A grey model with periodic term for sea-level analysis and its application to the Guangxi coast

A grey model with periodic term for sea-level analysis is presented.The present model keeps some advanloges of the GM (1,1)model,which well reflects the trend of sea-level changes and gives out the change rate as well as the acceleration of sea level conveniently.In addition,the present model can reproduce the periodic phenomena of sea level,hence,it overcomes the shortcatnings of the GM(1,1) model that is unsuitable for forecasting monthly mean.level with apparent periodicity,and its prediction accuracy is improved.The present model is used to analyse Guangxi coast.level,the rasults show that the rise rates of relative,level at 13eihei,Weizhou and Bailongwei are 1.67,2.51 and 0.89 mm/a respectively,the relative sea level at Shitoubu has a falling trend with a rate of 0.5-1.0 mm/a,the rise rate of eustatic sea level along the Guangxi coast is 2.0 mm/a.In comparison with the model with a linear trend term plus a periodic term,the simulation accuracies of both models are about the same.