Secular trends in mean tidal range around the British Isles and along the adjacent European coastline

Abstract

S U M M A R Y Time series of annual Mean Tidal Range (MTR) have been assembled from 13 ports around the British Isles and secular trends in MTR computed at each site. Trends vary between -1.8 and 1.3 mm yr-' depending on location. At many sites the values are significantly non-zero implying different trends in Mean High Waters (MHWs) and Mean Low Waters (MLWs). Such tidal behaviour has also been observed previously at stations along the adjacent European coastline, but is not well understood. At several places, the trends are sufficiently large that they should be taken into account in investigations of impacts of sea level change and in extreme level engineering studies. They also suggest that, in general, time series of MWH should not be used as proxies for series of Mean Sea Level (MSL). For most of the British Isles data, MTR secular trend is larger (more positive) for larger trend in local MSL, or water depth. Lerwick and Newlyn hourly heights have been used to show that the observed MTR trends at most locations must be due primarly to changes in the dominant M2 tidal constituent. A comparison is given of the British Isles findings to those from neighbouring countries; British, Irish, French, Belgian and perhaps southern Dutch MTR trends are found to be considerably less than those reported from the northern Netherlands and the German Bight.

A survey of recent changes in the main components of the ocean tide

“…We present first the values of the four parameters obtained from the regression fits for the stations in each region, and then discuss the significance of the findings. Scotland and of the order of 1% or less elsewhere around the UK, consistent with previous research (Woodworth et al, 1991). Larger values can be seen in the eastern North Sea and smaller ones on the Atlantic coasts of Norway and Iberia.…”

“…As a check on the method, parameterizations were made to time series for stations reported by Woodworth et al (1991), , Ray (2006Ray ( , 2009 and Jay (2009) using the same spans of data employed by those authors. In each case, almost identical findings were obtained for trends in tidal constants and, in the case of Ray (2006), for the amplitude of nodal variations.…”

Analyzing Monthly Extreme Sea Levels with a Time-Dependent GEV Model

“…This variability is usually expressed in terms of regional climate indices such as the Southern Oscillation index (SOI), the Pacific decadal oscillation (PDO), or the North Atlantic Oscillation (NAO). Recently, Woodworth and Blackman (2004) analyzed a large number of tidal gauges and found a close relation between extreme sea levels and climate indices, supporting the existence of decadal variability in extreme sea levels. Moreover, there exists external forcing acting on the globe, due to the sun and the moon affecting sea level.…”

“…Concerning secular trends, mean sea level rise is one of the main contributions to extreme sea levels (e.g., Woodworth et al 1999;Flick et al 2003;Pugh 2004, chapter 7). This aspect is well known and has been widely studied by the scientific community because of the potential effects on coastal areas (Houghton et al 2001).…”

Secular changes in the solar semidiurnal tide of the western North Atlantic Ocean

“…Secular changes in tides are, in fact, not uncommonly detected when measurements over a long timespan are examined [Cartwright, 1972]. Flick et al [2003] recently compiled statistics for rates in mean tidal range for 90 tide gauges in the United States, as Woodworth et al [1991] had previously done for 13 British ports. More recently Jay [2009] analyzed tidal changes at 34 stations along the western coasts of North and South America and found secular trends in the M 2 and K 1 tides with surprisingly wide-scale coherence: all stations between Panama and Alaska showed increasing amplitudes, with an average increase of 2.2% per century.…”