A global analysis of subsidence, relative sea-level change and coastal flood exposure

Climate-induced sea-level rise and vertical land movements, including natural and human-induced subsidence in sedimentary coastal lowlands, combine to change relative sea levels around the world's coast. Global-average coastal relative sea-level rise was 2.5 mm/yr over the last two decades. However, as coastal inhabitants are preferentially located in subsiding locations, they experience an average relative sea-level rise up to four times faster at 7.8 to 9.9 mm/yr. This first global quantification of relative sea-level rise shows that the resulting impacts, and adaptation needs are much higher than reported global sea-level rise measurements would suggest. Hence, coastal subsidence is an important global issue that needs more assessment and action. In particular, human-induced subsidence in and surrounding coastal cities can be rapidly reduced with appropriate policy measures for groundwater utilization and drainage. This offers substantial and rapid benefits in terms of reducing growth of coastal flood exposure due to relative sea-level rise.

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Multiple drivers of extreme sea levels in the northern Adriatic Sea

10.5194/egusphere-egu21-8727 ◽

2021 ◽

Author(s):

Christian Ferrarin ◽

Piero Lionello ◽

Mirko Orlic ◽

Fabio Raicich ◽

Gianfausto Salvadori

Keyword(s):

Sea Level Rise ◽

Sea Level ◽

Adriatic Sea ◽

Driving Factors ◽

Northern Adriatic Sea ◽

Relative Sea Level ◽

Northern Adriatic ◽

Sea Levels ◽

Extreme Sea Levels ◽

Relative Sea Level Rise

Extreme sea levels at the coast result from the combination of astronomical tides with atmospherically forced fluctuations at multiple time scales. Seiches, river floods, waves, inter-annual and inter-decadal dynamics and relative sea-level rise can also contribute to the total sea level. While tides are usually well described and predicted, the effect of the different atmospheric contributions to the sea level and their trends are still not well understood. Meso-scale atmospheric disturbances, synoptic-scale phenomena and planetary atmospheric waves (PAW) act at different temporal and spatial scales and thus generate sea-level disturbances at different frequencies. In this study, we analyze the 1872-2019 sea-level time series in Venice (northern Adriatic Sea, Italy) to investigate the relative role of the different driving factors in the extreme sea levels distribution. The adopted approach consists in 1) isolating the different contributions to the sea level by applying least-squares fitting and Fourier decomposition; 2) performing a multivariate statistical analysis which enables the dependencies among driving factors and their joint probability of occurrence to be described; 3) analyzing temporal changes in extreme sea levels and extrapolating possible future tendencies. The results highlight the fact that the most extreme sea levels are mainly dominated by the non-tidal residual, while the tide plays a secondary role. The non-tidal residual of the extreme sea levels is attributed mostly to PAW surge and storm surge, with the latter component becoming dominant for the most extreme events. The results of temporal evolution analysis confirm previous studies according to which the relative sea-level rise is the major driver of the increase in the frequency of floods in Venice over the last century. However, also long term variability in the storm activity impacted the frequency and intensity of extreme sea levels and have contributed to an increase of floods in Venice during the fall and winter months of the last three decades.

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A global analysis of subsidence, relative sea-level change and coastal flood exposure

Nature Climate Change ◽

10.1038/s41558-021-00993-z ◽

2021 ◽

Author(s):

Robert J. Nicholls ◽

Daniel Lincke ◽

Jochen Hinkel ◽

Sally Brown ◽

Athanasios T. Vafeidis ◽

...

Keyword(s):

Sea Level ◽

Global Analysis ◽

Sea Level Change ◽

Relative Sea Level ◽

Level Change ◽

Coastal Flood ◽

Flood Exposure

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Sedimentation strategies provide effective but limited mitigation of relative sea-level rise in the Mekong delta

Communications Earth & Environment ◽

10.1038/s43247-021-00331-3 ◽

2022 ◽

Vol 3 (1) ◽

Author(s):

Frances E. Dunn ◽

Philip S. J. Minderhoud

Keyword(s):

Sea Level Rise ◽

Sea Level ◽

Anthropogenic Activities ◽

Mekong Delta ◽

Relative Sea Level ◽

Sediment Delivery ◽

Limited Effectiveness ◽

Relative Sea Level Rise ◽

Present Context ◽

Global Sea Level

AbstractThe Mekong delta is experiencing rapid environmental change due to anthropogenic activities causing accelerated subsidence, sea-level rise and sediment starvation. Consequentially, the delta is rapidly losing elevation relative to sea level. Designating specific areas for sedimentation is a suggested strategy to encourage elevation-building with nature in deltas. We combined projections of extraction-induced subsidence, natural compaction and global sea-level rise with new projections of fluvial sediment delivery to evaluate the potential effectiveness of sedimentation strategies in the Mekong delta to 2050. Our results reveal that with current rates of subsidence and sediment starvation, fluvial sediments alone can only preserve elevation locally, even under optimistic assumptions, and organic sedimentation could potentially assume a larger role. While sedimentation strategies alone have limited effectiveness in the present context, combined with enhanced organic matter retention and interventions reducing anthropogenic-accelerated subsidence, they can considerably delay future relative sea-level rise, buying the delta crucial time to adapt.

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Assessment of Sea Level Rise at West Coast of Portugal Mainland and Its Projection for the 21st Century

Journal of Marine Science and Engineering ◽

10.3390/jmse7030061 ◽

2019 ◽

Vol 7 (3) ◽

pp. 61 ◽

Cited By ~ 5

Author(s):

Carlos Antunes

Keyword(s):

Sea Level Rise ◽

Sea Level ◽

21St Century ◽

West Coast ◽

Satellite Altimetry ◽

Tide Gauge ◽

Relative Sea Level ◽

Mean Sea Level ◽

Relative Sea Level Rise ◽

Global Sea Level

Based on the updated relative sea level rise rates, 21st-century projections are made for the west coast of Portugal Mainland. The mean sea level from Cascais tide gauge and North Atlantic satellite altimetry data have been analyzed. Through bootstrapping linear regression and polynomial adjustments, mean sea level time series were used to calculate different empirical projections for sea level rise, by estimating the initial velocity and its corresponding acceleration. The results are consistent with an accelerated sea level rise, showing evidence of a faster rise than previous century estimates. Based on different numerical methods of second order polynomial fitting, it is possible to build a set of projection models of relative sea level rise. Applying the same methods to regional sea level anomaly from satellite altimetry, additional projections are also built with good consistency. Both data sets, tide gauge and satellite altimetry data, enabled the development of an ensemble of projection models. The relative sea level rise projections are crucial for national coastal planning and management since extreme sea level scenarios can potentially cause erosion and flooding. Based on absolute vertical velocities obtained by integrating global sea level models, neo-tectonic studies, and permanent Global Positioning System (GPS) station time series, it is possible to transform relative into absolute sea level rise scenarios, and vice-versa, allowing the generation of absolute sea level rise projection curves and its comparison with already established global projections. The sea level rise observed at the Cascais tide gauge has always shown a significant correlation with global sea level rise observations, evidencing relatively low rates of vertical land velocity and residual synoptic regional dynamic effects. An ensemble of sea level projection models for the 21st century is proposed with its corresponding probability density function, both for relative and absolute sea level rise for the west coast of Portugal Mainland. A mean sea level rise of 1.14 m was obtained for the epoch of 2100, with a likely range of 95% of probability between 0.39 m and 1.89 m.

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Relative sea-level rise during the Main Postglacial Transgression in NE Scotland, U.K.

Transactions of the Royal Society of Edinburgh Earth Sciences ◽

10.1017/s0263593300002480 ◽

1999 ◽

Vol 90 (1) ◽

pp. 1-27 ◽

Cited By ~ 16

Author(s):

D. E. Smith ◽

C. R. Firth ◽

C. L. Brooks ◽

M. Robinson ◽

P. E. F. Collins

Keyword(s):

Sea Level Rise ◽

Sea Level ◽

Sea Level Changes ◽

Relative Sea Level ◽

Sea Levels ◽

Relative Sea Level Rise ◽

The Mean ◽

Run Up ◽

Storegga Slide

AbstractFlandrian (Holocene) relative sea level changes in the lower Ythan valley, NE Scotland, U.K., are inferred from detailed stratigraphical evidence including microfossil analysis and radiocarbon assay. The principal event recorded is the Main Postglacial Transgression, which was under way in the area by c. 8300 and had culminated before c. 4000 radiocarbon years BP. It is concluded that the rise in relative sea levels during the transgression in the area exceeded 12 m; that the mean rate of rise there was 8·05 mm a−1 between c. 8300 and c. 7100 radiocarbon years BP, or 7·09 mm a−1 based upon calibrated dates for the same period, before declining markedly to 1·75 mm a−1 (radiocarbon) or 1·86 mm a−1 (calibrated) to the culmination of the event. By comparison with other sites, the culmination appears to have been time-transgressive in eastern Scotland. Deposits of the Second Storegga Slide tsunami, which occurred during the Main Postglacial Transgression, are present in the Ythan valley, where the sediment run-up of the event at the sites studied is estimated to have been within the range 2·99–5·19 m.

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Quantifying Thresholds of Barrier Geomorphic Change in a Cross-Shore Sediment Partitioning Model

10.5194/esurf-2020-88 ◽

2020 ◽

Author(s):

Daniel J. Ciarletta ◽

Jennifer L. Miselis ◽

Justin L. Shawler ◽

Christopher J. Hein

Keyword(s):

Sea Level Rise ◽

Sea Level ◽

Cross Sections ◽

Sediment Flux ◽

State Transitions ◽

Morphologic Change ◽

Relative Sea Level ◽

Coastal System ◽

Sea Levels ◽

Relative Sea Level Rise

Abstract. Barrier coasts, including barrier islands, beach-ridge plains, and associated landforms, can assume a broad spectrum of morphologies over decadal scales that reflect conditions of sediment availability, accommodation, and relative sea-level rise. However, the quantitative thresholds of these controls on barrier-system behavior remain largely unexplored, even as modern sea-level rise and anthropogenic modification of sediment availability increasingly reshape the world’s sandy coastlines. In this study, we conceptualize barrier coasts as sediment partitioning frameworks, distributing sand delivered from the shoreface to the subaqueous and subaerial components of the coastal system. Using an idealized morphodynamic model, we explore thresholds of behavioral/morphologic change over decadal to centennial timescales, simulating barrier evolution within quasi-stratigraphic morphological cross-sections. Our results indicate a wide diversity of barrier behaviors can be explained by the balance of fluxes delivered to the beach versus the dune/backbarrier, including previously understudied forms of transgression that allow the subaerial system to continue accumulating sediment during landward migration. Most importantly, our results show that barrier state transitions between progradation, cross-shore amalgamation, aggradation, and transgression are controlled largely through balances within a narrow range of relative sea-level rise and sediment flux. This suggests that, in the face of rising sea levels, subtle changes in sediment fluxes could result in significant changes in barrier morphology. We also demonstrate that modeled barriers with reduced vertical sediment accommodation are highly sensitive to the magnitude and direction of shoreface fluxes. Therefore, natural barriers with limited sediment accommodation could allow for exploration of the future effects of sea-level rise and changing flux magnitudes over a period of years as opposed to the decades required for similar responses in sediment-rich barrier systems. Finally, because our model creates stratigraphy generated under different input parameters, we propose it could be used in combination with stratigraphic data to hindcast the sensitivity of existing barriers and infer changes in pre-historic morphology, which we anticipate will provide a baseline to assess the reliability of forward modeling predictions.

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Quantifying thresholds of barrier geomorphic change in a cross-shore sediment-partitioning model

Earth Surface Dynamics ◽

10.5194/esurf-9-183-2021 ◽

2021 ◽

Vol 9 (2) ◽

pp. 183-203

Author(s):

Daniel J. Ciarletta ◽

Jennifer L. Miselis ◽

Justin L. Shawler ◽

Christopher J. Hein

Keyword(s):

Sea Level Rise ◽

Sea Level ◽

Cross Sections ◽

Sediment Flux ◽

State Transitions ◽

Morphologic Change ◽

Relative Sea Level ◽

Coastal System ◽

Sea Levels ◽

Relative Sea Level Rise

Abstract. Barrier coasts, including barrier islands, beach-ridge plains, and associated landforms, can assume a broad spectrum of morphologies over multi-decadal scales that reflect conditions of sediment availability, accommodation, and relative sea-level rise. However, the quantitative thresholds of these controls on barrier-system behavior remain largely unexplored, even as modern sea-level rise and anthropogenic modification of sediment availability increasingly reshape the world's sandy coastlines. In this study, we conceptualize barrier coasts as sediment-partitioning frameworks, distributing sand delivered from the shoreface to the subaqueous and subaerial components of the coastal system. Using an idealized morphodynamic model, we explore thresholds of behavioral and morphologic change over decadal to centennial timescales, simulating barrier evolution within quasi-stratigraphic morphological cross sections. Our results indicate a wide diversity of barrier behaviors can be explained by the balance of fluxes delivered to the beach vs. the dune or backbarrier, including previously understudied forms of transgression that allow the subaerial system to continue accumulating sediment during landward migration. Most importantly, our results show that barrier state transitions between progradation, cross-shore amalgamation, aggradation, and transgression are controlled largely through balances within a narrow range of relative sea-level rise and sediment flux. This suggests that, in the face of rising sea levels, subtle changes in sediment fluxes could result in significant changes in barrier morphology. We also demonstrate that modeled barriers with reduced vertical sediment accommodation are highly sensitive to the magnitude and direction of shoreface fluxes. Therefore, natural barriers with limited sediment accommodation could allow for exploration of the future effects of sea-level rise and changing flux magnitudes over a period of years as opposed to the decades required for similar responses in sediment-rich barrier systems. Finally, because our model creates stratigraphy generated under different input parameters, we propose that it could be used in combination with stratigraphic data to hindcast the sensitivity of existing barriers and infer changes in prehistoric morphology, which we anticipate will provide a baseline to assess the reliability of forward modeling predictions.

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Submergence, nutrient enrichment, and tropical storm impacts on Spartina alterniflora in the microtidal northern Gulf of Mexico

Marine Ecology Progress Series ◽

10.3354/meps13342 ◽

2020 ◽

Vol 644 ◽

pp. 33-45

Author(s):

JM Hill ◽

PS Petraitis ◽

KL Heck

Keyword(s):

Gulf Of Mexico ◽

Sea Level Rise ◽

Sea Level ◽

Spartina Alterniflora ◽

Anthropogenic Impacts ◽

Interactive Effects ◽

Relative Sea Level ◽

Hurricane Disturbance ◽

Submergence Stress ◽

Relative Sea Level Rise

Salt marshes face chronic anthropogenic impacts such as relative sea level rise and eutrophication, as well as acute disturbances from tropical storms that can affect the productivity of these important communities. However, it is not well understood how marshes already subjected to eutrophication and sea level rise will respond to added effects of episodic storms such as hurricanes. We examined the interactive effects of nutrient addition, sea level rise, and a hurricane on the growth, biomass accumulation, and resilience of the saltmarsh cordgrass Spartina alterniflora in the Gulf of Mexico. In a microtidal marsh, we manipulated nutrient levels and submergence using marsh organs in which cordgrasses were planted at differing intertidal elevations and measured the impacts of Hurricane Isaac, which occurred during the experiment. Prior to the hurricane, grasses at intermediate and high elevations increased in abundance. After the hurricane, all treatments lost approximately 50% of their shoots, demonstrating that added nutrients and elevation did not provide resistance to hurricane disturbance. At the end of the experiment, only the highest elevations had been resilient to the hurricane, with increased above- and belowground growth. Added nutrients provided a modest increase in above- and belowground growth, but only at the highest elevations, suggesting that only elevation will enhance resilience to hurricane disturbance. These results empirically demonstrate that S. alterniflora in microtidal locations already subjected to submergence stress is less able to recover from storm disturbance and suggests we may be underestimating the loss of northern Gulf Coast marshes due to relative sea level rise.

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