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Coastal flood risk Croatia

The Croatian coast

The total length of Croatia’s coast is 6,278 km of which 1,880 km belong to the mainland and 4,398 km to the island coastline. With its 78 islands, 524 islets and 640 cliffs and reefs Croatia’s Adriatic coast ranks among the most indented in Europe. The islands are divided into the Istrian, the Kvarner, the northern Adriatic, the central Adriatic and the southern Adriatic group, with the largest islands being Cres (405.68 km2), Krk (405.24 km2), Brač (394.57 km2) and Hvar (299.66 km2). The coastal area of Croatia is separated from the inland by high mountains. Relatively few low-lying parts of the coast are especially vulnerable to sea level rise due to climate change (1).


Numerous islands are located in two or three groups lying parallel to the mainland (length 4058 km). Only 67 out of 1185 Croatian islands are inhabited. Generally, the coastal strip is very narrow (1–5 km) and is separated from the hinterland by chains of mountains, the slopes of which often form the shoreline. Only two large coastal plains, the western part of the Istrian coast and the northern Dalmatia coast, lie between the towns of Zadar and Sibenik. The Croatian coastal zone occupies 12,450 km2 out of the total national area of 56,610 km2. It has some 1,2 million inhabitants (1991 census), or about a quarter of the total Croatian population. In many places along the coast, historical towns, residential houses, tourist complexes, roads, and other infrastructure are constructed very close to the coastline (2).

Mediterranean-style agriculture is important for the local population, particularly on the islands and on the alluvial plain of the Neretva River estuary. The total national olive and grape production of 1999 (45% of the total country production) was produced in the coastal area (3).

Ten relatively small rivers of karstic type are located along the coast. The largest one is the Neretva River (mean annual water flow 296 m3/s), which is characterised by a delta-type estuary with a relatively large reclaimed alluvial plain. However, the majority of the other rivers have a canyon-type estuary. Rivers or their springs are used as the main freshwater sources for the entire coastal region (2).

Sea level rise in the past

At Rovinj, sea level is falling with respect to the land at a rate of -0.50 mm/y; at Bakar, a relative rise is occurring (+0.53 mm/y); at Split, relative sea level is dropping at -0.82 mm/y; and in the Dubrovnik area, relative sea level is rising by about +0.96 mm/y. … These differences are probably the result of differential local uplift and subsidence of the coast, in that the east Adriatic coast is a tectonically active region. Year-to-year sea-level fluctuations can be related to climate variability over Europe, whereas longer term changes can be related to differential local tectonic movement (2).

Sea level rise in the future

For Croatia, scenarios of sea-level rise for 2030, 2050, and 2100 have been reported of +18 ±12 cm, +38 ±14 cm, and +65 ±35 cm, respectively (2).

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 (8), 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 (9). 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 (10).

Vulnerabilities - Coastal flood risk

Since the Croatian Adriatic coast is mostly rocky and relatively steep, risk of sea level rise is not particularly high. Low-lying coastal areas covered with alluvial or flish deposits and sandy beaches can be endangered. The urban settlements along the west coast of Istria (towns of Rovinj and Pula), areas of Zadar, Split, Neretva River delta and Rijeka dubrovačka Bay, can be affected by sea flooding, and many economical and historical or cultural important buildings can be submerged or devastated (1).


The vulnerability of the Croatian coastal zone to flooding has been assessed for a sea level rise of 20 cm and 86 cm, respectively (4).

A sea level rise of 20 cm would have little effect on flood risk due to storms or river floods for the entire coastal area for two main reasons. The low-lying coast that might be exposed to stormy weather is protected by islands, with an exception of the western Istria coast. As a rule, related to the mainland coast areas the islands are laid in the direction of storms, and the island settlements are mostly located on the northeastern sides of the islands. The river mouths are also generally protected from storms, so the water stream levels will also not increase. The main socio-economic effect of the expected sea level increase, would be the direct consequence of flooding due to sea level rise rather than those caused by storms or river floods (4).

The potential effects of sea level rise include inundation, flooding, saltwater intrusion, and coastal erosion. For Croatia, a sea level rise of 20 cm would not have significant consequences on the coastal zone in terms of inundation and surge flooding. However, individual areas, such as the towns of Rovinj, Pula, and Split, currently suffer from surge flooding and would therefore continue to be at risk (2).

A sea level rise of 86 cm would have a major impact on coastal flood risk. Flooding of coastal areas caused by coastal storms would significantly affect the western Istrian coast and the low-lying coast in the northern and central Dalmatia. The sea level increase could significantly increase flood risk of the Mirna, Zrmanja, Cetina and Neretva rivers. The expected impact will not significantly affect the main business sectors in the coastal area(Republic of Croatia, Ministry of Environmental Protection and Physical Planning, 2001). The small inhabited island of Krapanj, however, would be almost totally inundated because its altitude is approximately 1 m above sea level. Also historical town centres, such as Split, Pula, Rovinj, and Trogir, would also be at risk from inundation and surge floods (2).

The coastal flooding, as a consequence of the sea level rise of 86 cm, will significantly impact a large part of the coast. The impact of the said consequences on the economic activities, such as agriculture and fishery, will be negligible. However, some impact will be suffered by the tourist industry and human settlement, and high negative impact on the coastal infrastructure (harbors, marinas and small marinas, outfalls). The greatest potential effect would be on sewerage systems of coastal settlements located in low-lying areas. Sea level rise would severely affect their functioning, and in many places, new sewage systems would be required (2).

In addition, agricultural activities could be threatened, notably in the estuary of the Neretva River, where a large part of the alluvial plain has been reclaimed via the construction of dikes, channels, and pumping stations. Increased sea level might endanger this infrastructure, resulting in frequent surge flooding and intrusion of saline water (2). At this sea level increase, the saline water ingress into the areas, referred to above, would be more pronounced, and the negative impacts would probably be suffered by agricultural and some other sectors (4).

Groundwater is not used as the main freshwater source for either water supply or agriculture. However, at some locations, projected sea level rise might affect the groundwater supply used locally for irrigation. In addition, the water supply function of the freshwater lake on Cres could be endangered by sea level rise, which would drastically affect the population of two islands (2).

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 (11). 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 protection of all the low-lying areas in Croatia from inundation is not feasible. However, programmes should be initiated to protect sites of great natural, socio-economic, and cultural importance (2).

It is likely that for the protection of some historical monuments, particularly those included in the UNESCO World Heritage list, international assistance would be required. This would include Diocletian’s Palace in Split and the historic core of the town of Trogir. Unfortunately, proactive measures for sea level rise are not being implemented so far (2).


It is widely agreed that there are three generic response strategies to sea level rise: retreat, accommodation, and protection. Because of the diverse characteristics of the Croatian coast, it would be necessary to implement all types of response strategies, depending on the site characteristics and its importance from various perspectives (2).

The retreat response strategy involves no effort to protect the land from the sea which, because of its characteristics, seems to be the most appropriate strategy for the major part of the Croatian coast. Accommodation and protection strategies would be best implemented in selected locations (2).

The accommodation strategy implies implementation of partial measures to mitigate negative sea-level rise effects (e.g., erecting emergency flood shelters, elevating buildings, modifying drainage systems, etc.). This should be implemented for the protection of endangered settlements and economic activities (particularly tourism, transport, and agriculture), as well as some ecosystems (estuaries and wetlands of the rivers Neretva, Krka, and Cetina) (2).

The protection strategy is an ‘‘aggressive’’ form of adaptation that includes building sea walls and dykes, as well as other physical structures, with the objective of maintaining existing land uses and assets and allowing no loss of land or assets. This strategy is appropriate in coastal areas with no alternative land for resettlement, or with assets of high value. In Croatia, there are only a few locations for which this strategy would be necessary, notably the historical town centres of Pula, Trogir, and Split, the island of Krapanj, and the estuary of the Neretva River (2).

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 Croatia.

  1. Republic of Croatia, Ministry of Environmental Protection, Physical Planning and Construction (2006)
  2. Baric et al. (2008)
  3. ANONYMOUS (2000), in: Baric et al. (2008)
  4. Republic of Croatia, Ministry of Environmental Protection and Physical Planning (2001)
  5. Bindoff et al. (2007), in: IPCC (2012)
  6. Church and White (2011), in: IPCC (2012)
  7. Velicogna (2009); Rignot et al. (2011); Sørensen et al. (2011), all in: IPCC (2012)
  8. Marcos et al. (2009); Haigh et al. (2010); Menendez and Woodworth (2010), all in: IPCC (2012)
  9. Lionello et al. (2008), in: IPCC (2012)
  10. IPCC (2012)
  11. Bosello et al. (2012)
  12. Cazenave et al. (2014)
  13. IPCC (2014)
  14. Watson et al. (2015)
  15. Yi et al. (2015)
  16. Church et al. (2013), in: Watson et al. (2015)
  17. Shepherd et al. (2012), in: Watson et al. (2015)
  18. Church et al. (2013), in: Watson et al. (2015)
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