Estimating Vertical Land Motion from Long-Term Tide Gauge Records.

Abstract

This report documents a methodology that can be used to estimate the vertical land motion (VLM) at NOAA tide stations by performing an oceanographic analysis of the long-term data sets. In the near future, VLM measurements will be the primary adjustment needed to locally calibrate scenario projections of global sea level rise such as those being generated by the National Climatic Assessment (NCA) for the US Global Climate Research Program (USGCRP).

The methodology presented here involves the decomposition of the observed relative mean sea level data and their computed trends. It is recognized that the long-term sea level time series observed at tide stations contains a component due to oceanography and a component due to VLM. The oceanographic signal is not completely described by a simple global sea level trend estimate.

The purpose of the methodology is to provide a more accurate estimation of local VLM at tide stations with 30-60 years of data rather than just simply subtracting the estimated global sea level trend of 1.7mm/yr from the observed relative mean sea level trend. Relative sea level trends calculated from shorter data periods are more likely to be affected by anomalously high or low oceanographic levels at the beginning or end of their series. By removing the regional oceanographic variability as calculated based on longer-period stations, both more accurate and more precise estimates of land motion are possible at shorter-period stations.