Sea Level Data
Definition
Sea level data are measurements of the height of the ocean relative to a reference such as mean sea level or a fixed vertical datum. They come from tide gauges, satellite altimetry, GNSS stations, and pressure sensors. Records include tides, storm surges, seasonal cycles, long term trends from warming and ice melt, and vertical land motion that shifts the local baseline. Accurate sea level data require careful calibration, datum definition, and long time series to separate natural variability from trend.
Application
Coastal engineers design seawalls and drainage with local sea level statistics. City planners map flood zones and update building codes. Navigation and port operations use real time levels for safe draft. Climate scientists combine global altimetry with regional land motion to understand where rise will accelerate and who will be most exposed.
FAQ
How do you separate long term sea level rise from tides and interannual oscillations?
Detrend and deseasonalize the series, fit harmonic tide models, and use multi year windows to estimate the residual trend. El Niño and other oscillations require long records to average out. Uncertainty bands should reflect autocorrelation and the length of the record.
Why is vertical land motion as important as ocean rise for local planning?
Subsidence from groundwater withdrawal or sediment compaction can exceed the global ocean trend, raising relative sea level locally. Conversely, uplift reduces apparent rise. Combining GNSS and InSAR with tide gauges gives a realistic picture of future nuisance flooding.
What datum choices matter when sharing sea level data among agencies?
Use consistent vertical datums and clearly document conversions between chart datums, local mean sea level, and global reference frames. Misaligned datums can misstate flood depth by tens of centimeters. Metadata should state epoch and transformation parameters.
How can flood mapping account for compound events with rain and storm surge together?
Hydrodynamic models couple river discharge and surge, include tides, and simulate drainage blockages. Scenario libraries capture joint probabilities so planners see the range of possible water levels rather than a single worst case.