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Beside climate‐change‐induced sea‐level rise (SLR), land subsidence can strongly amplify coastal risk in flood‐prone areas. Mapping and quantifying contemporary vertical land motion (VLM) at continental scales has long been a challenge due to the absence of gridded observational products covering these large domains. Here, we fill this gap by using the new European Ground Motion Service (EGMS) to assess the current state of coastal VLM in Europe. First, we compare the InSAR‐based EGMS Ortho (Level 3) with nearby global navigation satellite systems (GNSS) vertical velocity estimates and show that the geodetic reference frame used to calibrate EGMS strongly influences coastal vertical land velocity estimates at the millimeter per year level and this needs to be considered with caution. After adjusting the EGMS vertical velocity estimates to a more updated and accurate International Terrestrial Reference Frame (ITRF2014), we performed an assessment of VLM in European low elevation coastal flood plains (CFPs). We find that nearly half of the European CFP area is, on average, subsiding at a rate faster than 1 mm/yr. More importantly, we find that urban areas and populations located in the CFP experience a near −1 mm/yr VLM on average (excluding the uplifting Fennoscandia region). For harbors, the average VLM is even larger and increases to −1.5 mm/yr on average. This demonstrates the widespread importance of continental‐scale assessments based on InSAR and GNSS to better identify areas at higher risk from relative SLR due to coastal subsidence. Plain Language Summary: Land subsidence increases the risk of flooding in low‐lying coastal zones by amplifying relative sea‐level rise (SLR). In this study, we assess for the first time current coastal land subsidence at the scale of Europe using the new Copernicus European Ground Motion Service (EGMS) that was released in 2022. Our results suggest that nearly half of the low‐lying coastal areas in Europe are currently subsiding at a rate faster than 1 mm/yr on average. We find that coastal subsidence is higher on average in areas hosting more people, urban centers and critical infrastructure. This raises concerns that coastal subsidence, and therefore relative SLR, tends to be underestimated in Europe and presumably in many other regions around the world. Our study demonstrates that emerging continental‐scale land motion services such as EGMS are useful to better characterize the issue and anticipate coastal risks and adaptation accordingly. Key Points: Continental‐scale coastal land motion assessment in Europe is performed based on the European Ground Motion Service released in 2022European flood‐prone coastal cities subside on average at 1 mm/yr (Fennoscandia excluded)The geocentric reference frame used to calibrate continental‐scale land motion affects the results for geodetic (non‐geophysical) reasons [ABSTRACT FROM AUTHOR]

Coastal zones are increasingly threatened by extreme sea level events. Storm surges are one of the most hazardous components of these extremes, especially in regions prone to tropical cyclones. This study aims to explore factors affecting the performance of numerical modelling in simulating storm surges in the tropical Atlantic region. The maxima, duration and time evolution of the extreme storm surge events are evaluated for four historical hurricanes by comparison against tide gauge records. The ADCIRC and NEMO ocean models are intercompared using a similar configuration in terms of domain, bathymetry and spatial resolution. These models are then used to perform sensitivity experiments on oceanic and atmospheric forcings, physical parameterizations for wind stress and baroclinic/barotropic modes. NEMO and ADCIRC show a similar skill to simulate storm surges induced by hurricanes. Storm surges simulated with ERA5 atmospheric reanalysis forcing are generally more accurate than those using parametric wind models for simulated hurricanes. The inclusion of the baroclinic processes improves storm surge amplitudes in some coastal locations such as along the southeastern Florida peninsula (USA). Experiments exploring different wind stress implementations and the interactions between storm surges, tides and mean sea level however have shown a minimal impact on storm surges induced by hurricanes. [ABSTRACT FROM AUTHOR]

Coastal flood risk assessment requires a reliable estimation of the frequency of inundation hazards, that is, characterising the hazard magnitude and assigning a probability of occurrence. In this work we analyse the uncertainty introduced in the assessment associated to the method to assign the probability of occurrence to coastal flood hazards. To this end we have compared the use of two general methods, the response and the event approaches. Different procedures are used to characterise coastal inundation hazards depending on the analysis scale and data availability. Thus, a range of possibilities has been analysed, from simple estimators such as run‐up to modelled flood‐prone areas. The analysis has been performed for all wave and water level conditions around the Spanish coast. The results show that the differences between the methods are location‐dependent, and thus, determined by the exposure to wave and water level conditions. When using the event approach, the run‐up or total water level (with good correlation between waves and surge) distributions reasonably approximate those of the response approach with low associated uncertainty. When the assessment aims to output overtopping discharges or inundation maps, observed differences suggest that the event approach would produce misleading conclusions in inundation‐related coastal management and decision‐making. [ABSTRACT FROM AUTHOR]

Shoreline recession due to the combined effect of waves, surges, tides and sea level rise (SLR) is increasingly becoming a major threat to beaches, one of the main seaside tourist destinations worldwide. Given such an uncertain future climate and the climate-sensitive nature of many decisions that affect the long term, there is a growing need to shift current approaches towards probabilistic frameworks able to consider uncertainty. We develop a methodology to assess climate change-driven coastal erosion risk based on the IPCC risk framework (IPCC, 2014), in which risk results from the interplay of hazard, represented by the coastal dynamics, exposure, described by physical and socioeconomic settings, and vulnerability, associated with the susceptibility and adaptive capacity of the system. The methodology consists of a multitiered process in which these components are developed individually but are finally integrated to derive expected losses. A statistical method to generate beach erosion hazards must take into account that this impact involves two or more random variables (i.e., significant wave height, sea level), and that the erosion process depends on storm duration and antecedent beach conditions, which relies in turn on beach recovery between storms. Multiple simulations of a process-based approach that combine cross section–based equilibrium models and long-shore sinks allow the reconstruction of thousands of potential shoreline evolutions over the 21st century (Toimil et al., 2017).Exposure is defined by the users' preferences (i.e., when they would rather go to the beach), expressed in terms of effective utilization rates and their purchasing power, as an indicator of how much they value the time for recreation (Toimil et al., 2018). Concerning vulnerability, aspects related to the typology, the quality (i.e., water, sand and services), and the number and distribution of access points and parking facilities are considered (Toimil et al., 2018).We present a regional approach for the assessment of erosion risks triggered by climate-related extreme events and SLR. The framework is applied regionally over the Asturian coast, a 345 km coastline on the Cantabrian Sea (North of Spain), where the risk of loss of beach recreation as a proxy for tourism is provided in probabilistic terms.ReferencesIPCC (2014) Summary for policymakers. In Climate Change 2014: Impacts, Adaptation and Vulnerability. Part A: Global and Sectoral Aspects. Contribution of Working Group II to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [eds. CB Field al.]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 2014, pp. 1-32.Toimil A, Losada IJ, Camus P, Diaz-Simal P. (2017). Managing coastal erosion under climate change at the regional scale. Coastal Engineering, 128, 106–122. Toimil A, Diaz-Simal P, Losada IJ, Camus P (2018) Estimating the risk of loss of beach recreation value under climate change. Tourism Management 68:387-400. [ABSTRACT FROM AUTHOR]