Impact of a shift in mean on the sea level rise: Application to the tide gauges in the Southern Netherlands

The rates of sea level rise during 1940–2002 estimated in the Southern Netherlands at tide gauges of Vlissingen, IJmuiden, Maassluis and Hoek van Holland vary from 1.7 to 2.7 mm/yr despite a relatively small distance (<140km) between these stations. We have supposed that the observed inconsistency between the sea level trends could be due to an abrupt shift in the mean level of the tidal records provoked by some natural or anthropogenic processes. A shift detector based on the decomposition of the observations in empirical orthogonal functions and on the generalized likelihood ratio statistic has been constructed to evaluate the probability of the presence of a shift in the observed tidal records. A rapid change of mean of 25 mm at Hoek van Holland during the 1972–1973 period and of 17 mm at Vlissingen between 1973 and 1976 have been found to be statistically significant. The estimates of the sea level rise after correcting for shifts in the Vlissingen and Hoek van Holland tidal records are highly coherent and range between 1.9 and 2.1 mm/yr.