Displays

The loss of life from natural hazards has decreased over the past century, due partly to much improved understanding and monitoring of hazards and partly to improvements in preparedness, communication, engineered infrastructure. This has happened at a time when human numbers have more than quadrupled and now approach 8 billion, and when populations in areas vulnerable to earthquakes and cyclones have greatly increased. Now, however, we may be on the doorstep of a ‘tipping point’ in human suffering and life loss due to the rapid changes in Earth’s climate that we are experiencing. Human-induced climate change is increasingly amplifying dangerous meteorological processes, including severe storms, drought, wildfires, heat waves, and flooding. These changes have no precedent in the past 10,000 years and are blurring the distinction between ‘natural hazards’ and human-induced hazards. The threats posed by climate change are legion; in this presentation, I discuss a set of linked phenomena that represent an emerging threat to people and society over the remainder of this century and beyond – specifically sea-level rise and coincident stronger cyclonic storms, which, on occasion, inundate low-lying coastal areas. Hurricanes and typhoons are likely to become more intense in a warmer climate and will produce higher storm surges that move ashore on an elevated sea surface. The average level of Earth’s oceans is currently rising at a rate of over 3 mm per year, which is nearly 50 percent higher than a century ago. The rate of sea-level rise is increasing due, in part, to increasing transfers of water into oceans from glaciers and ice sheets and, in part, to the warming and expansion of seawater. Scientists forecast that average global sea level will be about 1 m higher by the end of this century than today. Over 600 million people, nearly 10% of the human population, currently live less than 10 m above sea level, many in growing coastal megacities. That number will increase dramatically over the next 50 years, increasing the overall risk that people face from extreme storms. The number of people living at low elevations along coasts, and thus exposed to flooding from storm surges, is highest in Asia, particularly in China, India, Bangladesh, Indonesia, and Viet Nam, which are ill-equipped to deal with the emerging crisis. Within limits, humans can adapt to severe storms and higher sea levels, but few countries have the resources to adequately protect people and property from this threat. Thus, without urgent action on a global scale to limit the damage we are causing to Earth’s climate and without a stabilization of human numbers, many populated low-lying coastal areas could become uninhabitable by the end of this century. The forced relocation of large numbers of people is likely to cause suffering and conflict that we do not appreciate and have not planned for. More generally, human suffering stemming from human-induced climate change will outstrip the progress we have made over the past century in reducing life loss from ‘natural hazards’.

How to cite: Clague, J.: Notes from the Front Lines of the Climate Crisis - The Threat of Cyclonic Storms and Sea Level Rise in a Warming World, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2100, https://doi.org/10.5194/egusphere-egu2020-2100, 2020.

Storm surges are driven by low air pressure and strong winds in tropical (TC) and extratropical cyclones (ETC). Coastal flooding is often caused by this type of extreme weather with large socio-economic impacts in densely populated and low-lying coastal areas. Recent examples of coastal disasters include typhoon Hagibis that made landfall in Japan, Hurricane Dorian which devastated the northwestern Bahamas, and extratropical cyclone Xaver that affected northern Europe. Each of these storms generated dangerous storm surges, reaching 6m in some parts of the Bahamas during Hurricane Dorian with approximately 100 fatalities as a result. Economic losses are estimated at 10 billion U.S. Dollars for both typhoon Hagibis and hurricane Dorian.

To inform flood risk management and develop effective adaptation strategies it is important to have accurate information on return periods of extreme sea levels. To date, there exists no global database with return periods of extreme sea levels that fully includes TCs. Global databases of extreme sea levels are typically based on historical climate simulations covering multiple decades. While this is sufficient for ETCs, TCs will be underestimated in such databases. This because TCs have generally low probabilities and affect only a small stretch of coastline, compared to ETCs. A climate reanalysis covering multiple decades includes too few TCs to perform an extreme value analysis. To resolve this, previous studies at local scale have used synthetic TC tracks generated by a statistical model to estimate the probabilities of extreme sea levels.

The aim of this research is to develop a global database of extreme sea levels that include both ETCs and TCs. For ETCs, we force the hydrodynamic Global Tide and Surge Model (GTSM) with ERA5 10-meter wind speed and air pressure data to calculate the return periods of extreme sea levels based on the period 1979-2017. Since ERA5 includes all storms, we filter out extreme sea levels caused by TCs. Preliminary results show that GTSM forced with ERA5 atmospheric data performs well for ETCs. For TCs, we force GTSM with synthetic TC tracks that correspond to 10.000 year of TC statistics. The synthetic tracks of TCs are obtained from the STORM model (Bloemendaal et al., in review) based on the International Best Track Archive for Climate Stewardship (IBTrACS) TC database. With STORM it is possible to statistically extend the ~38-year observed dataset to a 10.000-year synthetic dataset. The synthetic dataset preserves the climatological statistics as found in the original dataset. Finally, we will merge the TC and ETC related return periods to create a global extreme sea level database.

How to cite: Dullaart, J.: Creating a global database with return periods of extreme sea levels caused by tropical and extratropical cyclones, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-308, https://doi.org/10.5194/egusphere-egu2020-308, 2020.

Typhoon-induced storm surges and waves are highly related with typhoon track and associated wind stresses and atmospheric pressures at sea surface. The effects of binary interaction may alter typhoon tracks and even forward speed, which might influence waves and surge heights in the ocean. In the present study, we execute a series of numerical experiments to investigate how isolated and binary typhoons would impact the ocean waves and generated surges offshore and nearshore. The responses of binary typhoons to sea level rise and land subsidence are also discussed. The Typhoon Tembin and Typhoon Bolaven influenced the East China Sea with equivalent intensity of tropical storm and Category 2, respectively, on the Saffir–Simpson hurricane wind scale. The Weather Research and Forecasting (WRF) model is utilized to hindcast the layered wind and atmospheric pressure fields above sea/land surface. Two synthetic scenarios isolating these individual typhoons are designed to investigate the potential impacts of the binary-interacted typhoons. By coupling with the SCHISM–WWMIII modelling system, the corresponding surge–tide–wave processes are solved and validated with measurements at tidal gauge and wave buoy stations. At the same time, The spatial-varied future relative sea level rise (RSLR) by the end of the century is projected from satellite altimeter data-based sea level analysis and is adjusted for the influence of the Glacial Isostatic Adjustment (GIA) using the ICE-6G/VM5a model. The results indicate that the surge and wave heights induced by these two typhoons were not exacerbated significantly, as the hours influencing the Yellow Sea by Typhoon Tembin were about 30 hours later than Typhoon Bolaven. We also present the spatial distribution of nonlinear responses of storm surge induced extreme sea levels to RSLR, implicating the regions of exacerbation and attenuation, respectively, due to future sea level trend. The present study helps identifying distribution patterns by binary-interacted typhoons and enhancing assessment accuracy of potential coastal hazards and flood risk.

How to cite: Yang, J., Li, Y., and Chen, M.: Impacts of Binary-interacted Typhoons Tembin and Bolaven in 2012 on Surges and Waves over the East China Sea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6345, https://doi.org/10.5194/egusphere-egu2020-6345, 2020.

Tropical cyclones (TCs) are natural disasters for coastal regions. TCs with maximum wind speeds higher than 32.7 m/s in the north-western Pacific are referred to as typhoons. Typhoons Sarika and Haima successively passed our moored observation array in the northern South China Sea in 2016. Based on the satellite data, the winds (clouds and rainfall) biased to the right (left) sides of the typhoon tracks. Sarika and Haima cooled the sea surface ~4 and ~2 °C and increased the salinity ~1.2 and ~0.6 psu, respectively. The maximum sea surface cooling occurred nearly one day after the two typhoons. Station 2 (S2) was on left side of Sarika’s track and right side of Haima’s track, which is studied because its data was complete. Strong near-inertial currents from the ocean surface toward the bottom were generated at S2, with a maximum mixed-layer speed of ~80 cm/s. The current spectrum also shows weak signal at twice the inertial frequency (2f). Sarika deepened the mixed layer, cooled the sea surface, but warmed the subsurface by ~1 °C. Haima subsequently pushed the subsurface warming anomaly into deeper ocean, causing a temperature increase of ~1.8 °C therein. Sarika and Haima successively increased the heat content anomaly upper than 160 m at S2 to ~50 and ~100 m°C, respectively. Model simulation of the two typhoons shows that mixing and horizontal advection caused surface ocean cooling, mixing and downwelling caused subsurface warming, while downwelling warmed the deeper ocean. It indicates that Sarika and Haima sequentially modulated warm water into deeper ocean and influenced internal ocean heat budget. Upper ocean salinity response was similar to temperature, except that rainfall refreshed sea surface and caused a successive salinity decrease of ~0.03 and ~0.1 psu during the two typhoons, changing  the positive subsurface salinity anomaly to negative.

How to cite: Zhang, H.: Ocean Response to Successive Typhoons Sarika and Haima (2016) in the Northern South China Sea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6882, https://doi.org/10.5194/egusphere-egu2020-6882, 2020.

In the past decade, many different projections of global and regional sea-level rise as a result of climate change have been published (Garner et al, 2018, Horton et al, 2018). This wide range of projections illustrates the large uncertainty about future sea-level rise, which is complicated for coastal decision makers relying on these projections. Here, we aim to provide insights into the available projections, by identifying the main contributing sources in each of the sea-level projections, and sorting the projections into ‘families’ that have contributing sources or methodologies in common. Using these ‘families’, we discuss the main differences between projections in terms of rates and timing of certain levels of sea-level rise. 

Sea-level rise projections are often compared by showing amounts or rates at a certain future point in time, e.g., 2050 or 2100. For many areas, a sea-level rise exceeding 1 to 2 m will require truly transformative decisions. Such decisions have a long lead time (in the order of 30 years) for planning and implementation. Showing the timing of a particular rate or magnitude of sea-level rise may provide insight that it is not a matter of if and how to adapt, but when to adapt. This may help decision makers in dealing with the uncertainties and it may accelerate adaptation.

We find that a sea-level rise of 25 cm (since 2000) is first reached for each of the RCP scenarios (the 95^th percentile) within a decade of each other. This indicates that for a structure with a lifetime based on a sea-level rise of 25 cm, decisions are not conditional on the RCP scenario. The latest year for crossing the 25 cm threshold (the 5^th percentile), however, does depend more on the RCP scenario: for the RCP2.6 scenario this is later than for the RCP8.5 scenario, because the acceleration is less strong. As the levels examined grow (0.25 m, 0.5 m, 0.75 m, etc.), the initial year of reaching that level starts to diverge more between the scenarios, and therefore the timing of decision points starts to be more and more conditional upon RCP scenario. However, for investments with a long envisioned lifetime such as coastal infrastructure, certain amounts of sea level rise may still be within the lifetime independent of the RCP scenario.

How to cite: Slangen, A. and Haasnoot, M.: Timing of rates and magnitude of sea-level rise projection families, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13301, https://doi.org/10.5194/egusphere-egu2020-13301, 2020.

Sea-level rise (SLR) is a major concern for coastal hazards such as flooding and erosion in the decades to come. Lately, the value of high-end sea-level scenarios (HESs) to inform stakeholders with low-uncertainty tolerance has been increasingly recognized. Here, we provide high-end projections of SLR-induced sandy shoreline retreats for Europe by the end of the 21st century based on the conservative Bruun rule. Our HESs rely on the upper bound of the RCP8.5 scenario “likely-range” and on high-end estimates of the different components of sea-level projections provided in recent literature. For both HESs, SLR is projected to be higher than 1 m by 2100 for most European coasts. For the strongest HES, the maximum coastal sea-level change of 1.9 m is projected in the North Sea and Mediterranean areas. This translates into a median pan-European coastline retreat of 140 m for the moderate HES and into more than 200 m for the strongest HES. The magnitude and regional distribution of SLR-induced shoreline change projections, however, utterly depend on the local nearshore slope characteristics and the regional distribution of sea-level changes. For some countries, especially in Northern Europe, the impacts of high-end sea-level scenarios are disproportionally high compared to those of likely scenarios.

How to cite: Thiéblemont, R., Le Cozannet, G., Toimil, A., Meyssignac, B., and Losada, I.: Likely and High-End Impacts of Regional Sea-Level Rise on the Shoreline Change of European Sandy Coasts Under a High Greenhouse Gas Emissions Scenario, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3553, https://doi.org/10.5194/egusphere-egu2020-3553, 2020.

Global scale assessment of coastal flood damage and adaptation costs under 21st century sea-level rise are associated with a wide range of uncertainties including those in future projections of socioeconomic development (SSP scenarios), of greenhouse gas emissions (RCP scenarios), and of sea-level rise (SLR). These uncertainties also include structural uncertainties related to the modeling of extreme sea levels, vulnerability functions, and the translation of flooding-induced damage to costs. This raises the following questions: what is the relative importance of each source of uncertainty in the final global-scale results? Which sources of uncertainty need to be considered? What uncertainties are of negligible influence? Hence, getting better insights in the role played by these uncertainties allows to ease their communication and to structure the message on future coastal impacts and induced losses. Using the integrated DIVA Model (see e.g. Hinkel et al., 2014, PNAS), we extensively explore the impact of these uncertainties in a global manner, i.e. by considering a large number (~3,000) of scenario combinations and by analyzing the associated results using a regression-based machine learning technique (i.e. regression decision trees). On this basis, we show the decreasing roles, over time, of the uncertainties in the extremes’ modeling together with the increasing roles of SSP and of RCP after 2030 and 2080 for the damage and adaptation costs respectively. This means that mitigation of climate change helps to reduce uncertainty of adaptation costs, and choosing a particular SSP reduces the uncertainty on the expected damages. In addition, the tree structure of the machine learning technique allows an in-depth analysis of the interactions of the different uncertain factors. These results are discussed depending on the SLR data selected for the analysis, i.e. before and after the recently released IPCC SROCC report on September 2019.

How to cite: Rohmer, J., Lincke, D., Hinckel, J., Le Cozannet, G., and Lambert, E.: Global analysis of the uncertainties prevailing in global-scale assessment of coastal flood damage and adaptation costs under 21st century sea-level rise, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7859, https://doi.org/10.5194/egusphere-egu2020-7859, 2020.

For how long low-elevation coastal areas will be habitable under the effects of mean sea-level rise and marine extreme hazards? Mean sea-level rise, despite having a global origin, has severe local coastal impacts, as it raises the baseline level on top of which extreme storm surges and wind-waves reach the coastlines and, consequently, increases coastal exposure. In this presentation we will show coastal modelling exercises, fed with regionalised climate information of mean sea level and marine extremes, and applied in different environments that include sandy beaches and atoll islands. The outputs are aimed at anticipating the potential impacts of the dominant drivers in terms of land loss, coastal flooding and erosion. Our examples will be focusing on islands, for which the effects of increased coastal exposure are relatively larger, where local economy is often linked to coastal activities and retreat and migration are hampered by the limited land availability.

How to cite: Marcos, M. and Amores, A.: Impacts of mean sea-level rise and marine extremes on islands, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10237, https://doi.org/10.5194/egusphere-egu2020-10237, 2020.

The Maldives, located in the Indian Ocean, are the paradigm of low-lying coral-reef islands where adaptation to climate change is essential. Besides the mean sea level rise in this region, that is expected to be around 1 m by the end of the century according to the last IPCC report, these islands are exposed to one of the largest swells in terms of significant wave height and peak period. In this study we characterize, using the output of global wind-wave models forced by wind fields from the CMIP5 ensemble delivered by CSIRO, the present conditions and future projections of the waves around the Maldivian archipelago, as well as the return periods for the predominant swell directions. We then propagate extreme waves inside the domain using WaveWatch III model run onto a high-resolution grid (down to 500 m at the coast). Finally, we evaluate the coastal impacts of extreme swell waves in two strategic case study islands with different exposures and where land reclamation and different adaptation solutions have been/are being done. To do so, we propagate waves using SWASH model with rising mean sea level towards the shoreline and assess the flooding extend under different conditions. This kind of studies are essential to help the policy makers in defining the most accurate and appropriate adaptation strategies.

How to cite: Amores, A., Marcos, M., Pedreros, R., Le Cozannet, G., Lecacheux, S., Rohmer, J., Hinkel, J., Gussmann, G., van der Pol, T., and Shareef, A.: Waves and sea-level rise induced flooding in the Maldives, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3056, https://doi.org/10.5194/egusphere-egu2020-3056, 2020.

Damage to coastal structures and surrounding properties from wave overtopping in extreme events is expected to be exacerbated in future years as global sea levels continue to rise and the frequency of extreme meteorological events and storm surges increases.  Approaches for protecting our coastal areas have traditionally relied on the development and ongoing maintenance of ‘hard’ defences.  However, the longer-term sustainability of coastal flood management that is underpinned by such defences is increasingly being questioned both in terms of dealing with climate change and in the environmental/ ecological consequences and associated losses of biodiversity that comes with these structural defence lines in coastal areas.

The term 'nature-based' has emerged in recent years to describe biomimicry-based engineered interventions in coastal defences. For example, the addition of artificial water-filled depressions on coastal structures e.g. ‘vertipools’ on seawalls and the use of ‘drill-cored rock pools in intertidal breakwaters that enhance biodiversity and species richness on sea defence surfaces and in adjacent coastal zones. While the ecological benefits of such interventions are increasingly being investigated, the additional roughness they bring to sea defences and the role of this roughness in wave energy dissipation and in the mitigation of wave overtopping remains less well studied.

Here we investigate the wave overtopping characteristics of artificially roughened seawalls in a suite of laboratory experiments conducted in a two-dimensional wave flume at the University of Warwick, UK.  An impermeable sloping foreshore with a uniform slope of 1 in 20 was constructed in front of a vertical seawall. The seawall was subsequently modified by including 10 no. different test combinations of surface protrusions of varying scale and surface density, replicating ‘green’ measures suitable for retrofitting to existing seawalls.  Wave overtopping was measured for each test.  All tests comprised approximately 1000 JONSWAP pseudo-random wave sequences. Both impulsive and non-impulsive wave conditions were considered in experiments with two constant deep-water wave steepness values of 2% and 5%.

Results from benchmark (plain seawalls) experiments showed an overall good agreement with predictions from new overtopping manual, EurOtop II, the European empirical design guidance for wave overtopping of sea defences and related structures.  However, test results for the ecologically modified sea defences under impulsive (breaking) wave conditions showed significant reductions (up to factor 4) in overtopping compared to predictions from EurOtop codes.  Reductions in overtopping for artificially roughened defences under non-impulsive wave conditions were less conclusive.  Overall, results indicate that there can be a dual benefit in retrofitting sea defences with ecological features, the first being enhanced biodiversity in the coastal zone and the second being reduced flood risk in coastal areas from reductions in overtopping, particularly for breaking wave conditions.

The work in this paper is being undertaken as part of the Interreg funded Ecostructure project (www.ecostructureproject.eu), part-funded by the European Regional Development Fund through the Ireland Wales Cooperation Programme 2014-2020.

How to cite: Salauddin, M., O'Sullivan, J., Abolfathi, S., and Pearson, J.: Extreme wave overtopping at ecologically modified sea defences, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6162, https://doi.org/10.5194/egusphere-egu2020-6162, 2020.

Intertidal coastal wetlands, including tidal marshes and mangrove forests, are at risk of disappearing under the influence of global sea level rise (SLR). Loss of their ecosystem services could significantly impact global carbon budgets, increase coastal erosion and flooding and lead to loss of fisheries, particularly along densely populated coastal zones such as large estuaries and deltas. Regional to global-scale projections suggest a reduction in present-day coastal wetland area by 20% to 90% in response to projected rates of future SLR. Recent studies have highlighted the importance of coastal squeeze, i.e. the inhibition of inland migration of tidal coastal wetlands due to the existence of anthropogenic infrastructure, in combination with wetland loss due to sea level rise, which is aggravated by a global decline in coastal sediment supply.

Nature-based adaptation, consisting of the reservation or creation of space for inland wetland expansion, is widely regarded as a promising strategy to counteract coastal squeeze and create/restore natural habitats through inland migration. Based on global and regional modelling outputs, this paper discusses how different scenarios of global population growth, expected declines in global sediment supply, delta subsidence and various coastal management strategies impact on global areas of intertidal coastal wetlands, and coastal squeeze in particular. For example, we estimate that until the year 2100 up to 280,000 km² of coastal wetlands may be lost due to coastal squeeze. If strategically implemented on a regional to global scale nature-based solutions to coastal management could increase the global total area of intertidal coastal wetlands by up to 60%.

However our current understanding of this process is very limited, partly due to the limited field evidence in sedimentary archives (e.g. during the early Holocene where SLR were high). We argue that this is related to the combined effects of wetland inland migration and wetland drowning during periods of high SLR rates, raising the question as to whether or not future coastal wetland will be able to provide ecosystem services comparable to those of natural systems.

How to cite: Schuerch, M., Spencer, T., Temmerman, S., and Kirwan, M.: Can we avoid coastal squeeze through nature-based coastal adaptation?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7677, https://doi.org/10.5194/egusphere-egu2020-7677, 2020.

The characterisation of past coastal flood events is crucial for risk prevention. However, it is limited by the partial character of historical information on flood events and the lack or limited quality of past hydro-meteorological data. In addition coastal flood processes are complex, driven by many hydro-meteorological processes, making mechanisms and probability analysis challenging. These issues are tackled by joining historical, statistical and modelling approaches. We focus on a macrotidal site (Gâvres, France) subject to overtopping and investigate the 1900-2010 period. A continuous hydro-meteorological database is built and a damage event database is set up based on archives, newspapers, maps and aerial photographies. Using together historic information, hindcasts and hydrodynamic models, we identified 9 flood events, among which 5 significant flood events (4 with high confidence: 1924, 1978, 2001, 2008; 1 with a lower confidence: 1904). These flood events are driven by the combination of sea-level rise, tide, atmospheric surge, offshore wave conditions and local wind. The critical conditions leading to flood are further analysed, including the effect of coastal defences, showing that the present coastal defences would not have allowed to face the hydro-meteorological conditions of 09/02/1924 for instance, whose bi-variate return periods of exceedance Tr (still water level relative to the mean sea level and significant wave height) is larger than 1000 y. In addition, Tr is expected to significantly decrease with the sea-level rise, reaching values smaller than 1 y, for 8 of the 9 historical events, for a sea-level rise of 0.63 m, which is equal to the median amount of sea-level rise projected by the 5^th Assessment Report of the IPCC in this region for RCP8.5 in 2100.

How to cite: Idier, D., Rohmer, J., Pedreros, R., Le Roy, S., Lambert, J., Louisor, J., Le Cozannet, G., and Le Cornec, E.: A composite method for past events characterisation providing insights in past, present and future coastal flood hazards: Joining historical, statistical and modeling approaches, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2725, https://doi.org/10.5194/egusphere-egu2020-2725, 2020.

Climate change may alter wave climate along most of world’s coasts (Morin et al., 2019). This could have implications on coastal impacts such as flooding and erosion (Wong et al., 2014). Traditional approaches to assess coastal impacts due to wind waves rely on, among other variables, the bulk sea-state parameters (e.g. significant wave height, peak period, mean wave direction). In this work, we analyse projected changes in wave climate considering the full directional spectra, particularly focusing on the added information this approach could offer. The analysed wave database consists of directional spectra and sea-state parameters at several coastal locations worldwide and in the western Mediterranean basin. Multi-model ensemble wave climate projections are obtained using WaveWatchIII model forced with surface wind fields and ice marine coverage outputs from several global and regional climate models (CMIP5 and CORDEX projects, respectively). Hourly spectra are stored with a discretization of 32 frequencies and 24 directions.

Results for sea-state parameters are coherent with previous studies about global wave climate changes (Camus et al., 2017; Collins et al., 2019), showing a wave height increase in the Southern Ocean and tropical eastern Pacific and a decrease in the North Atlantic and Mediterranean Sea. Nevertheless, the spectral analysis of wave climate changes provides new insights about the wave climate change signal. Thus, while projected changes of sea-state parameters provide an averaged information (both in magnitude and sign), the use of the full directional spectra makes it possible to study the projected change of each individual wave system. Also, this approach helps to note displacements of wave energy to higher or lower periods at each direction, which is especially relevant due to the important role that wave period and direction plays in coastal impacts such as dune erosion (Van Gent, 2008). The main conclusions reached in this study are the expected general increase of wave height in swells generated in the Southern Hemisphere that can travel north beyond the equator, and the decrease of wave systems generated in the Northern Hemisphere.

Finally, a comparison between the results from a coastal erosion assessment using estimated changes of sea-state parameters and climate change information from spectral wave data is shown.

How to cite: Lobeto, H., Menendez, M., Alvarez, M., and Mazzaretto, O.: Exploring future wave climate changes from directional spectra: Implications for coastal impacts, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7851, https://doi.org/10.5194/egusphere-egu2020-7851, 2020.

Coastal areas are under rapid changes. Management to face flooding hazards in changing climate is of great significance due to the major impact of flooding events in densely populated coastal regions, where also important and vulnerable infrastructure is located. The sea level of the Baltic Sea is affected by internal fluctuations caused by wind, air pressure and seiche oscillations, and by variations of the water volume due to the water exchange between the Baltic Sea and the North Sea through the Danish Straits. The highest sea level extremes are caused by cyclones moving over the region. The most vulnerable locations are at the ends of the bays. St. Petersburg, located at the eastern end of the Gulf of Finland, has experienced major sea floods in 1777, 1824 and 1924.

In order to study the effects of the depths and tracks of cyclones on the extreme sea levels, we have developed a method to generate cyclones for numerical sea level studies. A cyclone is modelled as a two-dimensional Gaussian function with adjustable horizontal size and depth. The cyclone moves through the Baltic Sea region with given direction and velocity. The output of this method is the gridded data set of mean sea level pressure and wind components which are used as an input for the sea level model. The internal variations of the Baltic Sea are calculated with a numerical barotropic sea level model, and the water volume variations are evaluated using a statistical sea level model based on wind speeds near the Danish Straits. The sea level model simulations allow us to study extremely rare but physically plausible sea level events that have not occurred during the observation period at the Baltic Sea coast. The simulation results are used to investigate extreme sea levels that could occur at selected sites at the Finnish coastline.

How to cite: Särkkä, J., Räihä, J., Kämäräinen, M., and Jylhä, K.: Simulating extreme sea levels at the Baltic Sea coast from synthetic cyclones, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10271, https://doi.org/10.5194/egusphere-egu2020-10271, 2020.

Climate warming is expected to change the functioning of regional seas substantially. However, it is still an open question how the global climate processes will affect in the future the regional seas, their wave climate, changes in the storm surges and, consequently, the coastal erosion, flooding risks, and coastal communities. In this study, we perform a detailed analysis of the wave climate of the Baltic Sea and the Caspian Sea based on the multi-mission satellite altimetry data in 1990 – 2017. The dataset of significant wave heights (SWH) from ten satellites was cross-validated against regional in situ buoy and echosounder measurements. In the Caspian Sea, due to the limited availability of the in-situ measurements, the satellite data were validated with visual wave measurements. After correction for systematic differences, the visual observations showed excellent correspondence with monthly averaged satellite data with a typical root mean square difference of 0.06 m. Even though several satellite pairs (ENVISAT/JASON-1, SARAL/JASON-2, ERS-1/TOPEX) exhibit substantial mutual temporal drift, and calm wave conditions are ignored, the overall picture is very consistent. The averaged over the whole basin annual mean SWH in the Baltic Sea shows an increase of 0.005 m/yr but no significant trend is detected in the Caspian Sea.

Interestingly, in both Baltic and Caspian seas, changes in the average SWH exhibit a strong spatial pattern. In the Baltic Sea, a meridional pattern is detected: an increase in the central and western parts of the sea and a decrease in the eastern part. This pattern has a timescale of ~13 yr. We also found a faster-varying region in the Baltic Proper where trends in the wave heights experience abrupt changes with a timescale of 3 years and show a strong relation to changes in the North Atlantic Oscillation. In the Caspian Sea, the wave height decreased by 0.019 ± 0.007 m/yr in the eastern segment of the central basin and by 0.04 ± 0.04 m/yr in the western segment of the southern basin when the other parts showed an increase of wave heights. These changes can be explained by an increase in the frequency of westerly winds at the expense of southerly winds. Analysing the changes in the atmospheric forcing we found that there is a cyclic behaviour with a timescale of ~12 years which result in abrupt changes in the wave climate every 12 years, causing the trends in different regions to reverse its sign.

We demonstrate that the impact on the coast and coastal community is caused by a complex chain of events, starting from changes in the wind direction due to large-scale atmospheric variability and atmospheric teleconnections, which create abrupt shifts in the wave climate of regional seas. We discuss that regional seas have a different response to the changing climate compared to the open ocean condition, which can lead to accelerated coastal erosion and a higher risk of flooding.

How to cite: Kudryavtseva, N.: Abrupt changes in wave climate of regional seas caused by large-scale atmospheric forcing and teleconnections, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22430, https://doi.org/10.5194/egusphere-egu2020-22430, 2020.

Sea-level rise induces a permanent loss of land with widespread ecological and economic impacts, most evident in urban and densely populated areas. The eventual coastline retreat combined with the action of waves and storm surges will end in more severe damages over coastal areas. These effects are expected to be particularly significant over islands, where coastal zones represent a relatively larger area vulnerable to marine hazards.

Managing coastal flood risk at regional scales requires a prioritization of resources and socioeconomic activities along the coast. Stakeholders, such as regional authorities, coastal managers and private companies, need tools that help to address the evaluation of coastal risks and criteria to support decision-makers to clarify priorities and critical sites. For this reason, the regional Government of the Balearic Islands (Spain) in association with the Spanish Ministry of Agriculture, Fisheries and Environment has launched the Plan for Climate Change Coastal Adaptation. This framework integrates two levels of analysis. The first one relates with the identification of critical areas affected by coastal flooding and erosion under mean sea-level rise scenarios and the quantification of the extent of flooding, including marine extreme events. The second level assesses the impacts on infrastructures and assets from a socioeconomic perspective due to these hazards.

In this context, this paper quantifies the effects of sea-level rise and marine extreme events caused by storm surges and waves along the coasts of the Balearic Islands (Western Mediterranean Sea) in terms of coastal flooding and potential erosion. Given the regional scale (~1500 km) of this study, the presented methodology adopts a compromise between accuracy, physical representativity and computational costs. We map the projected flooded coastal areas under two mean sea-level rise climate change scenarios, RCP4.5 and RCP8.5. To do so, we apply a corrected bathtub algorithm. Additionally, we compute the impact of extreme storm surges and waves using two 35-year hindcasts consistently forced by mean sea level pressure and surface winds from ERA-Interim reanalysis. Waves have been further propagated towards the nearshore to compute wave setup with higher accuracy. The 100-year return levels of joint storm surges and waves are used to map the spatial extent of flooding in more than 200 sandy beaches around the Balearic Islands by mid and late 21st century, using the hydrodynamical LISFLOOD-FP model and a high resolution (2 m) Digital Elevation Model.

How to cite: Luque Lozano, P., Gómez-Pujol, L., Marcos, M., and Orfila, A.: Coastal flooding in the Balearic Islands during the 21st century caused by sea level rise and extreme events, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4549, https://doi.org/10.5194/egusphere-egu2020-4549, 2020.

Coastal areas are one of the most vulnerable regions to climate change given their high exposure to the increasingly frequent extreme sea level (ESL) events and the high population density with around 680 million people (approximately 10% of the world’s population) residing at less than 10 m above sea level and projected to reach more than one billion by 2050 (IPCC, 2019).

Extreme sea level events include the combination of mean sea level, tides, surges and waves set-up. These events that historically occurred once per century are projected to become at least an annual occurrence at most parts of the world during the 21st century. Therefore, a crucial step towards coastal planning and adaption is the understanding of the drivers and impacts of ESL events (Hinkel et al., 2019).

Flooding and extreme events in river mouths and their adjacent coastline have a complex nature with oceanic and fluvial processes taking place. Their analysis requires, therefore, the consideration of several physical variables that play a role in water levels such as precipitation, waves, storm surge, and tides. In a climate change scenario, the effects of sea level rise and storminess changes must also be accounted for. The contribution of different processes to ESL events has often been analyzed independently given the difficulty to predict their combined effects.

This work focuses on the analysis of ESL events due to the combination of sea level rise, extreme waves, storm surges, tides and river flows in a climate change scenario, following:

1. Projections of wave variables for an ensemble of EURO-CORDEX RCMs under RCP8.5 using WavewatchIII v5.16 (Besio et al., 2019). Wave propagation of local hydrodynamic processes and storm surge with Delft3D.
2. Projections of river flow using a physical-based and distributed hydrological model under the same runs as the wave climate.
3. Joint statistical characterization of local waves and river flows and long-term temporal variability based on the methodology of Lira-Loarca et al. (2020).
4. Analysis of compound extreme sea level and flooding events.

The methodology is applied to a case study in the coast of Granada (Spain) where severe flood events have occurred in recent years. The results highlight the need for an integrated approach encompassing the relevant components of water levels, and specifically sea level rise and waves and the differences in the temporal variability of the significant wave height in a climate change scenario.

References:

• Besio et al., 2019. Trends and variability of waves under scenario RCP8.5 in the Mediterranean Sea. 2^ndInternational Workshop on Waves, Storm Surges, and Coastal Hazards, Melbourne, Australia
• Hinkel et al., 2019. Sea level rise and implications for low lying islands, coasts and communities. IPCC SROCC.
• IPCC, 2019. SPM Special Report on the Ocean and Cryosphere in a Changing Climate.
• Lira-Loarca et al., 2020. Storm characterization and simulation for damage evolution models of maritime structures. Coastal Engineering, 156, 103620.

How to cite: Lira Loarca, A., Cobos, M., Millares, A., Besio, G., and Baquerizo, A.: Integrated extreme sea level events in the Mediterranean coast of Spain, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7951, https://doi.org/10.5194/egusphere-egu2020-7951, 2020.

We present here a novel application of state-of-the-art surge modeling on a past climate of special interest. The Last Interglacial (LIG; 125,000 years ago) was the latest instance of a climate (slightly) warmer than present: for this reason its study can inform on the response of several climate components to a climate state with partial resemblance to possible futures. Climate variables like temperature and precipitation have been extensively studied for the LIG. Here, we calculate for the first time the implications of the altered LIG atmospheric circulation (both in mean state and extremes) for storm surges along the global coastline. This presents particular interest since it is often claimed that a warmer climate may imply enhanced storminess in some ocean basins. We use sub-daily results from simulations of the LIG and of the pre-industrial periods with the climate model CESM1.2 (equipped with atmosphere module CAM5, with ca. 1 degree horizontal resolution) to force the Global Tide and Surge Model (GTSM) for 30-years at climate equilibrium conditions. We analyze patterns of storminess and of storm surges, and report on the anomalies in those metrics between the LIG and the pre-industrial climate. These results can help contextualize proxy-based reconstructions of storms of the LIG, as well as projections of storm surges in a future warmer climate. Finally, we also reconstruct tides of the LIG, aiming to provide useful constrains to paleo sea-level reconstructions.

How to cite: Bakker, P., Scussolini, P., Muis, S., Dullaart, J., Rovere, A., Stocchi, P., and Aerts, J.: Global storm surges during a past warm climate, the Last Interglacial, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19936, https://doi.org/10.5194/egusphere-egu2020-19936, 2020.

Storm surge on the east coast of the United States can be generated by hurricanes or extratropical cyclones (ETCs). Understanding the differences in the impacts of these two phenomena is important for improving strategies to mitigate the damage created. As such, this work examines the magnitude, spatial footprint, and paths of hurricanes and ETCs that caused strong surge along the east coast of the US. Lagrangian cyclone track information, for hurricanes and ETCs, is used to associate surge events with individual storms. First, hurricane influence is examined using ranked surged events per site. The fraction of hurricanes among storms associated with surge decreases from 20-60% for the top 10 events to 10-30% for the top 50 events, and a clear latitudinal gradient of hurricane influence emerges for larger sets of events. Second, surge on larger spatial domains is examined by focusing on storms that cause exceedance of the probabilistic 1-year surge return level at multiple stations. Results show that if the strongest events, in terms of surge amplitude and spatial extent, are considered hurricanes are most likely to create the hazards. However, when slightly less strong events that still impact multiple areas during the storm life cycle are considered, the relative importance of hurricanes shrinks as that of ETCs grows.

Next we examine the details of the tracks of the storm events that cause strong surge events. We find that paths for ETCs causing multi-site surge at individual segments of the US east coast pass very close to the regions of impact. We find that the paths of hurricanes that cause the strongest multi-site surge are often influenced by nearby large-scale circulation patterns. We also examine the relationship between the storm surge time-evolution and the propagation speed of the low-pressure center of the storm events. For extratropical cyclones, slower moving events have weaker cyclonic winds which offsets the enhanced surge associated with the longer duration of the cyclone influence on surge. For hurricanes, there is less correlation between propagation speed and cyclonic wind motion, meaning slower moving events can still generate very strong winds. However, slow moving events still don’t cause the absolute largest events.

How to cite: Booth, J. and Rieder, H.: United States East Coast Storm Surge and Cyclone track Characteristics: Differences and Similarities for Extratropical Cyclones and Hurricanes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12444, https://doi.org/10.5194/egusphere-egu2020-12444, 2020.

Extreme water levels in the micro-tidal transition zone between the North Sea and the semi-enclosed Baltic sea are predominantly determined by wind forcing associated with synoptic-scale weather systems. This connection between the two seas is partly blocked by low-lying islands, and the bathymetry comprises a complex mixture of narrow, deep channels and shallow sills. Coastlines in the Southern Kattegat and the Western Baltic Sea are therefore exposed to wind forcing from a large range of directions, and the extent of water build-up varies strongly between locations.

In the present study, we aim to determine the most critical wind direction for most of the Danish coastlines by employing numerical modelling experiments. The simulations are conducted with two different regional 3D ocean models to enable model inter-comparison. The DMI-HBM model implements a structured grid with fully dynamic 2-way nesting, while the MIKE 3 FM invokes an unstructured mesh. Both models have grid resolutions of ~0.5–1 km within the Danish Straits and 4–6 km in the offshore Baltic Sea. The models are forced by synthetic wind fields, where both wind speed and wind direction are maintained at fixed levels over the entire model domains. Pairs of model simulations are then obtained by varying the angle from which the wind is blowing.

From the model outputs, we describe the temporal evolution of the water level by the site-specific peak water level, and the time required for the response to reach its peak value. Our results show a steady rise of the water level up until the peak value. The peak water level significantly overshoots the final equilibrium water level, which develops further into the simulations. Our study facilitates a better understanding of the sea level's response to extreme and persistent winds in a region with highly complex geometry.

How to cite: Andrée, E., Bendix Hansen, A., Dahl Larsen, M. A., Skovgaard Madsen, K., and Drews, M.: Storm surge modelling in the North Sea-Baltic sea transition zone: model inter-comparison of static wind simulations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18913, https://doi.org/10.5194/egusphere-egu2020-18913, 2020.

It is challenging to study the surface and sub-surface oceanic physical and biogeochemical response in the intense weather conditions like tropical cyclones (TC). Due to limitation of observed subsurface data, most of the studies utilize satellite measured parameters to examine the response of ocean to a passing cyclone. The Bay of Bengal (BoB) is a semi landlocked basin in the northeastern Indian Ocean. The supply of freshwater from rivers and precipitation cause a shallow mixed layer and warmer sea surface temperature leading to cyclogenesis in the BoB. A few studies used in-situ Bio-Argo float which is limited to specified single point location to study oceanic response during the passage of Hudhud cyclone. The genesis of TC Hudhud in the Andaman Sea was on 6 October 2014, later it was intensified as Cyclonic Storm (CS) on 8 October and made landfall near Visakhapatnam on 12 October as an Extremely Severe Cyclonic Storm (ESCS). The TC Hudhud travelled nearly 1600 km in the ocean from genesis to landfall location. Only a few studies carried out on surface and subsurface biogeochemical response during TC Hudhud using Bio-Argo float. There is only one float located on the cyclone track. At that position, the system was a severe cyclonic storm (SCS) around wind speed was 45-55 knots. In the present study, we demonstrate the surface and subsurface bio-physical response along the track from CS to ESCS of TC Hudhud using a fully coupled ecosystem (ocean-biogeochemical) model. The model is configured using Regional Ocean Modeling System (ROMS) coupled with Bio-fennel. The model well captures the variability of surface and subsurface features of biogeochemical and physical parameters like chlorophyll concertation, dissolved oxygen, nutrients and temperature, salinity to compare with Bio-Argo float, and satellite data. Analysis shows that TC Hudhud induced upwelling cause intense water mixing which has a substantial impact on biological processes from depth of oxycline, nutricline to the upper-ocean layer. The model results are further analyzed to understand upper-oceanic physical and biological processes for the pre- and post-cyclone periods and their along-track variations. Model simulation shows changes in subsurface chlorophyll maximum, oxycline, nutricline and chlorophyll blooms with the passage of TC Hudhud in the BoB. The physical and biological processes are discussed to explain the observed and modelled variations in the upper-ocean characteristics.

How to cite: Vivek, S., Nigam, T., and Pant, V.: Biogeochemical response to tropical cyclone Hudhud in the Bay of Bengal using an ocean-biogeochemical coupled model, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2054, https://doi.org/10.5194/egusphere-egu2020-2054, 2020.

Abstract：In order to find out the hydrochemistry and salinization of shallow groundwater in coastal aquifers, 76 ground- and surface-water samples, contained phreatic upper water, phreatic water, confined water, river water and seawater were collected for major ion and isotope analysis(²H/¹⁸O, ¹⁴C). The results show that: (1) The phreatic upper groundwater changes along the general flowpath towards the coast from fresh(TDS <1 g/L), brackish (1–3 g/L) to saline (3–50 g/L). The phreatic water and first confined water are basically unchanged, but mainly saline water. (2) Shallow groundwater is mainly derived from atmospheric precipitation and undergoes significant evaporation processes. The phreatic upper groundwater is mainly derived from modern atmospheric precipitation recharge. The phreatic water and first confined water are mainly derived from precipitation replenishment during the warm period of the Holocene and some relict seawater. (3) The processes for salinity sources of the shallow groundwater are that oceanic evaporative salt formed during the transgression and retreat period since the late Pleistocene was dissolved by atmospheric precipitation and river water for many periods. The salt in phreatic upper water of the estuary area is also derived from modern seawater intrusion.

Key words: coastal zone; groundwater; hydrochemistry; hydrogen and oxygen stable isotope; salinization

_____________

Corresponding author. Qingdao Institute of Marine Geology, China Geologic Survey, Qingdao, 266071, PR China.

E-mail address: gms532@163.com.

This study was financially supported by the National Natural Science Foundation of China (41977173), China Geology Survey project(DD20189503) and National key research and development projects(2016YFC0402801)

How to cite: Hou, G., Gao, M., and Dang, X.: Hydrochemical characteristics and processes for salinity sources of the shallow groundwater along the coast of northern Jiangsu, China, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4362, https://doi.org/10.5194/egusphere-egu2020-4362, 2020.

The Pearl River networks is a typical river networks system with channel density ranging from 0.81-0.88m/m². Recent years, with the rapid development of economy, the intensive human activities have great impacts on the networks system. Sand excavation is the most severe one, which directly led to the averaged 4-6m riverbed downcutting over the Pearl River networks. Consequently, salt water intrusion has become much serious than it was before. In this study, a coupled 1-D river networks and 3-D estuarine combined numerical model has been established to evaluate the influence of bathymetry changes and sea level rising on the salt water intrusion in the river networks. Two period of bathymetries in 1990s and 2000s have been used to simulate the length of salt water intrusion (LSR). It is found that the LSR in 2000s was 24 km farther upstream than that in 1990s. However, the LSR is no more than 3 km when sea level rises by 30 cm. This implies that impact of bathymetry changes overwhelms the sea level rise on LSR. The result also shows that LSR has the negative and positive correlation with river discharge and tide range respectively, which means that LSR will decrease and increase with river discharge and tidal range increasing. Furthermore, it is quite interesting to notice that the LSR is also quite relative to the flow ratio at the apex of the delta. With the same river discharge from the upper stream, the more the discharge come from the West River, the less LSR will happen, which would be quite useful to the authority to transfer the water to control the salt water intrusion in Pearl River networks.

How to cite: Zhang, W., Zhou, R., and Ji, X.: Salt water intrusion in the Pearl River networks, China, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1317, https://doi.org/10.5194/egusphere-egu2020-1317, 2020.

Korean coasts are exposed to high risks such as storm surge, storm-induced high waves and wave overtopping. Also, localized heavy rainfall events have occurred frequently due to climate change, too. Especially, since coastal urban areas depend heavily on pump and pipe systems, extreme rainfalls that exceed the design capacity of drainage facility result in increasing inland flood damage. Nevertheless, the population in Korea is concentrated in the coastal areas and the value and density of coastal utilization are increasing. In this study, the risk of hybrid disasters in the coastal areas was assessed for safe utilization and value enhancement of coastal areas. The framework of the coastal risk assessment has been adopted from the concept of climate change vulnerability of the IPCC(2001). Coastal Risk Index(CRI) in this study was defined as a function of Exposure and Sensitivity exclude Adaptive Capacity using GIS-based DBs. Indicators of Exposure consisted of a storm surge, storm-induced high waves, wave overtopping and rainfalls. Indicators of Sensitivity consisted of human(population density), property(buildings and roads), and geography(inundation area). All these indicators were gathered from government agencies, numerical model experiments(ADCIRC, unSWAN, FLOW3D and XP-SWMM model), and field surveys(Drone & Lidar survey). And then spatial analysis was performed by using a GIS program after passing the quality control and analyzed data were standardized and classified 4 grades; Attention(blue color), Caution(yellow color), Warning(orange color) and Danger(red color). This frame of risk assessment was first applied to Marine City, Haeundae in Busan, Korea which was heavily damaged by the typhoon CHABA in 2018. According to the assessment results, it was confirmed that the results were in good agreement with the observation data and damage range. At present, the study area of risk assessment is expanding to other areas. The results of coastal risk assessment are used as reference indicators to identify and prevent the cause of coastal disasters, establish countermeasures, determine the development or management of coastal areas based on GIS, thus will contribute to effective and safe coastal management.

How to cite: Kang, T.-S., Oh, H.-M., Hwang, S.-M., Kim, H.-K., and Jeong, K.-Y.: Coastal risk assessments due to hybrid disasters in Korea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13590, https://doi.org/10.5194/egusphere-egu2020-13590, 2020.

On 12 November 2019, an exceptional flood event occurred in Venice, second only to the one that occurred on 4 November 1966. The maximum recorded sea level value of 189 cm above local datum resulted in the flooding of more than 85% of the pedestrian surface of the historical city. Moreover, with four extremely high tides since 11 November 2019, this has been the worst week for flooding in Venice ever since 1872, when official statistics were first produced. The event that struck Venice and the northern Adriatic Sea on 12 November 2019, although having certain conditions seemingly typical of the events that cause exceptional high waters, also had some peculiar characteristics not observed before and therefore it requires an in-depth analysis. Several factors made this event exceptional: an in-phase timing of the peak of the storm surge and the astronomical tide; an anomalously high monthly mean sea level in the Adriatic Sea induced by a steady low-pressure and wind systems over the Mediterranean Sea associated with large-scale low-frequency atmospheric dynamics; a deep low-pressure system over the central-southern Tyrrhenian Sea that generated strong sirocco (south-easterly) winds along the main axis of the Adriatic Sea pushing the waters towards north; a fast-moving local depression - and the associated wind perturbation - travelling in the north-westward direction along the Italian coast that may have forced long ocean waves (e.g., edge wave); and very strong winds (100 km h^-1 on average, with gusts reaching 110 km h^-1) over the Lagoon of Venice which led to a further rise in water levels and damage to the historic city. In this study, a large set of available observations and the high-resolution numerical simulations are used to quantify the influence of these drivers on the peak flood event and to investigate the peculiar weather and sea conditions over the Mediterranean Sea during the Venice floods of November 2019.

How to cite: Ferrarin, C., Bajo, M., Barbariol, F., Bastianini, M., Benetazzo, A., Cavaleri, L., Chiggiato, J., Davolio, S., Lionello, P., Orlic, M., and Umgiesser, G.: Local and large-scale controls of the exceptional Venice floods of November 2019, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4562, https://doi.org/10.5194/egusphere-egu2020-4562, 2020.

Climate change and subsidence will likely have a significant role to increase coastal flooding risk. The socio-economic impact of inundations can be very relevant, and, in a context of climate change, it is necessary to develop effective methods for assessing coastal flood hazard suitable for large-scale studies. This work focuses on the application of a new modelling approach for mapping flooding hazard for future scenarios characterized by sea level rise and ground lowering due to subsidence. The flood intensity index approach (Iw, Dottori et al. 2015) will be used to quantitatively evaluate the flood extent. This recent methodology allows to create reliable scenarios with low computational costs. The effects of the storm surge are assessed using a base scenario corresponding to 100 years return period event. IW inputs are represented by water height set as storm level plus a part of wave height. The scenarios will be created by quantitatively combining IPCC sea level rise projections with subsidence data that will be compared to high-resolution digital terrain models. The study area of this work is the ∼205 km long coastal plain of Northern Italy, from Venice to Rimini, composed of low-lying sandy beaches and which includes the Po delta area. The coast is characterized by large portions of the territory below mean sea level and by geological features made by recent quaternary sediments which have a natural subsidence rate. In the past (1960-1980) the subsidence rate had an exceptional increase caused by excessive groundwater withdrawal for agricultural and industrial activities, human consumption and by natural gas extraction.

How to cite: Giusti, R., Martina, M., Armaroli, C., Figuereido, R., and Dottori, F.: Future scenarios of coastal flooding in north-east Italy, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13676, https://doi.org/10.5194/egusphere-egu2020-13676, 2020.

Nowadays, with possible changes in wind patterns and growing interests in the development of wind farms and other forms of renewable energy on the Baltic Sea, statistical characteristic of prevailing wave conditions at the site and changes in energy distribution, are essential. The Gulf of Gdańsk (Southern Baltic Sea) is an especially interesting area due to the presence of very characteristic long peninsula which strongly affects wave propagation and, in consequence, wave energy distribution. The objective of this work is to obtain most characteristic features of extreme storms that had significant impact on the Gulf of Gdańsk during the last half-century and associated meteorological conditions

In this study we analyse two hindcast datasets which are the result of an EU-funded project HIPOCAS (Cieślikiewicz & Paplińska-Swerpel 2008). The first one is the 44-year long reanalysis of meteorological data produced with the atmospheric model REMO (Jacob & Podzun 1997).

The second dataset used in this study is wave data produced with wave model WAM. For the modelling of waves over the Baltic Sea, a subset of gridded REMO data were extracted. Wave data have been produced in a rectangular grid in spherical rotated coordinates with the resolution 5’×5’.

The principal goal of our analysis is twofold. First, we want to estimate long-term stochastic characteristics of some basic meteorological parameters and wind wave fields. Atmospheric pressure at sea level and the wind velocity at 10 m height are analysed. As far as the wind wave data are concerned, we focus on the significant wave height (H_s), mean wave period and the mean direction of wave propagation. Secondly, this study aims to find out the characteristic features of atmospheric conditions causing extreme wind wave events in the Gulf of Gdańsk. To this end, a number of extreme storms, that are critical for a few chosen Gulf of Gdańsk regions, are selected based on H_s time series. For those selected storm periods, the storm depressions’ tracks and the overall evolution of atmospheric pressure and wind velocity fields are examined.

Our analysis showed two distinct metrological conditions that cause extreme storms in the Gulf of Gdańsk. Cyclones moving along the east side of the Baltic Sea are associated with strong northerly winds, which cause extremely high waves in the Gulf. On the other hand, cyclones travelling east in the zonal direction over the northern Baltic bring strong westerly winds. They significantly raise H_s, although not to the extent observed for the northerly winds.

In our study, we also look for the essential characteristics of the extreme meteorological conditions via results of the Empirical Orthogonal Functions (EOF) method, applied to the wind velocity vector fields.

Computations performed within this study were conducted in the TASK Computer Centre, Gdańsk with partial funding from eCUDO.pl project and the Project for Young Scientist No. 539-G210-B412-19.

Cieślikiewicz, W. & Paplińska-Swerpel, B. (2008), Coastal Engineering, 55, 894–905.

Jacob, D. & Podzun, R., (1997). Meteorol. Atmos. Phys., 63, 119–129.

How to cite: Cupial, A. and Cieslikiewicz, W.: Characteristics of extreme wind wave events in the Gulf of Gdańsk and associated atmospheric conditions over the Baltic Sea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20397, https://doi.org/10.5194/egusphere-egu2020-20397, 2020.

To determine the specificity of functioning the Southern Baltic coasts, it is necessary to identify the hydrometeorological conditions that have the greatest effect on the dynamics of geomorphological processes in detail. For the offshore coastal zone, it is important to determine temporal variability (including trend, cyclicality and seasonality) and spatial diversity (i.e. for cliff and dune coasts) of occurrence of main hydrometeorological and geomorphological processes and events. Among hydrometeorological and geomorphological factors - which are decisive for violent, intense and sometimes irreversible changes in the natural environment - extreme events play an important and sometimes dominant role (Tylkowski, Hojan 2018).

Geomorphological changes of the cliff coast depend mainly on the dynamics of marine and slope erosion. The high sea level that occurs during storm swells and intense precipitation lead to the transformation of the cliff coast, which is seen in the retraction of the cliff crown, among others (Kostrzewski et al. 2015).

The purpose of the work was to determine the temporal variability of hydrometeorological conditions, which have the greatest effect on the dynamics of the erosion of the cliff shores of the Wolin island. Hydrometeorological conditions from 1985 – 2019 period were compared to the annual measurements of the cliff crown retraction, which were carried out on 5 test sections in the coastal zone of the Pomeranian Bay on the island of Wolin. The work indicates the occurrence of above-average and extreme hydrometeorological events that potentially favoured the occurrence of erosive processes, e.g. mass movements, slopewash and aeolian erosion.

Using ARIMA modelling, time decomposition of hydrometeorological conditions was made and their short-term forecasts were formulated. The study determined non-seasonal and seasonal parameters that determine the occurrence of current and future meteorological and marine conditions. What is more, spatial differences in the scope of identification of the features of the analysed time series, estimation of parameters of selected models and the formulated forecast are indicated (Tylkowski, Hojan 2019).

References

Tylkowski J., Hojan M., 2018. Threshold values of extreme hydrometeorological events on the Polish Baltic coast. Water 10(10), 1337. doi:10.3390/w10101337

Kostrzewski A., Zwoliński Z., Winowski M., Tylkowski J., Samołyk M., 2015. Cliff top recesion rate and cliff hazards for the sea coast of Wolin Island (Southern Baltic). Baltica 28(2): 109-120. doi:10.5200/baltica.2015.28.10

Tylkowski J., Hojan M., 2019: Time decomposition and short-term forecasting of hydrometeorological conditions in the South Baltic coastal zone of Poland. Geosciences 9(68). doi.org/10.3390/geosciences9020068

How to cite: Tylkowski, J., Kostrzewski, A., and Winowski, M.: Impact of hydrometeorological conditions on the Southern Baltic cliff coast development in the annual and long-term weather cycle, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21462, https://doi.org/10.5194/egusphere-egu2020-21462, 2020.

In a probabilistic tsunami risk assessment framework, the definition of vulnerability of the physical assets of coastal communities plays a fundamental role. Therefore, current research is moving towards the definition of a general methodology for developing analytical tsunami fragility functions for the physical assets to be used in loss-assessment frameworks at community scale. Herein a methodology is proposed for developing analytical tsunami fragility functions and its application on an inventory of RC buildings representative of the Mediterranean coastal communities is illustrated. Simple mechanics-based models are defined for the damage assessment of reinforced concrete (RC) buildings with breakaway infills under tsunami lateral loads. A simulated design procedure is adopted for the definition of the buildings inventory, relying on Monte Carlo simulation to account for geometrical and mechanical uncertainties. One key feature of the approach is that intermediate damage states prior to collapse are defined to account for light/moderate damage to both structural and non-structural components subjected to tsunami onshore flows.

How to cite: Del Zoppo, M., Di Ludovico, M., and Prota, A.: Developing analytical tsunami fragility functions for Italian coastal communities, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12805, https://doi.org/10.5194/egusphere-egu2020-12805, 2020.

Many coastal regions lying on subduction zones are likely to experience the catastrophic effects of cascading earthquake and tsunami observed in recent events. The response of the structure to tsunami is difficult to quantify through damage observations from past events, which often provide information on the combined effects of both perils. Hence, the use of analytical methodologies is fundamental. The authors have recently proposed a nonlinear static pushover procedure for the design and assessment of structures for tsunami within the framework of ASCE 7-16 provisions. The latter offer a comprehensive and practical methodology for the design of structures for tsunami loads and effects. While they provide prescriptive tsunami loading and design requirements, they also permit the use of performance-based analysis tools. However, the specifics of load application protocol, and system and component evaluation are not specified. Through the proposed approach, the user can estimate the effective lateral-resisting capacity of a building. In addition, by applying the component loading procedure, the user can identify the structural elements that may need to be strengthened to meet the code acceptance criteria. For this purpose, a prototypical reinforced concrete multi-storey building exposed to high tsunami hazard in the USA Northwest Pacific coast is assessed. Based on the acceptance criteria of ASCE 7-16 provisions, the lateral-load resisting system needs to be strengthened to resist tsunami loading. Overall, the use of the tsunami nonlinear static analysis procedure is found to significantly reduce the extra-costs associated with tsunami strengthening of the building.

How to cite: Baiguera, M. and Rossetto, T.: A Nonlinear Static Procedure for the Design and Assessment of Buildings to Tsunami, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13247, https://doi.org/10.5194/egusphere-egu2020-13247, 2020.

Despite that the annual probability of an asteroid impact on earth is low, but over time, such catastrophic events are inevitable and can have negative global consequences. Several institutions around the world have come together to address global consequences of asteroids impacting earth. For example, interest in assessing the tsunami generation and impact consequences has led us to develop a physics-based framework to seamlessly simulate the event from source (asteroid entry) to ocean impact (splash) to long wave generation, propagation, and their catastrophic risk to people and infrastructure in coastal regions such inundation of the shoreline. The non-linear effects of the asteroid impact on the ocean surface are simulated using the hydrocode GEODYN to create the impact source for the shallow water wave propagation code, SWWP. The GEODYN-SWWP coupling is based on the structured adaptive mesh refinement infrastructure; SAMRAI developed at LLNL. Another consequence of ocean impact is the potentially global effects of an event that would otherwise be of only regional or local importance, should it occur on land. Only a fraction of the total impact energy is converted into water waves that have the ability to globally propagate in the oceans. The remaining energy is consumed by the “evaporation” of the asteroid, the ocean water being transformed into vapor and mist and the fractionization of ocean water and vapor into chlorine and bromine which alter the atmospheric chemistry, therefore impacting globally the Ozone layer and earth temperature. In this paper, we present our scheme of creating the source -- including nonlinear transient cratering and nearfield waves, generating the vapor cloud and the chemical speciation source load of chlorine and bromine to assess the global circulation of those plumes and their effects on the climate. We also present our coupling scheme of the hydrodynamic source using GEODYN with the global atmospheric circulation code GEOSCCM and illustrate the scheme on the PDC 2017 and PDC 2019 asteroid impact scenarios. We illustrate the coupling scheme for asteroids impact along the US, Europe and Asia shorelines. We illustrate, by examples, how the predictions of these numerical tools can help international, state and local government agencies reduce the risks and prepare and implement a  response and recovery plan.  This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

How to cite: Ezzedine, S., Oman, L., Dearborn, D., Miller, P., and Syal, M.: Tsunami Generation, Consequences on Coastlines, and Potential Global Climate Effects due to Asteroids Impacting Earth’s Oceans, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10579, https://doi.org/10.5194/egusphere-egu2020-10579, 2020.