To predict future coastal hazards, it is important to quantify any links between climate drivers and spatial patterns of coastal change. However, most studies of future coastal vulnerability do not account for the dynamic components of coastal water levels during storms, notably wave-driven processes, storm surges and seasonal water level anomalies, although these components can add metres to water levels during extreme events. Here we synthesize multi-decadal, co-located data assimilated between 1979 and 2012 that describe wave climate, local water levels and coastal change for 48 beaches throughout the Pacific Ocean basin. We find that observed coastal erosion across the Pacific varies most closely with El Niño/Southern Oscillation, with a smaller influence from the Southern Annular Mode and the Pacific North American pattern. In the northern and southern Pacific Ocean, regional wave and water level anomalies are significantly correlated to a suite of climate indices, particularly during boreal winter; conditions in the northeast Pacific Ocean are often opposite to those in the western and southern Pacific. We conclude that, if projections for an increasing frequency of extreme El Niño and La Niña events over the twenty-first century are confirmed, then populated regions on opposite sides of the Pacific Ocean basin could be alternately exposed to extreme coastal erosion and flooding, independent of sea-level rise

[1] We compare predictions of a coupled, wave-averaged, cross-shore wavescurrents-bathymetric evolution model to observations of onshore and offshore nearshore sandbar migration. The observations span a 10-and 44-day period with onshore/ offshore bar migration at Duck, North Carolina, and at Hasaki, Kashima Coast, Japan, respectively, a 3.5-month period of onshore bar migration at Duck, and a 22-day period of offshore bar migration at Egmond, Netherlands. With best fit parameter values the modeled temporal evolution of the cross-shore bed profiles agrees well with the observations. Model skill, defined as 1 minus the ratio of prediction to no-change error variances, ranges from 0.50 at Egmond to 0.88 for the prolonged onshore bar migration at Duck. Localized (in time and space) reductions in model skill coincide with alongshore variations in the observed morphology. Consistent with earlier observations, simulated offshore bar migration takes place during storms when large waves break on the bar and is due to the feedback between waves, undertow, suspended sediment transport, and the sandbar. Simulated onshore bar migration is predicted for energetic, weakly to nonbreaking conditions and is due to the feedback between near-bed wave skewness, bedload transport, and the sandbar, with negligible to small effects of bound infragravity waves and near-bed streaming. Under small waves and conditions, when breaking and nonbreaking conditions alternate with the tide, the sandbar is predicted to remain stationary. The intersite differences in the optimum parameter values are, at least partly, induced by insensitivity to parameter variations, parameter interdependence, and errors in the offshore wave forcing.

[1] Long-term (>years) bathymetric data sets collected in six multiple near-shore sandbar systems were analyzed with complex empirical orthogonal function analysis to quantify intersite differences and similarities in cyclic offshore progressive bar behavior. The observations came from a 37-year annually sampled data set of four regions along the Dutch coast (spanning 70 km of coastline), an 18-year fortnightly to monthly sampled data set at Duck, North Carolina (alongshore extent $1 km), and a 7-year daily sampled data set of a single cross-shore profile at the Hasaki coast of Japan. The first complex mode, typically representing 50-70% of the total depth variance, described the long-term offshore progressive behavior and allowed for an objective separation of the barred part of the profile from the shoreward-and seaward-located nonbarred parts by considering a threshold bar amplitude below which the spatial results from the first mode were not considered reliable. The sandbars at the six examined sites share common lengths and nondimensional amplitude characteristics, which can be described by a negatively skewed Gaussian function. The absolute amplitude dimensions and the cycle return intervals differ, however, considerably between the sites. The key geometric parameters that steer this intersite variation are the time-averaged mean depths at the shoreward and seaward side of the bar zone (d shore and d sea , respectively) as well as their difference d bz . The degree to which intersite differences in d shore , d sea , and d bz are related linearly to intersite differences in bulk statistics of external forcings (wave, tide, sediment, and bed profile characteristics) is inconclusive.

[1] The medium-term movement of a longshore bar and the associated cross-shore sediment transport were investigated using beach profile data obtained nearly daily for 8 years from the seaward foot of a dune to a water depth of about 5 m at Hazaki Oceanographical Research Station (HORS). Bar crests were found to move seaward repeatedly with a period of a year. The duration time of the seaward bar migration is shorter than those on the other coasts in the United States, the Netherlands, and New Zealand. Although bars migrated in one direction, seaward, the cross-shore sediment transport rate associated with the bar migrations fluctuated seaward and shoreward. Seaward sediment transport occurred on and around bar crests, whereas shoreward sediment transport occurred in trough regions. The cross-shore sediment transport was active when the offshore wave energy was large, from winter to spring and in autumn. However, the direction of the sediment transport in a region where bars were most developed was different during the two periods; it was seaward from winter to spring and shoreward in autumn. A numerical model for beach profile change confirmed that the development and decay of a bar was caused by the spatial and temporal variations of the cross-shore sediment transport rate.INDEX TERMS: 1824 Hydrology: Geomorphology (1625); 3020 Marine Geology and Geophysics: Littoral processes; 4546 Oceanography: Physical: Nearshore processes; 4558 Oceanography: Physical: Sediment transport; KEYWORDS: longshore bar, beach profile response, cross-shore sediment transport, empirical orthogonal eigenfunction analysis, numerical model, morphodynamics Citation: Kuriyama, Y., Medium-term bar behavior and associated sediment transport at Hasaki, Japan,

The influence of vegetation on aeolian sediment transport rate in the region from a backshore to a foredune was investigated at the Hasaki Coast in Japan, where an onshore wind was predominant and the creeping beach grasses Carex kobomugi and Calystegia soldanella were major species. The comparison of cross‐shore distributions of the cross‐shore component of aeolian sand transport rate with and without vegetation, which were estimated on the basis of the beach profile changes and a mass conservation equation, showed that the creeping grasses influenced the aeolian sand transport rate. The landward aeolian sand transport rate rapidly decreased landward from the seaward limit of vegetation when the grasses grew. The aeolian sand transport rate reduced by 95% with a vegetation cover of 28%. On the other hand, when the grasses were absent, the landward aeolian sand transport rate did not decrease near the seaward vegetation limit, but near the foot of the foredune.

[1] Field observations were conducted on a natural, open ocean beach system in Japan to investigate characteristics of wind-blown sand transport under various weather conditions including a storm event. Data sets over periods of several hours included blown sand impact counts, three-dimensional wind conditions, hourly precipitation, and moisture content of the sediment surface. The intermittent blown sand impact data shifted by 1 s ahead of the wind velocity correlated with the wind velocity during a no-rainfall period (for an assumed dry surface) and in the longshore wind direction (for sufficiently long fetch length). The 5-min mean wind velocity/impact counts relationship was well constrained by both second-and third-order polynomial fitting of velocity under similar weather conditions. During a no-rainfall period and in the longshore wind direction, the relationship between the wind velocity and sand flux estimated from the counts coincides with existing studies in wind tunnel experiments. The sand flux, however, decreased by 1 order of magnitude because of a change in the wind direction from longshore to cross-shore and then by more than 1 order of magnitude because of an increase in the moisture content. Threshold wind velocity calculated using the time fraction equivalence method with the impact counts and the horizontal wind velocity in 5-min sampling periods was approximately equal to the value predicted using Bagnold's equation during the no-rainfall period and increased significantly during the rainfall phase. The sand flux sensor has several limitations for complex conditions in the field; however, it provides a number of characteristics of sand transport under various meteorological conditions.

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[1] The interannual shoreline variation during a 22-year period from 1987 to 2008 at the Hasaki coast located in eastern Japan was found to be induced by the fluctuation of the deep water wave energy flux using an empirical shoreline prediction model. The correlation coefficients between the deep water wave energy flux and climate indices showed that the wave energy flux has a positive correlation with the Arctic Oscillation (AO) index during the period from January to April, and negative correlations with the Nino-West Sea Surface Temperature (SST) anomaly and the Southern Oscillation Index (SOI) during the period from September to December. The shoreline prediction model using the correlations between the wave energy flux and climate indices indicated that the large-scale variations in climate represented by the AO index, the SOI, and the Nino-West SST anomaly accounted for 45% of the interannual shoreline variation. Citation: Kuriyama, Y., M. Banno, and T. Suzuki (2012), Linkages among interannual variations of shoreline, wave and climate at Hasaki, Japan, Geophys. Res. Lett., 39, L06604,