Reinhard E. Flick

Multi-model projections of twenty-first century North Pacific winter wave climate under the IPCC A2 scenario

A dynamical wave model implemented over the North Pacific Ocean was forced with winds from three coupled global climate models (CGCMs) run under a medium-to-high scenario for greenhouse gas emissions through the twenty-first century. The results are analyzed with respect to changes in upper quantiles of significant wave height (90th and 99th percentile HS) during boreal winter. The three CGCMs produce surprisingly similar patterns of change in winter wave climate during the century, with waves becoming 10–15xa0% smaller over the lower mid-latitudes of the North Pacific, particularly in the central and western ocean. These decreases are closely associated with decreasing windspeeds along the southern flank of the main core of the westerlies. At higher latitudes, 99th percentile wave heights generally increase, though the patterns of change are less uniform than at lower latitudes. The increased wave heights at high latitudes appear to be due a variety of wind-related factors including both increased windspeeds and changes in the structure of the wind field, these varying from model to model. For one of the CGCMs, a commonly used statistical approach for estimating seasonal quantiles of HS on the basis of seasonal mean sea level pressure (SLP) is used to develop a regression model from 60xa0years of twentieth century data as a training set, and then applied using twenty-first century SLP data. The statistical model reproduces the general pattern of decreasing twenty-first century wave heights south of ~40xa0N, but underestimates the magnitude of the changes by ~50–70xa0%, reflecting relatively weak coupling between sea level pressure and wave heights in the CGCM data and loss of variability in the statistically projected wave heights.

Predicted Extreme High Tides for Mixed-Tide Regimes

Abstract There are a number of published studies of the astronomical conditions prevailing when extreme high tides are predicted, but usually these are directed toward tidal regimes that are dominantly semidiurnal. The published criteria are found to be inadequate for mixed regimes (diurnal tides roughly the same order of magnitude as the semidiurnal tides in the area). For the mixed tides on the California coast, added consideration must be given to tropic tides (diurnal tides larger than average when the moon is near maximum declination) and to the 18.61-year period of the lunar-node cycle. Furthermore, extreme high diurnal tides tend to occur when the sun is near maximum declination (summer and winter) whereas comparable semidiurnal tides ordinarily occur near the equinoxes (spring and fall). Because of these added complications, harmonic tide predictions were prepared for four California ports up to the year 2000 so that information on extreme high tides could be tabulated. These data help to alleviat...

Ground motions on rocky, cliffed, and sandy shorelines generated by ocean waves

[1]xa0We compare ground motions observed within about 100 m of the waterline on eight sites located on shorelines with different morphologies (rock slope, cliff, and sand beaches). At all sites, local ocean waves generated ground motions in the frequency band 0.01–40 Hz. Between about 0.01 and 0.1 Hz, foreshore loading and gravitational attraction from ocean swell and infragravity waves drive coherent, in-phase ground flexing motions mostly oriented cross-shore that decay inland. At higher frequencies between 0.5 and 40 Hz, breaking ocean waves and wave-rock impacts cause ground shaking. Overall, seismic spectral shapes were generally consistent across shoreline sites and usually within a few orders of magnitude despite the diverse range of settings. However, specific site response varied and was influenced by a combination of tide level, incident wave energy, site morphology, ground composition, and signal decay. Flexing and shaking increased with incident wave energy and was often tidally modulated, consistent with a local generation source. Flexing magnitudes were usually larger than shaking, and flexing displacements of several mm were observed during relatively large incident wave conditions (Hs 4–5 m). Comparison with traffic noise and earthquakes illustrate the relative significance of local ocean-generated signals in coastal seismic data. Seismic observations are not a simple proxy for wave-cliff interaction.

Matching Mean Sea Level Rise Projections to Local Elevation Datums

A method is presented to consistently tie future mean sea level rise (MSLR) scenario projections to local geodetic and tidal datums. This extends the U.S. Army Corps of Engineer (USACE) guidance for incorporating the effects of future MSLR into coastal projects. While USACE relies on the National Oceanic and Atmospheric Administration (NOAA) 19-year National Tidal Datum Epoch (NTDE) for its datum relationships,theapproachproposedhereingeneralizesthisguidancebychoosingtheappropriate19-yearepochcenteredonthestartyearofthe MSLR scenario under consideration. The procedure takes into account the local annual sea level variability, which confounds the matching to any given single year while generalizing and preserving the 19-year averaging long used by NOAA to calculate the NTDE. Examples of the MSLR scenario matching procedure are given using actual data and projections for La Jolla, California, and Sewells Point (Hampton Roads), Virginia. DOI: 10.1061/(ASCE)WW.1943-5460.0000145.

Storm surge along the Pacific coast of North America

Storm surge is an important factor that contributes to coastal flooding and erosion. Storm surge magnitude along eastern North Pacific coasts results primarily from low sea level pressure (SLP). Thus, coastal regions where high surge occurs identify the dominant locations where intense storms make landfall, controlled by storm track across the North Pacific. Here storm surge variability along the Pacific coast of North America is characterized by positive nontide residuals at a network of tide gauge stations from southern California to Alaska. The magnitudes of mean and extreme storm surge generally increase from south to north, with typically high amplitude surge north of Cape Mendocino and lower surge to the south. Correlation of mode 1 nontide principal component (PC1) during winter months (December–February) with anomalous SLP over the northeast Pacific indicates that the dominant storm landfall region is along the Cascadia/British Columbia coast. Although empirical orthogonal function spatial patterns show substantial interannual variability, similar correlation patterns of nontide PC1 over the 1948–1975 and 1983–2014 epochs with anomalous SLP suggest that, when considering decadal-scale time periods, storm surge and associated tracks have generally not changed appreciably since 1948. Nontide PC1 is well correlated with PC1 of both anomalous SLP and modeled wave height near the tide gauge stations, reflecting the interrelationship between storms, surge, and waves. Weaker surge south of Cape Mendocino during the 2015–2016 El Nino compared with 1982–1983 may result from changes in Hadley circulation. Importantly from a coastal impacts perspective, extreme storm surge events are often accompanied by high waves.

Source location impact on relative tsunami strength along the U.S. West Coast

Tsunami propagation simulations are used to identify which tsunami source locations would produce the highest amplitude waves on approach to key population centers along the U.S. West Coast. The reasons for preferential influence of certain remote excitation sites are explored by examining model time sequences of tsunami wave patterns emanating from the source. Distant bathymetric features in the West and Central Pacific can redirect tsunami energy into narrow paths with anomalously large wave height that have disproportionate impact on small areas of coastline. The source region generating the waves can be as little as 100 km along a subduction zone, resulting in distinct source-target pairs with sharply amplified wave energy at the target. Tsunami spectral ratios examined for transects near the source, after crossing the West Pacific, and on approach to the coast illustrate how prominent bathymetric features alter wave spectral distributions, and relate to both the timing and magnitude of waves approaching shore. To contextualize the potential impact of tsunamis from high-amplitude source-target pairs, the source characteristics of major historical earthquakes and tsunamis in 1960, 1964, and 2011 are used to generate comparable events originating at the highest-amplitude source locations for each coastal target. This creates a type of “worst-case scenario,” a replicate of each regions historically largest earthquake positioned at the fault segment that would produce the most incoming tsunami energy at each target port. An amplification factor provides a measure of how the incoming wave height from the worst-case source compares to the historical event.