Delft3D Sensitivity and Uncertainty Snalysis for Hurricane Simulations in the North Atlantic

We use model averaging techniques to estimate hurricane hazards and uncertainties of coastal surge and waves in the North Atlantic U.S. coast. First we determine the output uncertainty associated with the selection of appropriate model parameters by means of a thorough parameter sensitivity analysis of the Delft3D model using data from Hurricane Bob (1991) track. The sensitive model parameters (of eleven total considered) include wind drag, the depth-induced breaking (gamma_b), and the bottom roughness. Several parameters show no sensitivity (threshold depth, eddy viscosity, wave triad parameters and depth-induced breaking –alpha_b) and can therefore be excluded to reduce the computational overburden of probabilistic surge hazard estimates. The sensitive model parameters demonstrate a large amount of interactions between parameters and a non-linear model response. While model outputs showed sensitivity to several parameters, the ability of these parameters to act as tuning parameters for calibration is somewhat limited as proper model calibration is strongly reliant on accurate wind and pressure forcing data. We also present an analyis of the influence of three theoretical wind field parameterizations (NWS23, modified Rankine, and Holland) on the model performance and corresponding uncertainty. Finally, an overall estimate of the joint uncertainty related to the model parameters and the input wind fields is presented.