Storm surges (CLIM 045) - Assessment published Nov 2012
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Climate change (Primary topic)
Typology: Descriptive indicator (Type A - What is happening to the environment and to humans?)
- CLIM 045
Key policy question: What is the trend in storm surges and extreme sea levels across European seas?
- Several large storm surge events have caused loss of life and damage to property in Europe during the past century. The most notable event occurred in 1953 when more than 2 000 people were killed, and there was massive damage to property around the coastline of the southern North Sea.
- There is strong evidence that extreme coastal water levels have increased at many locations around the European coastline. However, this appears to be predominantly due to increases in time mean local sea level at most locations rather than to changes in storm activity.
- Large natural variability in extreme coastal sea levels makes detecting long-term changes in trends difficult in the absence of good quality long observational records.
- Multi-decadal projections of changes in storms and storm surges for the European region currently have high uncertainty. The most recent studies indicate that increases in extreme coastal water levels will likely be dominated by increases in local relative mean sea level, with changes in the meteorologically-driven surge component being less important at most locations.
The most comprehensive global studies of trends in extreme coastal sea level and storm surges examined trends from hourly tide gauge records at least for the period since 1970, and for earlier periods of the 20th century for some locations [ii]. The results show that changes in extreme water levels tend to be dominated by the change in the time mean local sea level. In the north-west European region there is clear evidence of widespread increase in sea level extremes since 1970, but much less evidence of such a trend over the entire 20th century. When the contribution from time mean local sea level changes and variations in tide are removed from the recent trends, the remaining signals due to changes in storminess are much smaller or even no longer detectable.
Additional studies are available for some European coastal locations, but typically focus on more limited spatial scales. A study that examined the trend in water levels at 18 sites around the English Channel found that the rates of change in extreme water levels were similar to the rates observed for mean sea level change [iii]. However, the study also noted sizeable variations in storm surge heights, with the largest surge intensity occurring in the late 1950s. This large natural variability makes it difficult to detect changes in the rate of change in water level extremes. A similar conclusion, that the change in annual maximum sea levels are increasing at a rate not significantly different from the observed increase in mean sea level, was found in separate analyses for Newlyn in the UK for the period 1915–2005 [iv] and for 73 tide gauges along the Atlantic and Mediterranean coastlines in southern Europe [v]. In contrast, significant increases in storm surge height during the 20th century were found along the Estonian coast of the Baltic Sea [vi].
We conclude that whilst there have been detectable changes in extreme water levels around the European coastline, most of these are dominated by changes in time mean local sea level. The contribution from changes in storminess is currently small in most European locations and there is little evidence that any trends can be separated from long-period natural variability.
Future projections in storm surges can be made using either dynamic or statistical modelling of storm surge behaviour driven by the output of general circulation climate models [vii]. Several climate modelling studies have projected changes in storm surge height and frequency for the 21st century, mostly using the SRES A1B, A2 or B2 scenarios. The results critically depend on the simulated changes in mid-latitude storms; this topic remains a highly uncertain and rapidly evolving scientific field. The limited number of studies that separate out any long-term climate change signal from multi-decadal climate variability suggests that changes in atmospheric storminess are likely to be less important than increases in mean local sea level
Early studies on future changes in surge magnitude in the North Sea region all identified certain areas where increase in surge magnitude were projected, but they did not agree over its magnitude or even which regions will be affected [viii]. Furthermore, most of these studies have not adequately considered that changes in various indices of storminess over the European region exhibit decadal and multi-decadal oscillations [ix].
Two recent studies addressed some of the deficiencies in earlier studies by using ensemble simulations of climate models to drive a surge model of the North Sea for the period 1950–2100. One study found no significant change in the 1 in 10 000 year return values of storm surges along the Dutch coastline during the 21st century [x]. The other study projected small changes in storm surge heights for the 21st century around much of the UK coastline. Most of these changes were positive but they were typically much less than the expected increase in time mean local sea level over the same time period [xi]. However, larger increases in storm surge for this region during the 21st century cannot yet be ruled out.
A study on the Mediterranean region projected a reduction in both the number and frequency of storm surge events during the 21st century [xii]. A study on the Baltic Sea projected increases in extreme sea levels over the 21st century that were larger than the time mean local sea-level rise for some future scenarios simulated by some of the climate models used [xiii]. The largest changes in storm surge height were in the Gulf of Finland, Gulf of Riga and the north-eastern Bothnian Bay. A study on storm surges around the coast of Ireland projected an increase in surge events on the west and east coasts but not along the southern coast [xiv]. However, not all of the changes were found to have a high statistical significance.
At some locations, such as Hamburg, local changes in bathymetry caused by erosion, sedimentation and waterworks can have a much larger impact than climate change [xv]. Finally, recent work has shown that sea-level rise may also change extreme water levels by altering the tidal range [xvi].
[ii] Philip L. Woodworth and David L. Blackman, „Evidence for Systematic Changes in Extreme High Waters since the Mid-1970s“, Journal of Climate 17, Nr. 6 (März 2004): 1190–1197, doi:10.1175/1520-0442(2004)017<1190:EFSCIE>2.0.CO;2; Melisa Menéndez and Philip L. Woodworth, „Changes in extreme high water levels based on a quasi-global tide-gauge data set“, Journal of Geophysical Research 115, Nr. C10 (Oktober 8, 2010), doi:10.1029/2009JC005997.
[iii] Ivan Haigh, Robert Nicholls, and Neil Wells, „Assessing changes in extreme sea levels: Application to the English Channel, 1900–2006“, Continental Shelf Research 30, Nr. 9 (Mai 2010): 1042–1055, doi:10.1016/j.csr.2010.02.002.
[iv] Isabel B. Araújo and David T. Pugh, „Sea levels at Newlyn 1915–2005: Analysis of trends for future flooding risks“, Journal of Coastal Research 24 (Juli 2008): 203–212, doi:10.2112/06-0785.1.
[v] Marta Marcos et al., „Changes in storm surges in southern Europe from a regional model under climate change scenarios“, Global and Planetary Change 77, Nr. 3–4 (Juni 2011): 116–128, doi:10.1016/j.gloplacha.2011.04.002.
[vi] Ü. Suursaar, T. Kullas, and R. Szava-Kovats, „Wind and wave storms, storm surges and sea level rise along the Estonian coast of the Baltic Sea“, WIT Transactions on Ecology and Environment 127 (November 17, 2009): 149–160, doi:10.2495/RAV090131.
[vii] Jason A. Lowe et al., „Past and Future Changes in Extreme Sea Levels and Waves“, in Understanding Sea-Level Rise and Variability, ed. John A. Church et al.(Oxford, UK: Wiley-Blackwell, 2010), 326–375, http://doi.wiley.com/10.1002/9781444323276.ch11.
[viii] J. A. Lowe, J. M. Gregory, and R. A. Flather, „Changes in the occurrence of storm surges around the United Kingdom under a future climate scenario using a dynamic storm surge model driven by the Hadley Centre climate models“, Climate Dynamics 18, Nr. 3–4 (Dezember 1, 2001): 179–188, doi:10.1007/s003820100163; M. Hulme et al., Climate Change Scenarios for the United Kingdom: The UKCIP02 Scientific Report (Norwich, UK: Tyndall Centre for Climate Change Research, 2002), http://www.ukcip.org.uk/wordpress/wp-content/PDFs/UKCIP02_Tech_sections/UKCIP02_Chapter1-3.pdf; J.A. Lowe and J.M. Gregory, „The effects of climate change on storm surges around the United Kingdom“, Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 363, Nr. 1831 (Juni 15, 2005): 1313–1328, doi:10.1098/rsta.2005.1570; Katja Woth, Ralf Weisse, and Hans Storch, „Climate change and North Sea storm surge extremes: an ensemble study of storm surge extremes expected in a changed climate projected by four different regional climate models“, Ocean Dynamics 56, Nr. 1 (August 30, 2005): 3–15, doi:10.1007/s10236-005-0024-3; Martin Beniston, „Linking extreme climate events and economic impacts: Examples from the Swiss Alps“, Energy Policy 35, Nr. 11 (November 2007): 5384–5392, doi:doi.org/10.1016/j.enpol.2006.01.032; Jens Boldingh Debernard and Lars Petter Røed, „Future wind, wave and storm surge climate in the Northern Seas: a revisit“, Tellus A 60, Nr. 3 (Mai 2008): 427–438, doi:10.1111/j.1600-0870.2008.00312.x.
[ix] A. Sterl et al., „An ensemble study of extreme storm surge related water levels in the North Sea in a changing climate“, Ocean Science 5, Nr. 3 (September 18, 2009): 369–378, doi:10.5194/os-5-369-2009; G. J. Jenkins, M. C. Perry, and M. J. O. Prior, The climate of the United Kingdom and recent trends (Exeter, UK: Met Office Hadley Centre, 2007).
[x] Sterl et al., „An ensemble study of extreme storm surge related water levels in the North Sea in a changing climate“.
[xi] J. A. Lowe et al., UK Climate Projections science report: Marine and coastal projections (Exeter, UK: Met Office Hadley Centre, 2009), http://ukclimateprojections.defra.gov.uk/media.jsp?mediaid=87905&filetype=pdf.
[xii] Marcos et al., „Changes in storm surges in southern Europe from a regional model under climate change scenarios“.
[xiii] H. E. Markus Meier, „Baltic Sea climate in the late twenty-first century: a dynamical downscaling approach using two global models and two emission scenarios“, Climate Dynamics 27, Nr. 1 (April 11, 2006): 39–68, doi:10.1007/s00382-006-0124-x.
[xiv] Shiyu Wang et al., „The impact of climate change on storm surges over Irish waters“, Ocean Modelling 25, Nr. 1–2 (2008): 83–94, doi:10.1016/j.ocemod.2008.06.009.
[xv] Hans von Storch and Katja Woth, „Storm surges: perspectives and options“, Sustainability Science 3, Nr. 1 (2008): 33–43, doi:10.1007/s11625-008-0044-2.
[xvi] M.D. Pickering et al., „The impact of future sea-level rise on the European Shelf tides“, Continental Shelf Research 35 (März 2012): 1–15, doi:10.1016/j.csr.2011.11.011.
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