Sea Level Rise Scenarios Research Articles

Migration, land loss and costs to 2100 due to coastal flooding under the IPCC AR6 sea-level rise scenarios and plausible adaptation choices

Sea-level rise (SLR) through the twenty-first century and beyond is inevitable, threatening coastal areas and their inhabitants unless there is appropriate adaptation. We investigate coastal flooding to 2100 under the full range of IPCC AR6 (2021) SLR scenarios, assuming plausible adaptation. The adaptation selects the most economically robust adaptation option: protection or retreat. People living in unprotected coastal areas that are frequently inundated (below 1-in-1-year flood level) are assumed to migrate, and the land is considered lost. Globally, across the range of SLR and related socioeconomic scenarios, we estimate between 4 million and 72 million people could migrate over the twenty-first century, with a net land loss ranging from 2,800 to 490,000 km2. India and Vietnam consistently show the highest absolute migration, while Small Island Developing States are the most affected when considering relative migration and land loss. Protection is the most robust adaptation option under all scenarios for 2.8% of the global coastline, but this safeguards 78% of the global population and 91% of assets in coastal areas. Climate stabilisation (SSP1–1.9 and SSP1–2.6) does not avoid all coastal impacts and costs as sea levels still rise albeit more slowly. The impacts and costs are also sensitive to the socioeconomic scenario: SSP3–7.0 experiences higher migration than SSP5–8.5 despite lower SLR, reflecting a larger population and lower GDP. Our findings can inform national and intergovernmental agencies and organisations on the magnitude of SLR impacts and costs and guide assessments of adaptation policies and strategies.

Tidal regime deformation due to sea level rise in the Malacca Strait: its impact on tidal bore generation in macro-tidal estuaries

The significance of this research lies in its contribution to understanding the changes in tidal characteristics in the Malacca Strait due to sea level rise (SLR) and the subsequent impacts on tidal bore generation in macro-tidal estuaries. As sea levels continue to rise, the semidiurnal tidal constituents (M2) in the southern Malacca Strait have shown a notably sensitive response, with an increased amplitude of ∼2 cm and a decreased phase shift of 2 ° over 33 years of field observations. Under future SLR scenarios, models predict that the amplitudes of tidal constituents will further increase by about 6–16% by the year 2100, while the phase will slightly decrease by around 10 ° , leading to a more accelerated tidal cycle. Of particular concern is the fact that the peak water level in the Malacca Strait is expected to rise more rapidly than the SLR itself due to the ‘double’ effect of SLR, which is becoming increasingly pronounced over time. This will lead to a significant rise in tidal bore height by ∼100 cm, with turbulent velocities during bore passages ranging from 1.1 to 1.5 m/s. Such changes increase the risk of local flooding and shoreline erosion. To address the long-term effects of SLR in the study area, it is crucial to regulate the proximity of settlements to riverbanks, manage land use effectively, and construct shoreline protection structures.

Impact of sea level rise on the hydrodynamic regime and sediment distribution in the Dong Nai-Sai Gon River basin of Southern Vietnam

Sea level rise (SLR) significantly impacts morphodynamics, altering hydrodynamics, sediment transport, and riverbed morphology. This study examines these effects in the Dong Nai-Sai Gon River (DNSG) basin, focusing on the Soai Rap River mouth. Using an integrated numerical model (TELEMAC-2D–SISYPHE–TOMAWAC), simulations were conducted under three SLR scenarios: baseline (SCE0), SLR+0.5 m (SCE1), and SLR+1.0 m (SCE2). Results indicate erosion in Zone 1 (upstream), sediment balance in Zone 2 (midstream), and deposition in Zone 3 (estuary and coastal areas). Regression-based linear equations were developed to understand the sediment deposition relationships among the zones under varying SLR conditions. We have discovered new insights into sediment dynamics, providing predictive tools for sustainable sediment management and adaptation to SLR in estuaries. Additionally, this work contributes to understanding regional morphodynamic responses to SLR and informs strategies for managing sediment resources in estuarine systems.

Coastal Marsh Vulnerability to Sea-Level Rise Is Exacerbated by Plant Species Invasion.

Coastal salt marshes and their valuable ecosystem services are vulnerable to degradation due to rising sea levels, to which they can adapt through biogeomorphic feedbacks. However, the invasion of plant species, particularly eco-engineering species that alter these interactions, may degrade the structural integrity and functionality of salt marshes, potentially reducing their resilience to sea-level rise. Such impacts presently remain poorly understood. Focusing on coastal marshes of China, we utilized a coupled biogeomorphic model to explore the effects of Spartina alterniflora invasion versus native Suaeda salsa on coastal geomorphology, considering different sea-level rise and tidal scenarios. Our results revealed that Spartina alterniflora invasion contributed to the formation of a "levee-basin" geomorphological structure at both the landscape scale (from seaward to landward zones) and the local scale (from channel fringes to marsh interiors). This pattern led to a prominent marsh depression, particularly in "basin" areas under microtidal conditions, indicating increased vulnerability to rising sea levels in invaded systems. Additionally, the proliferation of Spartina alterniflora could completely displace Suaeda salsa. Our findings emphasize the importance of controlling plant invasion to safeguard ecosystem resilience to environmental change.

Assessing the potential effects of climate change on the morphodynamics of the tropical coral reef islands in the Gulf of Mannar, Indian Ocean.

Assessing the potential effects of climate change on the morphodynamics of the tropical coral reef islands in the Gulf of Mannar, Indian Ocean.

Calculations of extreme sea level rise scenarios are strongly dependent on ice sheet model resolution

The West Antarctic Ice Sheet (WAIS) is losing ice and its annual contribution to sea level is increasing. The future behaviour of WAIS will impact societies worldwide, yet deep uncertainty remains in the expected rate of ice loss. High-impact low-likelihood scenarios of sea-level rise are needed by risk-averse stakeholders but are particularly difficult to constrain. Here, we combine traditional model simulations of the Amundsen Sea sector of WAIS with Gaussian process emulation to show that ice-sheet models capable of resolving kilometre-scale basal topography will be needed to assess the probability of extreme scenarios of sea-level rise. This resolution exceeds many state-of-the-art continent-scale simulations. Our ice-sheet model simulations show that coarser resolutions tend to project a larger range of sea-level contributions than finer resolutions, inflating the tails of the distribution. We therefore caution against relying purely upon simulations 5 km or coarser when assessing the potential for societally important high-impact sea-level rise.

Assessing the impacts of sea level rise on salinity intrusion in the Kelani River, Sri Lanka

ABSTRACT Salinity intrusion poses a significant threat to water treatment processes, especially in regions near coastal aquifers. This challenge is exacerbated by the ongoing impacts of global climate change. This study employs a three-dimensional numerical model to investigate the variation in the spatial and temporal distribution of salinity in a data-scarce river during the dry season and to predict their performance under sea level rise scenarios for the mid and end of this century, as outlined in the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. The model was validated using measured water levels, discharges, and conductive data. The model findings reveal that, compared to current conditions, the average increase in bottom layer salinity is projected to be 11.8, 4.5, and 13.1% in 2050 and 13.8, 17.4, and 27.5% in 2090 under the environmental scenarios Representative Concentration Pathways (RCP) 2.6, RCP 4.5, and RCP 8.5, respectively. Additionally, the simulated results indicate that a saline front of 1 ppt, which significantly impacts water treatment processes, is expected to intrude further inland by approximately 0.5, 3.5, 8.5, and 11 km for respective sea level rise values of 21, 32, 37, and 48 cm, relative to present conditions.

Eco-geomorphic modelling response of tidal marshes to sea level rise and changes in suspended sediment supply.

Eco-geomorphic modelling response of tidal marshes to sea level rise and changes in suspended sediment supply.

Probabilistic Tsunami Hazard Assessment from Manila Trench to Shantou City in China

Manila Trench is an ocean trench that lies to the west of Luzon Island in the Philippines, which has the potential to generate a significant tsunami that could affect the coastal areas around it. This paper analyzes the tsunami hazard at the southern coastline of China, and more specifically at the city of Shantou. A Monte Carlo-type probabilistic tsunami hazard assessment (PTHA) with 5000 simulation runs was conducted using the tsunami propagation model COMCOT. A wide range of earthquake magnitudes were stochastically simulated in these zones, ranging from 7.0 to 9.0 in magnitude, and the peak nearshore tsunami amplitude (PNTA), for return periods of 100, 1,000 and 10,000 years, was determined by propagation simulations to be 0.15 m, 0.65 m and 1.75 m, respectively. Inundation simulations for the case study area, which considered various scenarios of sea level rise between the present day and the year 2100, were also conducted. The results indicate the severe influence that sea level rise could have on tsunami risks, which can provide valuable information for disaster risk managers and planners on how to develop adaptation pathways not only for this city but also for other points in the southeast coastline of China.

High-resolution simulation of coastal flooding under extreme storm tides and sea level rise: A case study of Macau

In the face of climate change, coastal cities are challenged with growing risks from rising sea levels and intensified storm surges which could turn urban areas into temporary waterways. To address this, our study developed a high-resolution coastal urban flood model, OUC-CUFM (Ocean University of China – Coastal Urban Flood Model), designed to help municipal governments make precise coastal flood forecasts and reduce potential threats to people and property. This model is based on two-dimensional nonlinear Navier–Stokes shallow water equations, incorporating factors like local acceleration, convection, bottom friction, wind stress, and shallow water effects. Using the finite difference method with upwind spatial discretization and a leapfrog time scheme, it can simulate detailed street-level water flow interactions with buildings. In a case study on Macau, we used a 5-m resolution digital elevation model to simulate storm tide flooding from Typhoons Hato (2017) and Mangkhut (2018), with the former for model calibration and the later for validation. Comparisons between simulated and observed water levels showed that the model accurately captured storm water arrival, overtopping, and flood extent and depth. The model also projected flood changes under sea level rise (SLR) scenarios of 0.5 m (by 2070) and 1.0 m (by 2100) for Typhoon Hato, indicating that such SLRs would significantly increase storm-induced flood depth and extent. This model serves as a valuable tool for street-scale flood risk analysis, hazard mapping, and assessing the impact of coastal defenses, like dyke upgrades or new dyke construction, in densely built coastal cities.

Evaluating the feasibility of coastal protection scenarios on a city scale across plausible pathways scenarios for both sea level rise and urban development

Coastal flood risk accelerates rapidly due to rising sea levels and urban expansion in low-lying areas. Many strategies based on the widespread application of hard protection have been developed. However, the implementation of such measures has raised concerns due to their environmental impact, high costs, and a potential increase in exposure.This study focuses on the economic implications of coastal flood protection at the local level, examining impacts on small to medium-sized cities, which reflects many coastal communities around the world. We introduce a framework for assessing the economic burden or benefit of flood protection strategies on local communities and municipalities. We derive standardized values for protection costs, flood risk, and socioeconomic development for typical coastal topologies, i.e., the data usually used for cost-benefit analyses of coastal protection.Based on two illustrative examples of coastal cities in different topographies, we demonstrate that cost-effective protection strategies can lead to lock-in situations because their implementation cost likely exceeds local willingness to pay, and we argue that this risk needs to be considered when designing flood adaptation pathways.

Assessing the vulnerability of Cape Coral, Florida, to sea level rise using principal component analysis (2020–2050)

Assessing the vulnerability of Cape Coral, Florida, to sea level rise using principal component analysis (2020–2050)

An Assessment of the Tipping Point Behavior for Shoreline Retreat: A PCR Model Application at Vung Tau Beach, Vietnam

Storm waves and rising sea levels pose significant threats to low-lying coastal areas, particularly sandy beaches, which are especially vulnerable. The research on the long-time-scale changes in sandy coasts, especially the identification of tipping points in the shoreline-retreat rate, is limited. Vung Tau beach, characterized by its low terrain and rapid tourism-driven economic growth, was selected as a typical study area to quantify the shoreline retreat throughout the 21st century under various sea-level rise (SLR) scenarios, and to identify the existence of tipping points by investigating the projected annual change in shoreline retreat (m/yr). This study employs the Probabilistic Coastline Recession (PCR) model, a physics-based tool specifically designed for long-term coastline change assessments. The results indicate that shoreline retreat accelerates over time, particularly after a tipping point is reached around 2050 in the SSP1-2.6, SSP2-4.5, and SSP5-8.5 scenarios. Under the SSP5-8.5 scenario, the median retreat distance is projected to increase from 19 m in 2050 to 89 m by 2100, nearly a fourfold rise. In comparison, the retreat distances are smaller under the SSP1-2.6 and SSP2-4.5 scenarios, but the same accelerating trend is observed beyond 2050. These findings highlight the growing risks associated with sea-level rise, especially the rapid increase in exceedance probabilities for retreat distances by the end of the century. By 2100, the probability of losing the entire beach at Vung Tau is projected to be 22% under SSP5-8.5. The approach of identifying tipping points based on the PCR model presented here can be applied to other sandy coastal regions, providing critical references for timely planning and the implementation of adaptation measures.

Salt marsh litter decomposition varies more by litter type than by extent of sea-level inundation

Salt marshes are among the most efficient blue carbon sinks worldwide. The fate of this carbon is uncertain due to limited knowledge about organic matter (OM) decomposition processes under sea-level rise. In an in-situ manipulative experiment, we compared salt marsh OM decomposition and quality across simulated sea-level scenarios (by modifying the inundation) and litter types (absorptive root, fine transportive root, leaves, and rhizomes of Halimione portulacoide) for 170 days. The litter decomposition varied only between the inundation treatments with the longest and shortest durations, while the decomposition differed significantly across litter types, with absorptive roots releasing up to 40% less carbon than other litters. Changes in lignin composition were minimal for absorptive roots and were unaffected by sea-level rise scenarios. Our study suggests that (i) current projections of sea-level rise are unlikely to decrease litter decomposition; (ii) separating litter types might lead to better assessments of salt marshes’ OM dynamics.

Assessment of coastal flood risk scenarios on infrastructure in the Keta municipality in Ghana using a GIS approach

Assessment of coastal flood risk scenarios on infrastructure in the Keta municipality in Ghana using a GIS approach

Assessment of tangible coastal inundation damage related to critical infrastructure and buildings: The case of Mauritius Island

Assessment of tangible coastal inundation damage related to critical infrastructure and buildings: The case of Mauritius Island

Distributional justice and climate risk assessment: An analysis of disparities within direct and indirect risk.

Climate change and natural hazard risk assessments often overlook indirect impacts, leading to a limited understanding of the full extent of risk and the disparities in its distribution across populations. This study investigates distributional justice in natural hazard impacts, exploring its critical implications for environmental justice, equity, and resilience in adaptation planning. We employ high-resolution spatial risk assessment and origin-destination routing to analyze coastal flooding and sea-level rise scenarios in Aotearoa New Zealand. This approach allows the assessment of both direct impacts (property exposure) and indirect impacts (physical isolation from key amenities) on residents. Indirect impacts, such as isolation and reduced access to resources, have significant adverse effects on well-being, social cohesion, and community resilience. Including indirect impacts in risk assessments dramatically increases the overall population burden, while revealing complex effects on existing inequalities. Our analysis reveals that including indirect impacts increases the overall population burden, but the effect on inequalities varies. These inequalities can be exacerbated or attenuated depending on scale and location, underscoring the need for decision-makers to identify these nuanced distributions and apply context-specific frameworks when determining equitable outcomes. Our findings uncover a substantial number of previously invisible at-risk residents-from 61,000 to 217,000 nationally in a present-day event-and expose a shift in impact distribution toward underserved communities. As indirect risks exacerbate disparities and impede climate adaptation efforts, adopting an inclusive approach that accounts for both direct and indirect risks and their [un]equal distribution is imperative for effective and equitabledecision-making.

Applying portfolio theory to benefit endangered amphibians in coastal wetlands threatened by climate change, high uncertainty, and significant investment risk

The challenge of selecting strategies to adapt to climate change is complicated by the presence of irreducible uncertainties regarding future conditions. Decisions regarding long-term investments in conservation actions contain significant risk of failure due to these inherent uncertainties. To address this challenge, decision makers need an arsenal of sophisticated but practical tools to help guide spatial conservation strategies. Theory asserts that managing risks can be achieved by diversifying an investment portfolio to include assets – such as stocks and bonds – that respond inversely to one another under a given set of conditions. We demonstrate an approach for formalizing the diversification of conservation assets (land parcels) and actions (restoration, species reintroductions) by using correlation structure to quantify the degree of risk for any proposed management investment. We illustrate a framework for identifying future habitat refugia by integrating species distribution modeling, scenarios of climate change and sea level rise, and impacts to critical habitat. Using the plains coqui (Eleutherodactylus juanariveroi), an endangered amphibian known from only three small wetland populations on Puerto Rico’s coastal plains, we evaluate the distribution of potential refugia under two model parameterizations and four future sea-level rise scenarios. We then apply portfolio theory using two distinct objective functions and eight budget levels to inform investment strategies for mitigating risk and increasing species persistence probability. Models project scenario-specific declines in coastal freshwater wetlands from 2% to nearly 30% and concurrent expansions of transitional marsh and estuarine open water. Conditional on the scenario, island-wide species distribution is predicted to contract by 25% to 90%. Optimal portfolios under the first objective function – benefit maximization – emphasizes translocating frogs to existing protected areas rather than investing in the protection of new habitat. Alternatively, optimal strategies using the second objective function – a risk-benefit tradeoff framework – include significant investment to protect parcels for the purpose of reintroduction or establishing new populations. These findings suggest that leveraging existing protected areas for species persistence, while less costly, may contain excessive risk and could result in diminished conservation benefits. Although our modeling includes numerous assumptions and simplifications, we believe this framework provides useful inference for exploring resource dynamics and developing robust adaptation strategies using an approach that is generalizable to other conservation problems which are spatial or portfolio in nature and subject to unresolvable uncertainty.

Future Shorelines: A Living Shoreline Site Selection and Design Decision Support Tool that Incorporates Future Conditions Induced by Sea Level Rise

Most living shoreline site selection and design decision support tools are based upon existing environmental conditions. We developed a web-based, geospatial tool called Future Shorelines that integrates high-resolution landscape elevation data and a matrix of locally derived NOAA Interagency Sea Level Rise Scenarios to characterize future conditions of submergence and shoreline translation induced by sea level rise. Once the practitioner selects a location of interest, sea level rise scenario (e.g., high), and target year (e.g., 2050), the tool will generate plan view and cross-sectional informational graphics specific to their choices. This information can then be paired with other menu options, like parcel ownership, to facilitate the planning and construction of nature-based shoreline stabilization solutions that (1) are located where opportunities for horizontal migration are optimized, (2) remain accessible for monitoring and maintenance, and (3) perform as intended over the design life of the installation. The tool’s menu options and the user interface were informed by project partner input solicited during numerous workshops convened over the duration of the 2-year project. This coproduction created a product that was familiar to the end user and therefore increased the likelihood that it would be utilized by them during the planning and design of living shoreline projects. Although developed for use in the Indian River Lagoon, located along the east-central Florida coast, it can be seamlessly replicated for application in other coastal regions of the USA where the requisite data are available.

Urban Vulnerability Assessment of Sea Level Rise in Singapore through the World Avatar

This paper explores the application of The World Avatar (TWA) dynamic knowledge graph to connect isolated data and assess the impact of rising sea levels in Singapore. Current sea level rise vulnerability assessment tools are often regional, narrow in scope (e.g., economic or cultural aspects only), and are inadequate in representing complex non-geospatial data consistently. We apply TWA to conduct a multi-perspective impact assessment of sea level rise in Singapore, evaluating vulnerable buildings, road networks, land plots, cultural sites, and populations. We introduce OntoSeaLevel, an ontology to describe sea level rise scenarios, and its impact on broader elements defined in other ontologies such as buildings (OntoBuiltEnv ontology), road networks (OpenStreetMap ontology), and land plots (Ontoplot and Ontozoning ontology). We deploy computational agents to synthesise data from government, industry, and other publicly accessible sources, enriching buildings with metadata such as property usage, estimated construction cost, number of floors, and gross floor area. An agent is applied to identify and instantiate the impacted sites using OntoSeaLevel. These sites include vulnerable buildings, land plots, cultural sites, and populations at risk. We showcase these sea level rise vulnerable elements in a unified visualisation, demonstrating TWA’s potential as a planning tool against sea level rise through vulnerability assessment, resource allocation, and integrated spatial planning.