Future Relative Sea Level Rise Research Articles

Rising seas could cross thresholds for initiating coastal wetland drowning within decades across much of the United States

Accelerated sea-level rise is an existential threat to coastal wetlands, but the timing and extent of wetland drowning are debated. Recent data syntheses have clarified future relative sea-level rise exposure and sensitivity thresholds for drowning. Here, we integrate these advances to estimate when and where rising sea levels could cross thresholds for initiating wetland drowning across the conterminous United States. Our results show that there is much spatial variation in relative sea-level rise rates, which impacts the potential timing and extent of wetlands crossing thresholds. High rates of relative sea-level rise along wetland-rich parts of the Gulf of Mexico and Atlantic coasts highlight areas where wetlands are already drowning or could begin to drown within decades, including large wetland landscapes within the Mississippi River delta, Greater Everglades, Chesapeake Bay, Texas, Georgia, and the Carolinas. Collectively, our results underscore the need to prepare for transformative coastal change.

Coastal response to Holocene Sea-level change: A case study from Singapore

The deceleration of early to mid-Holocene (10–7 cal. ka BP) relative sea-level rise (RSLR) played a key role in transforming coastal systems from estuaries to deltas. Palaeoenvironmental reconstruction of coastal evolution provide case studies that can help project the response of modern coastal systems to future RSLR. The response of deltas to future RSLR is particularly important to South, Southeast and East Asia which collectively contain 71% of the global coastal population living below 10 m in elevation and 75% of the global coastal floodplain population. However, few Holocene studies of equatorial delta systems exist.Here, we investigate the early to mid-Holocene coastal response to decelerating rates of RSLR through paleoenvironmental reconstruction of the Kallang River Basin, Singapore. We produce a multi-proxy (sedimentology, stable carbon isotope, XRF elemental ratios) record from sediment core MSBH01B to compare with the Holocene relative sea-level record for Singapore. We identify different phases of coastal response through the interplay between accommodation space (A) driven predominantly by RSLR and sedimentation rate (S).In the early Holocene rapid RSLR coupled with low sedimentation rates (A/S = 5.1 ± 0.3) led to mangrove disappearance in the Kallang River Basin coastal area within ∼300 years (9.5–9.2 cal. ka BP). Estuarine sediments were deposited from 9.2 to 8.8 cal. ka BP during continued high rates of RSLR coupled with highest sedimentation rates (A/S = 3.1 ± 0.8) as the coastline retreated. Prodelta sediments were deposited from 8.8 to 8.2 cal. ka BP during decreasing rate of RSLR and high sedimentation rates (A/S = 4.6 ± 5.2). Delta front sediments were deposited during this delta initiation phase from 8.2 to 7.6 cal. ka BP as during a period of low and consistent RSLR and sedimentation rates (A/S = 1.7 ± 0.2). Finally, a prograding delta started forming from 7.6 to 7.2 cal. ka BP during lowest rates of RSLR and sedimentation rates (A/S = 1.7 ± 0.2). Our record provides a case study of possible responses of modern delta systems under a spectrum of predicted sea-level rise scenarios and accompanying sedimentation rates. This study provides an estimated threshold A/S value of 1.7 for coastal retreat to inform policy and mitigation/adaptation measures for Singapore and a simple methodology to obtain local threshold values of other equatorial cities built on floodplain and/or delta systems.

Implications of anomalous relative sea-level rise for the peopling of Remote Oceania

Beginning ~3,500 to 3,300 y B.P., humans voyaged into Remote Oceania. Radiocarbon-dated archaeological evidence coupled with cultural, linguistic, and genetic traits indicates two primary migration routes: a Southern Hemisphere and a Northern Hemisphere route. These routes are separated by low-lying, equatorial atolls that were settled during secondary migrations ~1,000 y later after their exposure by relative sea-level fall from a mid-Holocene highstand. High volcanic islands in the Federated States of Micronesia (Pohnpei and Kosrae) also lie between the migration routes and settlement is thought to have occurred during the secondary migrations despite having been above sea level during the initial settlement of Remote Oceania. We reconstruct relative sea level on Pohnpei and Kosrae using radiocarbon-dated mangrove sediment and show that, rather than falling, there was a ~4.3-m rise over the past ~5,700 y. This rise, likely driven by subsidence, implies that evidence for early settlement could lie undiscovered below present sea level. The potential for earlier settlement invites reinterpretation of migration pathways into Remote Oceania and monument building. The UNESCO World Heritage sites of Nan Madol (Pohnpei) and Leluh (Kosrae) were constructed when relative sea level was ~0.94 m (~770 to 750 y B.P.) and ~0.77 m (~640 to 560 y B.P.) lower than present, respectively. Therefore, it is unlikely that they were originally constructed as islets separated by canals filled with ocean water, which is their prevailing interpretation. Due to subsidence, we propose that these islands and monuments are more vulnerable to future relative sea-level rise than previously identified.

Assessing potential impacts of sea level rise on mangrove ecosystems in the Mekong Delta, Vietnam

Sea level rise (SLR) due to global climate change negatively impacts coastal zones, in particular wetland and mangrove ecosystems. Mangroves in the Mekong Delta (MD) in Vietnam provide critical ecosystem services in the region; however, escalated relative SLR is likely to affect all ecosystems in the region, with mangroves probably more vulnerable than others. Given the fact that documented information and studies on SLR impacts on mangroves are limited for the region, this study aims to investigate potential changes in mangrove distribution in response to future SLR scenarios in the coastal area in the south of the MD using the Sea Level Affects Marshes Model (SLAMM). Wetland maps for 2013 derived from Landsat 8 OLI sensor, digital elevation model (DEM), and localized site-specific parameters (i.e., subsidence/accretion, erosion, historic trend of SLR, and over-wash) were used as input for the SLAMM to simulate spatial distribution of mangroves under different relative SLR scenarios (i.e., RCP2.6, RCP4.5, RCP8.5, more extreme SLR), and surface elevation change (i.e., subsidence, stable, and accretion) scenarios by the year 2100. Simulation results show that the average annual mangrove losses are likely to be 0.54% and 0.22% for subsidence and stable scenarios, respectively. The findings demonstrate the considerable impacts of SLR on MD mangrove ecosystems and the strong influence of subsidence processes. Inundation was also identified as a main driver responsible for the mangrove loss by the end of this century. Our results are in agreement with findings of other studies at global scales and observed data at regional scales. The results also demonstrate the potential of the approach developed herein for simulating mangrove dynamics under future relative SLR scenarios in the region with acceptable accuracy. The findings from the present study are useful sources for development of proper strategies for minimizing the impacts of SLR on mangrove ecosystems and their vital associated services, to protect and conserve the mangrove ecosystems in the region.

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

The 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.

Tidal change in response to the relative sea level rise and marsh accretion in a tidally choked estuary

Tidal range is a key factor for flooding, mixing, and transport in estuaries. Sea level rise is expected to change tidal range in the future. This change is complex, and has been showed to either increase or decrease, and vary along the estuary axis. Large changes are expected to occur in costal Louisiana, as it is experiencing some of the highest relative sea level rise (RSLR) rates in the continental USA (0.92 cm yr−1). A finite volume community ocean model was used to investigate how tidal dynamics in Barataria Bay estuary will be affected by future RSLR and marsh accretion scenarios. Under the present sea level condition, five major tidal choking areas – where tidal range reduces sharply, and phase lags develops – were identified. RSLR reduced tidal choking intensity and thus increased tidal range within the estuary. Contrary to previous modeling analyses in other estuaries suggesting that flooding of the low-lying land with sea level rise would increase frictional effects and thus reduce tidal range, this study suggested that tidal range in a choked tidal system like Barataria Bay increases even when accompanied by extensive land inundation. This occurs because the channel conveyance effects are larger than the frictional effects of the low-lying areas. In the lower and the middle bay, the largest increase in tidal range occurred when the marsh area was assumed to keep pace with RSLR. Under this condition, mean tidal range could increase by a maximum of 16 cm compared to the present-day sea level condition. However, in the upper bay the largest increase in tidal range occurred when no accretion was assumed. Under this condition, mean tidal range could increase by a maximum of 13 cm. RSLR also induced amplification of tides at the head of the estuary. A detailed momentum balance analysis indicated that sea level rise shifts tidal wave regime from a dissipative tidal wave to a progressive wave, which is more susceptible to tidal amplification.

Multi-objective optimisation of a rock coast evolution model with cosmogenic <sup>10</sup>Be analysis for the quantification of long-term cliff retreat rates

Abstract. This paper presents a methodology that uses site-specific topographic and cosmogenic 10Be data to perform multi-objective model optimisation of a coupled coastal evolution and cosmogenic radionuclide production model. Optimal parameter estimation of the coupled model minimises discrepancies between model simulations and measured data to reveal the most likely history of rock coast development. This new capability allows a time series of cliff retreat rates to be quantified for rock coast sites over millennial timescales. Without such methods, long-term cliff retreat cannot be understood well, as historical records only cover the past ∼150 years. This is the first study that has (1) applied a process-based coastal evolution model to quantify long-term cliff retreat rates for real rock coast sites and (2) coupled cosmogenic radionuclide analysis with a process-based model. The Dakota optimisation software toolkit is used as an interface between the coupled coastal evolution and cosmogenic radionuclide production model and optimisation libraries. This framework enables future applications of datasets associated with a range of rock coast settings to be explored. Process-based coastal evolution models simplify erosional processes and, as a result, often have equifinality properties, for example that similar topography develops via different evolutionary trajectories. Our results show that coupling modelled topography with modelled 10Be concentrations can reduce equifinality in model outputs. Furthermore, our results reveal that multi-objective optimisation is essential in limiting model equifinality caused by parameter correlation to constrain best-fit model results for real-world sites. Results from two UK sites indicate that the rates of cliff retreat over millennial timescales are primarily driven by the rates of relative sea level rise. These findings provide strong motivation for further studies that investigate the effect of past and future relative sea level rise on cliff retreat at other rock coast sites globally.

Changing impacts of Alaska-Aleutian subduction zone tsunamis in California under future sea-level rise

The amplification of coastal hazards such as distant-source tsunamis under future relative sea-level rise (RSLR) is poorly constrained. In southern California, the Alaska-Aleutian subduction zone has been identified as an earthquake source region of particular concern for a worst-case scenario distant-source tsunami. Here, we explore how RSLR over the next century will influence future maximum nearshore tsunami heights (MNTH) at the Ports of Los Angeles and Long Beach. Earthquake and tsunami modeling combined with local probabilistic RSLR projections show the increased potential for more frequent, relatively low magnitude earthquakes to produce distant-source tsunamis that exceed historically observed MNTH. By 2100, under RSLR projections for a high-emissions representative concentration pathway (RCP8.5), the earthquake magnitude required to produce >1 m MNTH falls from ~Mw9.1 (required today) to Mw8.0, a magnitude that is ~6.7 times more frequent along the Alaska-Aleutian subduction zone.

Locked-in and living delta pathways in the Anthropocene

Delta systems are fundamental to the persistence of large human populations, food systems and ecosystem processes. Structural changes in natural and social components of deltas, emerging from past land-use changes, have led deltas to become locked-in loosing the ability to transform back into living deltas, and making them more at risk. We propose a framework to assess whether deltas become locked-in by changes in natural or social infrastructure, by examining the dynamic coupling between population and land-use development over 300 years for 48 deltas globally. We find that 46% of the deltas are defined as living, where population, irrigation, and cropland are correlated. Of the 54% locked-in deltas, 21% show changes in natural infrastructure to cropland (n = 6) or irrigation (n = 4), and 33% (n = 16) show changes in social infrastructure. Most locked-in deltas are in Europe but also in other continents due to decoupled development of population and cropland. While, locked-in deltas due to changes in natural infrastructure have highest average risks, those with changes in social infrastructure and the living deltas have highest risks from future relative sea level rise. These results show that deltas have varying natural and social components derived from a 300 years historical perspective, which are not taken into account in risk assessments for global deltas.

Modeled Sediment Availability, Deposition, and Decadal Land Change in Coastal Louisiana Marshes under Future Relative Sea Level Rise Scenarios

The ability, or lack thereof, for wetlands in coastal Louisiana to maintain elevation capital has been well documented in the literature to be a function of local and regional factors as well as environmental conditions. The Integrated Compartment Model (ICM) framework developed for the state of Louisiana’s Coastal Master Plan models hydrologic, vegetation, and wetland elevation dynamics and captures regional and local dynamics of wetland elevation, inundation and sedimentation processes. It provides insights into the relative sensitivities of wetland evolution to environmental drivers under uncertain future environmental conditions. A systematic, and computationally efficient modeling exercise was conducted to test coastal marsh survival across a wide range of possible future relative sea level rise rate scenarios. Model results indicate a diverse response with respect to sediment deposition and marsh survival driven by regional subsidence rates and proximity to suspended sediment sources. Sediment poor regions of coastal Louisiana are particularly sensitive to relative sea level rise under all but the most optimistic of future sea level rise rates simulated. Coastal marshes with high sediment availability fare much better under most scenarios tested, despite high rates of relative sea level rise.

Predicting marsh vulnerability to sea-level rise using Holocene relative sea-level data

Tidal marshes rank among Earth’s vulnerable ecosystems, which will retreat if future rates of relative sea-level rise (RSLR) exceed marshes’ ability to accrete vertically. Here, we assess the limits to marsh vulnerability by analyzing >780 Holocene reconstructions of tidal marsh evolution in Great Britain. These reconstructions include both transgressive (tidal marsh retreat) and regressive (tidal marsh expansion) contacts. The probability of a marsh retreat was conditional upon Holocene rates of RSLR, which varied between −7.7 and 15.2 mm/yr. Holocene records indicate that marshes are nine times more likely to retreat than expand when RSLR rates are ≥7.1 mm/yr. Coupling estimated probabilities of marsh retreat with projections of future RSLR suggests a major risk of tidal marsh loss in the twenty-first century. All of Great Britain has a >80% probability of a marsh retreat under Representative Concentration Pathway (RCP) 8.5 by 2100, with areas of southern and eastern England achieving this probability by 2040.

Spaceborne Synthetic Aperture Radar Survey of Subsidence in Hampton Roads, Virginia (USA)

Over the past century, the Hampton Roads area of the Chesapeake Bay region has experienced one of the highest rates of relative sea level rise on the Atlantic coast of the United States. This rate of relative sea level rise results from a combination of land subsidence, which has long been known to be present in the region, and rising seas associated with global warming on long timescales and exacerbated by shifts in ocean dynamics on shorter timescales. An understanding of the current-day magnitude of each component is needed to create accurate projections of future relative sea level rise upon which to base planning efforts. The objective of this study is to estimate the land component of relative sea level rise using interferometric synthetic aperture radar (InSAR) analysis applied to ALOS-1 synthetic aperture radar data acquired during 2007–2011 to generate high-spatial resolution (20–30 m) estimates of vertical land motion. Although these results are limited by the uncertainty associated with the small set of available historical SAR data, they highlight both localized rates of high subsidence and a significant spatial variability in subsidence, emphasizing the need for further measurement, which could be done with Sentinel-1 and NASA’s upcoming NISAR mission.

Shoreline change caused by the increase in wave transmission over a submerged breakwater due to sea level rise and land subsidence

Sandy beaches protected by submerged breakwaters, which have crests below sea level, are assumed to be vulnerable to relative sea level rise (SLR). In this study, the shoreline change due to sea level change and land subsidence along the Niigata West coast in Japan, which is protected by submerged breakwaters, was investigated using field data and a shoreline prediction model assuming that the shoreline change is caused by cross-shore sediment transport. The shoreline movement in the past 10years was not directly caused by sea level change and land subsidence. However, our model predicts that over the next 100years, the shoreline will retreat 60m owing to the increase in the energy flux of incoming waves over the breakwater caused by SLR and land subsidence. These results imply that other sandy beaches protected by low-crested breakwaters as well as those behind coral reefs, which are natural submerged breakwaters, would experience non-negligible erosions caused by future relative SLR.

The complex influences of back-barrier deposition, substrate slope and underlying stratigraphy in barrier island response to sea-level rise: Insights from the Virginia Barrier Islands, Mid-Atlantic Bight, U.S.A.

To understand the relative importance of back barrier environment, substrate slope and underlying stratigraphy in determining barrier island response to RSLR (relative sea-level rise), we use a morphological-behavior model (GEOMBEST) to conduct a series of sensitivity experiments, based on late-Holocene hindcast simulations of an island in the U.S. mid-Atlantic Bight (Metompkin Island, VA) having both salt marsh and lagoonal back-barrier environments, and we draw comparisons between these results and future simulations (2000–2100AD) of island response to RSLR. Sensitivity analyses indicate that, as a whole, the island is highly sensitive to factors that reduce overall sand availability (i.e., high sand-loss rates and substrates containing little sand). Results also indicate that for all predicted future RSLR scenarios tested, islands having high substrate sand proportions (if allowed to migrate freely) will likely remain subaerial for centuries because of sufficient substrate sand supply and elevation to assist in keeping islands above sea level. Simulation results also lead to basic insights regarding the interactions among substrate slope, back-barrier deposition and island migration rates. In contrast to previous studies, which suggest that changes in substrate slope directly affect the island migration trajectory, we find that—in the presence of back-barrier deposition—the connection between substrate slope and island behavior is modulated (i.e., variability in migration rates is dampened) by changes in back-barrier width. These interactions—which tend to produce changes in shoreface sand content—lead to a negative feedback when the back-barrier deposit contains less sand than the underlying layer, resulting in a stable back-barrier width. Alternatively, a positive feedback arises when the back-barrier deposit contains more sand than the underlying layer, resulting in either back-barrier disappearance or perpetual widening.

Modeling of Coastal Inundation, Storm Surge, and Relative Sea-Level Rise at Naval Station Norfolk, Norfolk, Virginia, U.S.A.

ABSTRACT Li, H.; Lin, L., and Burks-Copes, K.A., 2013. Modeling of coastal inundation, storm surge, and relative sea-level rise at Naval Station Norfolk, Norfolk, Virginia, U.S.A. The potential risk and effects of storm-surge damage caused by the combination of hurricane-force waves, tides, and relative sea-level-rise (RSLR) scenarios were examined at the U.S. Naval Station, Norfolk, Virginia. A hydrodynamic and sediment transport modeling system validated with measured water levels from Hurricane Isabel was used to simulate two synthesized storms representing 50-year and 100-year return-period hurricanes, a northeaster, and five future RSLR scenarios to evaluate the combined impacts of inundation on this military installation in the lower Chesapeake Bay. The naval base topography and nearshore water body of Hampton Roads were included in the coastal modeling system (CMS), a suite of surge, circulation, wave, sediment transport, and morphology evolution models. The modeling domain was a rectangular area c...

The morphological response of large tidal inlet/basin systems to relative sea level rise

The morphodynamic response of large tidal inlet/basin systems to future relative sea level rise (RSLR), incorporating both Eustatic sea level rise and local land subsidence effects, is qualitatively investigated using the state-of-the-art Delft3D numerical model and the Realistic analogue modelling philosophy. The modelling approach is implemented on a highly schematised morphology representing a typical large inlet/basin system located on the Dutch Wadden Sea (Ameland Inlet) over a 110-year study period. Three different RSLR Scenarios are considered: (a) No RSLR, (b) IPCC lower sea level rise (SLR) projection (0.2 m SLR by 2100 compared to 1990) and land subsidence, and (c) IPCC higher SLR projection (0.7 m SLR by 2100 compared to 1990) and land subsidence. Model results indicate that, for the 110-year study duration, the existing flood dominance of the system will increase with increasing rates of RSLR causing the ebb-tidal delta to erode and the basin to accrete. The rates of erosion/accretion are positively correlated with the rate of RSLR. Under the No RSLR condition, the tidal flats continue to develop while under the high RSLR scenario tidal flats eventually drown, implying that under this condition the system may degenerate into a tidal lagoon within the next 110 years. The tidal flats are stable under the low RSLR scenario implying that, at least for the next 100 years, this may be the critical RSLR condition for the maintenance of the system. Essentially the results of this study indicate that, as the Eustatic SLR is likely to be greater than the apparently critical rise of 0.2 m (by 2100 compared to 1990), the tidal flats in these systems will at least diminish. In the worst, but not unlikely, scenario that the Eustatic SLR is as high as the IPCC higher projections (0.7 m by 2100), the tidal flats may completely disappear. In either case, the associated environmental and socio-economic impacts will be massive. Therefore, more research focusing on the quantification of the physical and socio-economic impacts of RSLR on these systems is urgently needed to enable the development of effective and timely adaptation strategies.

Holocene evolution of the River Bann estuary and adjacent coast, Northern Ireland

From a variety of published and unpublished geomorphological and stratigraphical information, supported by 14C dates, an attempt is made to reconstruct the Holocene evolution of the estuary of the River Bann and the adjacent stretch of coastline, Northern Ireland. Submerged and buried peat beds have yielded early Holocene pollen assemblages and 14C dates that demonstrate a low stand of relative sea-level (RSL) at this time. Peat formation was terminated by the deposition of sands and diatomaceous muds, reflecting RSL rise as a result of both eustatic controls and a declining level of isostatic recovery. Holocene maximum RSL occurred at c. 6000 years bp and reached +2 to +3 m OD (Belfast). A gravel barrier developed at the estuary mouth and provided the anchor point for later aeolian dune development. Along the adjacent coast, basalt shore platforms were either formed or modified, having been within the range of effective wave erosion since the early Holocene. Relative sea-level then fell rapidly. By c. 5500 years bp, aeolian dunes had formed below OD at one site within the estuary. By c. 4000 years bp, the primary elements of the geomorphology of the Bann estuary were in place. Since that time, several phases of aeolian dune and sand sheet development are apparent from the occurrence of buried soils and archaeological materials, but the primary mechanisms controlling dune stability/instability phases are not known with certainty. Periods of temporary supra-elevated water levels, probably resulting from storm conditions, have also been recognized in the coastal sedimentary record; interbedded peat and silty sand with rounded clasts forms part of a terrace sequence at +6 to +8 m OD. Radiocarbon dates suggest that several such events occurred between c. 2300 and 1700 years bp, as peat was accumulating. Recent changes include the construction of estuary mouth training walls and river dredging. Resulting from these activities, aeolian dunes have extended their area, and increased wave erosion within the estuary has been recorded. Human activities and any future RSL rise, consequent upon global warming, seem likely to lead to continuing instability.

Relative sea level rise and its effects on environment and resources in China’s coastal areas

Due to global climate warming and natural and man-made land subsidence etc., relative sea level rise in the coastal plains of China will exceed 2–3 times over the golbal mean value during the first half part of the 21st century. It will result in a series of adverse impacts on evolution of natural environment and socioeconomic development of the coastal area. This paper analyses environmental and resource effects induced by relative sea level rise in China’s coastal areas on the basis of rough estimate of future relative sea level rise. These effects include inundating tidal flat and wetlands and increase in inundated risk of coastal habitable land, exacerbating storm surge. coastal erosion, flooding and salt water intrusion hazards, as well as endangering land, water, tourism and living resources and their utilization.

Assessment of Future Coast Land Loss Along the Upper Texas Gulf Coast to the Year 2050

Tidal gauge data from stations along the Texas Gulf Coast document high long-term rates of relative sea-level rise. Shoreline retreat and loss of coastal land in Texas have also been documented, and attributed to a combination of erosion and submergence. Submergence is caused by relative sea-level (RSL) rise: a combination of eustatic sea-level (ESL) rise and subsidence caused both by man9s withdrawal of pore fluids and natural consolidation. The Texas coastline is regressing at present and will continue into the future. We anticipate future accelerated loss of land in response to accelerated sea-level rise. Three scenarios (baseline, low-rise, and high-rise) for shoreline retreat and resulting loss of land to the year 2050 are developed for the Upper Texas Gulf Coast, north of Galveston Bay. The scenarios integrate projections of future RSL rise with empirical relations between RSL rise and shoreline retreat over a historical baseline period. The projections of future RSL rise combine estimates of eustatic sea-level rise derived from a delphic analysis with an assumed constant rate of land-surface subsidence. RSL rises of 0.49 m, 0.63 m, and 1.87 m are computed for the year 2050 in the baseline, low-rise, and high-rise scenarios, respectively. These rises correspond to losses of land of 17.1 km 2 (4,224 acres), 22.4 km 2 (5,533 acres), and 68.5 km 2 (16,920 acres) within the study area. Although the loss of land varies considerably throughout the study area, shoreline retreats of up to 1.85 km by 2050 are predicted in the worst-case (high-rise) scenario. Our assessment indicates that the Upper Texas Coast will experience significant loss of land in the future. Although this analysis contains much uncertainty, we believe it provides useful projections that should influence the future development and use of coastal resources. Such projections should be considered in geotechnical analysis, site investigations, and land-use planning.