Historical wave height trends in the South and East China Seas, 1911-2010

This study reconstructs 6 hourly significant wave heights (H-s) in the South and East China Seas for the period 1871-2010, using the Twentieth Century Reanalysis ensemble of mean sea level pressure (SLP) fields and a multivariate regression model to represent the H-s-SLP relationship in each study area. The regression model was calibrated and validated using the ERA-Interim reanalysis of H-s and SLP for the period 1981-2010. These reconstructions were found to reproduce reasonably well the seasonal mean and maximum H-s climates as represented by the ERA40 and ERA-Interim wave reanalyses. For each study area, an ensemble of 56 members of 6 hourly H-s was reconstructed for each grid point. The regional mean series of the ensemble mean of the reconstructed consecutive monthly mean H-s was tested for temporal homogeneity, which identified a few discontinuities in the pre-1946 period and led to the exclusion of the reconstructed H-s for 1871-1910 from trend analysis (due to data uncertainty and inhomogeneity). Each 6 hourly H-s time series for the period 1911-2010 was homogenized for the identified discontinuities, before being used to derive annual and seasonal mean and maximum H-s for trend analysis. The trend analysis results show that, in both study areas, the 1911-2010 wave height trends are dominantly negative, with the exception that the seasonal maximum significant wave heights seem to have increased in summer and spring in the central South China Sea and in summer in the East China Sea.