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Satellite observations of significant wave height (Hs) have recently reached 30 years of continuous record. Is this length sufficient to detect the effect of anthropogenically forced climate change on wave height trends? Wave height decadal variability is influenced by a combination of internal variability and forced variability caused by both anthropogenic and natural forcing. Using a statistical model to derive Hs from sea level pressure field and exploiting ERA‐5 reanalysis data as well as 80 members of the Community Earth System Model v2 large ensemble, we show that, over the North Atlantic (NA), altimetry‐based Hs trends are mostly caused by internal variability. This suggests that Hs changes computed over the satellite era are not yet controlled by anthropogenic climate change. Starting from 1993, the date of emergence, defined as the date when the forced signal becomes dominant over the internal variability, is later than 2050 for Hs in the NA. Plain Language Summary: Satellite observations of significant wave height will soon reach 30 years of continuous record. Changes in significant wave height over this period can either be attributed to both anthropogenic or "natural" climate forcing or to the intrinsic variability of the climate system. In this article, we show that the intrinsic variability effect largely dominates the significant wave height changes in the North Atlantic (NA) over the 30 years of satellite observations. We further estimate that the significant wave height changes associated with anthropogenically forced climate change will become dominant over those due to the intrinsic variability after 2050 in most of the NA region. Key Points: Altimeter based significant wave height trends in the North Atlantic (NA) are largely dominated by internal variabilityForced significant wave height changes in the NA will only be detectable in altimeter data after 2050 [ABSTRACT FROM AUTHOR]

The storm sequence of the 2013–14 winter left many beaches along the Atlantic coast of Europe in their most eroded state for decades. Understanding how beaches recover from such extreme events is essential for coastal managers, especially in light of potential regional increases in storminess due to climate change. Here we analyse a unique dataset of decadal beach morphological changes along the west coast of Europe to investigate the post‐2013–14 winter recovery. We show that the recovery signature is site specific and multi‐annual, with one studied beach fully recovered after 2 years, and the others only partially recovered after 4 years. During the recovery phase, winter waves primarily control the timescales of beach recovery, as energetic winter conditions stall the recovery process whereas moderate winter conditions accelerate it. This inter‐annual variability is well correlated with climate indices. On exposed beaches, an equilibrium model showed significant skill in reproducing the post‐storm recovery and thus can be used to investigate the recovery process in more detail. © 2018 John Wiley & Sons, Ltd. Beach recovery to a high energy winter is multi‐annual. It is not the subsequent summer conditions, but the subsequent winter conditions that primarily control the timescale of beach recovery to an outstanding series of severe winter storms. Indeed winter wave conditions can stall or accelerate the recovery process. [ABSTRACT FROM AUTHOR]

High–energy supratidal coastal boulder deposit (SCBD) dynamics were investigated on Vierge Island and Pors Carn Point, north and south of western Brittany, France, respectively. Morphological changes induced by boulder transport and quarrying were quantified using high–resolution topographic survey data taken between 2012 and 2017. Additional in–situ wave parameters and water levels were also recorded over this period (2014–2017) in order to compute the maximum water levels and assess the relationship between SCBD morphological changes and specific hydrodynamic conditions. During extreme water levels (for maximum water levels exceeding a one in ten year event), SCBDs were broadly reworked (up to 40% of the total volume). During lower intensity events, for which maximum water levels were still very high, morphological changes represented 1% to 5% of the total volume. These morphological and hydrodynamic observations were then used to calibrate a chronology of SCBD activation events based on 70 years of hindcast winter maximum water levels. These long–term time–series showed great interannual variability in SCBD activation but no significant long–term trend. Winter–frequency SCBD activation was better correlated to the WEPA index ( r = 0.46) than the NAO index ( r = 0.1). Therefore, the WEPA index can be considered to be a more significant climate proxy for assessing storm–related geomorphic changes in the temperate latitudes of the N–E Atlantic basin (36°–52° N), including the Brittany coast. The potential of SCBDs as a morphological storm proxy for macrotidal high–energy rocky coasts is addressed. [ABSTRACT FROM AUTHOR]

Abstract: Ocean surface gravity waves play a major role in many engineering and environmental problems, both in the open ocean and in coastal zones. Therefore, it is essential to improve our knowledge on spatial and temporal variability of wave climate. This study aims at investigating this variability in the North-East Atlantic Ocean (25°W–0°W and 30°N–60° N), using a 57-year hindcast (1953–2009) obtained with a spectral wave model forced with reanalysis wind fields. The hindcast analysis reveals firstly strong seasonal fluctuations of wave climate, with winters characterized by large and long-period waves of mean direction spreading from south-west to north-west, and summers characterized by smaller and shorter-period waves originating from norther directions. From northern (55°N) to southern (35°N) latitudes, the significant wave height (Hs) decreases by roughly 40%, the mean wave direction (Mwd) rotates clockwise by about 25% while the peak period (Tp) only grows by 5%. These three parameters also exhibit a strong inter-annual variability, particularly when winter-means (from 1st of December to 1st of April) are considered. Linear trend analysis over the studied period shows spatially variable long-term trends, with a significant increase of Hs (up to 0.02m yr−1) and a counterclockwise shift of Mwd (up to −0.1°yr−1) at northern latitude, contrasting with a fairly constant trend for Hs and a clockwise shift of Mwd (up to +0.15°yr−1) at southern latitudes. Long-term trends of Tp are less significant, with still a slight increase in the north-eastern part of the study area (up to +0.01 syr−1). Eventually, a comparison between the inter-annual variability of the winter-means of the three selected wave parameters and the North Atlantic Oscillation (NAO) reveals: (1) a strong positive correlation between Hs and the NAO index at northern latitudes (correlation coefficient up to R =0.91) and a significant negative correlation at southern latitudes (up to R =−0.6); (2) no significant correlation for Mwd north of 40°N and a clear positive correlation southward of 40°N (up to R =0.8) and (3) a northward increasing correlation for Tp (up to R =0.8). Long-term trends for Hs, Mwd and Tp are finally explained by a significant increase in the NAO index over the studied period. [Copyright &y& Elsevier]

Abstract: Tidal inlets are extremely dynamic, as a result of an often delicate balance between the effects of tides, waves and other forcings. Since the morphology of these inlets can affect navigation, water quality and ecosystem dynamics, there is a clear need to anticipate their evolution in order to promote adequate management decisions. Over decadal time scales, the position and size of tidal inlets are expected to evolve with the conditions that affect them, for instance as a result of climate change. A process-based morphodynamic modeling system is validated and used to analyze the effects of sea level rise, an expected shift in the wave direction and the reduction of the upper lagoon surface area by sedimentation on a small tidal inlet (Óbidos lagoon, Portugal). A new approach to define yearly wave regimes is first developed, which includes a seasonal behavior, random inter-annual variability and the possibility to extrapolate trends. Once validated, this approach is used to produce yearly time series of wave spectra for the present and for the end of the 21st century, considering the local rotation trends computed using hindcast results for the past 57 years. Predictions of the mean sea level for 2100 are based on previous studies, while the bathymetry of the upper lagoon for the same year is obtained by extrapolation of past trends. Results show, and data confirm, that the Óbidos lagoon inlet has three stable configurations, largely determined by the inter-annual variations in the wave characteristics. Both sea level rise and the reduction of the lagoon surface area will promote the accretion of the inlet. In contrast, the predicted rotation of the wave regime, within foreseeable limits, will have a negligible impact on the inlet morphology. [Copyright &y& Elsevier]

The beach-dune response at Truc Vert, SW France, is analysed using DGPS topographic surveys sampled every 2–4 weeks covering an alongshore distance of 1.5 km, combined with wave, tide and extreme water level hindcast and beach/dune photographs. During the 2013/2014 winter, which was the most energetic since at least 1948, the beach-dune system at Truc Vert eroded by approximately 180 m 3 per beach width divided equally between beach and dune erosion. Beach and dune erosion was strongly variable alongshore, with cuspate-type rhythmic dune erosion scarps stripped of vegetation with a cross-shore amplitude of 25 m. The alongshore-variable scarps were coupled with an alongshore variability in elevation of the beach, with lower beach levels co-located with the megacusp bays. The following 10 months showed modest morphological beach and dune changes with, for instance, destabilisation of the scarped dune by trough blowouts, scarp slumping and filling and seasonal beach berm dynamics. The most profound morphological and vegetation changes occurred during the subsequent 10 months. Only 1.5 years after that winter, the beach-dune system at Truc Vert almost recovered to its pre-winter volume, but not to its pre-winter foredune profile. Most of the sand volume recovery occurred during spring-summer-autumn 2015 when approximately 120 m 3 /m of sand naturally came back in the system. The beach volume recovery rate was relatively steady and uncorrelated with wave conditions, with rates twice as large across the megacusp bay profile as across the that of the megacusp horns. During that period, the widened and risen dry beach provided large fetch length enhancing onshore windblown transport and a rapid rising of the backshore. The slumped and filled dune scarp, which was providing a high barrier to aeolian transport from the beach to the dune since the 2013/2014 winter, reformed as a dune ramp providing efficient conduit for beach-dune delivery/exchange of sediment by the end of the study. This process favoured both natural revegetation into the scarp and incipient foredune formation. Despite the reinstatement of natural processes between the beach and the dune, the dune foot was still located landward by more than 10 m on average with respect to its pre-2013/2014 winter position. This study shows that even after the most severe winter over the last 68 years in terms of average wave energy arriving at the coast, beach recovery can be a relatively fast process along high-energy sandy beaches backed by large dunes. In contrast foredune recovery, which timing and magnitude can provide a proxy measure for the resilience of the system to climatic variability and change, is a much slower process that can take years to decades. [ABSTRACT FROM AUTHOR]