J.J. Beersma : "Extreme hydro-meteorological events and their probabilities"

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23 Apr 2007 13:30
Unit: Wageningen University
Location: Aula, building 362, Gen. Foulkesweg 1, Wageningen
Organisation: Wageningen University
Promotor: prof.dr. B. Holtslag (Meteorology and Air Quality)
Co Promotor: T.A. Buishand (KNMI, De Bilt)

 Extreme hydro-meteorological events usually have a large impact on our society. For safety standards regarding life and property and for design purposes of large structures extreme events with return periods between 100 and 10,000 years are often required. Due to the lack of long observational records such extremes are usually estimated by extrapolating a probability distribution that is fitted to the observations. The results obtained with statistical extrapolation methods, however, strongly depend on the assumed probability distribution. Time series resampling, which is used in this thesis, is an attractive alternative since it does not need assumptions about the underlying distributions of the data. In addition, time series resampling offers the opportunity to simulate different meteorological variables for different locations simultaneously, while the correlations between the variables and the spatial correlations are automatically preserved. Further, resampling makes it possible to simulate much longer time series than the standard historical records. Such very long time series usually contain several unprecedented extreme events which are very welcome in a frequency analysis of the extremes because they reduce the statistical uncertainty of the result. With specific hydrological applications in mind such very long resampled time series are used, in this thesis, to determine the size and exceedance probabilities of extremely wet periods in the Rhine basin (that may result in river flooding) and of extreme droughts in the Netherlands (leading to economic losses in agriculture and shipping). Resampling techniques are further used to determine the statistical uncertainty.
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