Interim report on the validation of Harmonie

For the derivation of the Hydraulic Boundary Conditions, information of extreme winds over open-water areas is required. Because previous methodologies provided contradictory results, a new method is being developed that relies on the results of a high-resolution atmospheric model rather than on the spatial interpolation of sparse point measurements. The Harmonie model, which has a grid spacing of 2.5 km, has been selected to perform the simulations. To test the model, Groen and Caires (2011) composed a test set of 17 historical storms to be simulated with the model. In this report, model results for two of these storms are compared with observations.

The results of the high-resolution model are encouraging. For both simulated storms, the model is able to reproduce the large-scale structure of the wind fields both in space and time. The extreme wind velocities of the storm peaks are well represented, especially over open water areas. The benefit of the high-resolution model simulations is most obvious in areas with large roughness transitions like coastlines.

Drawing general conclusion based on only two cases is impossible. In order to give additional and more specific conclusions there is need to i) simulate the remaining storms of the test set composed by Groen and Caires (2011), ii) further test and (if desirable) modify the model set-up, iii) include more measurements in the evaluation, and iv) consider surface wind-stress in more detail.