Netherlands Stations Made RLR

The PSMSL generally recommends that only Revised Local Reference (RLR) data be used for analysis of long-term variations in sea level. However, there are a few records, most notably those from the Netherlands, that have been suitable for time series analysis. These records have not been classified as RLR in the past because they have been reported relative to a national levelling system (Normaal Amsterdamsch Peil or NAP), which is explained in greater detail in the RLR page. However, a recent re-levelling of NAP in 2005 introduced a small datum shift for the tide gauge time series. In order to maintain utility of these long records, we have reclassified most of the Netherlands records as RLR and introduced different RLR factors for the periods before and after 2005. While these records do not meet the strict definition of RLR and may still include prior re-levelling adjustments, we believe this represents the best path forward.