Select a start year and end year from the date slider below to see a graph of annual Mean Sea Level (MSL) and it's associated annual rate of change. If a end year in the future is selected, i.e. beyond which there is available observed data, then the linear (black line) and polynomial (purple line) trendlines will show an estimate of MSL from the year which the observed data ends up to the year selected by the user.
The mean annual rate of Relative Sea Level (RSL) change for Dunedin between and is approximately mm per year with a Standard Error of +/- mm per year.
Corrected for subsidence and Vertical Land Movement (VLM) of +/- mm per year (GPS Solution: JPL14), the mean annual rate of Absolute Sea Level (ASL) change for Dunedin between and is approximately mm per year () with a Standard Error of +/- mm per year.
The mean Relative Sea Level acceleration for Dunedin between and is approximately mm/year2.
Data represented by the blue line in the above graph is the mean observed annual Relative Sea Level for the selected period. This is given as a height above the zero of the tide gauge. The black line is the linear trendline for the selected period and indicates the overall direction of the data. It's gradient is the average annual rate of MSL change and is shown in the legend at the top right hand corner of the graph in the form of the straight line equation 'y = mx + c'. The purple line is the corresponding quadratic or second degree polynomial trendline.
Hover over the blue line to see individual annual MSL values in the tooltip with values corresponding to +/- one standard deviation given alongside in brackets. Hover over the legend at the top of the graph to see each trendline's equation and it's corresponding coefficient of determination R2 value in the tooltip.
Please note that Mean Sea Level predicted from the facility to project the above trendlines into the future are estimates only.
I've created an R Shiny app which fits various degree (1-4) polynomials to the above data and also produces p-Values, R-Squared, F-Statistic and t-statistic error parameters which you can find here.
Data for 1899-2013 comes from the work of Paul H. Denys, R. John Beavan, John Hannah, Chris F. Pearson, Neville Palmer, Mike Denham, Sigrun Hreinsdottir and retrieved January 2020 from URL https://doi.org/10.1029/2019JB018055 "Sea Level Rise in New Zealand: The Effect of Vertical Land Motion on Century-Long Tide Gauge Records in a Tectonically Active Region".
Data for 2014-2019 kindly provided by Port Otago Ltd and processed by Sea Level NZ using the University of Hawaii Sea Level Center SLP64 software. The SLP64 software uses a 119-point convolution filter (Bloomfield, 1976) centered on noon applied to the hourly data with respective periods of the 95, 50, and 5% amplitude points at 124.0, 60.2, and 40.2 hours to obtain daily MSL values. A simple average of all daily values is calculated if 7 or fewer days are missing to give monthly values and a simple average of monthly values is calculated to give annual values.