Selected publications

In October 2023, the Baltic Sea coasts of Germany and Denmark experienced a severe storm surge, predominantly impacting the German state of Schleswig-Holstein and parts of southern Denmark. The surge led to extensive flooding in cities like Flensburg and Schleswig, causing the breaching of at least six (regional) dikes and causing over EUR200million in damages in Schleswig-Holstein. By chance, the peak water levels of this storm surge aligned well with those of recent hydrodynamic floodmodellingstudies of the region. This rare coincidence offers crucial insights for our understanding of flooding impacts, flood management, and modelling. By comparing those studies to the real-world example using extensive media reports, we aim to extract key insights and identify gaps to be tackled in order to improve f lood risk modelling in the Baltic Sea region and beyond.

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Information on urban land use, beyond the urban-rural dichotomy, can improve the assessment of potential impacts of coastal hazards by refining estimates of damages and supporting adaptation planning. However, the lack of a consistent definition of “urban” in previous studies has led to exposure estimates that vary considerably. Here, we explore the sensitivity of exposed population and built-up area in four settlement types, defined by four different built-up area datasets. We find large differences in the exposed population of up to 65% (127 million people) in the “Urban” class. The exposure estimates are highly sensitive to the density thresholds used to distinguish the settlement types, with a difference in exposed urban population of up to 53.5 million people when the threshold varies by 10%. We attribute the high sensitivity of the exposure estimates to the varying definitions of built-up area of the underlying datasets. We argue that the definition of urban land is crucial for coastal impact assessments and make recommendations for the use of the analyzed datasets.

Flood characteristics caused by extreme sea level (ESL) events depend largely on the magnitude of peak water levels (WLs) and their temporal evolution. However, coastal flood risk is generally assessed based on only a limited number of potential peak WLs and a selection of past events or a design hydrograph. We address this gap and systematically estimate (a) spatial annual and (b) event-based flood probabilities by comprehensively accounting for both a wide range of peak ESLs and their temporal evolution, herein referred to as hydrograph intensity. We simulate flooding at the German Baltic Sea coast with the hydrodynamic model Delft3D. We produce probabilistic flood maps, which detail flood exposed areas together with annual probability of flooding. Additionally, we show how the flood extent changes, when accounting for upper, median, and lower quantiles of hydrograph intensities. Our results demonstrate that the relevance of the intensity is site and ESL dependent. While flood extents of some ESLs of the upper and lower intensity bounds indicate no differences, others differ by up to 45%. Further, we consider two ESLs (2.24 and 2.55 m) and simulate 100 intensities for each. Compared to intensity quantiles, this results in flood extents of up to 60% difference. Hence, we find that quantiles of intensity do not cover the full range when addressing uncertainty due to hydrograph variability. We, therefore, recommend accounting for a wide range of hydrograph intensities in addition to using a wide range of ESL in future flood risk assessments.

Without upgrading existing adaptation, Germany is projected to be among those Europeancountries that will suffer severe flood damages in 2100. Here we use a validated modelingframework to explore the effectiveness of two hypothetical upgrades to existing dike lines inreducing flood extent and population exposure along the German Baltic Sea coast. Weperform a number of model runs where we increase the heights of existing dikes by 1.5 m,implement managed realignment as a nature-based solution, where physically plausible, andrun a 200-year surge under two sea-level rise scenarios (1 and 1.5 m). We show thatmanaged realignment is more effective in reducing future population exposure to coastalflooding compared to increasing dike heights. However, the maximum reduction in populationexposure compared to a do-nothing approach amounts to only 26%, suggesting that evenmanaged realignment is insufficient to maintain flood risk at today´s levels. The greatestpotential for protecting people and property from future flooding lies in developing adaptationstrategies for currently unprotected coastal sections.

Among the Baltic Sea littoral states, Germany is anticipated to endure considerable damage as a result of increased coastal flooding due to sea-level rise (SLR). Consequently, there is a growing demand for flood risk assessments, particularly at regional scales, which will improve the understanding of the impacts of SLR and assist adaptation planning.

Existing studies on coastal flooding along the German Baltic Sea coast either use state-of-the-art hydrodynamic models but cover only a small fraction of the study region or assess potential flood extents for the entire region but rely on global topographic data sources and apply the simplified bathtub approach. In addition, the validation of produced flood extents is often not provided.

Here we apply a fully validated hydrodynamic modelling framework covering the German Baltic Sea coast that includes the height of natural and anthropogenic coastal protection structures in the study region. Using this modelling framework, we extrapolate spatially explicit 200-year return water levels, which align with the design standard of state embankments in the region, and simulate associated coastal flooding. Specifically, we explore (1) how flood extents may change until 2100 if dike heights are not upgraded, by applying two high-end SLR scenarios (1 and 1.5 m); (2) hotspots of coastal flooding; and (3) the use of SAR imagery for validating the simulated flood extents.

Our results confirm that the German Baltic coast is exposed to coastal flooding, with flood extent varying between 217 and 1016 km² for the 200-year event and a 200-year event with 1.5 m SLR, respectively. Most of the flooding occurs in the federal state of Mecklenburg-Western Pomerania, while extreme water levels are generally higher in Schleswig-Holstein. Our results emphasise the importance of current plans to update coastal protection schemes along the German Baltic Sea coast over the 21st century in order to prevent large-scale damage in the future.

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As sea-level rise (SLR) accelerates due to climate change, its multidisciplinary field of science has similarly expanded, from 41 articles published in 1990 to 1475 articles published in 2021, and nearly 15,000 articles published in the Web of Science over this 32-year period. Here, big-data bibliometric techniques are adopted to systematically analyse this large literature set. Four main research clusters (themes) emerge: (I) geological dimensions and sea-level indicators, (II) impacts, risks, and adaptation, (III) physical components of sea-level change, and (IV) coastal ecosystems and habitats, with 16 associated sub-themes. This analysis provides insights into the evolution of research agendas, the challenges and opportunities for future assessments (e.g. next IPCC reports), and growing focus on adaptation. For example, the relative importance of sub-themes evolves consistently with a relative decline in pure science analysis towards solution-focused topics associated with SLR risks such as high-end rises, declining ecosystem services, flood hazards, and coastal erosion/squeeze.

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Climate change-induced sea-level rise will lead to an increase in internal migration, whose intensity and spatial patterns will depend on the amount of sea-level rise; future socioeconomic development; and adaptation strategies pursued to reduce exposure and vulnerability to sea-level rise. To explore spatial feedbacks between these drivers, we combine sea-level rise projections, socioeconomic projections, and assumptions on adaptation policies in a spatially-explicit model (‘CONCLUDE’). Using the Mediterranean region as a case study, we find up to 20 million sea-level rise-related internal migrants by 2100 if no adaptation policies are implemented, with approximately three times higher migration in southern and eastern Mediterranean countries compared to northern Mediterranean countries. We show that adaptation policies can reduce the number of internal migrants by a factor of 1.4 to 9, depending on the type of strategies pursued; the implementation of hard protection measures may even lead to migration towards protected coastlines. Overall, spatial migration patterns are robust across all scenarios, with out-migration from a narrow coastal strip and in-migration widely spread across urban settings. However, the type of migration (e.g. proactive/reactive, managed/autonomous) depends on future socioeconomic developments that drive adaptive capacity, calling for decision-making that goes well beyond coastal issues.

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Coastal space is one of the most valuable assets of the EU coastal member states, as the coast is highly urbanized. Hard engineering has traditionally been employed to protect communities in coastal lowlands, but as this alternative becomes less sustainable and more costly, coastal managers are increasingly turning to landuse planning strategies, such as setback zones or managed retreat. To explore the efficiency of these planning tools in reducing future urban exposure to sea-level rise and associated hazards, we developed spatially explicit projections of urban extent that account for different socio-economic futures and various types of setback zones. We find that the establishment of coastal setback zones can reduce the exposure of new urban development by at least 50% in the majority of EU countries by 2100. Our results emphasize that future urban exposure to sea-level rise will be significantly influenced by the ways in which we plan, design, and develop urban space in the EU coastal lowlands.

Natural Hazards and Earth System SciencesRecent studies have drawn special attention to the significant dependencies between flood drivers and the occurrence of compound flood events in coastal areas. This study investigates compound flooding from tides, river discharge (Q), and specifically waves using a hydrodynamic model at the Breede Estuary, South Africa. We quantify vertical and horizontal differences in flood characteristics caused by driver interaction and assess the contribution of waves. Therefore, we compare flood characteristics resulting from compound flood scenarios to those in which single drivers are omitted. We find that flood characteristics are more sensitive to Q than to waves, particularly when the latter only coincides with high spring tides. When interacting with Q, however, the contribution of waves is high, causing 10 %–12 % larger flood extents and 45–85 cm higher water depths, as waves caused backwater effects and raised water levels inside the lower reaches of the estuary. With higher wave intensity, the first flooding began up to 12 h earlier. Our findings provide insights on compound flooding in terms of flood magnitude and timing at a South African estuary and demonstrate the need to account for the effects of compound events, including waves, in future flood impact assessments of open South African estuaries.

Managed realignment (MR) involves the landward relocation of sea defences to foster the (re)creation of coastal wetlands and achieve nature-based coastal protection. The wider application of MR is impeded by knowledge gaps related to lacking data on its effectiveness under extreme surges and the role of changes in vegetation cover, for example due to sea-level rise. We employ a calibrated and validated hydrodynamic model to explore relationships between surge attenuation, MR width(/area) and vegetation cover for the MR site of Freiston Shore, UK. We model a range of extreme water levels for four scenarios of variable MR width. We further assess the effects of reduced vegetation cover for the actual MR site and for the scenario of the site with the largest width. We show that surges are amplified for all but the largest two site scenarios, suggesting that increasing MR width results in higher attenuation rates. Substantial surge attenuation (up to 18 cm km−1) is only achieved for the largest site. The greatest contribution to the attenuation in the largest site scenario may come from water being reflected from the breached dike. While vegetation cover has no statistically significant effect on surge attenuations in the original MR site, higher coverage leads to higher attenuation rates in the largest site scenario. We conclude that at the open coast, only large MR sites (> 1148 m width) can attenuate surges with return periods > 10 years, while increased vegetation cover and larger MR widths enable the attenuation of even higher surges.

Carbon sequestration and storage in mangroves, salt   marshes and seagrass meadows is an essential coastal ‘blue carbon’ ecosystem   service for climate change mitigation. Here we offer a comprehensive, global   and spatially explicit economic assessment of carbon sequestration and   storage in three coastal ecosystem types at the global and national levels.   We propose a new approach based on the country-specific social cost of   carbon that allows us to calculate each country’s contribution to, and   redistribution of, global blue carbon wealth. Globally, coastal ecosystems   contribute a mean ± s.e.m. of US$190.67 ± 30 bn yr−1 to blue carbon wealth.   The three countries generating the largest positive net blue wealth   contribution for other countries are Australia, Indonesia and Cuba, with   Australia alone generating a positive net benefit of US$22.8 ± 3.8 bn yr−1   for the rest of the world through coastal ecosystem carbon sequestration and   storage in its territory.

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This study provides a literature-basedcomparative assessment of uncertainties and biases in global to world-regionalscale assessments of current and future coastal flood risks, considering meanand extreme sea-level hazards, the propagation of these into the floodplain,people and coastal assets exposed, and their vulnerability. Globally, by farthe largest bias is introduced by not considering human adaptation, which can leadto an overestimation of coastal flood risk in 2100 by up to factor 1300. Buteven when considering adaptation, uncertainties in how coastal societies willadapt to sea-level rise dominate with a factor of up to 27 all otheruncertainties. Other large uncertainties that have been quantified globally areassociated with socio-economic development (factors 2.3–5.8), digital elevationdata (factors 1.2–3.8), ice sheet models (factor 1.6–3.8) and greenhouse gasemissions (factors 1.6–2.1). Local uncertainties that stand out but have notbeen quantified globally, relate to depth-damage functions, defense failuremechanisms, surge and wave heights in areas affected by tropical cyclones (inparticular for large return periods), as well as nearshore interactions betweenmean sea-levels, storm surges, tides and waves. Advancing the state-of-the-artrequires analyzing and reporting more comprehensively on underlyinguncertainties, including those in data, methods and adaptation scenarios.Epistemic uncertainties in digital elevation, coastal protection levels anddepth-damage functions would be best reduced through open community-basedefforts, in which many scholars work together in collecting and validatingthese data.

Managed realignment (MR) constitutes a form of nature-based adaptation to coastal hazards, including sea level rise and storm surges. The implementation of MR aims at the (re)creation of intertidal habitats, such as saltmarshes, for mitigating flood and erosion risks and for creating more natural shorelines. However, some evidence suggests that the desired coastal protection function of MR schemes (in terms of high water level (HWL) attenuation) may be limited and it was hypothesized that this was due to the configuration of the remaining seawalls, which we refer to as scheme design. Here we present the results of a hydrodynamic model application, which we used to analyse the effects of scheme design on within-site HWL attenuation by applying six scheme designs that differ in terms of breach characteristics and water storage capacity. In specific, we vary the configuration of the seaward defence line (including the seawall breaches) and the position of the landward dike by modifying the digital elevation model of the site.

Our results show that changes in scheme design, particularly storage area and number and width of breaches, had significant effects on the site's HWL attenuation capacity. Decreasing the tidal prism by changing the number and size of breaches, with the site area kept constant, leads to increased modelled HWL attenuation rates. However, average HWL attenuation rates of >10 cm km−1 are only achieved when site size increases. The mean high water depth of each scheme design scenario, calculated by dividing tidal prism by MR area, explains most of the variation in average HWL attenuation between all scenarios. Attention to potential within-site hydrodynamics at the design stage will aid the construction of more effective MR schemes with respect to coastal protection in the future.

Changes in the spatial patterns and rate of urban development will be one of the main determinants of future coastal flood risk. Existing spatial projections of urban extent are, however, often available at coarse spatial resolutions, local geographical scales or for short time horizons, which limits their suitability for broad-scale coastal flood impact assessments. Here, we present a new set of spatially explicit projections of urban extent for ten countries in the Mediterranean, consistent with the Shared Socioeconomic Pathways (SSPs). To model plausible future urban development, we develop an Urban Change Model, which uses input variables such as elevation, population density or road network and an artificial neural network to project urban development on a regional scale. The developed future projections for the five SSPs indicate that accounting for the spatial patterns of urban development can lead to significant differences in the assessment of future coastal urban exposure. The increase in exposure in the Extended Low Elevation Coastal Zone (E-LECZ = area below 20 m of elevation) until 2100 can vary, by up to 104%, depending on the urban development scenario chosen. This finding highlights that accounting for urban development in long-term adaptation planning, e.g. in the form of land-use planning, can be an effective measure for reducing future coastal flood risk on a regional scale.

Remineralization of organic matter at the seafloor is an important ecosystem function, as it drives carbon and nutrient cycling, supplying nutrients for photosynthetic production, but also controls carbon burial within the sediment. In the Arctic Ocean, changes in primary production due to rapid sea-ice decline and thinning affect the export of organic matter to the seafloor and thus, benthic ecosystem functioning. Due to the remoteness and difficult accessibility of the Arctic Ocean, we still lack baseline knowledge about patterns of benthic remineralization rates and their drivers in both shelf and deep-sea sediments. Particularly comparative studies across regions are scarce. Here, we address this knowledge gap by contrasting benthic diffusive and total oxygen uptake rates (DOU and TOU), both established proxies of the benthic remineralization function, between shelf and deep-sea habitats of the Barents Sea and the central Arctic Ocean, sampled during a RV Polarstern expedition in 2015. DOU and TOU were measured using ex situ porewater oxygen microprofiles and sediment core incubations, respectively. In addition, contextual parameters including organic matter availability and microbial cell numbers were determined as environmental predictors. Pan-Arctic regional comparisons were obtained by extending our analyses to previously published data from the Laptev and Beaufort Seas. Our results show that (1) benthic oxygen uptake rates and most environmental predictors varied significantly between shelf and deep-sea habitats; (2) the availability of detrital organic matter is the main driver for patterns in total as well as diffusive respiration, while bacterial abundances were highly variable and only a weak predictor of differences in TOU and DOU; (3) regional differences in oxygen uptake across shelf and deep-sea sediments were mainly related to organic matter availability and may reflect varying primary production regimes and distances to the nearest shelf. Our findings suggest that the expected decline in sea-ice cover and the subsequent increase in export of organic matter to the seafloor may particularly enhance remineralization in the deep seas of the Arctic Ocean, altering benthic ecosystem functioning in future climate scenarios.

We introduce a novel approach to statistically assess the non-linear interaction of tide and non-tidal residual in order to quantify its contribution to extreme sea levels and hence its role in modulating coastal protection levels, globally. We demonstrate that extreme sea levels are up to 30% (or 70 cm) higher if non-linear interactions are not accounted for (e.g., by independently adding astronomical and non-astronomical components, as is often done in impact case studies). These overestimates are similar to recent sea-level rise projections to 2100 at some locations. Furthermore, we further find evidence for changes in this non-linear interaction over time, which has the potential for counteracting the increasing flood risk associated with sea-level rise and tidal and/or meteorological changes alone. Finally, we show how accounting for non-linearity in coastal impact assessment modulates coastal exposure, reducing recent estimates of global coastal flood costs by ~16%, and population affected by ~8%.

The Mediterranean coastal zone is particularly vulnerable to climate-induced sea-level rise due to rapid coastal development, leading to increased flood exposure in coastal areas. In Croatia, the share of developed coastline is still lower than in other Mediterranean countries, but development has accelerated since the 1960s. Available assessments of future coastal flood risk take into account adaptation by hard structural protection measures but do not consider other options, such as retreat from exposed areas or restricting future development. In this study, we provide the first assessment of the effects of setback zones on future coastal flood impacts on national scale. We extend the flood impact and adaptation module of the DIVA modelling framework with models of restricted future development and slow retreat (managed realignment) in the form of setback zones. We apply this model to a downscaled database of coastal segments of the coastline of Croatia. We find that setback zones are an effective and efficient measure for coastal adaptation. Construction restriction and managed realignment reduce the future cost of coastal flooding significantly, especially in combination with protection. If protection and construction restriction by setback zones are combined, the future cost of coastal flooding can be reduced by up to 39%. Combining protection and managed realignment by setback zones can reduce the future cost of coastal flooding by up to 93%.

China experiences frequent coastal flooding, with   nearly US$ 77 billion of direct economic losses and over 7,000 fatalities   reported from 1989 to 2014. Flood damages are likely to grow due to climate   change induced sea-level rise and increasing exposure if no further   adaptation measures are taken. This paper quantifies potential damage and   adaptation costs of coastal flooding in China over the 21st Century,   including the effects of sea-level rise. It develops and utilises a new,   detailed coastal database of China developed within the Dynamic Interactive   Vulnerability Assessment (DIVA) model framework. The refined database   provides a more realistic spatial representation of coasts, with more than   2700 coastal segments, covering 28,966 km of coastline. Over 50% of China’s   coast is artificial, representing defended coast and/or claimed land.   Coastal flood damage and adaptation costs for China are assessed for   different Representative Concentration Pathway (RCP) and Shared   Socio-economic Pathways (SSP) combinations representing climate change and   socio-economic change and two adaptation strategies: no upgrade of currently   existing defences and maintaining current protection levels. By 2100,   0.7–20.0 million people may be flooded/yr and US$ 67–3,308 billion damages/yr   are projected without upgrade to defences. In contrast, maintaining the   current protection level would reduce those numbers to 0.2–0.4 million   people flooded/yr and US$ 22–60 billion/yr flood costs by 2100, with   protection investment costs of US$ 8–17 billion/yr. In 2100, maintaining   current protection levels, dikes costs are two orders of magnitude smaller   than flood costs across all scenarios, even without accounting for indirect   damages. This research improves on earlier national assessments of China by   generating a wider range of projections, based on improved datasets. The   information delivered in this study will help governments, policy-makers,   insurance companies and local communities in China understand risks and   design appropriate strategies to adapt to increasing coastal flood risk in   an uncertain world.

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This study explores the uncertainty introduced in global assessments   of coastal flood exposure and risk when not accounting for water-level   attenuation due to land-surface characteristics. We implement a range of   plausible water-level attenuation values for characteristic land-cover   classes in the flood module of the Dynamic and Integrated Vulnerability   Assessment (DIVA) modelling framework and assess the sensitivity of flood   exposure and flood risk indicators to differences in attenuation rates.   Results show a reduction of up to 44 % in area exposure and even larger   reductions in population exposure and expected flood damages when   considering water-level attenuation. The reductions vary by country,   reflecting the differences in the physical characteristics of the floodplain   as well as in the spatial distribution of people and assets in coastal   regions. We find that uncertainties related to not accounting for water   attenuation in global assessments of flood risk are of similar magnitude to   the uncertainties related to the amount of sea-level rise expected over the   21st century. Despite using simplified assumptions to account for the   process of water-level attenuation, which depends on numerous factors and   their complex interactions, our results strongly suggest that an improved   understanding and representation of the temporal and spatial variation of   water levels across floodplains is essential for future impact modelling.

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Based on previous studies of tide-gauge records fromlocations with semidiurnal tidal regimes, extreme skew surges are alwaysassumed independent of the high water (HW). However, differences in water depthbetween HW peaks of semidiurnal tidal regimes can be much lower than those inmixed semidiurnal regimes, where one daily HW is higher than the other. Westatistically analyze tide-gauge records of 15 sites worldwide with a mixedsemidiurnal regime and find that for approximately half of these sites extremeskew surges occur more often during smaller HWs. This dependence is not causedby seasonality effects, and the places that show dependence are all located inareas with a shallow continental shelf, thus indicating possible tide-skewsurge interactions. In those cases where dependence exists, using the skewsurge does not seem to offer any advantages over the nontidal residual.

The response of coastal wetlands to sea-level riseduring the twenty-first century remains uncertain. Global-scale projectionssuggest that between 20 and 90 per cent (for low and high sea-level risescenarios, respectively) of the present-day coastal wetland area will be lost,which will in turn result in the loss of biodiversity and highly valuedecosystem services1,2,3. These projections do not necessarily take into accountall essential geomorphological4,5,6,7 and socio-economic system feedbacks8. Herewe present an integrated global modelling approach that considers both theability of coastal wetlands to build up vertically by sediment accretion, andthe accommodation space, namely, the vertical and lateral space available forfine sediments to accumulate and be colonized by wetland vegetation. We usethis approach to assess global-scale changes in coastal wetland area inresponse to global sea-level rise and anthropogenic coastal occupation duringthe twenty-first century. On the basis of our simulations, we find that,globally, rather than losses, wetland gains of up to 60 per cent of the currentarea are possible, if more than 37 per cent (our upper estimate for currentaccommodation space) of coastal wetlands have sufficient accommodation space,and sediment supply remains at present levels. In contrast to previousstudies1,2,3, we project that until 2100, the loss of global coastal wetlandarea will range between 0 and 30 per cent, assuming no further accommodationspace in addition to current levels. Our simulations suggest that theresilience of global wetlands is primarily driven by the availability ofaccommodation space, which is strongly influenced by the building ofanthropogenic infrastructure in the coastal zone and such infrastructure is expectedto change over the twenty-first century. Rather than being an inevitableconsequence of global sea-level rise, our findings indicate that large-scaleloss of coastal wetlands might be avoidable, if sufficient additionalaccommodation space can be created through careful nature-based adaptationsolutions to coastal management.

We have developed anew coastal database for the Mediterranean basin that is intended for coastalimpact and adaptation assessment to sea-level rise and associated hazards on aregional scale. The data structure of the database relies on a linear representationof the coast with associated spatial assessment units. Using information oncoastal morphology, human settlements and administrative boundaries, we havedivided the Mediterranean coast into 13 900 coastal assessment units. To theseunits we have spatially attributed 160 parameters on the characteristics of thenatural and socio-economic subsystems, such as extreme sea levels, verticalland movement and number of people exposed to sea-level rise and extreme sealevels. The database contains information on current conditions and onplausible future changes that are essential drivers for future impacts, such assea-level rise rates and socio-economic development. Besides its intended usein risk and impact assessment, we anticipate that the Mediterranean CoastalDatabase (MCD) constitutes a useful source of information for a wide range ofcoastal applications.

The effectiveness of stringent climatestabilization scenarios for coastal areas in terms of reduction ofimpacts/adaptation needs and wider policy implications has received littleattention. Here we use the Warming Acidification and Sea Level Projector Earthsystems model to calculate large ensembles of global sea-level rise (SLR) andocean pH projections to 2300 for 1.5°C and 2.0°C stabilization scenarios, and areference unmitigated RCP8.5 scenario. The potential consequences of theseprojections are then considered for global coastal flooding, small islands,deltas, coastal cities and coastal ecology. Under both stabilization scenarios,global mean ocean pH (and temperature) stabilize within a century. This impliessignificant ecosystem impacts are avoided, but detailed quantification islacking, reflecting scientific uncertainty. By contrast, SLR is only slowed andcontinues to 2300 (and beyond). Hence, while coastal impacts due to SLR arereduced significantly by climate stabilization, especially after 2100,potential impacts continue to grow for centuries. SLR in 2300 under bothstabilization scenarios exceeds unmitigated SLR in 2100. Therefore, adaptationremains essential in densely populated and economically important coastal areasunder climate stabilization. Given the multiple adaptation steps that this willrequire, an adaptation pathways approach has merits for coastal areas.

We present an analysis of the long-term trends andvariability of extreme water and tidal levels and the main tidal constituentsusing long-term records from two tide gauges in the wider region of the Rio dela Plata estuary: Buenos Aires (1905–2013) and Mar del Plata (1956–2013). Wefind significant long-term trends in both tidal levels and the main tidalconstituents (M2, S2, K1, O1, and the overtide M4) from a running harmonicanalysis in both locations. The tidal range decreased on average 0.63mm y−1, asa result of an increase of the low water levels and a decrease of the highwater levels. We also find a secular decrease in the amplitude of thesemi-diurnal constituents and an increase of the diurnal ones, but of differentmagnitudes at each location, which suggests that different processes areproducing these changes. In Buenos Aires, an increase of river discharge intothe estuary seems to reduce the tidal range by hampering the propagation of thetidal wave into the estuary, whereas no influence of river discharge on waterand tidal levels can be detected in Mar del Plata. We believe that otherfactors such as thermohaline changes or the rise of mean sea-level may beresponsible for the observed tidal range decrease. Despite the tidal long-termtrends, we find no significant trends in the meteorological component of thetide-gauge records other than an increase in the mean sea-level. In addition,we explore teleconnections between the variability of the meteorological

Both the temporal and spatial variability of stormsurge water level (WL) curves are usually not taken into account in flood riskassessments as observational data are often scarce. In addition, sea-level rise(SLR) can further affect the variability of WLs. We analyze the temporal andspatial variability of the WL curve of 75 historical storm surge events thathave been numerically simulated for St. Peter-Ording at the German North Seacoast, considering the effects induced by three SLR scenarios (RCP 4.5, RCP8.5, and a RCP 8.5 high end scenario). We assess potential impacts of thesescenarios on two parameters related to flooding: overflow volumes and fullness.Our results indicate that due to both the temporal and spatial variability ofthose events the resulting overflow volume can be two or even three timesgreater. We observe a steepening of the WL curve with an increase of the tidalrange under the three SLR scenarios, although SLR induced effects are rela-tively higher for the RCP 4.5. The steepening of the WL curve with SLR producesa reduction of the fullness, but the changes in overflow volumes also depend onthe magnitude of the storm surge event.

This paper assesses sea-level rise related coastalflood impacts for Emilia-Romagna (Italy) using the Dynamic InteractiveVulnerability Assessment (DIVA) modeling framework and investigate thesensitivity of the model to four uncertainty dimensions, namely (1) elevation,(2) population, (3) vertical land movement, (4) scale and resolution ofassessment. A one-driver-at-a-time sensitivity approach is used in order toexplore and quantify the effects of uncertainties in input data and assessmentscale on model outputs. Of particular interest is the sensitivity of flood riskestimates when using datasets of different resolution. The change in assessmentscale is implemented through the use of a more detailed digital coastline andinput data for the coastline segmentation process. This change leads to a35-fold increase in the number of coastal segments and in a more realisticspatial representation of coastal flood impacts for the Emilia-Romagna coast.Furthermore, the coastline length increases by 43%, considerably influencingadaptation costs (construction of dikes). With respect to input data ourresults show that by the end of the century coastal flood impacts are moresensitive to variations in elevation and vertical land movement data than tovariations in population data in the study area. The inclusion of localinformation on human induced subsidence rates increases the relative sea-levelby 60 cm in 2100, resulting in coastal flood impacts that are up to 25% highercompared to those generated with the global DIVA values, which mainly accountfor natural processes. The choice of one elevation model over another canresult in differences of ~45% of the coastal floodplain extent and up to 50% inflood damages by 2100. Our results emphasize that the scale of assessment andresolution of the input data can have significant implications for the resultsof coastal flood impact assessments. Understanding and communicating theseimplications is essential for effectively supporting decision makers indeveloping long-term robust and flexible adaptation plans for future changes ofhighly uncertain scale and direction.