Climate Variability of Coastal Flooding Risk in San Francisco Bay: the Wonderful Problem

Coastal flooding is the result of the non-linear interaction of multiple oceanographic, hydrological, geological and meteorological forcings (i.e., astronomical tide, monthly mean sea level, large-scale storm surge, wave set-up, wind set-up, fluvial discharges, precipitation, subsidence). Additionally, interannual variability and trends in storminess and sea level rise are climate drivers that must be considered. In many cases, some of the factors can be neglected, resulting in a relatively manageable problem from a hydrodynamic and statistical point of view. However, the contribution of each component of total water levels in San Franciso Bay (SFB) can significantly alter spatially varying flood hazards, resulting in an extraordinarily complex problem when it comes to determination of the extreme value distribution of flooding extents. The problem is even more difficult if we want to project coastal flooding risk for different climate change scenarios.

To address this ‘wonderful problem’, we propose a hybrid approach that combines: (a) hydrodynamic models (WWIII for waves, statistically or dynamically downscaled winds, Delft3D for high resolution tide-surge-wave modeling); (b) long-term data bases (observational and hindcast); and (c) non-linear data mining and statistical downscaling methods. At monthly scales, variability is driven by astronomic tides (perigean and nodal cycles) and the El Niño Southern Oscillation (ENSO). At a daily scale, sea level pressure fields are the predictors of wind, waves and surge levels. The statistical downscaling models are based on circulation patterns for multivariate variables (Espejo et al., 2014) and on extremes (Izaguirre et al, 2012), resulting in a time-dependent climate emulators which define the hydraulic boundary conditions for Delft3D.

References Espejo, A., Camus, P., Mendez, F.J., Losada, I.J. (2014) Spectral ocean wave climate variability based on circulation patterns, J. Phys. Oceanography, doi: 10.1175/JPO-D-13-0276.1 Izaguirre, C., Menéndez, M., Camus, P., Méndez, F.J., Mínguez, R., Losada, I.J. (2012) Exploring the interannual variability of extreme wave climate in the northeast atlantic ocean, Ocean Modelling, 59-60, 31-40.