A surge refers to the change of sea level in coastal waters caused by winds and air pressures acting on the sea surface. A storm surge event or a storm tide event is an occasion with particularly high surges (Pugh and Woodworth 2014).
For the German North Sea and Baltic Sea coasts the standard DIN 4049 defines a storm surge as an event in which regionally defined thresholds are exceeded. These thresholds are defined such that an event with given severity can be expected on average once for a given period (e.g. the once in a 20 year event). For their forecasts, the German Federal Maritime and Hydrographic Agency (BSH) uses uniform exceedance thresholds for the North- and the Baltic Sea.
At the German North Sea coast, in Emden, Bremen and Hamburg, three levels of storm surge severity are distinguished:
1. Storm surge: 1.5 to 2.5 m above mean high water (MHW)
2. severe storm surge: 2.5 to 3.5 m above MHW
3. Very severe storm surge: more than 3.5 m above MHW
For the German Baltic Sea coast four levels are used:
1. Storm surge: 1.00 to 1.25 m above mean water level (MW)
2. medium storm surge: 1.25 to 1.50 m above MW
3. severe storm surge: 1.50 to 2.00 m above MW
4. very severe storm surge: more than 2.00 m above MW
Pugh, D. and Woodworth, P. 2014: Sea-Level Science. Cambridge Univ. Press
BSH Storm surges