Uncertainties in extreme surge level estimates from observational records.
Ensemble simulations with a total length of 7540 years are generated with a climate model, and coupled to a simple surge model to transform the wind field over the North Sea to the skew surge level at Delfzijl, The Netherlands. The 65 constructed surge records, each with a record length of 116 years, are analysed with the generalized extreme value (GEV) and the generalized Pareto distribution (GPD) to study both the model and sample uncertainty in surge level estimates with a return period of 104 years, as derived from 116-year records. The optimal choice of the threshold, needed for an unbiased GPD estimate from peak over threshold (POT) values, cannot be determined objectively from a 100-year dataset. This fact, in combination with the sensitivity of the GPD estimate to the threshold, and its tendency towards too low estimates, leaves the application of the GEV distribution to storm-season maxima as the best approach. If the GPD analysis is applied, then the exceedance rate, lambda, chosen should not be larger than 4. The climate model hints at the existence of a second population of very intense storms. As the existence of such a second population can never be excluded from a 100-year record, the estimated 104-year wind-speed from such records has always to be interpreted as a lower limit.
van den Brink
H W
HW
Royal Netherlands Meteorological Institute, PO Box 201, 3730 AE De Bilt, The Netherlands.
Können
G P
GP
Opsteegh
J D
JD
D003198:Computer Simulation; D004189:Disaster Planning / Q000379:methods*; D004190:Disasters; D004784:Environmental Monitoring / Q000379:methods*; D015233:Models, Statistical; D009426:Netherlands; D009659:North Sea; D009791:Oceanography / Q000379:methods*; D015203:Reproducibility of Results; D012212:Rheology / Q000379:methods*; D018570:Risk Assessment / Q000379:methods*; D012307:Risk Factors; D012680:Sensitivity and Specificity