Storm surges – the case of Hamburg, Germany Hans von Storch Institute for Coastal Research GKSS Research Center, Geesthacht Parallel 26: Global environmental change, natural disasters, and their implications for human security in coastal areas, 11. November 2006

Storm surges – the case of Hamburg, Germany Hans von Storch, Werner Krauss, Martin Döring and Iris Grossmann Along the coast of the North Sea, storm surges present the major geophysical risk. A long history of disaster has engraved the severity of this danger deeply into the cultural texture of the local population. While the situation has not much changed in rural regions, the situation has changed significantly in Hamburg, which is connected to the North Sea by the Elbe estuary. Here, the risk, and the vulnerability of the population has changed quite a bit. The geophysical risk has changed by more efficient coastal defence measures as well as a repeated deepening of the shipping channel. Climate change has played a very minor role so far, but may become more important after 2050, or so. The vulnerability of the population has increased as well. The effective coastal defence has created a perception of absolute security, even if scientists have demonstrated that a slight modification of past storms (in terms of path, and speed) could cause dangerously high storm surges. The vulnerability has also increased because of the influx of people not originating from the coastal zone, who simply are not aware of the severity of the risk. We discuss this multi-faceted situation as a case study, which features geophysical risks, globally and regionally induced changes related to globalisation, changing populations (urbanization) and alarmist claims on climate change. A brief comparison of the public perception of the Katrina disaster is included in the discussion.

Historically, the coast was a place of danger (and some opportunities) for humans. The first priority was to defend against storm surges. Life was adapted to this risk.

Nowadays, people consider themselves safe from the dangers of the sea, and are concerned about the health and the opportunities related to the coastal seas.

Hamburg – storm surges

In the early 90s, the specter of Global Warming entered the perception of people. Storm got worse Proxy for storm activity in the North Sea region (after Alexandersson, SMHI, 2003) Scientists related worsening of storm climate to GHG emissions (warmer world > more water vapor > more energy for storms > situation will continue to worsening). Insurance companies supported the claims. Media took up the message, which is consistent with cultural pre- conception of humans changing climate to become worse. Nowadays widely accepted among media and lay-people that storms are getting worse. However, the claim is false.

Proxy for storm activity in the North Sea region (after Alexandersson, SMHI, 2003) Bärring, 2005; blue - Lund; red – Stockholm

Where does the enhanced storm surge levels Hamburg come from? Sea level rise – a few centimeters Intensification of storm activity What else has happened in the coastal/estuarine environment?

The tidal change is due to coastal protection measures and modifications of the tributaries, and to the deepening of the shipping channel. These measure also had an effect on the heights of severe storm surges – estimates are 45 cm caused by measures of coastal defense and 15 cm by deepening the shipping channel (Haake, 2004: 27). Difference in storm surge heights – mouth of Elbe estuary and Hamburg,

Thus, so far, global warming had no discernible impact on the storm surge risk in Hamburg. Will it have an effect?

Katja Woth Global scenario Dynamical Downscaling Model of North Sea hydrodynamics Empirical “localization” Tide gauge St. Pauli Joint work with regional authorities. Regional and lcoal effect of expected anthropogenic climate change (A2 and B2)

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

Conclusions For storm surge risk in Hamburg, modifications of the estuary are presently more important than anthropogenic climate change; in the distant future they may be of comparable significance. Public perception is changing to: Storm surge risk is mostly related to GHG emissions. Thus storm surge risk can be controlled by regulating these emissions. Vulnerability enhanced by framing storm surge risk as GHG problem and not as natural hazard exaggerated by regional modifications. Sloppy talking about Global Warming has detrimental effect on better adaptation. The same true for Hurricane hazard?