Regional issues of changing storm surges and sea level - what is done at the Institute for Coastal HZG First CLISAP/KlimaCampus Workshop on Sea Level Variability and Change 27 May, 2013

Institute of Coastal HZG The Institute of Coastal Research deals with the issue of long-term change of the geophysical coastal environment, mainly in the North Sea and Baltic Sea. Long term = several decades, homogeneous quality into the past, mainly 1948 onwards as projections into the future: until 2100 Parameter: Sea level, storms, surges, waves, currents Researchers: Ralf Weisse, Frauke Albrecht, Iris Grabemann, Lidia Gaslikova, Hans von Storch, Katja Worth (North Sea) and Iris Grossmann (Elbe) Eduardo Zorita, Birgit Hünicke (Baltic Sea) In cooperation with BALTEX, TU Siegen, FSK Norderney, BAW, KLIFF, U Szczecin and others 2

North Sea 3 Usage of CoastDat data set, a downscaling effort, using a cascade of - NCEP/NCAR reanalysis (beginning in 1948), - CLM-atmospheric LAM (earlier REMO) forced with spectral nudging, - dynamical models of hydrodynamics and waves (with BAW) - empirical models for estimating local changes (Elbe) Analysis of homogenized sea level data (in cooperation with U Siegen) Discussion of significance of results of coastal defense planning with various stakeholders with responsibility for the North Sea coast; part of AKÜST-KLIFF assessment of different adaptation strategies to increasing extreme sea levels; operationalization in by Norddeutsches Klimabüro Usage of estimates for commercial applications, in particular planning for wind farming, shipping and other cases.

4 Temporal development of intra- seasonal 99%ile of high tide levels AFTER subtraction of annual mean high tide and mean annual high tide in Esbjerg (Denmark) and Den Helder (The Netherlands) until Sea level changes different at different locations, because of different drivers, and different dynamics. Mean and extreme sea level changes

Mean sea level changes in the German Bight Different methods yield comparable results after 1924 For this time interval there is little difference between VM and EOF approach correlation 0.996; trends1.64 mm/yr (VM) 1.74 mm/year (EOF) RMSL from different methods black – VM method (Wahl et al. 2011); green – EOF method (Albrecht et al. 2011)

Regionale Meeresspiegeltrends Beschleunigung des (globalen) Meeresspiegelanstiegs? Verschiedene Methoden führen zu ähnlichen Ergebnissen Gegenwärtige dekadische Trends sind relativ hoch Aber nicht ungewöhnlich im Vergleich zu früheren Perioden 37-jährige Trends des regionalen Meeresspiegels schwarz – VM Methode; grün – EOF Methode; rot – Cuxhaven (Albrecht et al. 2011)

7 Extreme sea level changes Extreme sea levels increased over the past years in the North Sea Primarily as a result from a rise in mean sea level Meteorologically induced components (waves, storm surges) show pronounced variation on time scales of years and decades but no substantial long-term trend Variations in storm surge and wave climate consistent with those in storm activity over the North Sea Annual mean high water and linear trend at Cuxhaven, Germany (bottom) and corresponding difference between annual 99-percentile and annual mean high water levels (top); In addition an 11-year running mean is shown in the upper panel.

8 The case of the Elbe and Hamburg

9 Difference of maximum heights in Hamburg and Cuxhaven Storm surges in Hamburg elevated because of modifying the river Elbe – both coastal defense and shipping channel deepening Storm surges in Hamburg in the past

Possible and plausible future changes in regional storm surge climate Changes in extreme storm surge levels / (Woth et al. 2006; Woth 2005) Here 99.5 percentile based on half hourly values; this compares to 99 percentiles derived from hourly values Contour lines show 99.5 percentile storm surge residuals from respective control runs

Future changes in regional storm surge climate A1B B2 1.Realisation 2.Realisation After Gaslikova et al. 2012

Projected changes in storm surges in the German Bight ScenarioWoth et al. (2006)Gaslikova et al. (2012)Weisse et al. (2012) A230 cm--- A1B-15 cm18 cm B220 cm-- B1-15 cm- Maximum changes along the German Bight coast at the end of the 21st century

13 Summary of knowledge about change of storm surge heights (per 2009) Significant drivers of changing storm surge heights Recent changes Possible changes until 2030 Possible changes until 2100 Global mean sea level riseca. 2 dmca. 1 – 2 dmca. 2 – 8 dm Meteororological short term effects (storms) noneca. 0 – 1 dmca. 1 – 3 dm Regional and local sea level change ca. 2 dmSo far unknown wavesnoneSo far unknown tidesRegionally very different So far unknown bathymetryRegionally very different So far unknown See: GKSS, 2009 : Nordseesturmfluten im Klimawandel.GKSS Wissenschaftler fassen aktuellen Forschungsstand zusammen.

Maps in the Internet highly misleading … Hünicke, 2012

Baltic Sea STOCKHOLM KRONSTADT SWINOUJSCIEKOLOBRZEG PSMSL*, TU Dresden (2005)PSMSL* (2005) Ekman (2003) Bogdanov et al. (2000) * Permanent Service for Mean Sea Level (Woodworth and Player, 2003) Zeitserien beinhalten Trend verursacht durch post- glaziale Landhebung und evtl eustatischen Meeresspiegeländerungen Winter (DJF) Anomalien Hünicke, 2012

Glacial isostatic vertical movement mm/year Rosentau et al., 2007 To get the relative sea level change, the crustal movement has to be subtracted. Tis movement is in the Baltic Sea region very strong as a response of the melting of the earlier ice sheets. Hünicke, 2012

Gauge series - detrended STOCKHOLM KRONSTADT SWINOUJSCIEKOLOBRZEG PSMSL*, TU Dresden (2005)PSMSL* (2005) Ekman (2003) Bogdanov et al. (2000) * Permanent Service for Mean Sea Level (Woodworth and Player, 2003) Winter (DJF) Anomalien Trend wird als linear angenommen und durch subtrahieren des linearen Langzeit-Trends von jeder Wasserstands-Zeitserie abgezogen 3. Datensätze Hünicke, 2012

Warnemünde Stockholm RE: 0.56 SLP + precipitation RE: 0.57 RE – relative error in validation period ( ) Variations of relative sea level in DJF Observations and estimates by regression Stockholm Warnemünde SLP+ precip+temp RE: 0.67 RE: 0.81 Hünicke, 2012

Summary for Baltic Sea The observational record discloses clear long-term variations, mostly uniform in the Baltic Sea Basin during the 20th century. The atmospheric circulation has a significant influence on the variations of sea level in the Baltic Sea. The NAO is an important contributor, but only part of the forcing. Additionally, precipitation and temperature variations relate to variations of regional sea level, in particular in summer. Determination of long-term trends beyond glacio-isostastic rebound is difficult to achieve, as the space-time pattern of the rebound is qualitatively similar to the expected climate change signal. Work done by Birgit Hünicke. Hünicke, 2012

Overall summary The Institute of Coastal Research is engaged in describing geophysical change of the environment in the North Sea and Baltic Sea regions. Efforts are underway to build homogeneous data sets (CoastDat) describing this past and current change, as well as possible and plausible changes in the future (next 100 years; climate) Efforts are underway to determine the most plausible mix of drivers behind tehse changes. The results are brought into the science-stakehodler interaction of HZG and CLiSAP. About 10 people involved in the ongoing work, which is associated both with CLiSAP as well as the HGF-programme PACES with AWI. 24