This study evaluates the performance of the SHYFEM (System of HydrodYnamic Finite Element Modules) ocean model in simulating storm surges within Donegal Bay (northwest Ireland) for climate projection applications. A high-resolution Basin Scale Model (BSM) configuration of SHYFEM, spanning the North Atlantic is employed in barotropic mode accounting exclusively for atmospheric forcing with no tidal contribution included. To evaluate its accuracy, the BSM is compared against a Limited Area Model (LAM) configuration of SHYFEM implemented at the same study site.
The LAM includes tidal constituents through the downscaling of sea surface height (SSH) from a calibrated deep-water ocean model provided by the Copernicus Marine Environment Monitoring Service (CMEMS). Comparison is performed to quantify the impact of non-linear tide-surge interaction on residual water levels computation.
On average the LAM achieves 3 cm greater accuracy than the BSM in reproducing the time series of residual water levels measured by four tide gauges within the bay. Nevertheless, although both models tend to underestimate the extreme values, the BSM better captures the climatological statistics of storm surge events, closely matching the observed return levels associated with 5, 10, 25, and 50 year return periods.
Further improvements in return level estimates and residual water level error metrics are obtained through iterative calibration of main model parameters, validating the BSM’s effectiveness in simulating storm surges despite the absence of tide-surge interaction.
A Chi-squared significance test applied to tide gauge observations confirms that tide-surge interaction is statistically non-significant within Donegal Bay for surge thresholds at the 99th, 99.95th, and 99.99th percentiles. These findings support the use of BSM, driven exclusively with atmospheric fields (without including tides), for reliable simulation of storm surges and their climatological statistics in this region.
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