Greece Greece Greece Greece

Coastal flood risk Greece

Sea level rise in Greece in the past

No systematic research has been carried out on the long-term trends of sea level changes in Greece. It should be noted that sea level measurements practically started after 1970, whereas the most reliable time series start in 1985 (1).

For the Mediterranean Sea a shift in sea level rise is observed at several tide gauge stations from an increasing trend (ca. 1.2-1.5 mm/year) before 1960 to a decreasing trend (ca. -1.3 mm/year) after 1960 (2). Recent data indicate another trend reversal around 1995 with a rapid rising of sea level, up to 20 mm/year in the eastern Mediterranean, as observed from field measurements as well as satellite altimetry (3). The rate of sea level rise in the Alboran and Aegean Sea estimated at the end of the 1990’s, is the highest value of the past 30 to 40 years, and would correlate with a continuous increase in sea surface temperature over the basin (0.12°C/year in the eastern part) (4).

Sea level rise in Greece in the future

Mean sea level in the Mediterranean is expected to rise at the rate of 5 cm/decade. In particular sea level will rise about 50 cm by the year 2100 (with an uncertainty range of 20-86 cm). Delta Nile, Venice and Thessalonica appear to be the more sensitive areas in the Mediterranean (1).

Global sea level rise

Observations

For the latest results: see Europe Coastal floods

Projections

For the latest results: see Europe Coastal floods

 

Extreme water levels - Global trends

More recent studies provide additional evidence that trends in extreme coastal high water across the globe reflect the increases in mean sea level (16), suggesting that mean sea level rise rather than changes in storminess are largely contributing to this increase (although data are sparse in many regions and this lowers the confidence in this assessment). It is therefore considered likely that sea level rise has led to a change in extreme coastal high water levels. It is likely that there has been an anthropogenic influence on increasing extreme coastal high water levels via mean sea level contributions. While changes in storminess may contribute to changes in sea level extremes, the limited geographical coverage of studies to date and the uncertainties associated with storminess changes overall mean that a general assessment of the effects of storminess changes on storm surge is not possible at this time.

On the basis of studies of observed trends in extreme coastal high water levels it is very likely that mean sea level rise will contribute to upward trends in the future.

Extreme waves - Future trends along the Mediterranean coast

Recent regional studies provide evidence for projected future declines in extreme wave height in the Mediterranean Sea (17). However, considerable variation in projections can arise from the different climate models and scenarios used to force wave models, which lowers the confidence in the projections (18).

Vulnerabilities - Coastal flood risk

According to a projection based on 0.5 m sea level rise by 2100, 15% of the current total area of coastal wetlands in Greece is expected to be flooded. The estimated economic losses from erosion (for land uses: urban, tourist, wetland, forest and agricultural) for the entire Greek territory for 2100 amounts approximately €356 million and €649 million for 0.5 m and 1 m sea level rise, respectively (21).

The city of Thessaloniki - Subsidence and sea level rise in the past

The City of Thessaloniki is established as the second most important urban centre of Greece. It is located in Central Macedonia and is situated in the inner part of the Thermaikos Gulf. It has an extended industrial zone in its suburbs and a major international port that constitutes the centre of merchant shipping for the Balkan countries (5).

The deltaic plains, with a bird-foot shape, at the river mouths indicate the dominance of fluvial over marine processes in forming the most active part of the Thermaikos shoreline. It has been estimated on the basis of hydrological charts that the area of the deltaic plain of the Axios river grew seawards by 175 km2 between 1850 and 1987 (6).


The west side of the city of Thessaloniki (the community of Kalohori) has been transformed into a very dynamic industrial area. Ground water extraction in this area has resulted in a dramatic subsidence. Starting from the decade of 1950, the public service of water supply of the city of Thessaloniki established water-pumping stations, in this area (51 from 1950 to 1980, nowadays 8 on a continuous base). Also, there are more than 700 industrial plants, many of them having their private water drillings. The number of these drillings is estimated to be more than 200. The Kalohori area suffers from ground subsidence that causes several problems to local environment. The greatest subsidence occurred in the southeastern area of Kalohori, where a subsidence speed of 2.8 - 5 cm/year was detected (7). The observed subsidence phenomena should be attributed to the intense and extended water pumping from the 1960s (8,9).

Subsidence in this area is estimated at 2.5m for the period 1955–1985 (10). This caused a gradual and significant fall in the level of the water table, and this fall caused the drainage of saturated sediments and their consolidation to be visible as subsidence of the ground surface. Therefore, the area between Kalochori and Sindos seems to have been affected by uniform subsidence reaching up to 3m from 1955 to 1980 (11).

The average height above sea level of the northern part of this area is approximately + 2.5 to + 3.0m. The south area (which expands to the sea) should have an average height approximately zero (0 m), some parts already being below the mean sea level. The area faced several problems in the past, mainly due to inundation (especially during the years 1968, 1974, 1976, 1979, and 1999). In order to minimize these problems, an embankment between land and sea was built (1968), while several improvements in the construction were made until 2000 (7).

Between 1980 to 1985 and 1985 to 1999, rates of relative height changes between 8 to 10 cm/year respectively, are observed based on triangulation re-measurement results (12).

The observed subsidence should be regarded as the cumulative effect of several factors, such as consolidation of near-surface sediments due to the decline of the piezometric level and the partial abandonment of the delta, oxidation of peat soils in the vadose area, syn-sedimentary deformation, as well as loading-induced consolidation of deeper sediments. The general local (over a few kilometers) subsidence has increased near shore water depths and thus provoked an increase in wave activity. Due to this the sea barriers that protect the deltaic plain were destroyed and catastrophic floods have occurred several times (5).

A subsidence rate of 20 mm/yr is observed in the western part of the Mygdonian Graben and specifically in the Langadhas area … According to estimates by the Directorate of Water resources and Agricultural Engineering of the Thessaloniki Prefecture in the greater area of Langadhas there exist 2.100 legal and illegal water boreholes. In relation with the drought period of the last two of decades (especially during the first half of the 1990s) a considerable decline in the piezometric level of about 80m has occurred mainly during the summer seasons. Based on the above considerations the observed deformations could be attributed either to the dominant active normal type of faulting of the Mygdonian Basin, or to intense water pumping in the basin for irrigation purposes. Finally the combined action of the above two factors could be the most fair interpretation of the detected subsidence (5).

Due the subsidence of the whole above mentioned area, the public service of water supply of Thessaloniki today pumps approximately 5,000 m3 of water per day, when a roughly estimation of the industrial water pumping varies between 10,000 to 36,000 m3 per day (7).

Despite from a serious danger of inundation, there is the danger of the intrusion of sea water into the aquifer (7).

Economic impacts of sea level rise for Europe

The direct and indirect costs of sea level rise for Europe have been modelled for a range of sea level rise scenarios for the 2020s and 2080s (19). The results show:

  1. First, sea-level rise has negative economic effects but these effects are not particularly dramatic. In absolute terms, optimal coastal defence can be extremely costly. However, on an annual basis, and compared to national GDP, these costs are quite small. On a relative basis, the highest value is represented by the 0.2% of GDP in Estonia in 2085.
  2. Second, the impact of sea-level rise is not confined to the coastal zone and sea-level rise indeed affects landlocked countries as well. Because of international trade, countries that have relatively small direct impacts of sea-level rise, and even landlocked countries such as Austria, gain in competitiveness.
  3. Third, adaptation is crucial to keep the negative impacts of sea-level rise at an acceptable level. This may well imply that some European countries will need to adopt a coastal zone management policy that is more integrated and more forward looking than is currently the case.

Adaptation strategies - The costs of adaptation

Both the risk of sea-level rise and the costs of adaptation to sea-level rise in the European Union have been estimated for 2100 compared with 2000 (20). Model calculations have been made based on the IPCC SRES A2 and B1 scenarios. In these projections both flooding due to sea-level rise near the coast and the backwater effect of sea level rise on the rivers have been included. Salinity intrusion into coastal aquifers has not been included, only salt water intrusion into the rivers. Changes in storm frequency and intensity have not been considered; the present storm surge characteristics are simply displaced upwards with the rising sea level following 20th century observations. The assessment is based on national estimates of GDP.


The projections show that without adaptation (no further raising of the dikes and no beach nourishments), the number of people affected annually by coastal flooding would be 20 (B1 scenario) to 70 (A2 scenario) times higher in 2100 than in 2000. This is about 0.05 - 0.13% of the population of the 27 EU countries in 2010 (20).

Without adaptation, damage costs would increase roughly by a factor of 5 during the century under both scenarios, up to US$ 17×109 in 2100. Total damage costs would amount to roughly 0.04% of GDP of the 27 EU countries in 2100 under both scenarios. Damage costs relative to national GDP would be highest in the Netherlands (0.3% in 2100 under A2). For all other countries relative damage costs do not exceed 0.1% of GDP under both scenarios (20).

Adaptation (raising dikes and beach nourishments in response to sea level rise) would strongly reduce the number of people flooded by factors of 110 to 288 and total damage costs by factors of 7 to 9. In 2100 adaptation costs are projected to be US$ 3.5×109 under A2 and 2.6×109 under B1. Relative to GDP, annual adaptation costs constitute 0.005 % of GDP under B1 and 0.009% under A2 in 2100. Adaptation costs relative to GDP are highest for Estonia (0.16% under A2) and Ireland (0.05% under A2). These results suggest that adaptation measures to sea-level rise are beneficial and affordable, and will be widely applied throughout the European Union (20).

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. Tsimplis and Baker (2000), in: Eisenreich (2005)
  3. Cazenave et al. (2001); Tsimplis and Rixen (2002), both in: Eisenreich (2005)
  4. Cazenave et al. (2001)
  5. Raucoules et al. (2008)
  6. Poulos et al. (1994), in: Raucoules et al. (2008)
  7. Doukas et al. (2004)
  8. Psimoulis et al. (2007)
  9. Andronopoulos et al. (1991), in: Raucoules et al. (2008)
  10. IGME (1989), in: Raucoules et al. (2008)
  11. Hatzinakos et al. (1990), in: Raucoules et al. (2008)
  12. Stiros (2001), in: Raucoules et al. (2008)
  13. Bindoff et al. (2007), in: IPCC (2012)
  14. Church and White (2011), in: IPCC (2012)
  15. Velicogna (2009); Rignot et al. (2011); Sørensen et al. (2011), all in: IPCC (2012)
  16. Marcos et al. (2009); Haigh et al. (2010); Menendez and Woodworth (2010), all in: IPCC (2012)
  17. Lionello et al. (2008), in: IPCC (2012)
  18. IPCC (2012)
  19. Bosello et al. (2012)
  20. Hinkel et al. (2010)
  21. Bank of Greece (2011), in: Shoukri and Zachariadis (2012)
  22. Cazenave et al. (2014)
  23. IPCC (2014)
  24. Watson et al. (2015)
  25. Yi et al. (2015)
  26. Church et al. (2013), in: Watson et al. (2015)
  27. Shepherd et al. (2012), in: Watson et al. (2015)
  28. Church et al. (2013), in: Watson et al. (2015)
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