Coastal flood risk Latvia
The Latvian coast
The total length of the Latvian coastal zone is 496.5 km. It mainly consists of sandy beaches and dunes. Gravel, pebble or boulder covered beaches are more rare and there are hardly any steep coasts. In the areas of sand accumulation beyond the beach, 1–4 m high predunes with typical vegetation have formed. Beyond these, there is typically a belt of grey dunes and forest-covered coastal dunes dominated by pine trees (1).
Sea level rise in Latvia in the past
Studies have identified that water level rise in the open Baltic Sea in the west of Kurzeme in the last year 100 years has not exceeded 10-15 cm. Faster level rise was observed in the southern part of Riga Bay between 1875 and 2000. Yet, this is mainly predetermined by local factors (sinking of the earth crust, pumping of ground waters and crowding of water mass under the impact of strong north-west winds) (2).
Global sea level rise
In their fourth assessment report the IPCC reported that there was high confidence that the rate of observed sea level rise increased from the 19th to the 20th century (3). They also reported that the global mean sea level rose at an average rate of 1.7 (1.2 to 2.2) mm yr-1 over the 20th century, 1.8 (1.3 to 2.3) mm yr-1 over 1961 to 2003, and at a rate of 3.1 (2.4 to 3.8) mm yr-1 over 1993 to 2003.
According to satellite altimetry-based data anthropogenic global warming has resulted in global mean sea-level rise of 3.3 ± 0.4 mm/year over the period 1994-2011 (9). According to a recent study, however, this previous estimate of global mean sea level rise is too high and global sea level rise over the period 1993 to mid-2014 has been between +2.6 ± 0.4 mm/year and +2.9 ± 0.4 mm/year (11). According to this same study sea-level rise is accelerating; this acceleration is in reasonable agreement with an accelerating contribution from the Greenland and West Antarctic ice sheets over this period (13,14), and the Intergovernmental Panel on Climate Change projections (13,15) of acceleration in sea-level rise during the early decades of the twenty-first century of about +0.07 mm/year. Sea-level rise varies from year to year, however, due to short-term natural climate variability (especially the effect of El Niño–Southern Oscillation) (9,12): the global mean sea level was reported to have dropped 5 mm due to the 2010/2011 La Niña and have recovered in 1 year (12).
Updated satellite data to 2010 show that satellite-measured sea levels continue to rise at a rate close to that of the upper range of the IPCC projections (4). Whether the faster rate of increase during the latter period reflects decadal variability or an increase in the longer-term trend is not clear. However, there is evidence that the contribution to sea level due to mass loss from Greenland and Antarctica is accelerating (5).
For 2081-2100 compared to 1986-2005, projected global mean sea level rises (metres) are in the range (10):
- 0.29-0.55 (for scenario RCP2.6)
- 0.36-0.63 (for scenario RCP4.5)
- 0.37-0.64 (for scenario RCP6.0) and
- 0.48-0.82 (for scenario RCP8.5)
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 (6), 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.
Vulnerabilities – Coastal flood risk
The main threats for the coastal area of Latvia are presented by the relatively frequent and severe southwest, west and north direction storms that make considerable drifts of the Baltic Sea water mass in the coastal zone with the relative sea level rises of 1,7 – 2 meter and higher. Due to that, the overflow of low coastal territories and wash-off of the coast, dunes, populated territories, buildings, roads and forest and agricultural areas occur (1).
More than one million inhabitants constituting a little less than half of the total population, live in a 5–10 km wide area along the coast of the Baltic Sea and the Gulf of Riga (1).
Due to relative sea level rise the groundwater level in the lowest coastal zone of Riga Bay could rise by approximately 50-70 cm. Risk of floods in the lower reaches of the big rivers (Lielupe, Daugava, Gauja) will become higher. Ground water elevation may cause serious problems to people living in lower settlements in the coastal zone where the height above the sea level is 0.7-2 m (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 (7). The results show:
- 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.
- 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.
- 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.
The “Law on Protected Belts” (1997) defines the principles for establishing a protected zone along the coast of the Baltic Sea and the Gulf of Riga – this belt is established to decrease the impact of pollution on the Baltic Sea, preserve forests for their protective function, avert the development of erosion process, protect the coastal landscape, ensure protection, preservation and sustainable long-term use of coastal nature resources and other important public territories, including those needed for leisure activities and tourism (1).
Aware of the vulnerability of Latvia to the expected climate change impacts in the Baltic Sea region (change of precipitation, temperature, river run-off and ice regime, vegetation period, increased frequency of severe storms and flooding, change of flora and fauna, etc.), a national adaptation programme will be elaborated (1).
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 (8). 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 (8).
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 (8).
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 (8).
The references below are cited in full in a separate map 'References'. Please click here if you are looking for the full references for Latvia.
- Ministry of the Environment of the Republic of Latvia (2006)
- Ministry of Environmental Protection and Regional Development of Latvia (2001)
- Bindoff et al. (2007), in: IPCC (2012)
- Church and White (2011), in: IPCC (2012)
- Velicogna (2009); Rignot et al. (2011); Sørensen et al. (2011), all in: IPCC (2012)
- Marcos et al. (2009); Haigh et al. (2010); Menendez and Woodworth (2010), all in: IPCC (2012)
- Bosello et al. (2012)
- Hinkel et al. (2010)
- Cazenave et al. (2014)
- IPCC (2014)
- Watson et al. (2015)
- Yi et al. (2015)
- Church et al. (2013), in: Watson et al. (2015)
- Shepherd et al. (2012), in: Watson et al. (2015)
- Church et al. (2013), in: Watson et al. (2015)