Extreme wind statistics for the Dutch primary water defenses
<p>For the determination of the Hydraulic Boundary Conditions (HBC) wind direction-dependent extreme wind speeds over open water are required, as they serve as input for surge- and wave-models. The required wind direction-dependent estimates of the wind speeds with return periods of up to 100,000-yr are based on analyses for the period 1979-2013 of the high-resolution meteorological model HARMONIE. For the area where HARMONIE is not available or appeared to be unreliable, the ERA-Interim data for the same period are used. For the grid points over sea of HARMONIE and ERA-Interim, the pseudo-wind is used, which is a measure of the surface wind stress. For grid points above inland waters, grid points that represent (a fraction of) land, a transformation to potential wind speed over open water is made, using a roughness that corresponds to a roughness that follows from a Charnock relation with a Charnock parameter of 0.0185. The analysis per grid point of the most extreme omni-directional wind speeds in 35 year indicate that, in the used HARMONIE domain, wind speeds are expectable with return periods up to approximately 10,000 years. Up to these return periods, the Gumbel distribution is the optimal distribution for extrapolation purposes. For a depression which has its centre outside the HARMONIE domain, the extreme winds are underestimated. For this reason, the HARMONIE data are only used south of 57°N.</p>