Climate-induced Sea Level Rise Research Articles

De ontdekking van Doggerland: de wetenschappelijke waarde van strandvondsten

The discovery of Doggerland: the scientific value of beach findsCoined in 1998 by archaeologist Bryony Coles, ‘Doggerland’ has become a widely recognised name for the prehistoric landscapes, now submerged beneath the North Sea. For more than 100 years, scholars have suspected remains of these landscapes and their inhabitants to have survived, but direct evidence such as bone and stone tools has long been relatively sparse. Today, much more is known about the preservation of prehistoric landforms, as well as the material remains of animals, humans and artefacts. As part of the NWO-funded project ‘Resurfacing Doggerland’, thousands of finds, collected on Dutch beaches and retrieved from fishing nets, are now being studied in detail. The results will provide new insights into the relationship between climate-induced sea-level rise and socio-cultural processes.

Climate-induced vulnerability and conservation strategies for coastal heritage sites in the southern Mediterranean Sea using integrated remote sensing and flood modeling

Coastal heritage sites along the southern Mediterranean Sea confront immediate and severe threats from climate change, intensified by rising sea levels and ongoing shoreline erosion. This study presents a comprehensive approach to monitor and safeguard these significant locations, addressing the challenges posed by climate change. Leveraging high-resolution satellite data sources such as Pleiades imagery and Landsat data, shoreline detection was optimized using the Lee Filter and Canny edge detection techniques. Flood modeling and sea-level rise projections were incorporated to comprehensively assess dynamic coastal landscapes. Advanced methods, including the Prophet model, were employed for temperature predictions, showcasing good predictive accuracy. The results provide crucial insights into climate resilience and temperature forecasting amid rising temperatures associated with climate change. Alarming statistics include an annual erosion rate of −4.47 m/year and critical vulnerability to sea-level rise scenarios. In the extreme 4-m sea-level rise scenario, approximately 35 % of the total surface area (approximately 116.79 m2) is projected to be at risk of submersion, emphasizing the severe susceptibility of these sites to climate-induced sea-level rise. Even in the less severe 2-m scenario, around 24 % of the total area (approximately 80.79 m2) could potentially face submersion, posing a substantial threat to the ancient fortifications of the El Borj heritage site. This study underscores the critical role of preserving coastal heritage in addressing the challenges posed by climate change.

Large-Scale Levee Breach Experiments With Foreshores

Coastal flood risk is expected to increase substantially in the near future. Main drivers are climate induced sea level rise, increased storm surge and land subsidence. Meanwhile, land subsidence compounds to increased extreme water levels as more land is susceptible to flooding. Without coastal defense or adaptation 50% more people are exposed to flooding than present day (Kireczi et al., 2020). Coastal regions are currently primarily protected by hard (grey) flood defenses such as storm surge barriers, seawall, dikes and dunes. Periodically, strengthening of these grey structures is necessary to comply with current or updated safety standards. For dikes, conventional strengthening methods are crest heightening or (base) widening. However, these methods have structural and financial limits. Instead, more sustainable methods are explored in which nature also plays a larger role. These solutions are known as Nature based Solutions (NbS). For flood protection, tidal marshes have gained great interest as a Nature based Solution in the past two decades. Tidal marshes provide a lot of ecosystem services (Barbier et al., 2011). One such service is flood protection, attributed to wave attenuation (Vuik et al, 2016). A secondary effect is flood impact reduction (Zhu et al., 2020) due to the high elevation of tidal marshes limiting the inflow to the breach. Secondly, the tidal marsh can act as a sill in front of the breach when water levels drop below the tidal marsh level. To quantify the effect of tidal marshes on flood impact the breaching process in combination with a tidal marsh (or foreshore in general) needs to be understood. In this study we performed a large-scale physical dike experiment where we breached a dike seven times. Three tests are done without a sediment layer in front of the dike (no foreshore), two with a sandy layer (sandy beach) and two with a clay layer (tidal marsh without vegetation). From the experiments we gain insight into differences in the dike breaching process with and without an erodible sediment layer in front of the dike

Is the insular coastal tourism of western Greece at risk due to climate induced sea level rise?

Coastal environments and, especially, beach zones are among the most common areas for tourism activity, comprising valuable economic resources. Beach zones are highly dynamic environments, recognized as highly vulnerable to climate change coastal ecosystems because of, amongst other, extreme events and sea-level rise. It is considerably important for beach tourism management the development of proper adaptation strategies. The scope of this study is to provide an assessment of the potential climate-related risk on touristic beaches of the Ionian Islands (Greece) by applying a three-step risk assessment methodology, following the impact chain conceptual framework. More specifically, the methodology integrates: (i) beach hazard as an expression of beach retreat calculation due to sea level rise to the extreme SSP5-8.5 scenario for 2050, (ii) beach exposure with regard to tourism economic losses according to the extent of beach touristic exploitation, and (iii) beach vulnerability with regard to both beach capacity considering its morphological characteristics and sensitivity considering the adverse impact of artificial structures and human development in the area. The results indicate a great heterogeneity in risk, with more than half beaches being at high or very high risk under the highest emissions scenario.

Sea level variability in Gulf of Guinea from satellite altimetry

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

Practitioner needs to adapt to Sea-Level Rise: Distilling information from global workshops

Climate-induced sea-level rise threatens the world’s coastal populations, critical infrastructure, and ecosystems. The science of sea-level rise (SLR) has developed to inform understanding of global climate mitigation and adaptation challenges, but there is much less engagement with practitioners to discern their climate services needs and support the development of adaptation planning and action on the ground. In addition, adaptation planning and implementation processes for SLR are relatively new and practitioners developing leading practices are seeking interaction with their peers and the SLR science community. To address these gaps, we co-produced online global workshops with sixty-nine practitioners from twenty-six countries. These workshops aimed to increase understanding of the state of SLR adaptation planning practice worldwide, gather information on practitioners' existing knowledge and service needs to advance their adaptation efforts, and facilitate exchange between practitioners engaged with coastal adaptation and the SLR science community. The workshops uncovered commonalities across contexts and identified consistent needs from scientists and other technical experts amongst the practitioner community. These needs include generating more localized SLR impact data, understanding of compound risk, creating data timelines for decision making, and developing clarity about uncertainties and probabilities. We also observed important differences between urban and rural locations and between places with different economic resources. To meet their needs, practitioners identified three crucial next steps: 1) Develop more online engagement opportunities, 2) Establish a global practitioner community of practice, and 3) Scale and improve the provision of climate services.

Understanding the impact of climate-induced sea level rise on groundwater inundation in a low-lying coastal area: A numerical simulation in Southeast India

Global warming has led to rising sea levels, severely threatening coastal areas, particularly in low-elevation coastal zones. The groundwater in coastal aquifers of lower elevation is susceptible to groundwater inundation (GWI), an emerging hidden long-term hazard earlier to marine inundation. The inundation is mainly due to the hydraulic connection between sea level and shallow unconfined aquifers, resulting in groundwater upsurging towards the ground surface. To understand the potential impact of sea level rise (SLR) induced GWI on low-lying coasts, a transient state model was simulated and predicted in the Cuddalore regions of South India under 0.3 m, 0.6 m, and 1 m SLR scenarios. The simulation reveals that the aerial extent of groundwater rise (GWR) was 331.9 km2, 566.2 km2, and 650.8 km2 for 0.3 m, 0.6 m, and 1 m SLR scenarios, respectively. About 50% of the response was observed in the northern and central parts of the study area within a 5 km buffer, which is attributed to the deeper groundwater table. In contrast, the southern region exhibited a 10% decline in response due to shallow groundwater discharge to drainage, which dampened the shoaling effect. The present-day shallow groundwater tables in the southern region are more vulnerable to GWI from rising sea levels. Specifically, a 0.3 m SLR could inundate 14.9 km2. In comparison, a 1 m SLR could inundate 40.5 km2 of the area, including the Pichavaram mangrove forest, agricultural land, municipal structures, and the other regions that flooding could threaten. These inundations could have potential impacts, such as wetland loss, agricultural flooding, deteriorating water quality, and infrastructural damage. The present study provides valuable insights into the subsurface hydrodynamic and exposure impacts of sea rise-induced inundations. This can aid coastal engineers, policymakers, and decision-makers to plan appropriate mitigation measures.

Assessing the Toxicity of Sea Salt to Early Life Stages of Freshwater Mussels: Implications for Sea Level Rise in Coastal Rivers.

Sea levels across the planet are rising, particularly along the eastern coast of the United States. Climate-induced sea level rise can result in the inundation and intrusion of seawater into freshwater drainages. This would alter salinity regimes and lead to the salinization of coastal freshwater ecosystems. Increased salinity levels in freshwater can negatively affect freshwater-dependent species, including native mussels belonging to the order Unionida, which are highly sensitive to changes in water quality. Sea salt is largely made up of sodium and chloride ions, forming sodium chloride, a known toxicant to freshwater mussels. However, sea salt is a mixture that also contains other major ions, including potassium, sulfate, calcium, strontium, and magnesium, among others. Freshwater mussels exposed to sea salt would be exposed to each of the sea salt ions at the same time, resulting in a mixture toxicity effect. The mixture toxicity of these ions on early life stages of freshwater mussels is largely unknown because most research to date has evaluated individual salt ions in relative isolation. Therefore, we conducted acute toxicity tests on early life stages (glochidia and juvenile) of three freshwater mussel species that inhabit Atlantic Slope drainages (nonsalinity-adapted Atlanticoncha ochracea, salinity-adapted A. ochracea, Sagittunio nasutus, and Utterbackiana implicata). Glochidia and juveniles of each species were exposed to a control and six concentrations of Instant Ocean® Sea Salt (IOSS), a synthetic sea salt that closely resembles the ionic composition of natural sea salt. Exposure concentrations were 1 part(s) per thousand (ppt), 2 ppt, 8.5 ppt, 12.5 ppt, 17 ppt, and 34 ppt. We calculated the median effect concentration (EC50) for each of the eight acute toxicity tests and found that glochidia were more sensitive than juveniles to IOSS. At hour 24 EC50s for the glochidia ranged from 0.38 to 3.6 ppt, with the most sensitive freshwater mussel being the nonsalinity-adapted A. ochracea, exhibiting an EC50 of 0.38 ppt (95% confidence interval [CI] 0.33-0.44). Juvenile freshwater mussels exhibited EC50s at hour 96 ranging from 5.0 to 10.4 ppt, with the least sensitive freshwater mussel being the nonsalinity-adapted A. ochracea, exhibiting an EC50 of 10.4 ppt (95% CI 9.1-12.0). Our results show that acute exposure to sea salt adversely affects freshwater mussel viability, particularly glochidia. This information can be used to enhance freshwater mussel conservation strategies in regions that are or will be impacted by climate-induced sea level rise and associated freshwater salinization. Environ Toxicol Chem 2023;42:2478-2489. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Assessment of the integrated coastal vulnerability index of Ghana toward future coastal infrastructure investment plans

Coastal vulnerability assessments are increasingly more important to investigate the exposure of coastal areas to coastal hazards. In recent decades, climate-induced sea-level rise (SLR) and human anthropogenic impacts are exacerbating the frequency and intensity of coastal hazards like storms, coastal erosion and flooding worldwide making coastal vulnerability assessments and coastal adaptation planning a priority. In Ghana, the assessment of the coastal vulnerability index (CVI) during the past decade has been infrequent, site-specific, and not complementary to provide the complete state of national coastal vulnerability during the past decade. This creates uncertainty, with limited information for coastal adaptation planning. To close this gap, we integrated three social variables with six fundamental physical variables to develop an integrated coastal vulnerability index (ICVI) for the coast of Ghana using the analytical hierarchical process (AHP). The ICVI results indicate that 6 coastal districts (18.18%) have very high vulnerability, 10 (30.30%) have high vulnerability, 8(24.24%) have moderate vulnerability, 6(18.18%) have low vulnerability, and 3 (9.09%) have very low coastal vulnerability. Overall, 72% of the coast exhibit moderate to very high coastal vulnerability. The results are significant to update the state of coastal vulnerability and help coastal planners to revise the short, medium, and long-term coastal adaptation policies along the coast of Ghana.

Sea level rise adaptation pushes an insular endemic rodent closer to extinction

Understanding how species will respond to a rapidly changing global climate is requisite to conserving biodiversity. Though habitat losses from human development and land use change remain the most critical threats to biodiversity globally, some regions, such as low-lying islands, are particularly vulnerable to the effects of climate change. Despite this vulnerability, there may be opportunities for imperiled species on islands to adapt to the effects of climate-induced sea level rise. To understand how the response to rising seas may influence the amount of future habitat, we investigated shifts in the elevational range of the endangered silver rice rat (Oryzomys palustris natator; hereafter “rice rat”), a species endemic to tidal environments of the Lower Florida Keys, USA. We quantified fine-scale habitat use using radio telemetry of collared animals, first in 2004, and again in 2021, thus spanning a 17-year period during which the local sea level rose by 0.142 m. We observed a shift in the elevational range limits of rice rats which closely mirrored the rise in sea level, and that this apparent ability to adapt to rising sea level decreased the extent of habitat loss in subsequent decades. However, over longer time scales (~ 100 yrs), the extent of habitat loss from sea level rise outpaced rice rats’ ability to adapt. As such, the conservation of biodiversity on low-lying islands hinges on the ability of the global community to decrease anthropogenic greenhouse gas emissions and mitigate the associated consequences for the global climate. Otherwise, conservation practitioners will be increasingly forced to make difficult decisions about how to conserve imperiled species on low-lying islands.

Mapping and assessment of coastal infrastructure for adaptation to coastal erosion along the coast of Ghana

Globally, coastal managers are challenged to make informed decisions when selecting coastal infrastructure to respond to climate-induced sea-level rise and associated coastal hazards like coastal erosion and flooding. Classifying the types of coastal infrastructure permits the comparison of their potential efficiency, environmental and socioeconomic impacts, and long-term response to sea-level rise. At present, information on coastal infrastructure implemented along the coastal area of Ghana is not known thus creating a research gap to catalog this information. To achieve this, we combined satellite images from Google Earth Pro and the use of ArcGIS capabilities to conduct a national assessment of coastal infrastructure and its distribution along the coast of Ghana. Even though similar approaches have been applied in different geographic contexts, this article focuses on evaluating coastal infrastructure in Ghana. Results show that between 2004 and 2022, at least 110 km or approximately 20% of the coast of Ghana has been protected using grey infrastructure, distributed as groins 35.9 km (6.5%), revetments and seawalls 50 km (9%), and jetties and port breakwaters 25 km (4.5%) of the 550 Km coastline. These do not include the numerous private recreational infrastructure that could increase coastal vulnerability. The increasing use of grey infrastructure, particularly seawalls, and revetments along the coast has adverse impacts on overall coastal evolution and causes socioeconomic challenges. This study supports coastal managers to review coastal adaptation policy and develop shoreline management plans for the coast of Ghana.

Future socioeconomic development along the West African coast forms a larger hazard than sea level rise

Sea level rise will exacerbate the vulnerability of low-lying coastal regions around the world in the coming decades, posing a severe threat to coastal populations. Here, we assess the future population and asset exposure of West Africa (WA) to normal and extreme coastal flooding based on the projected sea level rise scenarios reported in the IPCC Sixth Assessment Report using a bathtub modeling approach, MERIT DEM and gridded population gross domestic product datasets that are consistent with the Shared Socioeconomic Pathways. We find that socioeconomic development will be responsible for the maximum increase in future coastal flooding along the WA coast towards the end of the century. While contributions from climate-induced sea level rise will dominate and be responsible for changes in coastal flooding events in some countries, exposure to these events is likely to dominate in many countries if the ongoing horizontal infrastructural development and economic-oriented transformation continue. These results have important implications for both sustainable coastal planning and flooding risk mitigation for WA’s coastal areas and should be considered as a cautionary tale for managing increasing socioeconomic development and coastward migration at the expense of the region’s coastal ecosystems.

Population development as a driver of coastal risk: Current trends and future pathways

AbstractCoastal areas are subject to hazards that can result in severe impacts due to the high concentration of people and assets in exposed locations. While climate-induced sea-level rise will exacerbate these hazards in the course of the 21st century, future dynamics in socioeconomic development will play an important role in driving impacts – as well as adaptation responses – in particular in countries with rapid population growth in low-lying coastal areas. Here, we synthesize the current state of knowledge related to current and future population development in coastal locations and the underlying trends in socioeconomic development affecting coastal impacts at continental to global scales. Currently, 2.15 billion people live in the near-coastal zone and 898 million in the low-elevation coastal zone globally. These numbers could increase to 2.9 billion and 1.2 billion, respectively, depending on the socioeconomic scenario (i.e., Shared Socioeconomic Pathway [SSP]) considered. Nevertheless, although these numbers indicate a rapid increase in exposure of population and assets to coastal hazards, they bear limited information about the actual impacts as they do not include information on the vulnerability of coastal population. Based on these insights, we stress the need to account for dynamics in socioeconomic development in coastal risk assessments, including exposure as well as vulnerability, and additionally exploring potential feedbacks due to adaptation responses and migration decisions. Last, we propose action points for future work that can inform long-term coastal planning for managing coastal risks.

Evaluation of coastal protection strategies and proposing multiple lines of defense under climate change in the Mekong Delta for sustainable shoreline protection

Coastal protection measures and management play an important role in coping with coastal disasters and climate-induced sea-level rise. In this study, the success and failure of typical coastal protection works of the Vietnamese Mekong Delta (VMD) are reported and documented from field observations over a study period of 10–15 years. The coastal protection structures evaluated include revetments, geotubes, t-shaped bamboo fences, Pile-rock breakwaters, Busadco's breakwaters, Semi-Circular breakwaters, and Hollow triangle breakwaters. This paper briefly reviews the current situation of coastline erosion problem and accretion in the VMD and illustrates the severity of the current erosion rate that threatens the safety of coastal communities. The paper then evaluates the advantages and disadvantages of various coastal management approaches currently in practice in the VMD to classify different types of possible measures for coastal management with the aim to find holistic measures for planning which require low construction investment. Integrated coastal management and planning are outlined at a regional scale followed by the lessons learned from the previous coastal protection works, and finally the multiple lines of defense (MLD) solution is proposed, which is a green infrastructure inspired nature-based solution. The MLD solution can improve biodiversity, facilitate mangrove forest restoration, and ensure sustainable livelihoods for local communities. Integrated coastal planning and management solutions that are based on the MLD principle are expected to withstand coastal disasters under future climate change, and sea-level rise on the VMD.

Cost–benefit analysis of coastal flood defence measures in the North Adriatic Sea

Abstract. The combined effect of global sea level rise and land subsidence phenomena poses a major threat to coastal settlements. Coastal flooding events are expected to grow in frequency and magnitude, increasing the potential economic losses and costs of adaptation. In Italy, a large share of the population and economic activities are located along the low-lying coastal plain of the North Adriatic coast, one of the most sensitive areas to relative sea level changes. Over the last half a century, this stretch of coast has experienced a significant rise in relative sea level, the main component of which was land subsidence; in the forthcoming decades, climate-induced sea level rise is expected to become the first driver of coastal inundation hazard. We propose an assessment of flood hazard and risk linked with extreme sea level scenarios, under both historical conditions and sea level rise projections in 2050 and 2100. We run a hydrodynamic inundation model on two pilot sites located along the North Adriatic coast of Emilia-Romagna: Rimini and Cesenatico. Here, we compare alternative extreme sea level scenarios accounting for the effect of planned and hypothetical seaside renovation projects against the historical baseline. We apply a flood damage model to estimate the potential economic damage linked to flood scenarios, and we calculate the change in expected annual damage according to changes in the relative sea level. Finally, damage reduction benefits are evaluated by means of cost–benefit analysis. Results suggest an overall profitability of the investigated projects over time, with increasing benefits due to increased probability of intense flooding in the near future.

Morphodynamic changes in the Yangtze Estuary under the impact of the Three Gorges Dam, estuarine engineering interventions and climate-induced sea level rise

The estuarine turbidity maximum (ETM) in the Yangtze Estuary Delta (YED) is muddy by definition and lacks bottom undulations. However, since 2013, a remarkable change has occurred in the YED. Recent images detected by a multibeam echosounder system, SeaBat 7125, for the first time have confirmed widespread regions of subaqueous dunes in the Yangtze ETM channel. This abnormal change is the result of morphodynamic transformation from the combination of an abrupt decline in sediment supply resulting from the construction of the Three Gorges Dam (TGD) and hydrodynamic changes caused by sea level rise. The latter includes anthropogenic-induced sea level rises (from land subsidence and coastal engineering) of 7–37 cm and a climate-induced sea level rise of 8 cm during the past four decades. Obvious evidence of hydrodynamic changes includes tidal amplification, i.e., a 10–28 cm rise in the tidal range, 42–65 cm rise in the lowest tidal level in the dry season, 45–67 cm rise in the highest tidal level in the flood season and 10–30% increase in the amplitude of the major tidal component. These findings will likely have global implications in formulating strategies to combat the superimposed effects of human interventions and climate change on upstream river and downstream coastal developments.

Coastal Flood Responses in Manila Bay, the Philippines

In 2011, Sitio Pariahan in the northern part of Metro Manila, the Philippines’ capital region, was submerged after Typhoon Nesat hit the country. In fact, Sitio Pariahan is not the only one. Many parts of Manila Bay have slowly been sinking, causing the populations to be prone to coastal floods. According to the existing studies, coastal floods in Manila Bay areas are caused by climate-induced sea-level rise and land subsidence due to the excessive groundwater extraction and rapid urban development. However, it appears that the policies implemented by the government tend to be infrastructural, for example, dike construction, which could provide immediate protection but do not really solve the problem. This case study, therefore, presents a detailed account of coastal flooding in Manila Bay, particularly on its causes and policy options to address it. More specifically, it introduces the application of social contract to understand how the terms and conditions governing the state-citizens relations in the Philippines affect government’s rationale in choosing policy options to solve the coastal flood problem.

Three emergencies of climate change: The case of Louisiana’s coast

Climate challenge brings three, not just one, emergencies. These are the visible, conceptual and existential, all of which are urgent and important. The three emergencies are starkly highlighted in Louisiana, where historical coastal development and climate-induced sea level rise is causing visible emergencies in the form of extensive land loss and increased impacts of flooding and storm surges, leading to forced relocation of settlements. The visible emergencies cannot be overcome without addressing conceptual emergencies where current ways of organising, thinking and approaching the challenges are inadequate for the scale, nature and rate of change. The conceptual emergencies, in turn, cannot be overcome without addressing the existential, where different cultures, values and identities are needed to overcome existing conceptual challenges. Louisiana’s state government is beginning to go beyond the visible to wrestle with the conceptual and, to some extent, awareness is growing about the existential. The need to address the conceptual and existential will only increase as the limits of current approaches to addressing the visible emergencies become more apparent. As such, the case highlights how climate change will force a transformation that will be characterised by fundamentally new social attributes. The nature of what emerges, however, is not guaranteed and will depend on how those in Louisiana and beyond seek to work with all three emergencies and their interconnections.

Rising seas and subsiding cities

Coastal adaptation aims to reduce impacts of relative sea-level rise from climate-induced sea-level rise and land elevation changes. Now, a global projection of relative sea-level rise to 2050 suggests the critical role of managing land subsidence for coastal cities on sinking deltas.

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 coasts. Although this affects local rates of sea-level rise, assessments of the coastal impacts of subsidence are lacking on a global scale. Here, we quantify global-mean relative sea-level rise to be 2.6 mm yr−1 over the past 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−1. These results indicate that the impacts and adaptation needs are much higher than reported global sea-level rise measurements suggest. In particular, human-induced subsidence in and surrounding coastal cities can be rapidly reduced with appropriate policy for groundwater utilization and drainage. Such policy would offer substantial and rapid benefits to reduce growth of coastal flood exposure due to relative sea-level rise.