Changes In Wave Height Research Articles

The Influence of Climate Change on Coastal Erosion Vulnerability in Northeast Brazil

In this paper, an adapted methodology to evaluate coastal erosion vulnerability, which provides a basis for decision-making concerning risk management strategies, is described. The vulnerability evaluation was based on weighted indicators and assessed the vulnerability under different climate change scenarios. To generate the vulnerability index, dynamic processes, geo-indicators, and social and morphological parameters associated with modeled scenarios of sea level rise and predicted wave height changes were integrated. The study area included the sandy beaches in Pernambuco, NE Brazil, and was used to describe the practical application of this approach. Because the occupation of large sectors of the coastline was low, the vulnerability was concentrated in urbanized areas. The high-vulnerability sections of the coast were those with high population densities, high-rise buildings, induced coastal squeeze and hard engineering structures. The low-vulnerability beaches generally had low urbanization rates and well-conserved, resilient coastlines. Under future scenarios, the vulnerability of this coastal region will increase with sea level rise and wave height changes.

Low-cost time-lapse seismic with distributed compressive sensing — Part 2: Impact on repeatability

Irregular or off-the-grid spatial sampling of sources and receivers is inevitable in field seismic acquisitions. Consequently, time-lapse surveys become particularly expensive because current practices aim to replicate densely sampled surveys for monitoring changes occurring in the reservoir due to hydrocarbon production. We have determined that under certain circumstances, high-quality prestack data can be obtained from cheap randomized subsampled measurements that are observed from nonreplicated surveys. We extend our time-jittered marine acquisition to time-lapse surveys by designing acquisition on irregular spatial grids that render simultaneous, subsampled, and irregular measurements. Using the fact that different time-lapse data share information and that nonreplicated surveys add information when prestack data are recovered jointly, we recover periodic densely sampled and colocated prestack data by adapting the recovery method to incorporate a regularization operator that maps traces from an irregular spatial grid to a regular periodic grid. The recovery method is, therefore, a combined operation of regularization, interpolation (estimating missing fine-grid traces from subsampled coarse-grid data), and source separation (unraveling overlapping shot records). By relaxing the insistence on replicability between surveys, we find that recovery of the time-lapse difference shows little variability for realistic field scenarios of slightly nonreplicated surveys that suffer from unavoidable natural deviations in spatial sampling of shots (or receivers) and pragmatic compressed-sensing-based nonreplicated surveys when compared with the “ideal” scenario of exact replicability between surveys. Moreover, the recovered densely sampled prestack baseline and monitor data improve significantly when the acquisitions are not replicated, and hence they can serve as input to extract poststack attributes used to compute time-lapse differences. Our observations are based on experiments conducted for an ocean-bottom cable survey acquired with time-jittered continuous recording assuming source equalization (or the same source signature) for the time-lapse surveys and no changes in wave heights, water column velocities or temperature, and salinity profiles.

Coastal dune activity and foredune formation on Moreton Island, Australia, 1944–2015

Abstract The stabilization process of coastal dunes is complex, involving feedback mechanisms and lag times between changes in climatic conditions, vegetation establishment and dune movement. In this study our aim was to examine changes in dune activity and in the establishment of foredunes on Moreton Island, Australia. We used historical aerial photos, satellite images and Lidar data to quantify changes in bare sand areas, dune movement rates, foredune development and coastline changes between 1944 and 2015. We used wind data (1957–2016), to quantify changes in sand drift potential (DP) and in wind directionality, and wave data (1977–2016) to examine changes in wave height and wave direction. We found that transgressive dunes on Moreton Island have started stabilizing in the early 1970s, after a series of continuous foredunes developed on the eastern coast of Moreton Island, in spite of the increase in DP values. Foredunes have started establishing in the 1960s and 1970s during a period of lower wave height and decreased wind directionality. Once established, these foredunes have diminished sand supply to the transgressive dunes, causing a phase shift in the state of dune activity on the island. Coastal dune activity should therefore be examined over time scales of several decades at least, in order to quantify trends and to understand the underlying and causes to observed processes. Understanding the factors responsible for foredune formation is important for explaining dune stabilization on Moreton Island.

Projected changes in significant wave height toward the end of the 21st century: Northeast Atlantic

AbstractWind field ensembles from six CMIP5 models force wave model time slices of the northeast Atlantic over the last three decades of the 20th and the 21st centuries. The future wave climate is investigated by considering the RCP4.5 and RCP8.5 emission scenarios. The CMIP5 model selection is based on their ability to reconstruct the present (1971–2000) extratropical cyclone activity, but increased spatial resolution has also been emphasized. In total, the study comprises 35 wave model integrations, each about 30 years long, in total more than 1000 years. Here annual statistics of significant wave height are analyzed, including mean parameters and upper percentiles. There is general agreement among all models considered that the mean significant wave height is expected to decrease by the end of the 21st century. This signal is statistically significant also for higher percentiles, but less evident for annual maxima. The RCP8.5 scenario yields the strongest reduction in wave height. The exception to this is the north western part of the Norwegian Sea and the Barents Sea, where receding ice cover gives longer fetch and higher waves. The upper percentiles are reduced less than the mean wave height, suggesting that the future wave climate has higher variance than the historical period.

Impacts of climate change on wave regimes in the East Sea

The study applied the PRECIS and SWAN modelling packages to simulate wind and wave regimes under climate change in the Vietnam East Sea. The results indicated that under RCP4.5 climate change scenario, by the end of the century, there are significant changes in both wave height and wave period in summer and winter months. In the East Sea during July, wave height is expected to increase 11.5% while wave period expected to increases 3.3%. On the other hand, wave height in January is projected to decrease approximately 7% while wave period in the same month is projected to decreases 4.4%. There are no significant changes in wave direction.

Tensile loading induced phase transition and rippling in single-layer MoS2

Molecular dynamics (MD) simulation is performed to study the structural evolution of single-layer MoS2 nanosheets under tensile loading and a phase transition from hexagonal structure to quadrilateral one is observed at a large strain when loaded along the zigzag direction but not along the armchair direction. Density functional theory (DFT) calculation illustrates that the newly generated quadrilateral phase is metallic. Further loading along the zigzag direction promotes an inhomogeneous distribution of lateral and shear stress around the phase boundaries due to local mechanical mismatch. As a result, periodic rippling parallel to the loading direction emerges and the wavelength and wave height change with strain according to λ∼ε−1/4 and h∼ε1/4. Accordingly, a graded distribution of strain can be produced or modulated by a simple tensile loading and the strategy might be utilized to enhance the photoelectrical properties of 2D materials and design strain-tunable nanodevices.

Projection of tropical cyclone-generated extreme wave climate based on CMIP5 multi-model ensemble in the Western North Pacific

Climate change impacts on future ocean wave climate have been studied using a suite of Global Climate Models (GCM). We investigated the representation of extreme (annual maximum) wave climate in the Atmosphere-Ocean GCM (AOGCM) driven wave climate projections, specifically looking at tropical cyclone (TC)-generated extreme waves in the Western North Pacific. The representation of the extreme wave climate by AOGCM driven wave climate projections was evaluated by comparing with higher-resolution AGCM driven wave climate projections, reanalysis and observations. We find better performance of AOGCM’s to simulate TCs leads to significantly improved representation of the extreme wave climate. The better performing models can produce more than $$30\hbox { ms}^{-1}$$ wind speed in TCs and the frequency of occurrence of TCs is 80 % of the observed frequency of occurrence. The projected changes in the extreme wave climate are dominated by changes in TC-generated waves. Although the projected changes in TC-generated wave heights show the coherent decreases in some models with greater TC skill, there is a large variation in the projected changes among models. The other models which are less able to resolve the TC characteristics display projected changes dominated by non-TC generated waves systems, which is the decrease in wave heights around latitudes 30 $$^{\circ }$$ N. Although there is a large variation in the projected changes in TC-generated waves, the change ratio is 2 times larger than those of non-TC waves. Therefore, appropriate interpretation of the TC-generated wave changes and its variation is important for risk assessment.

Wave climate in the Arctic 1992–2014: seasonality and trends

Abstract. Over the past decade, the diminishing Arctic sea ice has impacted the wave field, which depends on the ice-free ocean and wind. This study characterizes the wave climate in the Arctic spanning 1992–2014 from a merged altimeter data set and a wave hindcast that uses CFSR winds and ice concentrations from satellites as input. The model performs well, verified by the altimeters, and is relatively consistent for climate studies. The wave seasonality and extremes are linked to the ice coverage, wind strength, and wind direction, creating distinct features in the wind seas and swells. The altimeters and model show that the reduction of sea ice coverage causes increasing wave heights instead of the wind. However, trends are convoluted by interannual climate oscillations like the North Atlantic Oscillation (NAO) and Pacific Decadal Oscillation. In the Nordic Greenland Sea the NAO influences the decreasing wind speeds and wave heights. Swells are becoming more prevalent and wind-sea steepness is declining. The satellite data show the sea ice minimum occurs later in fall when the wind speeds increase. This creates more favorable conditions for wave development. Therefore we expect the ice freeze-up in fall to be the most critical season in the Arctic and small changes in ice cover, wind speeds, and wave heights can have large impacts to the evolution of the sea ice throughout the year. It is inconclusive how important wave–ice processes are within the climate system, but selected events suggest the importance of waves within the marginal ice zone.

Derivation of design waves along the Indian coastline incorporating climate change

The climate change induced by global warming has raised concerns over safety of coastal and offshore infrastructure. At several places in the world therefore studies are being made to know the effect of such change on design and operational ocean parameters. This paper is oriented in this direction and its aim is to specify future changes in the design significant wave height (Hs) over a series of locations along the Indian coastline. Thirty-nine sites were selected along the 7000-km-long Indian coast and design Hs with a return period of 100 years were calculated on the basis of past as well as future wave data of duration 27 years each. The simulation of waves was done by running a numerical wave model forced by wind derived from a modeling experiment called CORDEX. Fitting of data to Generalized Pareto Distribution gave the 100-year Hs at all 39 locations. The results indicate that the design Hs calculated on the basis of projected data was much higher than the one based on historical data. Such increase was as small as 5 % and as high as 58 % as per the location. The west coast sites showed a higher rise in the Hs value than the east ones.

Variability and future decreases in winter wave heights in the Western North Pacific

AbstractOcean surface wave climate is a key consideration for a number of industrial and environmental systems, both offshore and at the coast. A dynamical spectral wave model forced with global climate models (GCMs) was used to produce an ensemble of simulations of both historical and projected future wave climate. To estimate the uncertainty of the projected wave climate, we combined a multimember ensemble experiment using MRI‐AGCM3.2H with a multimodel ensemble using eight CMIP5 GCMs. Future changes in wintertime wave heights from the end of the 20th to the 21st century were analyzed. Projected decreases in wave heights over the Western North Pacific are highly consistent among the ensemble. The future decreases in wave heights are significantly related to changes in the West Pacific pattern. Both locally generated waves and remotely generated swells are important to estimate future changes in the wave climate on a regional scale.

Effect of sea level rise on nearshore significant waves and coastal structures

In this paper, the method to assess the impact of sea level rise under regular waves, as proposed by Townend (1994), is extended to irregular waves in order to estimate the changes in nearshore significant waves and the parameters related to hydraulic performance and stability of inclined coastal structures. The relative changes in wavelength, refraction coefficient, shoaling coefficient, and wave height for significant waves are presented as functions of the relative change in water depth. The calculated relative changes in wave characteristics are then used to estimate the effect of sea level rise on coastal structures by calculating the relative changes in wave run-up height, overtopping discharge, crest freeboard, and armor weight of the structures. The relative changes in wave characteristics are expressed as functions of relative water depth and deepwater wave angle or wave steepness. The relative changes in the structure-related parameters are expressed as functions of the relative change in wave height and the wave height and crest freeboard before the sea level rise.

Field and theoretical investigation of sediment mass fluxes on an accretional coastal mudflat

Variations in suspended sediment concentrations (SSCs) in tidal mudflats are an important influence on the ecological environment, morphological evolution, and pollutant transport. To better understand how the behavior of suspended sediment influences small-scale variations in SSC in the water column, we took simultaneous measurements of water depth, wave height, current velocity, SSC profiles, and intratidal bed-level changes during a series of continuous tidal cycles on a highly turbid macrotidal mudflat, part of a larger accretional coastal mudflat on the Jiangsu Coast, China. We estimated the relative contributions of erosion, deposition, and advection processes to variations in SSC from the field data. We used an empirical orthogonal function (EOF) analysis to examine the influence of hydrodynamic factors (water depth, wind, wave height, and current velocity) and environmental factors (salinity and temperature) on SSC variability, to determine why the contributions of the three processes (erosion, deposition, and advection) to the variability in SSC differed. Our results showed that on average, advection flux was about an order of magnitude higher than erosion–deposition flux of corresponding tide, and that advection, driven by the tidal current velocity, wind, and associated alongshore transport, accounted for most of the variability in SSC at the study site over a complete tidal cycle. An abundant sediment supply and limited resuspension of the bed sediments meant that advection was the main transport process. Our results also demonstrate that detailed analyses of transport processes provide useful information on the sources and fates of suspended sediments, and support the interpretation of morphological changes in accretional intertidal mudflats.

Performance of a data-driven technique applied to changes in wave height and its effect on beach response

In this study the medium-term response of beach profiles was investigated at two sites: a gently sloping sandy beach and a steeper mixed sand and gravel beach. The former is the Duck site in North Carolina, on the east coast of the USA, which is exposed to Atlantic Ocean swells and storm waves, and the latter is the Milford-on-Sea site at Christchurch Bay, on the south coast of England, which is partially sheltered from Atlantic swells but has a directionally bimodal wave exposure. The data sets comprise detailed bathymetric surveys of beach profiles covering a period of more than 25 years for the Duck site and over 18 years for the Milford-on-Sea site. The structure of the data sets and the data-driven methods are described. Canonical correlation analysis (CCA) was used to find linkages between the wave characteristics and beach profiles. The sensitivity of the linkages was investigated by deploying a wave height threshold to filter out the smaller waves incrementally. The results of the analysis indicate that, for the gently sloping sandy beach, waves of all heights are important to the morphological response. For the mixed sand and gravel beach, filtering the smaller waves improves the statistical fit and it suggests that low-height waves do not play a primary role in the medium-term morphological response, which is primarily driven by the intermittent larger storm waves.

Surface gravity wave transformation across a platform coral reef in the Red Sea

AbstractThe transformation of surface gravity waves across a platform reef in the Red Sea is examined using 18 months of observations and a wave transformation model developed for beaches. The platform reef is 200 m across, 700 m long, and the water depth varies from 0.3 to 1.2 m. Assuming changes in wave energy flux are due to wave breaking and bottom drag dissipation, the wave transformation model with optimal parameters characterizing the wave breaking (γm = 0.25) and bottom drag (hydrodynamic roughness zo = 0.08 m) accounts for 75%–90% of the observed wave‐height variance at four sites. The observations and model indicate that wave breaking dominates the dissipation in a 20–30 m wide surf zone while bottom drag dominates the dissipation over the rest of the reef. Friction factors (drag coefficients) estimated from the observed wave energy balance range from fw = 0.5 to fw = 5 and increase as wave‐orbital displacements decrease. The observed dependence on wave‐orbital displacement is roughly consistent with extrapolation of an empirical relationship based on numerous laboratory studies of oscillatory flow. As a consequence of the dependence on wave‐orbital displacement, wave friction factors vary temporally due to changes in water depth and incident wave heights, and spatially across the reef as the waves decay.

Future Projections of Extreme Ocean Wave Climates and the Relation to Tropical Cyclones: Ensemble Experiments of MRI-AGCM3.2H*

Abstract Future projections of extreme ocean surface wave climates were carried out with single-model ensemble experiments of the atmospheric global climate model MRI-AGCM3.2H. The ensemble experiments of MRI-AGCM3.2H consist of four future sea surface temperature (SST) ensembles and three perturbed physics (PP) ensembles. This study showed that future changes in extreme wave heights strongly depend on the global climate model (GCM) performance to simulate tropical cyclones (TCs), indicating a need to acknowledge that results in a study that employs a low-performance model are not able to account for extreme waves associated with TCs (TC waves). The spatial distribution of future changes in non-TC extreme wave heights on the global scale was similar to that for mean wave heights; namely, wave heights increase over the middle-to-high latitudes in the Southern Ocean and central North Pacific and decrease over midlatitudes and the North Atlantic, although the magnitude of future changes for extreme wave heights is greater than for mean wave heights. The variance of future changes mainly depends on differences in physics among PP ensemble experiments rather than differences in SST ensembles. The 10-yr return wave heights of TC waves over the western North Pacific showed either an increase or a decrease of 30% for different regions, maximally. The spatial distribution of future changes in TC waves can be explained by an eastward shift of TC tracks.

ASSESSMENT OF CHANGES OF EXTREME WAVE CONDITIONS AT THE GERMAN BALTIC SEA COAST ON THE BASIS OF FUTURE CLIMATE CHANGE SCENARIOS

Information on possible changes in extreme wave heights is needed to determine the future effectiveness and safety of coastal and flood protection structures. In this study, an assessment of possible changes in the extreme wave heights at selected locations along the German Baltic Sea coast has been carried out on the basis of numerical simulations of waves in the western Baltic Sea and regional climate model data for the past and the future (1961-2100). The future climate change signal of significant wave heights with a return period of 200 years mainly depends on: (i) the location, (ii) the climate change scenario run, (iii) the time period of the comparison, and (iv) the approach adopted to calculate the wave climate. The results show increases of up to +0.5 m and decreases of up to -0.5 m of the extreme wave heights. The increases might have considerable effect on the constructional design of coastal and flood protection structures-such as breakwaters, sea dykes, and vertical walls-because the extreme wave heights are used as input parameters for the design of the structures.

Analysis of Climate Change Effects on Seawall Reliability

Crown heights of seawalls should be designed to suppress overtopping discharge to a permissible level. The permissible level is determined from viewpoints of the structure types of coastal seawalls and hinterland use. It is usually difficult to design the crown heights of seawalls, especially in the present time where climate change due to global warming is expected. This study analyzes climate change effects such as sea level rise (SLR) and increase of waves and surges on the failure probability of seawalls under various conditions of crown height, toe depth and slope by using a Level III reliability analysis. It was found that the difference of SLR trends (fast, medium or low) has less impact on overtopping rates than the differences in wave height change for a seawall at a target location.

Decadal variability of global ocean significant wave height

This paper presents the long-term climate changes of significant wave height (Hs) in 1958–2001 over the entire global ocean using the 45-year European Centre for Medium-Range Weather Forecasts (ECMWF) Reanalysis (ERA-40) wave data. The linear trends in Hs and regional and seasonal differences of the linear trends for Hs were calculated. Results show that the Hs exhibits a significant increasing trend of about 4.6 cm decade-1 in the global ocean as a whole over the last 44 years. The Hs changes slowly during the periods 1958–1974 and 1980–1991, while it increases consistently during the periods 1975–1980 and 1995–1998. The Hs reaches its lowest magnitude in 1975, with annual average wave height about 2 m. In 1992, the Hs has the maximum value of nearly 2.60 m. The Hs in most ocean waters has a significant increasing trend of 2–14 cm decade-1 over the last 44 years. The linear trend exhibits great regional differences. Areas with strong increasing trend of Hs are mainly distributed in the westerlies of the southern Hemisphere and the northern Hemisphere. Only some small areas show obvious decreasing in Hs. The long-term trend of Hs in DJF (December, January, February) and MAM (March, April, May) is much more stronger than that in JJA (June, July, August) and SON (September, October, November). The linear trends of the Hs in different areas are different in different seasons; for instance, the increasing trend of Hs in the westerlies of the Pacific Ocean mainly appears in MAM and DJF.

Spectral analysis of irregular waves in wave–mud and wave–current–mud interactions

The dissipation of irregular waves passing over muddy beds is investigated through two series of wave flume laboratory experiments with and without currents, where commercial kaolinite is used as the muddy sediment bed material. The changes in spectral characteristics of waves along the muddy bed and the effects of following and opposing currents are investigated. A numerical multi-layered model was also employed to simulate the attenuation of regular/irregular waves assuming viscoelastic rheological behavior for fluid mud, and the outputs were compared with the laboratory data. The first series of the experiments show that propagation of a wave spectrum over a short fluid mud section does not result in a shift in peak frequencies of wave spectra. The comparisons of spectral width parameters of various wave spectra also reveal that higher values of spectral peakedness parameters generally result in higher rates of wave energy dissipation. This can be related to the frequency dependency of wave energy dissipation on the mud layer. The results of the second series of experiments show higher dissipation rates in the opposing current and lower rates in the following current, which can be attributed to the changes in incident wave heights due to existence of currents. The study confirms that the dynamic pressure of wave propagation on the mud surface is the governing factor in regular/irregular wave–current–mud interaction and the current itself has little direct effect on the mud layer.

Statistical multi-model climate projections of surface ocean waves in Europe

In recent years, the impact of climate change on sea surface waves has received increasingly more attention by the climate community. Indeed, ocean waves reaching the coast play an important role in several processes concerning coastal communities, such as inundation and erosion. However, regional downscaling at the high spatial resolution necessary for coastal studies has received less attention. Here, we present a novel framework for regional wave climate projections and its application in the European region. Changes in the wave dynamics under different scenarios in the Northeast Atlantic Ocean and the Mediterranean are analyzed.The multi-model projection methodology is based on a statistical downscaling approach. The statistical relation between the predictor (atmospheric conditions) and the predictand (multivariate wave climate) is based on a weather type (WT) classification. This atmospheric classification is developed by applying the k-means clustering technique over historical offshore sea level pressure (SLP) fields. Each WT is linked to sea wave conditions from a wave hindcast. This link is developed by associating atmospheric conditions from reanalysis with multivariate local waves. This predictor–predictand relationship is applied to the daily SLP fields from global climate models (GCMs) in order to project future changes in regional wave conditions. The GCMs used in the multi-model projection are selected according to skill criteria. The application of this framework uses CMIP5-based wave climate projections in Europe. The low computational requirements of the statistical approach allow a large number of GCMs and climate change scenarios to be studied.Consistent with previous works on global wave climate projections, the estimated changes from the regional wave climate projections show a general decrease in wave heights and periods in the Atlantic Europe for the late twenty-first century. The regional projections, however, allow a more detailed spatial characterization of the projected changes under different climate scenarios. For example, changes in significant wave heights for the RCP8.5 scenario for the 2070–2099 time period indicate a general decrease of about 10 cm in Southern Europe (Portuguese, Spanish and French coasts) with respect to present conditions. This decrease is due to a higher occurrence of dominant and moderate Azores high pressure systems over the North Atlantic Ocean and a decrease in the persistence of intense low pressure systems at high latitudes.