Air temperature changes until now

Annual temperature over the period 1961–1990 showed a trend of statistically significant warming over land in south-east Europe of approximately 0.4–0.6 °C per decade (17). In the middle of the ’50s a cooling period started in northern Greece and progressively extended also in the southern regions of the country where it started to be detected in the beginning of the’70s. The lowest average annual temperatures in Greece occurred in the decade of 1970 up to the beginning of 1980, due mainly to the very cold summers and autumns. However, during the last years of the ’90s (while a little earlier in some meteorological stations), a progressive increase of temperature was observed. … This seems to be due to a more intensive warming during the summer period (1).

In Greece, as it was also the case of Spain, the frequency of heat waves in the ’90s was about three times higher than the one of the three previous decades. However, there are no signs of a similar reverse trend in the frequency of cold extremes. The data from both stations of Athens and Corfu present statistical important increasing trends with respect to the duration of heat waves, during the summer period as well as on annual basis, while the occurrence of cooling waves during winter as well as on annual basis becomes much less frequent. The time series from the other stations do not show a certain trend or they show negative trends with respect to the duration of heat waves (2).

In the eastern Mediterranean, the intensity, length and number of heat waves have increased by a factor of six to eight since the 1960s (14). The period of hot extremes has significantly lengthened for Crete since 1960 (23).

Precipitation changes until now

During 1960-1990 the highest precipitation amounts were found in western Greece and southeastern Aegean Sea, during winter, autumn and on annual basis, while summer precipitation amounts are small, especially over the islands of Aegean Sea, Israel and Syria (3).

Recent studies have shown an increasing tendency of dry spell length during the last two decades in Eastern Mediterranean, which extends from the Ionian Sea to the Cyprus area (4), as well as a tendency towards drier conditions (5,6). Over the last 50 years extreme rainfall events exhibit increased variability (1,6).

Precipitation in Greece has reduced during the second half of the 20th century on an annual basis and for the winter period (-8 and –5 mm/decade, respectively) and the reduction period seems to start in the ’70s. Locally much higher reduction rates have been observed for certain stations on islands (-64 mm/decade in Corfu and -52 mm/ decade in Mitilini) (1). This steady decline in annual rain over Greece since 1950 was found in many studies (20). Similar results have been presented for the neighboring regions and the Mediterranean Sea in general, most of them presenting a significant decrease in annual rainfall (21). These results agree with climate model projections that point towards a gradual aridification of the Mediterranean region. These changes may not be due to climate change, however, but can be attributed to natural variability (19); decadal variability of precipitation over Greece is quite strong. In fact, recent precipitation data do not point at an ongoing decline in rainfall: monthly precipitation sums and annual daily maxima records derived from 136 stations across Greece during the period 1940-2012 show a decline since 1950, an increase since 1980 and stable precipitation during the last 15 years of this period in most regions in Greece (19). 

With respect to events of extreme precipitation, the average daily intensity of summer precipitation presents a positive trend during the second half of the 20th century in all stations except the one in Larissa, while the intensity of winter and annual precipitation presents a negative trend. The situation is completely different in Athens, where the annual precipitation presents a positive trend due to the severe precipitation events that occurred during the last years (1).

Besides global warming during the recent decades, a physical explanation of the enhanced precipitation in Athens could be the urban heat island effect: the effect of extensive building after the Second World War and the rapid increase of the population and the number of vehicles mainly after 1970. The possible main factors, which cause urban induced changes in precipitation, are the mechanical turbulence resulting from increased surface roughness, the addition of sensible heat from the urban warm air and the anthropogenic condensation nuclei floating in the urban air. These factors are responsible for heavy storms of convective nature in the developed mega-cities (7).

The precipitation decline over the Mediterranean region during the last decades of the past century may be due to the positive trend in the East Atlantic Western Russia pattern, which was induced by the positive trend of the North Atlantic Oscillation (8).

Regarding Greece, the observed downward trend in winter and annual precipitation in Greece is thought to be linked mainly to a rising trend in the hemispheric circulation modes of the NAO Index, which are connected with the Mediterranean Oscillation Index (9). Moreover, low frequency fluctuations in the circulation over the Atlantic have been closely linked to the coherent large-scale precipitation anomalies that have persisted, particularly in winter, over Turkey since the early 1960s (10).

No statistically significant trends for both the annual total precipitation and the annual number of rain days have been found for Crete during the period 1951–2010 (24)

Air temperature changes in the 21st century

According to a moderate scenario of climate change (the so-called RCP4.5 scenario), the largest warming of maximum temperatures in Greece is obtained over the eastern part of the country reaching up to 2 °C in the period 2025–2049 and extends more towards southeastern areas up to 2.5 °C in the period 2075–2099, compared with the historical period of 1980–2004 (25).

According to climatic simulations for 2100, in the case of the IPCC Α2 scenario (up to 250% more greenhouse gas emissions in 2100 compared with 1961-1990), the mean maximum temperature over the entire Eastern Mediterranean is projected to increase. In July the mean maximum temperature in the Balkan countries is projected to increase by up to 12⁰C compared to current values. In Greece, the increase is in the order of 7-8⁰C in southern regions (including the area of Athens), while in central and northern Greece the increase is higher and varies between 8 and 10⁰C. In June and September the increase of the maximum temperature is slightly lower, varying from 6 up to 8⁰C in Greece (1).

Under the B2 scenario (up to 62% more greenhouse gas emissions in 2100 compared with 1961-1990), the increase of the mean maximum temperature in Greece during July is clearly lower compared to the one obtained for the A2 scenario and varies between 6-7⁰C in southern regions (including the Athens area) up to 7-8⁰C in central and northern Greece (1).

As it was the case for the mean maximum temperature, there is an increase of the mean minimum temperatures over the entire region examined, particularly in the Balkans where the mean minimum temperature in July increases by up to 9⁰C compared to current values. In Greece, the increase is about 6-7 ⁰C in southern regions (including the area of Athens) and between 7-8⁰C in central and northern Greece (1).

Eastern Mediterranean and the Middle East (EMME) - Warming 

For the Eastern Mediterranean and the Middle East an analysis was carried out of long-term meteorological datasets (period 1901-2006) along with regional climate model projections for the 21st century (SRES scenario A1B) (6). The results suggest a continual, gradual and relatively strong warming of the area of about 1-3°C in the near-future (2010–2039), to 3–5°C in the mid-century period (2040–2069) and 3.5–7°C by the end of the century (2070–2099). Daytime maximum temperatures appear to increase most rapidly in the northern part of the region, i.e. the Balkan Peninsula and Turkey. Maximum daytime temperature increases more strongly than mean night time minimum temperature (15).

Extremely high summer temperatures are projected to become the norm by 2070–2099; the coolest summers at the end-of-century may be warmer than the hottest ones in the recent past. As an example, the hottest summer on record in Athens in 2007 would be among the 5% coolest ones by the end of the century (11,15). 

Current and future daytime mean temperature trends in the Eastern Mediterranean and the Middle East typically vary from 0.28° to 0.46°C per decade. The largest increases appear in some continental locations such as Belgrade, Sofia, Ankara, Baghdad and Riyadh with trends in excess of 0.4°C/decade. The same analysis was performed for daytime maximum and night-time minimum temperature; for daytime maximum temperature the largest upward trends are calculated for Belgrade, Sofia, Tirana and Ankara with 0.48°, 0.46°, 0.45° and 0.44°C per decade, respectively. For night-time minimum temperature, large positive trends exceeding 0.40°C/decade are derived for Belgrade, Riyadh, Baghdad, Athens, Sofia and Ankara (11,15).

A1B scenario results suggest that by the end of the century, the frequency of very hot days (maximum day time temperature >35°C) may increase up to 1–2 weeks per year in mountainous parts of the northern EMME and by about a month in much of the rest of the region. The frequency of ‘‘tropical’’ nights (mean night time minimum temperature > 25°C) also increases strongly, by nearly a month per year in the Balkans and coastal areas, and more than two months in the Gulf region, exacerbating the daytime heat stress. By the end of the century in most cities, the coolest summers may be warmer than the hottest ones today (15). For the same scenario, the number of warm days at the end of the century (defined as days with maximum temperature >25°C) is found to increase by 50–60 additional days per year by the end of the 21st century. In contrast, frost days and wet days are projected to decrease (17).

Eastern Mediterranean and the Middle East (EMME) - Heat wave characteristics

The relatively strong upward trend in the northern parts of the Eastern Mediterranean and the Middle East indicates a continuation of the increasing intensity and duration of heat waves observed in this region since 1960 (12). 

Changes in heat wave characteristics for the eastern Mediterranean and the Middle East have been estimated for the end of this century, as compared with the period 1961 - 1990 (18, see also 15). This was done for a low-end (optimistic), intermediate and high-end (pessimistic) scenario of climate change (the so-called SRES scenarios B2, A1B and A2); one regional climate model was used. Reference point for the definition of heat waves in this study is the maximum daily temperature that is exceeded 10% of the year: heat waves were defined as periods with at least six consecutive days with maximum temperatures exceeding this 10% value. This reference point was calculated for the period 1961 – 1990. The heat waves with respect to this referent point were calculated for 1961 – 1990 and the future horizon of 2071 – 2099.

The results show that in the summer season May to September heat waves in the eastern Mediterranean and the Middle East are expected to change from events with a return period of about once every 2 years on average to a common phenomenon with multiple occurrences per year. The mean number of heat wave days will increase dramatically by 20 - 130 days per year and will be the most pronounced over the Arabian Peninsula and the Gulf area. Currently, these heat waves have an average duration that varies from 6 to 12 days. At the end of this century these heat waves will last for several weeks (under the optimistic scenario) to months. In addition, much hotter heat extremes are expected by the end of the century: changes in severity of heat waves in terms of peak temperatures will probably exceed by far the projected mean summertime warming that ranges from 3 to 9°C (depending on the scenario of climate change) (15,18).

Crete

For Crete, projected changes in daily maximum and daily minimum temperatures have been calculated for the period 2031-2060 compared with 1971-2000. This was done for a moderate (RCP4.5) and high-end (RCP8.5) scenario of climate change. The calculations are based on five regional climate models (RCMs) (22). Under the moderate scenario of climate change, maximum temperatures are projected to increase by about 1.9 °C for Crete in the summer, and a little less (at least 1.2 °C) in the other seasons. Under the high-end scenario of climate change, the projected increase of maximum temperatures is higher than 2 °C for all seasons for Crete. Daily minimum temperatures are projected to increase more than 1.2 °C for both scenarios of climate change.

Precipitation changes in the 21st century

According to a moderate scenario of climate change (the so-called RCP4.5 scenario), annual precipitation in Greece is projected to decrease over the eastern part of the country, and the number of dry days is projected to increase, in the period 2025–2049 and even more so in the period 2075–2099, compared with the historical period of 1980–2004 (25).

From model calculations and a medium low greenhouse gas emissions scenario (B2 IPCC) a general future tendency for 2070-2100 compared with 1960-1990 was found towards drier Eastern Mediterranean, with reduced rainfall intensity. Longer dry spells are expected in all seasons, except autumn, with the largest increase in the southern part of the area. Extreme wet spells will shorten everywhere during all seasons, except autumn. Precipitation intensity was found reduced for all seasons and mostly for summer in South Aegean Sea (3). Future projections (based on the SRES A1B emissions scenario) for the period 2070–2099 compared with 1961–1990 suggest decreases in the number of wet days and the heavy precipitation events towards the end of the 21st century: the number of wet days may decrease by 10–30 days per year, while heavy  precipitation is likely to decrease in the high-elevation areas by about 15 days year per by the end of the 21st century (17).

December at present is the most rainy month in the majority of Greek regions. According to climatic simulations for 2100, in the case of the IPCC Α2 scenario (up to 250% more greenhouse gas emissions in 2100 compared with 1961-1990), the reduction of precipitation in December is significant, mainly over the marine regions of the Eastern Mediterranean as well as in western Greece, where the mean precipitation for the period 2071-2100 is approximately 60-70% of the current levels. In northern and eastern Greece, in the islands of the Eastern Aegean and in Crete the decrease of precipitation is lower (1).

During summer, the Α2 scenario shows a very significant reduction of precipitation for 2100, mainly in northern Greece and in the Balkans. The mean precipitation in these regions for the period 2071-2100 is approximately 20-30% of the current precipitation levels. Especially in regions of Serbia, Bulgaria and Romania, where at present the precipitation during summer is very important, the reduction is exceptionally high and disturbing because precipitation in these regions supplies water to big rivers which flow through Greece as well. The reduction of precipitation is also very important in regions of northern Greece where during summer a significant storm activity is evident. In southern Greece the reduction of precipitation is also high but these regions are characterized in general by very low precipitation during summer even under the current climate (1).

The length of extreme dry spells is projected to increase in the future for the Mediterranean, as compared to the present climate on annual basis. The magnitude of change varies spatially and seasonally. More specifically, during winter, this length will be greater in almost the whole Eastern Mediterranean, except in North Western Greece, where no significant change was found. Southern Aegean, Crete and West Cyprus present the largest increase of dry spell length for 2070-2100, of about 6 to 7 days (3).

In spring, extreme dry spells are longer in the future in the whole Eastern Mediterranean, with no substantial variations. In summer the increase of the length of extreme dry spells is highest, as compared to winter and spring, with maximum values being found mainly in the continental West Greece (10-14 days), and west coast of Turkey (10 days). Contrary to the other seasons, the duration of extreme dry spells is slightly reduced at about 2 to 6 days, in autumn in almost the whole Eastern Mediterranean. Therefore, it seems that the apparent drying of Eastern Mediterranean will continue in future, especially in the dry period of the year and the wetter regions (3).

In the future the wettest areas of Greece show a reduction of extreme wet spells length during the wet period of the year, except in Crete and Cyprus. On the contrary, in autumn, extreme wet spells are longer in future, especially in Aegean Sea and west coast of Turkey. Future changes of rainfall intensity are smaller and show substantial spatial and seasonal variability. The rainfall intensity decreases in winter, spring and summer, but increases in autumn. The greatest reduction is found in summer in south Aegean region. Response of precipitation extremes to global warming in Eastern Mediterranean should be handled with caution, though, in view of uncertainties (3).

Eastern Mediterranean and the Middle East

From the analysis of long-term meteorological datasets (period 1901-2006) along with regional climate model projections for the 21st century (SRES scenario A1B) a decline of annual precipitation is projected of 5–25% in 2040–2069 and 5–30% in 2070–2099 relative to the reference period 1961–1990 (11). The decreases will be particularly large (>15%) in Cyprus, Greece, Israel, Jordan, Lebanon, the Palestine territories and Syria. As a result of precipitation decrease, and also due to population growth rates, the per capita available internal water resources may decline strongly, for example by 50% or more by mid-century in Cyprus (16).

In the Balkans, Turkey, Cyprus, Lebanon and Israel, the number of rainy days may decrease, e.g. by 5–15 days at mid-century and by 10–20 days per year at the end-of-century (11). This appears to be a continuation of a trend observed in Greece since about 1960 (13).

The intensity of precipitation (maximum amount of rain per day) is expected to decrease except over the northern Balkans and the Caucasus (11).

Crete

Projected changes of daily precipitation for the period 2031-2060 compared with 1971-2000, based on five regional climate models, do not show clear changes of precipitation or precipitation extremes for Crete under a moderate (RCP4.5) and high-end (RCMs) scenario of climate change (22).

References

The references below are cited in full in a separate map 'References'. Please click here if you are looking for the full references for Greece.

1. Hellenic Republic,Ministry for the Environment, Physical Planning and Public Works of Greece (2006)
2. Larissa and Methoni, in: Hellenic Republic,Ministry for the Environment, Physical Planning and Public Works of Greece (2006)
3. Oikonomou et al. (2008)
4. Anagnostopoulou et al. (2003); Kutiel (1985), both in: Oikonomou et al. (2008)
5. Kutiel et al. (1996); Turkes (1996); Tolika et al. (2004), all in: Oikonomou et al. (2008)
6. Kioutsioukis et al. (2009)
7. Nastos and Zerefos (2007)
8. Krichak and Alpert (2005), in: Nastos and Zerefos (2008)
9. Feidas et al. (2007), in: Nastos and Zerefos (2008)
10. Turkes and Erlat (2003), in: Nastos and Zerefos (2008)
11. Lelieveld et al. (2012)
12. Kuglitsch et al. (2010), in: Lelieveld et al. (2012)
13. Nastos and Zerefos 2009, in: Lelieveld et al. (2012)
14. Kuglitsch et al. (2010), in: Coumou and Rahmstorf (2012)
15. Lelieveld et al. (2014)
16. Chenoweth et al. (2011), in: Lelieveld et al. (2013)
17. Kostopoulou et al. (2014)
18. Zittis et al. (2016)
19. Markonis et al. (2017)
20. Xoplaki et al. (2000); Maheras and Anagnostopoulou (2003); Maheras et al. (2004); Feidas et al. (2007); Kambezidis et al. (2010), all in: Markonis et al. (2017)
21. González-Hidalgo et al. (2001); Xoplaki et al. (2004); Cannarozzo et al. (2006); Norrant and Douguédroit (2006); Partal and Kahya (2006); Nastos (2011); Philandras et al. (2011), all in: Markonis et al. (2017)
22. Varotsos et al. (2021)
23. Founda et al. (2019) in: Varotsos et al. (2021)
24. Philandras et al. (2011); Varouchakis et al. (2018), both in: Varotsos et al. (2021)
25. Politi et al. (2023)