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You are here : eLibrary : IAHR World Congress Proceedings : 32nd Congress - Venice (2007) : THEME D: Maritime and Coastal Research and Engineering : Estimation of trend breaks and their uncertainties in water level series for design purposes
Estimation of trend breaks and their uncertainties in water level series for design purposes
Author : Henk van den Boogaard, Herman Gerritsen
The present paper describes a technique for trend assessment in water level time series, which can detect and quantify significant changes in trend, such as due to accelerated sea level rise. Assuming that at some point, a trend break occurs in a particular measurement series, the technique provides joint estimates of the most likely point in time when the change occurred, the associated level and the linear trends before and after the trend break, including appropriate quantitative measures for the uncertainties in these estimates. In the actual determination of the uncertainties resampling techniques are used, which allow to fully determine the probability density distributions of the estimates avoiding assumptions on the uncertainty such as absence of skewness. The technique is illustrated on an application for Saint Petersburg, Russia. Long period historic water level series since 1703 show that the local flood level (+160 cm) has a return period 0.98 year, with the data until 1980 showing a largely linear trend. Based on only the data since 1980, however, this return period is twice as large. This suggests a substantial change in trend or trend break, possibly due to accelerated sea level rise. Application of the method and evaluation of the estimates of the break point and the associated two linear trends plus the 95% confidence intervals show that a trend break in 1969 gives the best joint estimates. The identified probability distributions reveal that skewness indeed plays a role. Moreover, a further analysis showed that the trend break is significant in statistical sense.
File Size : 1,204,038 bytes
File Type : Adobe Acrobat Document
Chapter : IAHR World Congress Proceedings
Category : 32nd Congress - Venice (2007)
Article : THEME D: Maritime and Coastal Research and Engineering
Date Published : 01/07/2007
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