs-MC during the historical period of 1985–2014 and the future epochs of 2021–2050, 2046–2075, 2071–2100 under the (a) RCP 4.5 and (b) RCP 8.5 IPCC scenarios. The definition of ΔTDI is given in the text.
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Climate 09 00010 g004 550
Figure 4. Summer (JJA) mean ΔTDIs for all HNMS sites (in alphabetical order) as derived from the TMYs-MC during the historical period of 1985–2014 and the future epochs of 2021–2050, 2046–2075, 2071–2100 under the (a) RCP 4.5 and (b) RCP 8.5 IPCC scenarios. The definition of ΔTDI is given in the text.
Figure 4. Summer (JJA) mean ΔTDIs for all HNMS sites (in alphabetical order) as derived from the TMYs-MC during the historical period of 1985–2014 and the future epochs of 2021–2050, 2046–2075, 2071–2100 under the (a) RCP 4.5 and (b) RCP 8.5 IPCC scenarios. The definition of ΔTDI is given in the text.
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Climate 09 00010 g005a 550Climate 09 00010 g005b 550
Figure 5. Intra-annual variation of the monthly mean TDIs in the epochs: (a) RCP 4.5 2021-2050, (b) RCP 4.5 2046–2075, (c) RCP 4.5 2071–2100, (d) RCP 8.5 2021–2050, (e) RCP 8.5 2046–2075, (f) RCP 8.5 2071–2100, and (g) historical 1985–2014. The black solid lines are the monthly means, the green solid curves are the best-fit polynomial lines to the means, and the red and blue dashed lines determine the upper and lower limits of the 95% confidence interval, respectively. Table 6 gives the equations of the best-fit polynomial lines; their extremely high R2 (approximately equal to 1) imply an excellent fit to the calculated intra-annual TDI values.
Figure 5. Intra-annual variation of the monthly mean TDIs in the epochs: (a) RCP 4.5 2021-2050, (b) RCP 4.5 2046–2075, (c) RCP 4.5 2071–2100, (d) RCP 8.5 2021–2050, (e) RCP 8.5 2046–2075, (f) RCP 8.5 2071–2100, and (g) historical 1985–2014. The black solid lines are the monthly means, the green solid curves are the best-fit polynomial lines to the means, and the red and blue dashed lines determine the upper and lower limits of the 95% confidence interval, respectively. Table 6 gives the equations of the best-fit polynomial lines; their extremely high R2 (approximately equal to 1) imply an excellent fit to the calculated intra-annual TDI values.
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Climate 09 00010 g006a 550Climate 09 00010 g006b 550
Figure 6. Intra-annual variation of the mean ΔTDIs as derived from the TMYs-MC during the historical period of 1985–2014 and the future epochs of 2021–2050, 2046–2075, 2071–2100 under the (a) RCP 4.5 and (b) RCP 8.5 IPCC scenarios. The definition of ΔTDIs is given in the text.
Figure 6. Intra-annual variation of the mean ΔTDIs as derived from the TMYs-MC during the historical period of 1985–2014 and the future epochs of 2021–2050, 2046–2075, 2071–2100 under the (a) RCP 4.5 and (b) RCP 8.5 IPCC scenarios. The definition of ΔTDIs is given in the text.
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Figure 7. Intra-annual variation of TDI in the epochs: (a) RCP 4.5 2021–2050, (b) RCP 4.5 2046–2075, (c) RCP 4.5 2071–2100, (d) RCP 8.5 2021–2050, (e) RCP 8.5 2046–2075, (f) RCP 8.5 2071–2100, and (g) historical 1985–2014 at selected sites in Greece. The dashed lines are the interfaces between the class A (TDI < 21 °C) and class B (TDI ≥ 21 °C).
Figure 7. Intra-annual variation of TDI in the epochs: (a) RCP 4.5 2021–2050, (b) RCP 4.5 2046–2075, (c) RCP 4.5 2071–2100, (d) RCP 8.5 2021–2050, (e) RCP 8.5 2046–2075, (f) RCP 8.5 2071–2100, and (g) historical 1985–2014 at selected sites in Greece. The dashed lines are the interfaces between the class A (TDI < 21 °C) and class B (TDI ≥ 21 °C).
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Figure 8. Frequency of occurrence (in %) for the various TDI classes (see Table 1 for definition) across all epochs: (a) RCP 4.5 2021–2050, (b) RCP 4.5 2046–2075, (c) RCP 4.5 2071–2100, (d) RCP 8.5 2021–2050, (e) RCP 8.5 2046–2075, (f) RCP 8.5 2071–2100, and (g) historical 1985–2014. The frequencies are averages over all 33 sites in Greece.
Figure 8. Frequency of occurrence (in %) for the various TDI classes (see Table 1 for definition) across all epochs: (a) RCP 4.5 2021–2050, (b) RCP 4.5 2046–2075, (c) RCP 4.5 2071–2100, (d) RCP 8.5 2021–2050, (e) RCP 8.5 2046–2075, (f) RCP 8.5 2071–2100, and (g) historical 1985–2014. The frequencies are averages over all 33 sites in Greece.
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Figure 9. Distribution of annual mean TDI values (in °C) across Greece for the various epochs studied: (a) historical 1985–2014, (b) RCP 4.5 2021–2050, (c) RCP 4.5 2046–2075, (d) RCP 4.5 2071–2100, (e) RCP 8.5 2021–2050, (f) RCP 8.5 2046–2075, and (g) RCP 8.5 2071–2100.
Figure 9. Distribution of annual mean TDI values (in °C) across Greece for the various epochs studied: (a) historical 1985–2014, (b) RCP 4.5 2021–2050, (c) RCP 4.5 2046–2075, (d) RCP 4.5 2071–2100, (e) RCP 8.5 2021–2050, (f) RCP 8.5 2046–2075, and (g) RCP 8.5 2071–2100.
Climate 09 00010 g009aClimate 09 00010 g009b
Climate 09 00010 g010a 550Climate 09 00010 g010b 550
Figure 10. Scatter plots of the monthly mean TDI values averaged over all 33 sites; the x-axis has the TDI values in the historical period and the y-axis in the future epoch of (a) RCP 4.5 2021–2050, (b) RCP 4.5 2046–2075, (c) RCP 4.5 2071–2100, (d) RCP 8.5 2021–2050, (e) RCP 8.5 2046–2075, and (f) RCP 8.5 2071–2100. The solid black line is the best-fit to the data pairs. The 95% confidence and prediction intervals are also shown. R2 has the following values: (a) 0.9635, (b) 0.9609, (c) 0.9600, (d) 0.9626, (e) 0.9601, and (f) 0.9638.
Figure 10. Scatter plots of the monthly mean TDI values averaged over all 33 sites; the x-axis has the TDI values in the historical period and the y-axis in the future epoch of (a) RCP 4.5 2021–2050, (b) RCP 4.5 2046–2075, (c) RCP 4.5 2071–2100, (d) RCP 8.5 2021–2050, (e) RCP 8.5 2046–2075, and (f) RCP 8.5 2071–2100. The solid black line is the best-fit to the data pairs. The 95% confidence and prediction intervals are also shown. R2 has the following values: (a) 0.9635, (b) 0.9609, (c) 0.9600, (d) 0.9626, (e) 0.9601, and (f) 0.9638.
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Table
Table 1. Description, classes and ranges of Thom’s discomfort index (TDI) [26].
Table 1. Description, classes and ranges of Thom’s discomfort index (TDI) [26].
DescriptionTDI ClassRange (°C)
No discomfortA<21
Under 50% of the population feels discomfortB21–23.99
Over 50% of the population feels discomfortC24–26.99
Most of the population feels discomfortD27–28.99
Everyone feels discomfortE29–31.99
State of medical emergencyF≥32
Table
Table 2. Meteorological sites of the Hellenic National Meteorological Service (HNMS) network used in this study.
Table 2. Meteorological sites of the Hellenic National Meteorological Service (HNMS) network used in this study.
Nr.Station Name 1 (Region in Greek/English language) 1Station’s World Meteorological Organisation code (16xxx)Latitude
(deg N)		Longitude
(deg E)		Elevation
(m amsl)
1Serres (Kentriki Makedonia/Central Macedonia)60641.08323.56734.5
2Kastoria (Dytiki Makedonia/Western Macedonia)61440.45021.283660.9
3Mikra, outskirts of Thessaloniki (Kentriki Makedonia/Central Macedonia)62240.51722.9674.8
4Alexandroupoli (Anatoliki Makedonia and Thraki/Eastern Macedonia and Thrace)62740.85025.9333.5
5Kozani (Dytiki Makedonia/Western Macedonia)63240.28321.783625.0
6Kerkyra, known as Corfu (Ionioi Nisoi/Ionian Islands)64139.61719.9174.0
7Ioannina (Ipiros/Epirus)64239.70020.817484.0
8Larisa (Thessalia/Thessaly)64839.65022.45073.6
9Limnos (Voreio Aigaio/Northern Aegean)65039.91725.2334.6
10Anchialos (Thessalia/Thessaly)66539.21722.80015.3
11Lesvos (Voreio Aigaio/Northern Aegean)66739.06726.6004.8
12Agrinio (Dytiki Ellada/Western Greece)67238.61721.38325.0
13Lamia (Sterea Ellada)67538.85022.40017.4
14Andravida (Dytiki Ellada/Western Greece)68237.91721.28315.1
15Skyros (Sterea Ellada)68438.90024.55017.9
16Araxos (Dytiki Ellada/Western Greece)68738.13321.41711.7
17Tanagra (Sterea Ellada)69938.31723.550139.0
18Chios (Voreio Aigaio/Northern Aegean)70638.35026.1504.0
19Tripoli (Peloponissos/Peloponnese)71037.53322.400652.0
20Elliniko (Attica)71637.90023.75015.0
21Zakynthos, known as Zante (Ionioi Nisoi/Ionian Islands)71937.78320.9007.9
22Samos (Voreio Aigaio/Northern Aegean)72337.70026.9177.3
23Kalamata (Peloponissos/Peloponnese)72637.06722.00011.1
24Naxos (Notio Aigaio/Southern Aegean)73237.10025.5339.8
25Methoni (Peloponissos/Peloponnese)73436.83321.70052.4
26Spata (Attiki/Attica)74137.96723.91767.0
27Kythira (Attiki/Attica)74336.13323.017166.8
28Thira, known as Santorini (Notio Aigaio/Southern Aegean)74436.41725.43336.5
29Souda (Kriti/Crete)74635.55024.117140.0
30Rodos, known as Rhodes (Notio Aigaio/Southern Aegean)74936.40028.11711.5
31Irakleio, also written as Heraklion (Kriti/Crete)75435.33325.18339.3
32Siteia (Kriti/Crete)75735.12026.100115.6
33Kasteli (Kriti/Crete)76035.12025.333335.0
1 The names have been converted into Latin characters from the Greek alphabet according to the Hellenic Standardisation Organisation (ELOT) 743 standard [31], which is the adoption of the ISO 843 one [32].
Table
Table 3. The HNMS stations of Agrinio, Irakleio, Kastoria, and Tripoli with their typical meteorological months (TMMs) selected from years within the period 1985–2014.
Table 3. The HNMS stations of Agrinio, Irakleio, Kastoria, and Tripoli with their typical meteorological months (TMMs) selected from years within the period 1985–2014.
StationJanFebMarAprMayJunJulAugSepOctNovDec
Agrinio199920042000199420011997200019992004198820101994
Irakleio199520012004199419971987200319961996199720042003
Kastoria198719882005198519951996199619981991199419892008
Tripoli199919851993199319951987198719861986199120041994
Table
Table 4. Average annual TDI (in °C) and average annual ΔTDI (in °C) values for all sites and periods considered; the standard deviation from the mean is shown in parenthesis. The definition of ΔTDI is given in the text.
Table 4. Average annual TDI (in °C) and average annual ΔTDI (in °C) values for all sites and periods considered; the standard deviation from the mean is shown in parenthesis. The definition of ΔTDI is given in the text.
ParameterPeriod
Historical 1985–2014RCP 4.5 2021–2050RCP 4.5 2046–2075RCP 4.5 2071–2100RCP 8.5 2021–2050RCP 8.5 2046–2075RCP 8.5 2071–2100
Annual average TDI15.89 (±1.70)16.32 (±1.63)16.52 (±1.60)16.74 (±1.65)16.22 (±1.64)17.33 (±1.60)18.40 (±1.54)
Annual average ΔTDI00.43 (±0.48)0.64 (±0.51)0.85 (±0.54)0.33 (±0.51)1.44 (±0.50)2.51 (±0.51)
Table
Table 5. Average summer TDI (in °C) and average summer ΔTDI (in °C) values for all sites and periods considered; the standard deviation from the mean is shown in parenthesis. The definition of ΔTDI is given in the text.
Table 5. Average summer TDI (in °C) and average summer ΔTDI (in °C) values for all sites and periods considered; the standard deviation from the mean is shown in parenthesis. The definition of ΔTDI is given in the text.
ParameterPeriod
Historical 1985–2014RCP 4.5 2021–2050RCP 4.5 2046–2075RCP 4.5 2071–2100RCP 8.5 2021–2050RCP 8.5 2046–2075RCP 8.5 2071–2100
Summer average TDI22.37 (±1.02)22.47 (±0.81)22.72 (±0.83)22.91 (±0.91)22.71 (±0.86)23.43 (±0.87)24.53 (±0.88)
Summer average ΔTDI00.10 (±0.56)0.35 (±0.59)0.55 (±0.58)0.34 (±0.58)1.07 (±1.22)2.16 (±0.58)
Table
Table 6. Best-fit 6th-order polynomial regression equations for the monthly mean TDIs (in °C); t is the month of the year in the range 1–12; R2 is the coefficient of determination.
Table 6. Best-fit 6th-order polynomial regression equations for the monthly mean TDIs (in °C); t is the month of the year in the range 1–12; R2 is the coefficient of determination.
IPCC Scenario, PeriodEquationR2
RCP 4.5, 2021–2050TDI = −0.0003 t6 + 0.0127 t5 − 0.2110 t4 + 1.5271 t3 − 4.6786 t2 + 6.7114 t + 6.87590.9997
RCP 4.5, 2046–2075TDI = −0.00009 t6 + 0.0053 t5 − 0.0986 t4 + 0.7052 t3 − 1.6694 t2 + 1.6710 t + 9.81820.9975
RCP 4.5, 2071–2100TDI = −0.0002 t6 + 0.0102 t5 − 0.1697 t4 + 1.1906 t3 − 3.2756 t2 + 4.0542 t + 8.74190.9995
RCP 8.5, 2021–2050TDI = −0.0003 t6 + 0.0138 t5 − 0.2226 t4 + 1.5943 t3 − 4.9267 t2 + 7.5063 t + 5.45030.9991
RCP 8.5, 2046–2075TDI = −0.0003 t6 + 0.0113 t5 − 0.1791 t4 + 1.2151 t3 − 3.2224 t2 + 3.7653 t + 9.54270.9998
RCP 8.5, 2071–2100TDI = −0.0003 t6 + 0.0119 t5 − 0.2000 t4 + 1.4613 t3 − 4.5338 t2 + 6.7582 t + 8.65530.9997
historical (1985–2014)TDI = −0.0003 t6 + 0.0130 t5 − 0.2113 t4 + 1.4895 t3 − 4.3529 t2 + 5.9352 t + 6.65040.9997
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Kambezidis HD, Psiloglou BE, Varotsos KV, Giannakopoulos C. Climate Change and Thermal Comfort in Greece. Climate. 2021; 9(1):10. https://doi.org/10.3390/cli9010010

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Kambezidis, Harry D., Basil E. Psiloglou, Konstantinos V. Varotsos, and Christos Giannakopoulos. 2021. "Climate Change and Thermal Comfort in Greece" Climate 9, no. 1: 10. https://doi.org/10.3390/cli9010010

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Kambezidis, H. D., Psiloglou, B. E., Varotsos, K. V., & Giannakopoulos, C. (2021). Climate Change and Thermal Comfort in Greece. Climate, 9(1), 10. https://doi.org/10.3390/cli9010010

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