1. Storm surges: Phenomena, modelling and scenarios Hans von Storch Institute of Coastal Research Helmholtz-Zentrum Geesthacht Germany 19-24 August, 2012 Mini-symposium "Mechanics of natural disasters" at the 23rd International Congress of Theoretical and Applied Mechanics, Beijing

2. Who is this? Hans von Storch Director of Institute for Coastal Research, Helmholtz Zentrum Geesthacht (HZG), near Hamburg, Professor at the Meteorological Institute of Hamburg University Works also with social and cultural scientists.

3. Overview 1.Storm surges – global phenomenon, with regional manifestation. 2.Physics of storm surges: The kid in the bathtub 3.The case of the German Bight 4.Modelling storm surges 5.Examples for attribution of causes for changing storm surge risk

4. Overview 1.Storm surges – global phenomenon, with regional manifestation. 2.Physics of storm surges: The kid in the bathtub 3.The case of the German Bight 4.Modelling storm surges 5.Examples for attribution of causes for changing storm surge risk

6. Midlatitude storms The Netherlands and UK, 1953 German Bight and Hamburg 1962 Baltic Sea – Germany and Denmark, 1872

7. Storm Nargis, 2008 Bhola, 1970 Bangladesh cyclone, 1991 Katrina, 2005

8. Spatial distribution of storm surge risks according to Munich Re

10. Scientific Issues a)Physics of storm surges b)Prediction of storm surges c)Coastal defense – new options d)Disaster management – new options e)Changing risks – Climate change and other factors

11. Overview 1.Storm surges – global phenomenon, with regional manifestation. 2.Physics of storm surges: The kid in the bathtub 3.The case of the German Bight 4.Modelling storm surges 5.Examples for attribution of causes for changing storm surge risk

12. Meteorological component of anomalous sea level (Storm, waves, seiches) Regional sea level Ocean currents, filling of marginal seas (Baltic Sea), Regional affects of changing mass distributions Global sea level Volume of the ocean (thermal expansion, melting of ice sheets, glaciers etc.)

13. Graphics: Michael Schrenk

18. Coastal Defense: acceptable wave overtopping Niemeyer & Kaiser 2008, NLWKN presently accepted 3% of all waves – Lower Saxony (Germany) 2 l/(m∙s) – Schleswig-Holstein (Germany) 0,1-1,0 l/(m∙s) – The Netherlands

19. Niemeyer & Kaiser 2008, NLWKN Coastal Defense: acceptable wave overtopping Tests with elevated wave overtopping in Delfzijl (The Netherlands) No damages at the grass surface with overtopping of up zo 50 l/(m∙s) Functionality maintained even in case of pre-set surface damages up to 50 l(m∙s)

20. Cascading flood compartments Example Hamburg Erik Pasche, TU HH

21. Cascading flood compartments Example Hamburg Erik Pasche, TU HH

22. Cascading flood compartments Example Hamburg Erik Pasche, TU HH

23. Overview 1.Storm surges – global phenomenon, with regional manifestation. 2.Physics of storm surges: The kid in the bathtub 3.The case of the German Bight 4.Modelling storm surges 5.Examples for attribution of causes for changing storm surge risk

24. Albrecht et al., 2010 [m] Increase of sea level in the German Bight

25. Temporal development of intra- seasonal 99%ile of high tide levels AFTER subtraction of annual mean high tide and mean annual high tide in Cuxhaven (Germany) until 2005. Case of German Bight

26. Overview 1.Storm surges – global phenomenon, with regional manifestation. 2.Physics of storm surges: The kid in the bathtub 3.The case of the German Bight 4.Modelling storm surges 5.The case of Hamburg – assessment and options

27. Tidal modelling: hydraulic vs. numerical

28. 1 shallow water equation of vertically averaged movement

31. von Storch, H., 2001: Models. In: H. von Storch and G. Flöser (Eds): Models in Environmental Research. Springer Verlag, 17-33

32. Aspelien, T., 2006: The use of long-term observations in combination with modelling and their effect on the estimation of the North Sea storm surge climate. PhD thesis, Hamburg, 106pp Operational modelling by assimilation of „upstream“ data Trygve Aspelien, pers. comm

35. Inter-annual variability (1958-2001) Cuxhaven After nudging: Better reproduced inter-annual variability Linear long-term trends are closer to the observed trends Black curve: observed values Blue curve: Aberdeen nudged (ABE) Red curve: Control experiment (CTL) Improvement from CTL in the percentiles (1,5,10,90,95,99) of surge when Aberdeen is nudged (Brier skill score): Cuxhaven: 58-80% Borkum: 10-76% Trygve Aspelien, pers. comm

36. Overview 1.Storm surges – global phenomenon, with regional manifestation. 2.Physics of storm surges: The kid in the bathtub 3.The case of the German Bight 4.Modelling storm surges 5.Examples for attribution of causes for changing storm surge risk

37. http://www.loicz.org/imperia/md/content/loicz/stormsurges/15_syvitski.pdf

38. Hamburg – storm surges

39. Difference of water level maxima at the mouth of the estuary (Cuxhaven) and in Hamburg (St. Pauli)

40. Scenarios 2030, 2085 Only the effect of anthropogenic climate change (A2, B2) - No effect of water works.

41. Conclusions Storm surges are a serious issue Storm surges are an interesting issue. Storm surges is a global phenomenon but usually considered on a regional or even local scale. Issues relate to the phenomenon, prediction, risk management, disaster management and dealing with changing conditions The phenomenon allows for efficient description (risk statistics, forecast) by numerical modeling Risks are changing due to geophysical conditions (sea level, wind statistics), delta sinking (resource extraction) and water works (dredging shipping lanes, coastal protection) Storm surges is a societal issue, which needs transdis- ciplinary attention.

42. Hans von Storch hvonstorch@web.de