Coastal Sea Level Research Articles

Why Is the Westward Rossby Wave Propagation from the California Coast “Too Fast”?

Abstract Past work has shown that interannual California coastal sea level variability is mostly of equatorial origin, and decades of satellite sea surface height (SSH) and in situ dynamic height observations indicate that this interannual signal propagates westward from the California coast as nondispersive Rossby waves (RWs). These observations agree with standard linear vertical mode theory except that even when mean flow and bottom topography are considered, the fastest baroclinic vertical mode RW in each case is always much slower (1.6–2.3 cm s−1) than the observed 4.2 cm s−1. This order-1 disagreement is only resolved if the standard bottom boundary condition that the vertical velocity w′ = 0 is replaced by perturbation pressure p′ = 0. Zero p′ is an appropriate bottom boundary condition because south of San Francisco the northeastern Pacific Ocean boundary acts approximately like an impermeable vertical wall to the interannual equatorial wave signal, and therefore equatorial quasigeostrophic p′ is horizontally constant along the boundary. Thus, if equatorial p′ = 0 at the bottom, then this condition also applies off California. The large-scale equatorial ocean boundary signal is due to wind-forced eastward group velocity equatorial Kelvin waves, which at interannual and lower frequencies propagate at such a shallow angle to the horizontal that none of the baroclinic equatorial Kelvin wave signal reaches the ocean floor before striking the eastern Pacific boundary. Off California this signal can thus be approximated by a first baroclinic mode with p′ = 0 at the bottom, and hence the long RW speed there agrees with that observed (both approximately 4.2 cm s−1). Significance Statement The California Current System is one of the most biologically rich and best-documented coastal regions in the world. In this region coastal sea level propagates westward from the coast at about 110 km month−1, slow enough to enable us to make large-scale ocean climate forecasts of the California Current ecosystem using coastal sea level. Although the westward speed seems slow, theoretically it is about double what we would expect. Offered here is an explanation of why this speed is “too fast” by linking the California wave signal to the equator, El Niño, and the shallow equatorial ocean response to the wind.

Loop Current Eddies as a Possible Cause of the Rapid Sea Level Rise in the Gulf of Mexico

AbstractThe Gulf of Mexico (GOM), with its densely populated coastline, is one of the world's most vulnerable regions to climate change and sea level (SL) rise. Over the last three decades, various works have been conducted to assess coastal SL trends around the basin using tide gauge stations, separately from studies dealing with regional dynamical processes. Using altimetry, Argo, and eddy atlas products over the period from January 1993 to December 2020, we have analyzed the regional SL variations in the area to define their characteristics and explore their possible dynamical causes. We observe a mean GIA‐corrected SL rise rate of 4.81 ± 0.85 mm yr−1, which is 25% higher than that of the adjacent Caribbean Sea and 44% higher than that of the global ocean. This result highlights the singular SL evolution in the GOM over the 28‐year study period. Over 2010–2020, the SL trend in the GOM has even accelerated, along with a strong warming of the upper‐layer (0.58 ± 0.17°C), which explains ∼60% of the SL rise rate through the thermosteric effect. Finally, the heat input estimates emphasize the role of the Loop Current eddies as a major contributor to the recent acceleration of SL rise due to upper‐layer warming.

Sea level variability in Gulf of Guinea from satellite altimetry

Coastal zones with dense populations, low elevations and/or inadequate adaptive capacity are on the frontline of unprecedented impacts from climate change. The Gulf of Guinea (GoG), stretching from Liberia to Gabon, is in particular vulnerable to coastal flooding caused by local and/or climate-induced sea level rise. In this region, interannual to decadal coastal sea level changes remain poorly understood, mainly due to a lack of tide gauge stations. Here we use nearly three decades (1993–2021) of satellite altimetry data to study the link between the Equatorial Atlantic and coastal GoG sea level variability. The rate of mean sea level rise increased from 3.47 to 3.89 ± 0.10 mm/yr from the Equatorial oceanic domain to the GoG coastal area, with an acceleration of 0.094 ± 0.050 mm/yr2. This corresponds to a mean sea level rise of about 8.9 cm over the entire altimetry period, 1993–2021. We focus on the (extreme) warm/cold events that occur in both the GoG during Atlantic Niños, and along the Angola-Namibia coast during Benguela Niños. Both events are driven by remote forcing via equatorial Kelvin waves and local forcing by local winds, freshwater fluxes and currents intensifications. Analysis of altimetry-based sea level, sea surface temperature anomalies, 20 °C isotherm based PIRATA moorings, and the Argo-based steric and thermometric sea level allows us to follow the coastal trapped waves (CTWs) along the GoG, and its link with major events observed along the strong Equatorial Atlantic warmings in 2010, 2012, 2019 and 2021. Both 2019 and 2021 warming have been identified as the warmest event ever reported in this region during the last 40 years. A lag of 1 month is observed between equatorial and West African coastal trapped wave propagation. This observation may help to better anticipate and manage the effects of extreme events on local ecosystems, fisheries, and socio-economic activities along the affected coastlines. In order to enable informed decision-making and guarantee the resilience of coastal communities in the face of climate change, it emphasises the significance of ongoing study in this field.

Subseasonal Variability of U.S. Coastal Sea Level from MJO and ENSO Teleconnection Interference

Abstract Climate variability affects sea levels as certain climate modes can accelerate or decelerate the rising sea level trend, but subseasonal variability of coastal sea levels is underexplored. This study is the first to investigate how remote tropical forcing from the MJO and ENSO impact subseasonal U.S. coastal sea level variability. Here, composite analyses using tide gauge data from six coastal regions along the U.S. East and West Coasts reveal influences on sea level anomalies from both the MJO and ENSO. Tropical MJO deep convection forces a signal that results in U.S. coastal sea level anomalies that vary based on MJO phase. Further, ENSO is shown to modulate both the MJO sea level response and background state of the teleconnections. The sea level anomalies can be significantly enhanced or weakened by the MJO-associated anomaly along the East Coast due to constructive or destructive interference with the ENSO-associated anomaly, respectively. The West Coast anomaly is found to be dominated by ENSO. We examine physical mechanisms by which MJO and ENSO teleconnections impact coastal sea levels and find consistent relationships between low-level winds and sea level pressure that are spatially varying drivers of the variability. Two case studies reveal how MJO and ENSO teleconnection interference played a role in notable coastal flooding events. Much of the focus on sea level rise concerns the long-term trend associated with anthropogenic warming, but on shorter time scales, we find subseasonal climate variability has the potential to exacerbate the regional coastal flooding impacts. Significance Statement Coastal flooding due to sea level rise is increasingly threatening communities, but natural fluctuations of coastal sea levels can exacerbate the human-caused sea level rise trend. This study assesses the role of tropical influences on coastal subseasonal (2 weeks–3 months) sea level heights. Further, we explore the mechanisms responsible, particularly for constructive interference of signals contributing to coastal flooding events. Subseasonal signals amplify or suppress the lower-frequency signals, resulting in higher or lower sea level heights than those expected from known climate modes (e.g., ENSO). Low-level onshore winds and reduced sea level pressure connected to the tropical phenomena are shown to be indicators of increased U.S. coastal sea levels, and vice versa. Two case studies reveal how MJO and ENSO teleconnection interference played a role in notable coastal flooding events. Much of the focus on sea level rise concerns the long-term trend associated with anthropogenic warming, but on shorter time scales, we find subseasonal climate variability has the potential to exacerbate the regional coastal flooding impacts.

Wave contributions to sea levels along the coast of northern South China Sea over 2002–2022

To better understand the wave contribution to coastal sea level variation in the northern South China Sea (SCS), the total sea level time series, which is estimated as the sum of waves, tides, atmospheric surges and altimetric sea levels, over the period of 2002–2022 are used in this study. It is found that tides and waves are two dominate contributors to coastal sea level changes at seasonal (45.7 % and 40.8 %) and interannual (58.6 % and 28.4 %) time scales. The sea level trend is dominated by the altimetric sea levels, but waves can also influence the trends in the Taiwan Strait and Beibu Gulf. The amount of sea level rise that doubles the frequency of the former 50-year return level is analyzed by using the Generalized Extreme Value Distribution (GEVD) model. The results show that the amount of sea level rise is closely related to the amplitude and variance of extreme sea levels. Because waves can significantly increase probability of occurrence of exceedingly large extreme sea levels, the amount of sea level rise (∼1 m) that doubles the coastal flooding frequency is much greater than that (∼10 cm) without the wave contribution. This result demonstrates the important role of waves in changing the coastal flooding frequency.

A Case Study of Green Infrastructure Training in Delaware

Despite increased funding and demonstrated need, green infrastructure projects are not being constructed at the scale or pace needed to address coastal pollution, flooding, and sea level rise in Delaware (Barnes et al., 2021). To address this need, in 2019, Delaware Sea Grant formed a collaborative partnership with Delaware Technical Community College, the state’s open-​admission institution of higher education, to provide workforce training for students and early career professionals.

Interannual Sea Level Variability along the U.S. East Coast during the Satellite Altimetry Era: Local versus Remote Forcing

Abstract The contributions of local and remote forcings to the interannual sea level anomalies (SLAs) along the U.S. East Coast (USEC) during the satellite altimetry era from 1993 to 2019 are quantified with analytical models assisted by statistical methods. The local forcings from alongshore wind stress, sea level pressure via inverted barometer (IB) effect, and river discharges together explain 47%, 60.4%, and 66.8% of coastal sea level variance in the South Atlantic Bight (SAB), Mid-Atlantic Bight (MAB), and Gulf of Maine (GOM), respectively, with river discharges having the minimum contribution. Over a longer period of 1960–2019, the contribution of local forcings reduces significantly, with the IB effect having the minimum contribution. The remote forcings associated with open-ocean signals from the east and from the northern boundary at the Scotian coast together with the Gulf Stream (GS) variability explain 45.7%, 28.5%, and 37.7% of coastal sea level variance in the SAB, MAB, and GOM, respectively, playing a role comparable to that of local forcings in the SAB. The open-ocean sea level signals from 35° to 38°N strongly influence coastal SLAs in the SAB. The coastal SLAs in the SAB are also affected by the upstream GS strength (28°–36°N) and basin-scale wind stress curl anomaly, which is linked to the meridional shift in the downstream GS (74°–68°W). Remote forcings from the subpolar North Atlantic and wind stress curl from the Grand Banks to the Scotian coast influence coastal SLAs in the GOM and MAB via the northern boundary of the USEC at the Scotian coast.

Delayed-mode reprocessing of in situ sea level data for the Copernicus Marine Service

Abstract. The number of tide gauges providing coastal sea level data has significantly increased in recent decades. They help in the issue of coastal hazard warnings, in the forecasting (indirectly through models) of storm surges and tsunamis, and in operational oceanography applications. These data are automatically quality controlled in near-real time in the Copernicus Marine Service. A new initiative seeks to provide delayed-mode reprocessed data for the Copernicus Marine Service by developing a new product and upgrading the software used in its automated quality control. Several new modules, such as buddy checking or the detection of attenuated data, are implemented. The new product was launched in November of 2022. The entire reprocessing is discussed in detail. An example of the information that can be extracted from the delayed-mode reprocessed product is also given.

Offsets in tide-gauge reference levels detected by satellite altimetry: ten case studies

Comparing measurements of absolute sea level by satellite altimetry and relative sea level by a tide gauge can reveal errors in either measurement system. Combining the measurements can determine vertical land motion (VLM) at the tide gauge. We here discuss ten case studies in which a tide gauge has likely experienced a small (≤10\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\le 10$$\\end{document} cm), discontinuous offset in the vertical, suggesting inadvertent loss of reference-level stability. Proper interpretation of offsets is helped if independent VLM measurements from nearby geodetic stations are available. In two cases, earthquake-induced VLM cannot be ruled out, although it appears unlikely. Offsets as small as 1–2 cm can be detected when both altimeter and tide gauge successfully observe the same ocean signal. This is most likely to occur for tide gauges located on small, open-ocean islands. Tide gauges near large land masses are typically more challenging owing to inadequacies of satellite altimetry near land and to differences between coastal and open-ocean sea levels. The case studies highlight the utility of satellite altimetry for tide-gauge quality control.

Sea-level trends and variability along the coast of Vietnam over 2002–2018: Insights from the X-TRACK/ALES altimetry dataset and coastal tide gauges

The changes in coastal sea levels are now considered a significant concern for densely-populated coastal regions such as Vietnam, which hosts a long coastline and two large deltaic areas. In this study, we used high-resolution (20-Hz) altimetry data from the X-TRACK/ALES product to investigate the trends and variability of sea-level anomalies (SLAs) along the Vietnam coast from 2002 to 2018. We conducted comparisons of SLAs from X-TRACK/ALES with SLAs from four coastal tide gauges, and the results present a good root mean square error (0.03 m on average) and good statistically significant correlation (for p < 0.05) with an average value of 0.66. There is an exception for the Quy Nhon site (r ∼ 0.5) as its closest altimetry points lie in the open ocean. Regarding trend calculations, the tide gauge sites exhibit two-to-three times larger trends than altimetry points, indicating a significant deviation from the coast to the open ocean. We then examined the contribution of various forcing factors by stepwise regression analysis for the 2002 – 2018 and 2008–2018 periods. The stepwise model can explain the observed data in the latter period (about 63 % on average). As local factors, SST and meridional wind stress appear important, whereas PDO and ENSO are significant as remote factors, particularly at the southern sites. However, we could not find the best common forcing factors for all sites suggesting the inconsistent mechanisms causing sea-level variability along the Vietnam coast. Our study demonstrates complicated regional sea-level variability and emphasizes the benefit of high-resolution altimetry data in studying dynamic coastal regions.

Dairy farming exposure and impacts from coastal flooding and sea level rise in Aotearoa-New Zealand

Globally, episodic coastal flooding is expected to have increasingly severe impacts on agriculture in low-lying coastal areas, as climate change continues to cause relative sea level rise (RSLR). This study analyses dairy farm exposure and impacts from extreme sea levels (ESL) and RSLR in Aotearoa-New Zealand (A-NZ). Spatio-temporal modelling is undertaken using: 1) a dairy production land layer; 2) a static coastal inundation model from 10, 100, 200 and 500-year annual recurrence interval (ARI) ESL events at 0–2 m RSLR (0.5 m increments); and 3) an Impact State (IS) scheme relating percentage of farmland inundated and depth of flooding at milking shed locations to categorise the severity of damage. Through this analysis we highlight the increasing exposure of the dairy industry to coastal flooding, with 472 farms potentially impacted (at or greater than IS 1) by a 10-year ARI event and 1276 farms exposed to a 500-year ARI event at current sea levels, rising to 1276 (10-year ARI) and 1344 farms (500-year ARI) with 2 m RSLR. RSLR is identified as the factor driving this increase in exposure and severity of impacts to dairying, with the increase in the number of farms impacted in a 500-year compared to 10-year event only 5 % greater when considered with 1 m of RSLR, compared to 37 % greater at 0 m RSLR. This has significant implications for A-NZ where the dairy industry is of high economic and social importance, demonstrating the need for industry targeted climate change adaptation and disaster risk reduction measures.

Combined Coastal Sea Level Estimation Considering Astronomical Tide and Storm Surge Effects: Model Development and Its Application in Thermaikos Gulf, Greece

Tide gauge recordings furnish the longest and almost the most continuous data source of sea level monitoring. Traditionally, they are collected using tide gauge instrumentation fixed at seaport locations to provide a time series of sea level estimates relative to a local geodetic benchmark. Sea level tidal observables are distinguished in the astronomical tide component originating from the attraction of the Earth–Moon–Sun gravitational system, and the storm surges ought to have meteorological effects due to wind and atmospheric air pressure variation. This study provides a comprehensive methodological approach and software to compute sea level considering astronomical tides enhanced by storm surge effects. The model is realized and assessed using a long-standing set of 21 consecutive years of tidal and meteorological measurements originating from Thermaikos Gulf, Greece. Analyses show model verification and conclusions about the tidal behavior of the test area, suggesting a satisfactory agreement (86% Willmott Skill factor, 9 cm standard deviation) between predicted and observed sea level estimates, accounting for amplitude and the time shift of skew surges.

MULTI-HAZARD RISK ASSESSMENT FOR TONGATAPU – A COASTAL INUNDATION LENS

A multi-hazard disaster risk assessment was undertaken for Tongatapu through the Asian Development Bank (ADB) on behalf of the Government of Tonga. This was to inform investments, urban planning and improvements to natural hazard resilience across the island (ADB, 2021). This paper presents the methodology and findings of the coastal inundation and sea level rise components and how these relate to other hazards assessed and the overarching risk assessment. Due to its low elevation and flat topography, Tongatapu, and the Tongan capital of Nukualofa, are vulnerable to pluvial (surface) flooding associated with heavy rainfall and coastal flooding from extreme sea levels and cyclone induced storm surge. Similarly, Tongatapu is vulnerable to damaging winds associated with tropical cyclones, earthquakes particularly associated with the nearby Kermadec Tonga Trench, and tsunami inundation. The study assessed these hazards and considered the influence of climate change on intensity of rainfall and sea levels.

Assessment and exploitation of coastal low resolution mode sea level data from CryoSat-2 on the entrance to the Gulf of California

The CryoSat-2 mission (CS2), initially conceived for sea ice measurements, is also useful for sea level monitoring in oceanic and coastal areas. Only specific regions have two high resolution modes (SAR Delay/Doppler and SAR-Interferometric modes), while the rest of the areas are measured in low-resolution mode (LRM). The entrance to the Gulf of California presents this mode of operation. Sea Level Anomalies (SLA) obtained from CS2 are compared with tide gauges at three locations, Cabo San Lucas (CSL) south of the Baja California peninsula, Mazatlán (MZ) and San Blas (SB) on the continental margin. The comparison shows good agreement between SLAs in CSL and MZ, with standard deviations of the differences (SDD) lower than 0.09 m and Pearson’s correlations higher than 0.7 (95% of confidence level). San Blas is in a complex location and with less data, presenting an SDD greater than 0.13 m and a correlation below 0.55. We present the cross-shore seasonal and interannual variability in CSL and MZ using the CS2 SLA time series from 2011 to 2020. The variability shows the presence of events such as El Niño (2015 to early 2016), La Niña (2011) and the warm event of 2014 (nicknamed “the Blob”). Additionally, the residual time series of CS2 obtained after extracting the annual, semi-annual and monthly components, shows the East side (at MZ) is more affected by El Niño/La Niña variability while the West side (at CSL) is more influenced by the Blob/El Niño. Estimated long-term SLA trend at both locations are around 3.1 mm/yr, supporting similar findings by previous studies.

Atlantic meridional overturning circulation increases flood risk along the United States southeast coast

The system of oceanic flows constituting the Atlantic Meridional Overturning Circulation (AMOC) moves heat and other properties to the subpolar North Atlantic, controlling regional climate, weather, sea levels, and ecosystems. Climate models suggest a potential AMOC slowdown towards the end of this century due to anthropogenic forcing, accelerating coastal sea level rise along the western boundary and dramatically increasing flood risk. While direct observations of the AMOC are still too short to infer long-term trends, we show here that the AMOC-induced changes in gyre-scale heat content, superimposed on the global mean sea level rise, are already influencing the frequency of floods along the United States southeastern seaboard. We find that ocean heat convergence, being the primary driver for interannual sea level changes in the subtropical North Atlantic, has led to an exceptional gyre-scale warming and associated dynamic sea level rise since 2010, accounting for 30-50% of flood days in 2015-2020.

Nonstationary Roles of Regional Forcings in Driving Low‐Frequency Sea Level Variability Along the U.S. East Coast Since the 1950s

AbstractThe nonstationary roles of regional forcings from alongshore wind stress and sea level pressure (SLP) in driving low‐frequency (interannual‐to‐decadal) sea level variability along the U.S. east coast for the 1959–2020 period are investigated. The role of regional forcings increases with time north of Cape Hatteras particularly during summer when their contributions to the variance of observed summertime coastal sea level anomalies increase by approximately 58%–87% from 1959–1989 to 1990–2020. The enhanced impact of regional forcings in recent decades results from an increase in the Inverted Barometer (IB) effect that act constructively with alongshore wind stress especially during summer, and to a lesser extent for the Gulf of Maine during fall. The summertime North Atlantic Oscillation (NAO) is largely responsible for the increased IB effect, owing to the stronger NAO‐associated low SLP anomalies centered around the Mid‐Atlantic Bight in recent decades compared to earlier decades.

Statistical Connections between Large-Scale Climate Indices and Observed Mean and Extreme Temperatures in the US from 1948 to 2018

In order to better understand the extent to which global climate variability is linked to the frequency and intensity of heat waves and overall changes in temperature throughout the United States (US), correlations between long-term monthly mean, minimum, and maximum temperatures throughout the contiguous US on the one hand and low-frequency variability of multiple climate indices (CIs) on the other hand are analyzed for the period from 1948 to 2018. The Pearson’s correlation coefficient is used to assess correlation strength, while leave-one-out cross-validation and a bootstrapping technique (p-value) are used to address potential serial and spurious correlations and assess the significance of each correlation. Three parameters defined the sliding windows over which surface temperature and CI values were averaged: window size, lag time between the temperature and CI windows, and the beginning month of the temperature window. A 60-month sliding window size and 0 lag time resulted in the highest correlations overall; beginning months were optimized on an individual site basis. High (r ≥ 0.60) and significant (p-value ≤ 0.05) correlations were identified. The Western Hemisphere Warm Pool (WHWP) and El Niño/Southern Oscillation (ENSO) exhibited the strongest links to temperatures in the western US, tropical Atlantic sea surface temperatures to temperatures in the central US, the WHWP to temperatures throughout much of the eastern US, and atmospheric patterns over the northern Atlantic to temperatures in the Northeast and Southeast. The final results were compared to results from previous studies focused on precipitation and coastal sea levels. Regional consistency was found regarding links between the northern Atlantic and overall weather and coastal sea levels in the Northeast and Southeast as well as on weather in the upper Midwest. Though the MJO and WHWP revealed dominant links with precipitation and temperature, respectively, throughout the West, ENSO revealed consistent links to sea levels and surface temperatures along the West Coast. These results help to focus future research on specific mechanisms of large-scale climate variability linked to US regional climate variability and prediction potential.

Risk-based transportation infrastructure management: An integrated framework and case study in USVI against coastal flood and sea level rise

This paper develops a comprehensive analytical framework for evaluating transportation infrastructure investment strategies for asset management considering the impacts of extreme natural hazards and climate change. We integrate quantitative risk analysis (RA) and economic impact analysis (EIA) into a comprehensive assessment of the benefits and costs of infrastructure maintenance, rehabilitation and reconstruction (MR&R) strategies. Moving beyond this, the framework explicitly incorporates the bidirectional feedback/impact between asset management (in normal situations) and risk management (against extreme conditions). To illustrate the application, the framework is applied to a case study on the roadway transportation system of the United States Virgin Islands (USVI), considering flood risk and the impact of future sea level rise. The case study demonstrates quantitative measures of the agency and user cost, risk, and other economic and environmental impacts under different MR&R, coastal flood and sea level rise scenarios. The framework supports high-level decision-making that transportation agencies face such as project prioritization, resilience planning, and capital planning. It can be generalized to analyze different types of infrastructure and natural hazards.

Extreme Sea Levels and Their Attribution for the Canadian Pacific Coast From a Baroclinic Regional Ocean Model and Tide‐Gauge Data

AbstractThe existing operational storm surge model for the Canadian Pacific coast is barotropic without coupling with tides. Here a baroclinic ocean model, which includes tides, storm surges, intra‐seasonal, seasonal, and interannual variations, is developed to reproduce coastal sea levels in the northeast Pacific from 1993 to 2020. The model results are validated against observations at tide‐gauge sites, demonstrating overall good skills for tides and non‐tidal sea levels. The Gumbel distribution is applied to derive extreme sea levels from hourly sea level anomalies. The model‐based extreme sea levels agree approximately with the observation‐based ones. For the 100‐year return period, modeled total extreme sea levels range from 2.14 m at Victoria Harbour to 4.43 m at Queen Charlotte City, and modeled non‐tidal extreme sea levels from 1.02 m at Bella Bella to 1.78 m at Queen Charlotte City. On average, the model‐based values underestimate the 100‐year return level by 0.18 m for total extreme sea levels and by 0.23 m for non‐tidal extreme sea levels. Both the model‐ and observation‐based results reveal that the storm surge at periods less than 10 d accounts for 60% of the 100‐year non‐tidal extreme sea level, and the intra‐seasonal, seasonal, and interannual variations account for 40% of it. The present study improves coastal sea level modeling and model‐based extreme level estimates. Moreover, this study also demonstrates for the first time that the intra‐seasonal to interannual changes contribute substantially to extreme sea levels and that El Niño can enhance this contribution on the Canadian Pacific coast.

Mapping the impacts of coastal erosion on the heritage assets of Ynys Enlli (Bardsey Island), North Wales, UK

Coastal erosion and sea level rise has become a significant threat to coastal heritage due to climate change. Management bodies are monitoring the risks posed by undertaking studies, ranging from Rapid Coastal Zone Assessments to much larger government and research council funded studies. These studies have incorporated varying techniques and datasets such as environmental sampling, LiDAR, GPS, and UAV surveys. However, these approaches rarely combine study of historic shoreline change with physical susceptibility modeling. This paper presents a combined methodology, utilizing LiDAR and survey data collected by the Climate, Heritage, Environments of Reefs, Islands and Headlands (CHERISH) project, along with historic mapping and aerial photography to produce a risk assessment for the heritage assets located on Ynys Enlli (Bardsey Island), North Wales. By constructing an Historic Erosion Model and an Erosion Susceptibility Model using ESRI’s ArcGIS 10.5.1. with the DSAS Plugin and combining them with the LiDAR-derived spatial extents of archaeological features on the island, this project has shown that using both methodologies alongside each other can create a more complete overview of coastal environment change for the creation of vulnerability indexes.