Statistical analysis of extreme waves from satellite altimetry from 2002 to 2020

Statistical analysis of extreme wave heights over the globe requires long and sufficiently resolved time series of data that have so far only been available in model reanalyses. In recent years, time series of altimetry observations that allow us to perform this study have become available.

 

Global maps of extreme significant wave heights were produced over 2002-2020 using a level-4 gridded CMEMS product merging CMEMS significant wave height along-track measurements from 7 altimetric satellites. ERA5 reanalysis data, developed by the ECMWF and available from 1950 onwards, were used as a means of comparison.

 

The extreme significant wave heights were first analyzed using quantiles such as the 95th percentiles. A second approach based on the Peak-Over-Threshold and the Generalized Pareto Distribution allowed us to estimate 100-year significant wave heights. Global maps obtained on CMEMS altimetric were eventually compared with maps obtained on ERA5 reanalysis.

 

Extreme wave heights estimated with both approaches show a spatial structure similar to the maxima in the climatological mean but with greater magnitude. Largest trends are exhibited in the Southern Ocean, where the wave heights tend to increase significantly in all results, while the North Atlantic and North Pacific exhibit more complex patterns of trends.