Trends of Southern african sea level: statistical analysis and interpretation

Abstract

Records of monthly mean sea level from tide-gauge sites along the coast of Namibia and South Africa are examined for evidence of long-term trends. Four records (Luideritz, Port Nolloth, Simonstown and Mossel Bay) approach 30 years in duration. An exploratory statistical analysis revealed the presence of high frequency fluctuations, a distinct seasonal signal and a slowly varying interannual structure. The serial correlation suggested the use of Box-Jenkins models to separate out the various contributions and enabled statistical estimates of underlying trends in sea level with realistic error estimates to be made. A linear trend at Port Nolloth was significantly different from zero, and its consistency with the trend from the two other West Coast sites led to the conclusion that, over the past 30 years, sea level has been rising on the west coast of Namibia and South Africa at a rate estimated at 0,12 ± 0,04 cm·year−1. By contrast there was no consistent upward trend at Mossel Bay on the South Coast. These...