Extreme Sea Levels Research Articles

Climate change and seaports: hazards, impacts and policies and legislation for adaptation

Seaports are critical for global trade and development but are at risk of climate change-driven damages, operational disruptions and delays with extensive related economic losses. The aim of the present contribution is to (a) provide an overview of the main impacts of climate variability and change (CV&C) on ports; (b) present recent research on trends and projections involving the main climatic factors/hazards affecting global ports; (c) provide an analytical overview of emerging international and regional policies and legislation relevant to port risk assessment and resilience-building under climate change; and (d) consider issues and areas for further action. As shown by projections under different climatic scenarios and timelines, many global ports will increasingly be exposed to significantly growing hazards under increasing CV&C, including extreme sea levels (ESLs), waves, and extreme heat events. Depending on scenario (RCP 4.5 and RCP 8.5) by 2050, 55% to 59% of the 3630 global ports considered could face ESLs in excess of 2 m above the baseline mean sea levels (mean of the 1980–2014 period); by 2100, between 71% and 83% of ports could face ESLs of this magnitude. Ports in most tropical/sub-tropical settings will face the baseline (mean of the 1976 – 2005 period) 1-in-100 year extreme heat every 1 – 5 years, whereas with 3 oC global warming, most global ports (except some in higher latitudes) could experience the baseline 1-in-100 years extreme heat event every 1 – 2 years. A range of policy and legal instruments to support climate change adaptation, resilience-building and disaster risk reduction have been agreed internationally as well as at regional levels. At the EU level, relevant legal obligations and related normative technical guidance aimed at ensuring the climate proofing of new infrastructure are already in place as a matter of supra-national law for 27 EU Member States. These could significantly enhance levels of climate-resilience and preparedness for ports within the EU, as well as for EU funded port projects in other countries, and may serve as useful examples of good practices for other countries. However, further action is needed to advance and accelerate the implementation of effective adaptation measures for ports across regions.

Policy priorities to enable engaged and transformational adaptation on the coast: Learning from practitioner experiences in England

Coastal communities and their environments are facing unprecedented changes, with climate change driving rising global mean sea level, exacerbating extreme sea level events, and increasing hazards. Whilst adaptations to change have been central to coastal life for millennia, climate change brings a speed and intensity of change not previously experienced. Researchers are noting that adaptations are needed that are large scale and systemic with significant changes to lives and livelihoods – Transformational Adaptations – yet there is little evidence of this in practice, and there remains an operationalisation gap between ambitions and actions. This paper uses a qualitative case study method to assess how existing policy may enable and inhibit local stakeholder involvement in transformational adaptation in English coastal flood and erosion risk management. Through twenty interviews with coastal management stakeholders, the capacity for local coastal management stakeholders to initiate transformational adaptation and the perceived involvement of residents are analysed. The results indicate that transformational adaptation remains a distant aspiration in the English coastal management system, with local stakeholders possessing limited capacity to initiate it. The perceived role for residents in adaptation processes is often focused on their being recipients of adaptation interventions, and there are a range of barriers to their further involvement. The paper concludes that despite the theoretical interest in transformational adaptation, there is limited evidence its implementation in English coastal flood and erosion risk management, and there are multiple priority areas for policy development to support capacity for engaged transformational adaptation practices in coastal management contexts.

A systemic and comprehensive assessment of coastal hazard changes: method and application to France and its overseas territories

Abstract. In the context of climate change, height and frequency variations in extreme sea levels (ESLs) are studied using deterministic and probabilistic approaches. However, this type of approach does not highlight the dynamic effects (waves, currents) generated by metocean events (storms, cyclones, long swells, and tsunamis) beyond their effects on sea levels. In particular, ESL estimates are calculated by considering the main determining physical factors but cannot include all the effects of these factors. Ultimately, this can lead to confusion between ESL and hazard. This article proposes a systemic assessment method to analyze coastal hazard changes at regional scales, integrating parameters influencing sea levels, as well as factors describing the geomorphological context (length and shape of the coast, width of the continental shelf), metocean events, and the marine environment (e.g., coral reef state and sea ice extent). French mainland and overseas territories were selected to apply the method. The present study highlights the need to consider not only the sea level variability, but also the current and future characteristics of metocean events. The long, concave coasts bordered by a wide continental shelf appear particularly sensitive to variations in the intensity or trajectory of metocean events. Coral reef degradation in the tropics and the decrease in seasonal sea ice extent in the polar regions can also significantly change the nearshore hydrodynamics and impacts on the shoreline. These results help us to predict the types of hazard (shoreline erosion, rapid submersion, and/or permanent flooding) that will increase the most in different coastal zones.

The role of wave setup on extreme water levels around Australia

Estimates of extreme sea levels have mainly been derived using atmospheric and tidal forcing only, but surface gravity waves are a key process that can cause a substantial elevation of mean sea level at the coast. In this paper a coupled wave-circulation model was used to simulate storm surge and wave setup across a broad range of coastal topographies and storm types around Australia. The main aim was a practical assessment of the benefits and limitations of using a coupled wave-surge model to determine wave effects for extreme sea level studies on the continental scale. The simulations included: tropical cyclones Yasi (2011) and George (2007) on the northeast and northwest coasts of Australia; Cyclone Alby (1978) that underwent extratropical transition in southwest Australia; and a large extratropical winter storm in the Southern Ocean (2016). Predicted wave setup was highly variable both spatially and temporally, with values up to 0.45 m, 35% of maximum storm surge height, and 9% of incident significant wave heights. In general, where storm surge heights were smaller, the relative importance of wave setup increased in the presence of large waves. The model best resolved wave setup in shallow gently sloping coastal areas, whilst unrealistically low values were predicted for steep coastlines. Predictions improved when wave setup was included for most sites and events, however, these wave effects were often secondary to other assumptions implicit in modeling extreme events. This was especially true for tropical cyclones where reliable wind forcing was not available. The results showed similar contributions from wave setup to other studies but highlighted the high temporal and spatial variability of wave setup across a wider variety of storms and coastal morphologies. The results also revealed that the maximum wave setup did not always coincide with the maximum storm surge. Overall, the coupled wave-surge model presented a useful tool to predict extreme water levels including wave setup when accurate depth and atmospheric data are available, however, significant challenges still exist to model this process at the continental scale.

Climate projections of oceanographic variables in the Exclusive Economic Zone of Ecuador: A 21st century perspective to inform impact and adaptation assessment

Climate projections of ocean variables are essential to inform adaptation strategies and plans involving open and coastal oceanic regions. Assessment of baseline and projections of sea surface temperature (SST), pH, dissolved oxygen (DO), mean sea level (MSL), waves coastal flooding within Ecuador’s Exclusive Economic Zone, including Galapagos Islands are reported herein. With different magnitudes of change, both near-future (2021–2050) and far-future projections (2051–2080) show a statistically robust increase in SST, MSL rise and a reduction in pH, a proxy for acidification. In contrast, DO decrease is only observed in surface (0–100 m) but not in subsurface waters (100–400 m). The likelihood of extreme sea level events in the coastal cities of La Libertad, Manta and Esmeraldas would remain almost unchanged for near-future projections (2026–2045) whereas, for end-of-century projections (2081–2100), historical 1 in a 100-year extreme flooding events would become yearly occurrences. The generated data product offers a state-of-the-art research and management tool for the 21st century under the combined stressors of global climate change. Since the eastern Tropical Pacific Ocean is one of the most productive and biodiverse worldwide due to the equatorial upwelling system, possible impacts on marine biodiversity, social, and economic systems are discussed.

Climate change and healthy ageing: An assessment of the impact of climate hazards on older people.

Climate change not only directly impacts older people's longevity but also healthy ageing, which is the process of maintaining physical and mental capacities while optimising functional abilities. The urgency to address both population ageing and climate change necessitates a rethink and assessment of the impact of climate change on older people. This includes identifying what can be done to anticipate, mitigate and adapt to climate change and engage older persons. A review of climate change and healthy ageing forms the basis of evidence in this report. We developed a comprehensive search to assess current literature, combining terms related to ageing and climate change across four major data sets and assessing articles published up to the end of 2021. We summarised the current and future impact of climate change on older people and developed a framework identifying climate change impacts on older persons, recognising social and environmental determinants of healthy ageing. Major hazards and some key exposure pathways include extreme temperatures, wildfire, drought, flooding, storm and sea level rise, air quality, climate-sensitive infectious diseases, food and water insecurities, health and social care system displacement, migration, and relocation. Strategies to address climate change require interventions to improve systems and infrastructure to reduce vulnerability and increase resilience. As a heterogeneous group, older people's perceptions of climate change should be integrated into climate activism. Increasing climate change literacy among older people and enabling them to promote intergenerational dialogue will drive the development and implementation of equitable solutions. Pathways may operate via direct or indirect exposures, requiring longitudinal studies that enable assessment of exposures and outcomes at multiple time points, and analyses of cumulative impacts of hazards across the life course. The lack of systematic reviews and primary research on the impact of most climate hazards, except for heat, on older people is apparent. Future research should include outcomes beyond mortality and morbidity and assess how older people interact with their environment by focusing on their capacities and optimising abilities for being and doing what they value.

Simulating sea level extremes from synthetic low-pressure systems

Abstract. In this article we present a method for numerical simulations of extreme sea levels using synthetic low-pressure systems as atmospheric forcing. Our simulations can be considered to be estimates of the high sea levels that may be reached when a low-pressure system of high intensity and optimal track passes the studied region. We test the method using sites located along the Baltic Sea coast and simulate synthetic cyclones with various tracks. To model the effects of the cyclone properties on sea level, we simulate internal Baltic Sea water level variations with a numerical two-dimensional hydrodynamic model, forced by an ensemble of time-dependent wind and air-pressure fields from synthetic cyclones. The storm surges caused by the synthetic cyclones come on top of the mean water level of the Baltic Sea, for which we used a fixed upper estimate of 100 cm. We find high extremes in the northern Bothnian Bay and in the eastern Gulf of Finland, where the sea level extreme due to the synthetic cyclone reaches up to 3.5 m. In the event that the mean water level of the Baltic Sea has a maximal value (1 m) during the cyclone, the highest sea levels of 4.5 m could thus be reached. We find our method to be suitable for use in further studies of sea level extremes.

Optimal dynamic climate adaptation pathways: a case study of New York City

AbstractAssessing climate risk and its potential impacts on our cities and economies is of fundamental importance. Extreme weather events, such as hurricanes, floods, and storm surges can lead to catastrophic damages. We propose a flexible approach based on real options analysis and extreme value theory, which enables the selection of optimal adaptation pathways for a portfolio of climate adaptation projects. We model the severity of extreme sea level events using the block maxima approach from extreme value theory, and then develop a real options framework, factoring in climate change, sea level rise uncertainty, and the growth in asset exposure. We then apply the proposed framework to a real-world problem, considering sea level data as well as different adaptation investment options for New York City. Our research can assist governments and policy makers in taking informed decisions about optimal adaptation pathways and more specifically about reducing flood and storm surge risk in a dynamic settings.

Wave setup estimation at regional scale: Empirical and modeling-based multi-approach analysis in the Mediterranean Sea

Wave setup is a physical process that induces a temporal increase of the mean water level due to wave dissipation by bottom friction and breaking in the surf zone, extending over tens to hundreds of meters in the cross-shore direction. Wave setup contribution to coastal sea level solely induced by wind and atmospheric effects can increase by more than 100% under extreme events and conditions favoring its formation. It is therefore crucial to consider this phenomenon when assessing sea-level-related coastal hazards. Previous studies estimated the wave setup effect by means of numerical modeling and empirical formulations at regional and global scale. Such analyses require either high computational capacity to implement high-resolution numerical models over large domains, and/or accurate information on coastal morphological features from global or regional databases. Although the Mediterranean Sea is a fetch-limited environment, waves generated from extra-tropical cyclones are powerful enough for wave setup to develop, and subsequently for a potential significant wave setup contribution to extreme coastal sea level. Through the use of both numerical and empirical methods, we investigate the uncertainty associated to wave setup representation on the frequency and magnitude of coastal extreme sea levels occurring on sandy beaches in the Mediterranean Sea. Wave setup values are compared at beach scale between process-based modeling and empirical approaches, showing highly variable results. We also quantify the impact of wave setup on return levels of coastal sea level extremes using reconstructed sea levels. We employ various methods to calculate the wave setup component. Results show high spatial dispersion, with clear differences between the numerical and empirical approaches, especially in regions prone to the development of energetic waves. The total inter-method dispersion of 100-year return levels is often higher than 30 cm for average values of 62.4 cm. We emphasize the important limitations related to wave setup modeling (i.e., its underestimation) at large scale, and call for caution when applying empirical formulations (generally developed from local studies) at regional to global scale, which can lead to unrealistic wave setup values.

Amplification factors for extreme sea level frequency have problematic features as a metric of coastal hazard

Abstract The future projected frequency of a specified baseline extreme sea level (ESL), often called the amplification factor (AF), is extensively used as a metric of evolving coastal flood hazard with sea level rise (SLR). The baseline ESL is typically analyzed using extreme value analysis, and the SLR is added to the resulting distribution. In the presence of SLR uncertainty, it is natural to analyze AFs probabilistically. I derive probability density functions (PDFs) of AF, given uncertainty distributions of SLR. If the ESL distribution is modeled as Gumbel and the SLR distribution as normal, then the AF distribution is log normal. However, in active tropical cyclone regions, ESL often has a longer tail than Gumbel, and a Frechet (Type-II) Generalized Extreme Value (GEV) is more appropriate. In this case, I show that the AF distribution has a divergent mean, preventing its use as a hazard metric. In addition, I show that for Frechet ESL, the AF cannot even be defined for SLR above a threshold β / ξ f 0 − ξ , where f 0 is the specified baseline frequency (e.g., f 0 = 0.01 yr−1 for the 100-year exceedance), β is the GEV scale parameter and ξ the shape parameter. This SLR threshold can be as low as 0.5 m in the southeast US and Caribbean, within reach mid to late century. Above the threshold, ESL at all frequencies exceeds the baseline reference frequency, preventing the calculation of AF. The resulting probabilistic distribution of AF is insensitive to SLR above the threshold. These features detrimentally impact the utility of AF as a hazard metric. Frechet distributions are appropriate and commonly used for ESL in tropical cyclone regions, but AFs applied to such distributions must interpreted with caution. In such regions, coastal risk managers should consider other flood hazard metrics, such as probabilistic estimates of flood depth.

Tropical Atmospheric Intraseasonal Oscillations Leading to Sea Level Extremes in Coastal Indonesia during Recent Decades

Abstract Coastal flooding induced by sea surface high extreme (HEX) events is an increasing risk to human society and infrastructure as both urban growth in coastal areas and anthropogenic sea level rise continue, especially for island nations like Indonesia. This paper investigates the role of atmospheric intraseasonal oscillations (ISOs), which are dominated by the Madden–Julian oscillation (MJO), in forcing HEXs on the coasts of Indonesia bordering the Indian Ocean. We use satellite altimetry data from 1993 to 2021 and tide gauge observations to detect HEXs, and modeling experiments using both the Regional Ocean Modeling System and a Bayesian dynamic linear model to understand the forcing and processes. We find that HEXs exhibit strong seasonality, with most events occurring during boreal winter (December–February) and spring (March–May) that are dominated by seasonal-to-decadal and intraseasonal variability respectively. In 32% of the 56 HEX events detected, the amplitude of ISO-induced sea level anomalies (SLAs) exceeds that of seasonal-to-decadal SLAs. Surface wind stress associated with atmospheric ISOs is the major forcing for intraseasonal SLAs, and both the remote westerly wind stress from the Indian Ocean equator and northwesterly longshore wind stress at the Indonesian coasts play important roles in driving the HEXs. The MJO is the dominant cause of ISO-dominated HEXs and its impact shows strong seasonal differences. Spring MJOs are associated with stronger convective anomalies over the eastern Indian Ocean equator that drive stronger zonal winds across the equatorial basin that lead to more HEX events compared to winter MJOs when the convection is shifted southward.

Assessing coastal flood risk under extreme events and sea level rise in the Casablanca-Mohammedia coastline (Morocco)

Assessing coastal flood risk under extreme events and sea level rise in the Casablanca-Mohammedia coastline (Morocco)

Sonarlogger: Enabling long-term underwater sonar observations

Coastal seas are under increasing pressure from extreme weather events and sea level rise, resulting in impacts such as changing hydrodynamic conditions, coastal erosion, and marine heat waves. To monitor changes in coastal marine habitats, such as reefs and macrophytes meadows, which add to the resilience of our coasts, consistent, medium- to long-term seafloor observations are needed. This project aims to deliver repeated, high-frequency sonar surveys on a stationary seabed mooring of a specific target area over a period of up to several months. A new stand-alone subsea system, the Sonarlogger, based on a battery pack, low-power logger and a high-resolution scanning sonar, was developed. It allows for long-term deployments with a customisable battery pack, WI-FI download and configurable sleep state. The system has been tested for over 130 days in dynamic coastal environments off the Belgian coast. Combined with auxiliary sensors, such as for measuring currents, waves and turbidity, this system enables comprehensive studies of morphologic changes and changing benthic ecosystems. Moreover, this system has the capacity to provide measurements of coastal environments during storms, where conventional systems may fall short, providing insights into event-based changes of the seafloor.

Variability Assessment of Global Extreme Coastal Sea Levels Using Altimetry Data

This study assesses the variability of coastal extreme sea levels globally by utilizing nearly three decades of along-track, multi-mission satellite altimetry data. An altimetry-based global coastal database of the non-tidal residual sea level component has been produced. The climate variability of extremes is modeled through a parametric, non-stationary statistical model. This model captures intra-annual, inter-annual and long-term variations in non-tidal residual return levels. Comparisons with tide gauge data demonstrate the ability of altimetry data to capture the variability of coastal extreme sea levels. Our findings reveal a greater complexity in the monthly variability patterns of non-tidal residual extremes in tropical latitudes, often exhibiting multiple storm periods, contrasting with coasts in extratropical latitudes, which are mostly controlled by a winter–summer pattern. This study also highlights the significant influence of established climate circulation patterns on sea level extremes. The positive phase of the Arctic Oscillation pattern leads to increases of over 25% in non-tidal residual return levels in Northwestern Europe with respect to a neutral phase. Furthermore, return levels in the western coast of Central America could be 50% higher during El Niño compared to La Niña. Our results show a robust increasing trend in non-tidal residual return levels along most global coastlines. A comparative analysis shows that variations during the 1995–2020 period were primarily driven by intra-annual variations.

The risk of concurrent heatwaves and extreme sea levels along the global coastline is increasing

Concurrent heatwaves and extreme sea levels could pose a serious threat to coastal communities under climate change; however, the spatiotemporal characteristics and dynamic evolution of them along global coastline remain poorly understood. Here, we use reanalysis datasets and model projections to assess historical and future changes in global concurrent heatwaves and extreme sea levels. We find that 87.73% of coastlines experienced such concurrent extremes during 1979–2017. There is an average increase of 3.72 days in the occurrence during 1998–2017 compared to 1979–1998. A one-percentile increase in heatwave intensity is associated with a 2.07% increase in the likelihood of concurrent extremes. Global coastlines are projected to experience 38 days of concurrent extremes each year during 2025–2049 under the highest emission scenario. The weakening of geopotential height associated with a surface low-pressure system may serve as an important indicator for the occurrence of extreme sea levels during heatwaves.

Coastal Restoration Challenges and Strategies for Small Island Developing States in the Face of Sea Level Rise and Climate Change

The climate crisis poses a grave threat to numerous small island developing states (SIDS), intensifying risks from extreme weather events and sea level rise (SLR). This vulnerability heightens the dangers of coastal erosion, chronic water quality degradation, and dwindling coastal resources, demanding global attention. The resultant loss of ecological persistence, functional services, and ecosystem resilience jeopardizes protection against wave action and SLR, endangering coastal habitats’ economic value, food security, infrastructure, and livelihoods. Implementing integrated strategies is imperative. A thorough discussion of available strategies and best management practices for coastal ecosystem restoration is presented in the context of SIDS needs, threats, and major constraints. Solutions must encompass enhanced green infrastructure restoration (coral reefs, seagrass meadows, mangroves/wetlands, urban shorelines), sustainable development practices, circular economy principles, and the adoption of ecological restoration policies. This requires securing creative and sustainable funding, promoting green job creation, and fostering local stakeholder engagement. Tailored to each island’s reality, solutions must overcome numerous socio-economic, logistical, and political obstacles. Despite challenges, timely opportunities exist for coastal habitat restoration and climate change adaptation policies. Integrated strategies spanning disciplines and stakeholders necessitate significant political will.

A framework to evaluate the impact of a hazard chain and geographical covariates on spatial extreme water levels: A case study in the Pearl River Delta

The interactions and collective impacts of different types of hazards within a compound hazard system, along with the influence of geographical covariates on flooding are presently unclear. Understanding these relationships is crucial for comprehending the formation and dynamic processes of the hazard chain and improving the ability to identify flood warning signals in complex hazard scenarios. In this study, we presented a multivariate spatial extreme value hierarchical (MSEVH) framework to assess the spatial extreme water levels (EWL) at different return levels under the influence of a hazard chain and geographical covariates. The Pearl River Delta (PRD) was selected as a research example to assess the effectiveness of the MSEVH framework. Firstly, we identified a hazard chain (extreme streamflow from the Xijiang River (XR) - extreme streamflow from the Beijiang River (BR) - extreme sea level) and three geographical covariates influencing EWL in the PRD. Then, we compared four hazard scenarios in the MSEVH framework to evaluate the spatial EWL at different return levels under the influence of the hazard chain in the PRD. The final step involves assessing spatial EWL with the effect of the hazard chain and geographical covariates. The results indicate that when extreme streamflow from XR and BR occurs concurrently, the extreme streamflow from BR weakens the influence of extreme streamflow from XR on EWL in the PRD. However, it cannot fully offset the overall impact of extreme streamflow from XR on EWL. In addition, when extreme streamflow from XR, extreme streamflow from BR, and extreme sea level occur simultaneously, the extreme sea level enhances the influence of concurrent extreme streamflow from XR and BR on EWL in the PRD. The proposed MSEVH is not only applicable to the PRD but also shows promising potential for evaluating extreme hydrometeorological variables under the influence of other hazard chains.

Thresholds for estuarine compound flooding using a combined hydrodynamic–statistical modelling approach

Abstract. Estuarine compound flooding can happen when extreme sea level and river discharges occur concurrently, or in close succession, inundating low-lying coastal regions. Such events are hard to predict and amplify the hazard. Recent UK storms, including Storm Desmond (2015) and Ciara (2020), have highlighted the vulnerability of mountainous Atlantic-facing catchments to the impacts of compound flooding including risk to life and short- and long-term socio-economic damages. To improve prediction and early warning of compound flooding, combined sea and river thresholds need to be established. In this study, observational data and numerical modelling were used to reconstruct the historic flood record of an estuary particularly vulnerable to compound flooding (Conwy, North Wales). The record was used to develop a method for identifying combined sea level and river discharge thresholds for flooding using idealised simulations and joint-probability analyses. The results show how flooding extent responds to increasing total water level and river discharge, with notable amplification in flood extent due to the compounding drivers in some circumstances, and sensitivity (∼ 7 %) due to a 3 h time lag between the drivers. The influence of storm surge magnitude (as a component of total water level) on the flooding extent was only important for scenarios with minor flooding. There was variability as to when and where compound flooding occurred; it was most likely under moderate sea and river conditions (e.g. 60th–70th and 30th–50th percentiles) and only in the middle-estuary zone. For such cases, joint-probability analysis is important for establishing compound flood risk behaviour. Elsewhere in the estuary, either the sea state (lower estuary) or river flow (upper estuary) dominated the hazard, and single-value probability analysis is sufficient. These methods can be applied to estuaries worldwide to identify site-specific thresholds for flooding to support emergency response and long-term coastal management plans.

Nonlinear Interactions of Sea‐Level Rise and Storm Tide Alter Extreme Coastal Water Levels: How and Why?

AbstractSea‐level rise (SLR) increasingly threatens coastal communities around the world. However, not all coastal communities are equally threatened, and realistic estimation of hazard is difficult. Understanding SLR impacts on extreme sea level is challenging due to interactions between multiple tidal and non‐tidal flood drivers. We here use global hourly tidal data to show how and why tides and surges interact with mean sea level (MSL) fluctuations. At most locations around the world, the amplitude of at least one tidal constituent and/or amplitude of non‐tidal residual have changed in response to MSL variation over the past few decades. In 37% of studied locations, “Potential Maximum Storm Tide” (PMST), a proxy for extreme sea level dynamics, co‐varies with MSL variations. Over all stations, the median PMST will be 20% larger by the mid‐century, and conventional approaches that simply shift the current storm tide regime up at the rate of projected SLR may underestimate the flooding hazard at these locations by up to a factor of four. Micro‐ and meso‐tidal systems and those with diurnal tidal regime are generally more susceptible to altered MSL than other categories. The nonlinear interactions of MSL and storm tide captured in PMST statistics contribute, along with projected SLR, to the estimated increase in flood hazard at three‐fourth of studied locations by mid‐21st century. PMST is a threshold that captures nonlinear interactions between extreme sea level components and their co‐evolution over time. Thus, use of this statistic can help direct assessment and design of critical coastal infrastructure.

The Impact of Serial Cyclone Clustering on Extremely High Sea Levels in the Baltic Sea

AbstractIn the Baltic Sea, sea level variations are often very pronounced. During the winter season, storm surges caused by strong extratropical cyclones (ETCs) can have major societal impacts on coastal cities. In this study, using reanalysis‐based cyclone tracks and in‐situ tide gauge records, we show that serial cyclone clustering (SCC) leads to higher sea levels in the Baltic Sea than situations where only one ETC passes the tide gauge. Consequently, almost half of extreme sea level events in the Baltic Sea are associated with cyclone clustering periods. For example, in Helsinki, 45% of the extreme sea level events coincided with SCC periods of three or more ETCs, while only 6% of the events coincided with a single ETC. Our study represents a significant advance in the understanding of the factors influencing sea level variations in the Baltic Sea.