Annual and seasonal extreme sea levels in the Northwest Atlantic: Hindcasts over the last 40 years and projections for the next century

Over the next century, sea level rise and plausible climate change scenarios point to increased flooding risk for many low lying coastal regions. Unfortunately, many regions at risk have insufficient data for standard extremal analysis which requires long time series of annual maxima of hourly sea level observations. It is therefore difficult to evaluate the distribution of extremes under the current conditions and even more problematic to assess the effect of climate change on the return period of extremes. In this thesis, a dynamical surge model is used to reconstruct multidecadal sea level records and evaluate how climate change may modify flooding risk for coastal communities.; The approach is to perform a 40 year hindcast of storm surges in the Northwest Atlantic using a 2-D nonlinear barotropic ocean model forced by realistic 6 hourly winds and air pressures. Total sea levels are reconstructed by combining (i) the 40 year hindcast of storm surges, (ii) tidal predictions, and (iii) a statistical parameterization that represents baroclinic and seiche effects. An extremal analysis of the reconstructed total sea levels shows that the 40 year return levels are in good agreement (within 10 cm) with the levels calculated from multi-decadal sea level records. The approach therefore allows the calculation of flooding risk at locations for which there are few or even no data. The approach has also been tailored to focus on a season of interest such as the breeding season of an endangered bird species. The effects of sea level rise and changes in the frequency and intensity of atmospheric storms are also evaluated.; A Digital Elevation Model is used to downscale the results of the annual and seasonal extremal analyzes to the community/urban level. Spatial maps of the return period of extreme sea levels, under current conditions and following plausible climate change scenarios, are presented.; The observation records are also used to identify areas where tide-surge interaction contributes to sea level variability. Numerical simulations performed with a tidally forced storm surge model are used to identify the cause of tide-surge interaction. It is shown that bottom friction is a principal contributor.