Low-lying Coastal Areas Research Articles

A Framework for Cloud to Coast Adaptation: Maturity and Experiences from across the North Sea

The low-lying coastal areas of the countries around the North Sea are exposed to flooding and the influence of sea level rise. The countries in the North Sea Region need to continue to adapt if the associated risk is to be well-managed into the future. In addition to reducing flood risk, adaptation measures can bring development opportunities for those same places. These opportunities, however, are unlikely to be achieved through a ‘defence only’ paradigm, and instead a new approach is needed that simultaneously reduces risk and promotes liveable places, ecosystem health and social well-being. The building blocks of this new approach are promoted here and are based on an adaptation process that is collaborative and takes a whole-system, long-term perspective. The approach developed through the Interreg funded project, C5a, brings together governments, practitioners and researchers from across the North Sea to share policies, practices and the emerging science of climate change adaptation and enabling sustainable development. The new approach reflects a Cloud to Coast management paradigm and emerged through a combination of knowledge exchange and peer-to-peer learning across seven case studies. Central to the case studies was a maturity analysis of existing capabilities across the North Sea countries and their ability to adopt the new approach. This paper presents the results of this analysis, including the common challenges that emerged and the methods and examples of good practice to overcome them. Building upon these findings, the paper concludes by presenting four priority policy directions to support the uptake of the Cloud to Coast approach.

A Comprehensive Assessment of Climate Change and Coastal Inundation through Satellite-Derived Datasets: A Case Study of Sabang Island, Indonesia

Climate-change-induced hazards are negatively affecting the small islands across Indonesia. Sabang Island is one of the most vulnerable small islands due to the rising sea levels and increasing coastal inundation which threaten the low-lying coastal areas with and without coastal defences. However, there is still a lack of studies concerning the long-term trends in climatic variables and, consequently, sea level changes in the region. Accordingly, the current study attempts to comprehensively assess sea level changes and coastal inundation through satellite-derived datasets and model-based products around Sabang Island, Indonesia. The findings of the study show that the temperature (both minimum and maximum) and rainfall of the island are increasing by ~0.01 °C and ~11.5 mm per year, respectively. The trends of temperature and rainfall are closely associated with vegetative growth; an upward trend in the dense forest is noticed through the enhanced vegetation index (EVI). The trend analysis of satellite altimeter datasets shows that the sea level is increasing at a rate of 6.6 mm/year. The DEM-based modelling shows that sea level rise poses the greatest threat to coastal habitations and has significantly increased in recent years, accentuated by urbanisation. The GIS-based model results predict that about half of the coastal settlements (2.5 sq km) will be submerged completely within the next 30 years, provided the same sea level rise continues. The risk of coastal inundation is particularly severe in Sabang, the largest town on the island. The results allow regional, sub-regional, and local comparisons that can assess variations in climate change, sea level rise, coastal inundation, and associated vulnerabilities.

Holocene Environmental Evolution Response to the Human Activities and East Asian Summer Monsoon Variation in the Liangzhu Ancient City Complex, Eastern China

The Liangzhu Ancient City Complex is located in a low-lying coastal delta area, and its environmental evolution would have had a significant impact on the human-environment interactions. In this study, element geochemistry and grain size of the sediment sequence from a dam section in Ganggongling (GGL) reveal crucial aspects of sedimentary dynamics, environmental evolution, human activities, and East Asian Summer Monsoon(EASM) variation in the Liangzhu area since 5500 a. Starting from the middle-to-late Holocene, the GGL section shows an overall transition from warm humidity to cold-dry, which is consistent with the climate record dimension in southern China. Through comprehensive analysis of the sedimentary environment before and after the dam’s completion, it can be found that the Ganggongling dam has played a positive role in regulating mountain torrents and met the needs of production and domestic water, such as rice planting through water storage. Further applications on the multi-decadal to centennial time scale demonstrate that variations in solar activity may control the EASM intensity mainly in southern China, which is subject to ENSO intensity changes.

Soil Moisture Influence on the FTIR Spectrum of Salt-Affected Soils

Soil salinity has a major impact on agricultural production. In a changing climate with rising sea-levels, low-lying coastal areas are increasingly inundated whereby saltwater gradually contaminates the soil. Drought prone areas may suffer from salinity due to high evapotranspiration rates in combination with the use of saline irrigation water. Salinity is difficult to monitor because soil moisture affects the soil’s spectral signature. We conducted Fourier-transform infrared spectroscopy on alluvial and sandy soil samples in the coastal estuary of the Red River Delta. The soils are contaminated with NaCl, Na2CO3 and Na2SO4 salts. In an experiment of salt contamination, we established that three ranges of the spectrum were strongly influenced by both salt and moisture content in the soil, at wavenumbers 3200–3400 cm−1 (2.9–3.1 µm); 1600–1700 cm−1 (5.9–6.3 µm); 900–1100 cm−1 (9.1–11.1 µm). The Na2CO3 contaminated soil and the spectral value had a linear relationship between wavelengths 6.9 and 7.4 µm. At wavelength 6.99 µm, there was no relationship between absorbance and soil moisture, but the absorbance was proportional to the salt content (R2 = 0.85; RMSE = 0.68 g) and electrical conductivity (R2 = 0.50; RMSE = 3.8 dS/m). The relationship between soil moisture and spectral absorbance value was high at wavelengths below 6.7 µm, resulting in a quadratic relation between soil moisture and absorbance at wavelength 6.13 µm (R2 = 0.80; RMSE = 5.2%). The spectral signatures and equations might be useful for mapping salt-affected soils, particularly in difficult to access locations. Technological advances in thermal satellite sensors may offer possibilities for monitoring soil salinity.

Using TanDEM-X Global DEM to Map Coastal Flooding Exposure under Sea-Level Rise: Application to Guinea-Bissau

The increased exposure to coastal flooding in low-lying coastal areas is one of the consequences of sea-level rise (SLR) induced by climate changes. The coastal zone of Guinea-Bissau contains significant areas of low elevation and is home to most of the population and economic activity, making it already vulnerable to coastal flooding, especially during spring tides and storm surges (SS). Coastal flooding will tend to intensify with the expected SLR in the coming decades. This study aimed at quantifying and mapping the area exposed to the coastal flooding hazard using SLR scenarios by the years 2041, 2083, and 2100. The study analyzes and discusses the application of a the simple “bathtub” model coupled with a high-precision global digital elevation models (TanDEM-X DEM) to areas where no other data are available. Therefore, three coastal hazards hot-spots of Guinea-Bissau: Bissau, Bubaque, and Suzana, were used as case study. At each site, the area potentially exposed to coastal flooding was evaluated in a geographic information systems (GIS) environment, by estimating the Total Water Levels for each SLR scenario. For all areas, land exposed to coastal flooding hazard increases significantly and progressively with increasing SLR scenarios. Bissau and Suzana, where housing, infrastructure, and agricultural land are low-lying, presented the greatest flood exposure, while Bubaque, where housing and infrastructure are located in relatively high-lying land and rain-fed agriculture is practiced, present lesser flood exposure. The methodology presented is simple to use but powerful in identifying potentially vulnerable places to coastal flooding hazard, and its results can aid low developed countries to assess their exposure to coastal risks, thus supporting risk awareness and mitigation measures.

Recent retreat and flood dominant areas along the muddy Mahin coastline of Ilaje, Nigeria

The rates of retreat around the world, especially in low-lying coastal areas, have been pernicious in recent years. For some time, coastal retrogradation may follow a historically observed trend. However, a slight increase in ocean and climate indices, including sea level, temperature, and precipitation, can cause significant modification in the littoral profile. This study reports the recent changes and possible future threats along the Mahin mud coastline, Ilaje Local Government Area of Nigeria, West Africa. This study aims to understand the present evolution of the coastal area in order to manage the environmental and human risks in the future. Satellite images and Digital Elevation Model (DEM) map in the Geographic Information System (GIS) were used to evaluate the retreat rates of 20 years and delineate flooded coastal areas under some sea level rise (SLR) scenarios. Results showed that the areas of retreat dominance in recent years were once mostly accreting. In comparison, some areas that were receding have gained more land. Still, the rates of retreat in other areas have further intensified. Based on the DEM map analysis results, coastal flooding may very soon extend several kilometers inland, covering large areas of the southeastern sector. Therefore, this observation is essential to ensuring appropriate coastal protection plans are put in place.

Impact of Coastal Disasters on Women in Urban Slums: A New Index

Coastal hazards, particularly cyclones, floods, erosion and storm surges, are emerging as a cause for major concern in the coastal regions of Vijayawada, Andhra Pradesh, India. Serious coastal disaster events have become more common in recent decades, triggering substantial destruction to the low-lying coastal areas and a high death toll. Further, women living in informal and slum housing along the Vijayawada coastline of Andhra Pradesh (CAP), India, suffer from multiple social, cultural and economic inequalities as well. These conditions accelerate and worsen women’s vulnerability among this coastal population. The existing literature demonstrates these communities’ susceptibility to diverse coastal disasters but fails to offer gender-specific vulnerability in urban informal housing in the Vijayawada area. Accordingly, the current study developed a novel gender-specific Women’s Coastal Vulnerability Index (WCVI) to assess the impact of coastal disasters on women and their preparedness in Vijayawada. Field data was collected from over 300 women through surveys (2) and workshops (2) between November 2018 and June 2019, and Arc-GIS tools were used to generate vulnerability maps. Results show that women are more vulnerable than men, with a higher death rate during coastal disaster strikes. The current study also found that gender-specific traditional wear is one of the main factors for this specific vulnerability in this area. Furthermore, the majority of the women tend to be located at home to care for the elders and children, and this is associated with more fatalities during disaster events. Homes, particularly for the urban poor, are typically very small and located in narrow and restricted sites, which are a barrier for women to escape from unsafe residential areas during disasters. Overall, the research reveals that most of the coastal disaster events had a disproportionately negative impact on women. The results from this present study offer valuable information to aid evidence-based policy- and decision-makers to improve existing or generate innovative policies to save women’s lives and improve their livelihood in coastal areas.

Still normal? Near-real-time evaluation of storm surge events in the context of climate change

Abstract. Storm surges represent a major threat to many low-lying coastal areas in the world. In the aftermath of an extreme event, the extent to which the event was unusual and the potential contribution of climate change in shaping the event are often debated. Commonly analyzes that allow for such assessments are not available right away but are only provided with often considerable time delay. To address this gap, a new tool was developed and applied to storm surges along the German North Sea and Baltic Sea coasts. The tool integrates real-time measurements with long-term statistics to put ongoing extremes or the course of a storm surge season into a climatological perspective in near real time. The approach and the concept of the tool are described and discussed. To illustrate the capabilities, several exemplary cases from the storm surge seasons 2018/2019 and 2019/2020 are discussed. It is concluded that the tool provides support in the near-real-time assessment and evaluation of storm surge extremes. It is further argued that the concept is transferable to other regions and/or coastal hazards.

Effect of Summer Sea Level Rise on Storm Surge Analysis

Typhoons occur intensively between July and October, and the sea level is the highest during this time. In particular, the mean sea level in summer in Korea is higher than the annual mean sea level about 14.5cm in the west coast, 9.0 to 14.5cm in the south coast, and about 9.0 cm in the east coast. When the rising the sea level and a large typhoon overlap in summer, it can cause surges and flooding in low-lying coastal areas. Therefore, accurate calculation of the surge height is essential when designing coastal structures and assessing stability in order to reduce coastal hazards on the lowlands. In this study, the typhoon surge heights considering the summer mean sea level rise (SH_m) was calculated, and the validity of the analysis of abnormal phenomena was reviewed by comparing it with the existing surge height considering the annual mean sea level (SH_a). As a result of the re-analyzed study of typhoon surge heights for BOLAVEN (SANBA), which influenced in August and September during the summer sea level rise periods, yielded the differences of surge heights (cm) between SH_a and SH_m 7.8~24.5 (23.6~34.5) for the directly affected zone of south-west (south-east) coasts, while for the indirect south-east (south-west) coasts showed -1.0~0.0 (8.3~12.2), respectively. Whilst the differences between SH_a and SH_m of typhoons CHABA (KONG-REY) occurred in October showed remarkably lessened values as 5.2~ 14.2 (19.8~21.6) for the directly affected south-east coasts and 3.2~6.3 (-3.2~3.7) for the indirectly influenced west coast, respectively. The results show the SH_a does not take into account the increased summer mean sea level, so it is evaluated that it is overestimated compared to the surge height that occurs during an actual typhoon. Therefore, it is judged that it is necessary to re-discuss the feasibility of the surge height standard design based on the existing annual mean sea level, along with the accurate establishment of the concept of surge height.

Sensitivity, Hazard, and Vulnerability of Farmlands to Saltwater Intrusion in Low-Lying Coastal Areas of Venice, Italy

Saltwater intrusion is a growing threat for coastal aquifers and agricultural practices in low-lying plains. Most of the farmlands located between the margin of the Southern Venice lagoon and the Northern Po delta, Italy, lie a few meters below mean sea level and are drained by a large network of artificial channels and hydraulic infrastructures to avoid frequent flooding and allow agricultural practices. This work proposes an assessment of the vulnerability to saltwater intrusion, following a new concept of the hazard status, resulting in combining the depth of the freshwater/saltwater interface and the electrical resistivity of the shallow subsoil. The sensitivity of the farmland system was assessed by using ground elevation, distance from freshwater and saltwater sources, permeability, potential runoff, land subsidence, and sea-level rise indicators. Relative weights were assigned by a pairwise comparison following the Analytic Hierarchy Process approach. The computed vulnerability map highlights that about 30% of the farmlands is under strong and extreme conditions, 28% between marginal and moderate, and 40% under negligible conditions. Results from previous vulnerability assessments are discussed in order to explain their differences in terms of hazard status conceptualization and sensitivity characterization of farmland system.

From the Frying Pan into the Fire? Climate Change, Urbanization and (In)Security in Pacific Island Countries and Territories

Most Pacific Island Countries and Territories (PICTs) have experienced urban population growth for some time although the rates vary across the region. The drivers have traditionally been economic and social although the role of environmental degradation has been largely overlooked. As the populations of towns and cities have grown in PICTs, urban population densities have increased and available land for expansion has been restricted. Accordingly, many urban migrants live in informal peri urban settlements with little or no land security and limited government services such as sanitation, water supply and electricity. Employment is difficult to find and there are significant amounts of poverty. In this context there are high levels of individual and human insecurity and crimes including violence are often attributed to these problems. In some countries land related violence in urban areas has escalated into major conflicts. More recently climate change has been seen as an additional driver of urbanization and its role is expected to increase, although separating the social, economic and climate change causes is extremely difficult if not impossible. Already some communities have been relocated in several countries and some individual or family migration has been attributed to deteriorating human (land, livelihood, and habitat) security caused by climate change in rural areas. Because in most PICTs there are few alternatives, urban areas are likely to be the destinations for many climate change migrants and urbanization rates can be expected to further increase. Moreover, as options for settlement in peri urban areas lessen and numbers grow, more migrants are likely to find themselves occupying densely populated and increasingly environmentally marginal areas (such as steep and unstable slopes, river flood plains and low-lying coastal areas) that may be as exposed as their original homes. At the same time many of the migrants may be facing increasing social and economic insecurity related to urban living.

Powering an island energy system by offshore floating technologies towards 100% renewables: A case for the Maldives

Low-lying coastal areas and archipelago countries are particularly threatened by the impacts of climate change. Concurrently, many island states still rely on extensive use of imported fossil fuels, above all diesel for electricity generation, in addition to hydrocarbon-based fuels to supply aviation and marine transportation. Land area is usually scarce and conventional renewable energy solutions cannot be deployed in a sufficient way. This research highlights the possibility of floating offshore technologies being able to fulfil the task of replacing fossil fuels with renewable energy solutions in challenging topographical areas. On the case of the Maldives, floating offshore solar photovoltaics, wave power and offshore wind are modelled on a full hourly resolution in two different scenarios to deal with the need of transportation fuels: By importing the necessary, carbon neutral synthetic e-fuels from the world market, or by setting up local production capacities for e-fuels. Presented results show that a fully renewable energy system is technically feasible in 2030 with a relative cost per final energy of 120.3 €/MWh and 132.1 €/MWh, respectively, for the two scenarios in comparison to 105.7 €/MWh of the reference scenario in 2017. By 2050, cost per final energy can be reduced to 77.6 €/MWh and 92.6 €/MWh, respectively. It is concluded that floating solar photovoltaics and wave energy converters will play an important role in defossilisation of islands and countries with restricted land area.

Observing the influences of climatic and environmental variability over soil salinity changes in the Noakhali Coastal Regions of Bangladesh using geospatial and statistical techniques

Climate change is an intensive threat to the coastal areas of Bangladesh. Low-lying coastal areas suffer from salinity intrusion, especially in the geomorphologically active central coastal areas of Bangladesh (CAB). The intrusion of soil salinity has been particularly evident from studies on the CAB, which exhibits the effects of climate change and salinity changes along the coast. On a local scale, studies like these are essential, but current, when dealing with climate-driven changes considering the field of study, it is rarely observed and recorded in the literature. Therefore, this present study focuses on observing the influence of climate and environmental variability over soil salinity changes trend in the Noakhali coastal regions (NCR) of Bangladesh using geospatial and statistical techniques. To achieve this goal, the present study analyzed the historical climatic data of Bangladesh Meteorological Department (BMD) from 1987 to 2018, which showed that there were irregularities with deviation from normal distribution of temperature and rainfall data in the region. The study also shows maximum temperature raise of about 3°C and 1500 mm annual rainfall in the area. In addition, amplification of tides have been observed in the east and decreases in the west coast. On the other hand, the study suggested a significant reduction of about 22 dS/m in soil salinity data analysis from 1996 to 2019, which was a maximum of 2.27 dS/m in 2019 compared to 25 dS/m in 1996. However, in-depth observations of temperature and rainfall data revealed strong seasonal control over soil salinity levels. Abundance of rainfall is negatively correlated where tidal level is positively correlated with soil salinity level of the study area. There is a positive correlation between the soil salinity level and a minimum level of temperature change. The present study systematically focuses on the change in soil salinity of the NCR on climate and environmental changes, which provides information on historical influence. Finally, the study confirms that rainfall and tides are the main and temperature as the secondary soil salinity controlling factors of the CAB. The results of this study might be used scientifically to attain the sustainable agricultural practices, coastal development and regional planning of the country.

Deriving the 100-Year Total Water Level around the Coast of Corsica by Combining Trivariate Extreme Value Analysis and Coastal Hydrodynamic Models

As low-lying coastal areas can be impacted by flooding caused by dynamic components that are dependent on each other (wind, waves, water levels—tide, atmospheric surge, currents), the analysis of the return period of a single component is not representative of the return period of the total water level at the coast. It is important to assess a joint return period of all the components. Based on a semiparametric multivariate extreme value analysis, we determined the joint probabilities that significant wave heights (Hs), wind intensity at 10 m above the ground (U), and still water level (SWL) exceeded jointly imposed thresholds all along the Corsica Island coasts (Mediterranean Sea). We also considered the covariate peak direction (Dp), the peak period (Tp), and the wind direction (Du). Here, we focus on providing extreme scenarios to populate coastal hydrodynamic models, SWAN and SWASH-2DH, in order to compute the 100-year total water level (100y-TWL) all along the coasts. We show how the proposed multivariate extreme value analysis can help to more accurately define low-lying zones potentially exposed to coastal flooding, especially in Corsica where a unique value of 2 m was taken into account in previous studies. The computed 100y-TWL values are between 1 m along the eastern coasts and a maximum of 1.8 m on the western coast. The calculated values are also below the 2.4 m threshold recommended when considering the sea level rise (SLR). This highlights the added value of performing a full integration of extreme offshore conditions, together with their dependence on hydrodynamic simulations for screening out the coastal areas potentially exposed to flooding.

Rapid assessment of tsunami source impacts on low-lying coastal areas using offshore wave superposition and static sweep of onshore terrain

ABSTRACT Tsunami source impacts in coastal areas should be investigated thoroughly; however, investigating the associated source uncertainties can incur large computational costs. This study presents a technique for rapid assessment of the impacts and their uncertainties based on a combination of the linear wave superposition for Green’s functions and a static sweep algorithm for onshore terrain. A waveform from a tsunami source is quickly estimated at a shore based on the aforementioned superposition of single-point sources simulated by a linearized Boussinesq model. The maximum water surface elevation change in the waveform, the maximum tsunami elevation, is then determined. In addition, a digital elevation model for onshore terrain that can be inundated by a tsunami is scanned using the sweep algorithm to statically compare the tsunami and ground elevations. As a result, areas with lower ground elevation than the tsunami are quickly identified as potential tsunami hazard zones. This combined analysis is applied to assess potential tsunami sources in the Japan Sea, and the source impacts are comprehensively investigated for Sakata and Akita cities in Japan. Our analysis successfully and quantitatively indicates source impacts while considering their great uncertainty. Additionally, critical areas for expanding tsunami inundation are quickly and efficiently identified.

Oceanic passage of hurricanes across Cay Sal Bank in The Bahamas over the last 530 years

Islands across the Bahamian Archipelago have been devastated by five major hurricanes from 2010 to 2020 CE, including Category 5 Hurricane Dorian in 2019 that inundated parts of Abaco and Grand Bahama with up to 4 m of surge, killing 84 people and leaving >245 others missing. Up to 1 m relative sea-level rise is estimated for The Bahamas by 2100 CE, which could enhance flooding from weaker storms (<Category 3) in low-lying coastal areas. Problematically, Bahamian hurricane activity is highly spatially-heterogenous over the last 170 years, meaning that long-term regional hurricane frequency remains poorly constrained, especially for weaker Category 1–2 events that are less-likely to be detected by most sediment-based paleo-hurricane reconstructions. We present a 530-year record of hurricane passage from Hine's Blue Hole on Cay Sal Bank, The Bahamas. Hine's Hole has an accumulation rate of 2–3.2 cm/yr, making it among the highest-resolution hurricane reconstructions to date. Unlike many paleo-hurricane reconstruction sites, Hine's Hole is not surrounded by coastal landmasses that can dampen currents and waves produced by hurricanes, so it archives most ≥Category 1 hurricanes passing within 115 km during the 170-year instrumental record (1850 CE-present) and may also document intense tropical or winter storms. Hine's Hole archives ~16 intense storms per century from 1850 to 2016 CE, but documents three periods from 1505 to 1530 CE, 1570 to 1620 CE, and ~ 1710 to 1875 CE with over twice as many intense storms per century. These active periods correspond to other high-resolution reconstructions from the Bahamian Archipelago and Florida Keys, but the magnitude of the increase is much higher given that Hine's Hole archives evidence of weaker and more distal storms. As such, this reconstruction provides unprecedented insight into changes in hurricane activity within the pre-industrial climate system and demonstrates that recurrence intervals based on the 170-year instrumental record can severely underestimate the threat hurricanes pose certain localities.

Evaluating adaptation options to sea level rise and benefits to agriculture: The Ebro Delta showcase

Sea level rise (SLR) is threatening low-lying coastal areas such as river deltas. The Ebro river Delta (Spain) is representative of coastal systems particularly vulnerable to SLR due to significant sediment retention behind upstream dams (up to 99%), thereby dramatically reducing the capacity for deltaic sediment accretion. Rice production is the main economic activity, covering 66% of the delta area, and is negatively affected by SLR because of flooding and soil salinization. Therefore, appropriate adaptation measures are needed to preserve rice production. We combined Geographic Information Systems and Generalized Linear Models to identify zones prone to flooding and increasing soil salinity, and to calculate the so-called sediment deficit, that is the amount of sediment needed to raise the land to compensate flooding and soil salinization. We modelled SLR scenarios predicted by the IPCC Fifth Assessment Report, and analysed the economic feasibility (not the technical feasibility) of reintroducing fluvial sediments retained in the upstream river dam reservoirs into the delta plain, which can contribute to maintaining land elevation and rice production with SLR. To do this, the costs of the sediment reintroduction measures and their benefits in terms of avoided loss of rice production income were evaluated with an approximate economic cost-benefit analysis. Results predicted that between 35 and 90% of the rice field area will be flooded in the best and worst SLR scenarios considered (SLR = 0.5 m and 1.8 m by 2100, respectively), with a sediment deficit of 130 and 442 million tonnes, with an associated cost of sediment reintroduction of 13 and 226 million €. The net benefit of rice production maintenance was 24.6 and 328 €/ha. The proposed adaptation measure has a positive effect on rice production and can be considered as an innovative management option for maintaining deltaic areas under SLR.

Modeling surface waves and tide–surge interactions leading to enhanced total water levels in a macrotidal bay

ABSTRACT Large waves and storm surge generated by powerful storms can have detrimental impacts on coastal areas. The Gulf of Maine and Bay of Fundy system in the Atlantic Ocean is a particularly dynamic environment where storm surge can synergistically combine with the large tides to yield serious impacts on low-lying coastal areas. In this study, impacts from Hurricane Arthur in 2014 were investigated with observations and numerical simulations using a coupled hydrodynamic-wave model. The results indicate that the storm generated significant wave heights up to 5 m in the Gulf of Maine and a storm surge of over 0.5 m in coastal areas in the Upper Bay of Fundy, however this surge occurred during the neap tide with no associated flooding. Additional simulations, including a historically important event called the Saxby Gale of 1869, were also simulated. This powerful storm occurred during a perigean spring tide, and the model results indicate wave heights of over 10 m and storm surge of over 0.7 m that caused significant flooding. The results indicate that a well-timed tropical cyclone during a high spring tide has the potential to create a storm surge that could overtop existing dyke systems, causing extensive flooding and damage.

Coastal Adaptation to Climate Change and Sea-Level Rise

The Earth’s climate is changing; ice sheets and glaciers are melting and coastal hazards and sea level are rising in response. With a total population of over 300 million people situated on coasts, including 20 of the planet’s 33 megacities (over 10 million people), low-lying coastal areas represent one of the most vulnerable areas to the impacts of climate change. Many of the largest cities along the Atlantic coast of the U.S. are already experiencing frequent high tide flooding, and these events will increase in frequency, depth, duration and extent as sea levels continue to rise at an accelerating rate throughout the 21st century and beyond. Cities in southeast Asia and islands in the Indo-Pacific and Caribbean are also suffering the effects of extreme weather events combined with other factors that increase coastal risk. While short-term extreme events such as hurricanes, El Niños and severe storms come and go and will be more damaging in the short term, sea-level rise is a long-term permanent change of state. However, the effects of sea-level rise are compounded with other hazards, such as increased wave action or a loss of ecosystems. As sea-level rise could lead to the displacement of hundreds of millions of people, this may be one of the greatest challenges that human civilization has ever faced, with associated inundation of major cities, loss of coastal infrastructure, increased saltwater intrusion and damage to coastal aquifers among many other global impacts, as well as geopolitical and legal implications. While there are several short-term responses or adaptation options, we need to begin to think longer term for both public infrastructure and private development. This article provides an overview of the status on adaptation to climate change in coastal zones.

Characterizing the Non-linear Interactions Between Tide, Storm Surge, and River Flow in the Delaware Bay Estuary, United States

Low-lying coastal areas in the mid-Atlantic region are prone to compound flooding resulting from the co-occurrence of river floods and coastal storm surges. To better understand the contribution of non-linear tide-surge-river interactions to compound flooding, the unstructured-grid Finite Volume Community Ocean Model was applied to simulate coastal storm surge and flooding in the Delaware Bay Estuary in the United States. The model was validated with tide gauge data in the estuary for selected hurricane events. Non-linear interactions between tide-surge-river were investigated using a non-stationary tidal analysis method, which decomposes the interactions’ components at the frequency domain. Model results indicated that tide-river interactions damped semidiurnal tides, while the tide-surge interactions mainly influenced diurnal tides. Tide-river interactions suppressed the water level upstream while tide-surge interaction increased the water level downstream, which resulted in a transition zone of damping and enhancing effects where the tide-surge-river interaction was prominent. Evident compound flooding was observed as a result of non-linear tide-surge-river interactions. Furthermore, sensitivity analysis was carried out to evaluate the effect of river flooding on the non-linear interactions. The transition zone of damping and enhancing effects shifted downstream as the river flow rate increased.