Evidence for Systematic Changes in Extreme High Waters since the Mid-1970s

Sea level data from a set of 141 tide gauges with a reasonable global distribution have been used to seek evidence for significant changes during recent decades in the occurrence of extreme high-water levels, and for systematic differences between changes in high waters and mean sea levels. The relationships between the occurrence of extreme high waters and of indices of regional climate have also been investigated. It is found that there is indeed evidence for a general worldwide increase in extreme high-water levels since 1975, and that the variations in extremes in this period are closely related to changes in regional climate. However, for most of the stations in the dataset used here, the secular changes and the interannual variability in extremes are similar to those in mean sea level. Consequently, changes in both sea level parameters are consistent with being produced by the same type of atmospheric and/or oceanic forcing.