Changes In Significant Wave Height Research Articles

Transformation of significant wave height and set-up due to entrained air bubbles effect in breaking waves

The transformation of wave height is of paramount significance in coastal engineering and the design of coastal structures. Considering the influence of air bubbles, this study devised an optimal dissipation model for accurately calculating changes in significant wave height (Hm0) and wave set-up for irregular waves undergoing breaking. Existing regular wave breaking models, which consider the effects of air bubbles, were adapted for direct application to irregular waves by deriving novel formulations. The proposed models leverage the probability of the fraction of broken waves. Hm0 was computed using the energy balance equation, while the wave set-up was calculated based on the momentum balance equation. A wide range of test scenarios, incorporating diverse scales (small and large) and experimental field data, was considered for validation. One of the proposed models, namely model-I (M-I), particularly demonstrated superior performance, manifesting lower error indices (P20), root-mean-square relative error (RMSRE), and Brier skill score (BSS) values in computing both Hm0 and wave set-up. Therefore, utilising M-I is strongly recommended for the precise estimation of Hm0 and set-up transformation.

ARE GLOBAL CHANGES IN WAVE AND STORM SURGE CONDITIONS CORRELATED WITH COASTAL EROSION/ACCRETION?

Both satellite and reanalysis model data have shown statistically significant changes in global wave height in recent decades. It is often speculated that, if such changes continue in the future, they may have an impact on coastal erosion. A global study to investigate whether the observed changes in significant wave height have had a measurable impact on beach stability has, not however, previously been attempted. This presentation will bring together global datasets of changes in wave height, storm surge and coastal erosion over the last 30 years, to investigate possible links.

Evaluating a Poroelastic Model via Pore Pressure Signals in Seafloor Sediments

AbstractBelow a certain threshold of wave energy for a given depth, unconsolidated sediment should respond to wave action poroelastically. To this end, a generalized simple poroelastic model was applied to in situ data collected in coastal sediments near Oceanside, California. Pore pressure data were recorded by sensors attached to cylindrical unexploded ordinance surrogates, and water pressure sensors on bottom moorings. Orientation data were collected from inertial motion units attached to the surrogates, which were placed on the seabed and subsequently shallow buried during a high‐energy event on 13 February 2021. The model is characterized by two parameters. A consolidation coefficient controls the depth of diffusive flow, and Skempton's coefficient represents the ratio of the original signal into components transmitted by the sediment matrix and the pore fluid. The model assumes that the pore pressure signal is coherent with the seafloor signal; spectral coherence above 0.75 was used to select the frequency range from 0.05 to 0.2 Hz for the analysis. Spectral analysis methods were then applied to obtain averaged auto spectral densities of the pore pressure and bottom mooring signals over the coherent frequency band. Attenuation between sensor pairs was calculated. The results yielded burial depths over time for the surrogates that agreed with changes in significant wave heights, liquefaction, and recovery depths.

Regional forecasting of significant wave height and mean wave period using EOF-EEMD-SCINet hybrid model

Most studies only focus on single-point wave forecasting, while regional wave forecasting has more important significance for ocean engineering construction, navigation safety and disaster warning. To solve the problems of high computational cost and poor performance of regional wave forecasting models, a novel hybrid model for regional significant wave height (SWH) and mean wave period (MWP) forecasting, called EOF-EEMD-SCINet, is proposed by combining empirical orthogonal functions (EOF) analysis, ensemble empirical mode decomposition (EEMD) and sample convolution and interaction network (SCINet). After determining the optimal input steps, the number of intrinsic mode functions (IMFs) and the decomposition method, the forecasting performance of the model for SWH and MWP with lead times of 24, 48 and 72 h is evaluated based on SWH, MWP, wind speed (WSPD), significant height of first swell partition (SWH1) and significant height of wind waves (SHWW) in the South China Sea (SCS). The results show that the proposed model can not only accurately forecast the changes in SWH and MWP with time, but also has a high forecasting precision for regional waves, which is superior to other models. In addition, the increase of wave lead time has less negative effect on the forecasting performance of the proposed model compared to other models. As the lead time changes from 24 h to 72 h, the mean absolute error (MAE) of SWH increases by less than 6 cm, and the MAE of MWP changes around 0.04 s. Besides, EOF-EEMD-SCINet has enormous advantage in terms of efficiency. EOF-EEMD-SCINet is a model that can simultaneously forecast regional SWH and MWP with high precision.

Time of Emergence for Altimetry‐Based Significant Wave Height Changes in the North Atlantic

AbstractSatellite 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.

The effect of reclamation on the significant wave height changes in Jakarta Bay during Hagibis and Mitag typhoons

The effect of reclamation on the significant wave height changes in Jakarta Bay during Hagibis and Mitag typhoons

CMIP5 model performance of significant wave heights over the Indian Ocean using COWCLIP datasets

Wind-generated surface gravity waves forms an integral part in modulating the air-sea exchange processes. Information of wave parameters is also very essential in planning marine- and coastal-related activities. It is now well recognized that wind-wave activity shows changing trends over the global ocean basins. Numerous studies have addressed the projected changes in significant wave height for the Indian Ocean (IO) region, and there is a need to conduct thorough performance evaluation of global climate models (GCMs) over this region for futuristic planning. With this motivation, the present study examined the performance of historical dynamical wave climate simulations generated under the Coordinated Ocean Wave Climate Projections (COWCLIP) experiment. The simulations utilized near-surface wind speed datasets from 8 CMIP5 (Fifth phase of Coupled Model Intercomparison Project) GCMs to force a spectral wave model. The skill level of individual GCM forced wave simulations and multi-model mean (MMM) in reproducing the significant wave height (SWH) over four different sub-domains in the IO was evaluated with reference to the ECMWF Reanalysis 5th Generation (ERA5) datasets. Several performance metrics such as the Taylor Skill, M-Score, Model Climate Performance Index (MCPI), and Model Variability Index (MVI) are employed to establish the skill level of model simulations. The study deciphers that model performance is highly reliant on the region and its characteristics. Representation of the historical wave climate over the Arabian Sea (AS) and the Bay of Bengal (BoB) regions is remarkable in the COWCLIP datasets. However, there are discrepancies noticed in SWH distribution over the South Indian Ocean (SIO) attributed to model limitations in adequately reproducing swell wave fields over that region. The MMM constructed using the best-performing models (MRI-CGCM3, ACCESS1.0, INMCM4, HadGEM2-ES, and BCC-CSM1.1) is found consistent at all the sub-domains. The study signifies that the performance evaluation of GCM forced wave simulations is crucial before employing them for practical applications. Best-performing models listed from this study can be used to establish futuristic scenarios of SWH in a changing climate for the IO region.

Future Changes in Significant Wave Heights in the East/Japan Sea

Jang, C.J.; Kim, K.H.; Jung, H.; Do, K.; Yoo, J.; Kim, Y.S., and Lim, H.S., 2020. Future changes in significant wave heights in the East/Japan Sea. In: Malvarez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 1443-1448. Coconut Creek (Florida), ISSN 0749-0208.Future changes in wave climate play a crucial role in both coastal safety by changing coastal environments including erosion and marine ecosystem mainly by modulating nutrient input through vertical mixing changes. In this study, we investigated future changes in significant wave heights (SWHs) in the East/Japan Sea by using a regional wave model forced with future winds in the mid-21 century based on the RCP4.5 scenario. The future wind field was obtained from a regional climate model (SNU-MM5) contributing to CORDEX-EA (COordinated Regional climate Downscaling EXperiment-East Asia) project. In general, the mean SWHs are projected to increase, with a seasonally contrasting pattern: a greater increase in summer than in winter. In addition to the seasonal contrast, a basin-wide difference is also noticeable: larger changes in the northern basin than in the southern basin. The 99th percentile SWHs, a measure of extreme SWHs, show a significant spatial variation, with a maximum increase near Vladivostok, where a considerable intensification of wind is projected. Our findings suggest that the projected future changes in SWHs in the East/Japan Sea can be considerably different depending on seasons and basins.

Experimental assessment of tidal turbine loading from irregular waves over a tidal cycle

Waves interact with currents in tidal channels with the resulting wave–current environment largely determining the loads experienced by tidal stream turbines. Over a tidal cycle, the magnitude and direction of the current velocity changes and hence so does the combined wave–current conditions the turbines must operate within. Here we demonstrate this effect experimentally, generating a realistic irregular wave case in both following (in the same direction as the waves) and opposing currents prior to assessing the resulting loads on a fully instrumented 1:15 scale tidal turbine model aligned with the current direction. Large changes in the environmental conditions, along with the turbine performance and loads, are demonstrated through the presentation of temporal, spectral and statistical outputs. The experimental results demonstrate that the full-scale equivalent significant wave height changes from 2.25 m in zero current to 6.11 m in 3.2 m/s opposing current and 1.56hbox { m} in 3.2hbox {m/s} following current. The corresponding standard deviations of measured turbine parameters for the opposing condition range between 215 and 260% of the following case, and between 340 and 565% of the current-only measurements. Hence, when waves are present, significantly greater fatigue damage will be accumulated during one-half of the tidal cycle. The mean values, however, appear to be unaffected by the presence of waves suggesting that the overall turbine performance is unaltered. These results demonstrate the requirement to understand the combined wave–current environment and to test and de-risk tidal stream turbines for operation in both following and opposing wave–current conditions. Significant additional insight is gained into the nature of loads experienced by tidal turbines in irregular wave conditions, a scarcely documented phenomenon.

Assessment of coastal vulnerability in Chabahar Bay due to climate change scenarios

Summary A substantial body of research has shown that two key factors of global sea level rise are thermal expansion and melting of land-based ice, glaciers and ice sheets. Moreover, climate change may result in changes to wind speeds and directions, consequently resulting in contributions to variations in wind-wave components, wave heights and directions. In this research, climate change scenarios were used to assess the coastal vulnerability to the Chabahar port area due to global sea level rise, significant wave height changes and tidal regime effects. These three items were calculated separately using numerical models and the impacts of possible climate change scenarios were applied to estimate possible changes to these items by 2100. Significant wave heights for 25, 50 and 100-year return periods were evaluated. Based on statistical analysis, the maximum significant wave heights for the A2 and A1B scenarios were estimated at approximately 13.7 and 7.6, respectively. Since the main aim of this research was to assess the coastal zones at higher flood risk, therefore the mean global sea level rise, extreme values of significant wave heights and tidal heights were investigated. The height of sea during sea storms and for the most extreme case was calculated as 17.3 m and 11.2 m for A2 and the A1B scenarios, respectively. According to output maps of inundation areas, large coastal zones in the Chabahar port area are at risk due to the sea storms and possible climate change.

The impact of climate change on the wave climate in the Gulf of St. Lawrence

The purpose of this study is to investigate possible local changes in the wave climate for the coastal waters off eastern Canada, particularly in the Gulf of St. Lawrence (GSL) related to changes in marine winds, storm and the sea ice climate, due to climate change. These analyses are based on application of a dynamical downscaling approach whereby a regional climate model is driven by climate change estimates from the Canadian Global Climate Model (CGCM3) to provide relatively high resolution winds to drive a wave model. The CGCM3 simulation follows the A1B climate change scenario of the Special Report on Emission Scenarios from the Fourth Assessment Report (AR4) of the Intergovernmental Panel on Climate Change (IPCC AR4, 2007). The analyses of the wave climate are based on simulations of the waves from a third-generation wave model, WAVEWATCHIII™, and the downscaled winds obtained from the Canadian Regional (atmospheric) Climate Model (CRCM). We show that the significant wave heights in the Gulf of St. Lawrence (hereafter GSL) and neighboring coastal waters will slightly increase in the winter and decrease in the summer, in response to changes in storms and sea ice in the future climate (2040–2069) compared to the present wave climate, represented as 1970–1999. This time period is denoted as the “historical” wave climate in this study. In summer, the changes in significant wave heights (Hs) are associated with estimated decreases in the frequency of the occurrence of the cyclones. Projected changes in return values for summer extremes in the wave climate are consistent with the associated changes in the maximum Hs values. In winter, the projected increases in return values are mostly concentrated in the St. Lawrence Estuary, the northern and southwestern GSL, consistent with changes in the maximum waves in these regions. An important factor related to change in the winter wave climate is change in the sea ice.

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.

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.

Offshore wind farm impacts on surface waves and circulation in Eastern Lake Ontario

A coupled wave and hydrodynamic model was applied to the Kingston Basin of eastern Lake Ontario, a region with bathymetric variability due to channels and shoals, to assess the potential impacts on surface waves and wind-driven circulation of an offshore wind farm. The model was used to simulate a series of storm events with time-varying wind forcing and validated against wave, current and water level observations. The wind farm was simulated by adding semi-permeable structures in the surface wave model to represent the turbine monopiles, and by adding an energy loss term to the fluid momentum equations in the hydrodynamic model to represent the added drag of the monopiles on the flow. The results suggest that the wind farm would have a small influence on waves and circulation throughout the wind farm area, with spatial variability due to focussing of wave energy and re-direction of the flow. Overall, the results indicate that the wave height in coastal areas will be minimally affected with changes in significant wave height predicted to be <3%. Larger changes to the strength of circulation occur inside the wind farm region with localized changes in current magnitude of up to 8cms−1. The results of this study may help to understand the impacts of future offshore wind farms and other offshore structures in the Great Lakes.

Extreme values of coastal wave overtopping accounting for climate change and sea level rise

An integrated modelling system is presented for determining the wave overtopping of a sea wall due to offshore hydrodynamic conditions; the overtopping discharge depends mainly on the water level and the nearshore wave height. The modelling system enables joint probabilities for overtopping discharge to be assessed for different future climate scenarios with different rates of sea level rise. For the test case of a sea wall at Walcott, UK, where extensive flooding occurred on 9th November 2007, it is shown how the frequency of flooding of a given magnitude would increase with time, dependent on future climate projections and sea level rise, and, correspondingly, how the magnitude of flooding with a given return period would increase. For example, for an event with a return period of 100years (similar to the 2007 Walcott event), the return period, estimated by the proposed extreme event analyses, reduces to 5years with 0.35m sea level rise in 2100, thought to be the most likely level, and just over 1year with 1m sea level rise. The methodology applied here, based on state-of-the-art modelling of wave overtopping, shows that the future projected rates are more influenced by changes in water level than by changes in significant wave height.

Variability of the Winter Wind Waves and Swell in the North Atlantic and North Pacific as Revealed by the Voluntary Observing Ship Data

Abstract This paper analyses secular changes and interannual variability in the wind wave, swell, and significant wave height (SWH) characteristics over the North Atlantic and North Pacific on the basis of wind wave climatology derived from the visual wave observations of voluntary observing ship (VOS) officers. These data are available from the International Comprehensive Ocean–Atmosphere Data Set (ICOADS) collection of surface meteorological observations for 1958–2002, but require much more complicated preprocessing than standard meteorological variables such as sea level pressure, temperature, and wind. Visual VOS data allow for separate analysis of changes in wind sea and swell, as well as in significant wave height, which has been derived from wind sea and swell estimates. In both North Atlantic and North Pacific midlatitudes winter significant wave height shows a secular increase from 10 to 40 cm decade−1 during the last 45 yr. However, in the North Atlantic the patterns of trend changes for wind sea and swell are quite different from each other, showing opposite signs of changes in the northeast Atlantic. Trend patterns of wind sea, swell, and SWH in the North Pacific are more consistent with each other. Qualitatively the same conclusions hold for the analysis of interannual variability whose leading modes demonstrate noticeable differences for wind sea and swell. Statistical analysis shows that variability in wind sea is closely associated with the local wind speed, while swell changes can be driven by the variations in the cyclone counts, implying the importance of forcing frequency for the resulting changes in significant wave height. This mechanism of differences in variability patterns of wind sea and swell is likely more realistic than the northeastward propagation of swells from the regions from which the wind sea signal originates.

Modelling analysis of the sensitivity of shoreline change to a wave farm

Change of shoreline wave climate caused by the installation of a wave farm is assessed using the SWAN wave model. The 30 MW-rated wave farm is called the ‘Wave Hub’ and will be located 20 km off the north coast of Cornwall, UK. Changes in significant wave height and mean wave period due to the presence of the Wave Hub are presented. The results suggest that the shoreline wave climate will be affected, although the magnitude of effects decreases linearly as wave energy transmitted increases. At probable wave energy transmission levels, the predicted change in shoreline wave climate is small.

Towards a vulnerability assessment of the UK and northern European coasts: the role of regional climate variability

Within the framework of a Tyndall Centre research project, sea level and wave changes around the UK and in the North Sea have been analysed. This paper integrates the results of this project. Many aspects of the contribution of the North Atlantic Oscillation (NAO) to sea level and wave height have been resolved. The NAO is a major forcing parameter for sea-level variability. Strong positive response to increasing NAO was observed in the shallow parts of the North Sea, while slightly negative response was found in the southwest part of the UK. The cause of the strong positive response is mainly the increased westerly winds. The NAO increase during the last decades has affected both the mean sea level and the extreme sea levels in the North Sea. The derived spatial distribution of the NAO-related variability of sea level allows the development of scenarios for future sea level and wave height in the region. Because the response of sea level to the NAO is found to be variable in time across all frequency bands, there is some inherent uncertainty in the use of the empirical relationships to develop scenarios of future sea level. Nevertheless, as it remains uncertain whether the multi-decadal NAO variability is related to climate change, the use of the empirical relationships in developing scenarios is justified. The resulting scenarios demonstrate: (i) that the use of regional estimates of sea level increase the projected range of sea-level change by 50% and (ii) that the contribution of the NAO to winter sea-level variability increases the range of uncertainty by a further 10-20cm. On the assumption that the general circulation models have some skill in simulating the future NAO change, then the NAO contribution to sea-level change around the UK is expected to be very small (<4cm) by 2080. Wave heights are also sensitive to the NAO changes, especially in the western coasts of the UK. Under the same scenarios for future NAO changes, the projected significant wave-height changes in the northeast Atlantic will exceed 0.4m. In addition, wave-direction changes of around 20 degrees per unit NAO index have been documented for one location. Such changes raise the possibility of consequential alteration of coastal erosion.

North Atlantic Ocean Wave Climate Change Scenarios for the Twenty-First Century

Using the observed relationships between sea level pressure (SLP) and significant wave height (SWH) as represented by regression models, climate change scenarios of SWH in the North Atlantic were constructed by means of redundancy analysis (for seasonal means and 90th percentiles of SWH) and nonstationary generalized extreme value analysis (for seasonal extreme SWH). SWH scenarios are constructed using output from a coupled climate model under three different forcing scenarios. Scenarios of future anomaly seasonal statistics of SWH are constructed using climate model projections of anomaly seasonal mean SLP while projections of seasonal extreme SWH are made using projections of seasonal mean SLP and seasonal SLP gradient index. The projected changes in SWH are assessed by means of a trend analysis. The northeast Atlantic is projected to have increases in both winter and fall seasonal means and extremes of SWH in the twenty-first century under all three forcing scenarios. These changes are generally accompanied by decreases in the midlatitudes of the North Atlantic and increases in the southwest North Atlantic. The rate and sign of the projected SWH change is not constant throughout the twenty-first century. In the Norwegian and North Seas, the projected SWH changes are characterized either by faster increases in the late decades than in the early decades, or by decreases in the early decades followed by increases, depending on the forcing scenario and the specific location. Using lower or higher rates of increase in greenhouse gases forcing generally leads to reduced or increased rates of change, respectively, in ocean wave heights. The sign and rate of future wave height changes in the North Sea in particular appear to be quite dependent on the forcing conditions. In general, global warming is associated with more frequent occurrence of the positive phase of the North Atlantic Oscillation (NAO) and strong cyclones, which leads to increases of wave heights in the northeast Atlantic.

Irregular wave Refraction Due to Current

The phenomenon of wave refraction due to current is an important factor in the longshore current generation and the wave transformation in the vicinities of narrow strait and river mouth. The existing numerical models of wave refraction due to current are all for regular waves. A numerical model is proposed for the computation of the change of the directional spectral density of irregular waves due to current‐depth refraction. The wave action equation is applied as the basic equation, in which the wave direction is introduced as the fourth independent variable. Several sample computations show that this model can explain the change of the directional spectra due to current. It is found that the significant wave height changes more rapidly than that of the corresponding regular waves having the same wave height, period and direction as those of the irregular waves. The change of a mean wave direction of the irregular waves is different from that of the corresponding regular waves.