Deconvolving The Effects of Coastal Erosion and Sea-Level Rise in Assessing Shoreline Retreat Along Semi-Arid Urban Coasts

Abstract The alarming vulnerability of low-lying sandy beaches to the acceleration of global sea level rise has been confirmed in the recent IPCC AR6 report. The situation is worsened by increasing coastal erosion, resulting in additional shoreline retreat of sandy beaches along several semi-arid urban coastal areas around the globe. The additional shoreline retreats from erosion are indicative of the rising imbalance in coastal sedimentary processes, which are a direct consequence of changes in precipitation patterns, urban growth, and change in land use. To quantify the magnitude and timescale of both coastal erosion and sea-level rise (SLR) in generating shoreline retreat of sandy beaches in semi-arid urban areas, we combine photogrammetric and statistical methods to measure and forecast the decadal evolution of these coastlines using two well-characterized sites that are hypothesized herein to be globally representative of these types of coasts undergoing rapid urban growth. We use multi-decadal shoreline positioning and land use classification surveys of the Southern California (SC, USA) and the Hammamet-North (HAM, Tunisia) beaches from aerial and orbital photogrammetric images, combined with the Digital Shoreline Analysis System, for the period from 1985 to 2018. Our results suggest that the current average shoreline retreat rates of sandy beaches range from -0.75 to -1.24 m/yr in SC and from -0.21 to -4.49 m/yr in HAM under similar aridity, land coverage and precipitation patterns. The observed decadal changes in shoreline positions along these semi-arid urban coastal areas are found to be accentuated by anthropogenic drivers associated with extensive urbanization, causing sediment imbalance at the coastline, adding up to the effect of the accelerating SLR. We assess that ~81% and 57% of the observed shoreline retreat was due to SLR, and 19% to 43% due to coastal erosion from urban growth along SC and HAM beaches, respectively. Using these measured rates, we establish a semi-empirical numerical model that combines urban growth and the observed shoreline retreat rate to forecast retreat rates through 2100 for both of our study areas, inferred herein to be representative of other global semi-arid urban coasts. Our model suggests that future average total shoreline retreat rates, accounting for both urban growth and SLR, range from -2 to -4 m/yr for SC and HAM sandy beaches, respectively, through 2100. The above suggests that if no mitigation is made, by 2100 the cumulative shoreline retreat in these urban areas could significantly exceed the Global Scale Assessment Model’s [46] cumulative projected average retreat of -30 m, confirming the alarming vulnerability of the semi-arid coastal urban areas that would need intensive and costly beach nourishment to control increasing shoreline erosion.

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An examination of land use impacts of sea level rise induced flooding

10.5194/nhess-2016-157 ◽

2016 ◽

Author(s):

Jie Song ◽

Xinyu Fu ◽

Yue Gu ◽

Yujun Deng ◽

Zhong-Ren Peng

Keyword(s):

Land Use ◽

Sea Level Rise ◽

Sea Level ◽

Urban Sprawl ◽

Urban Growth ◽

Risk Mitigation ◽

Coastal Areas ◽

Coastal Hazards ◽

Sleuth Model ◽

Flooding Risk

Abstract. Coastal regions are under intense development because of their biodiversity and economic attractiveness. Meanwhile, these places are highly vulnerable to coastal hazards that are associated with sea level rise. Continuing urban development in these coastal areas that are prone to be flooded increasingly poses unnecessarily risk to their residents. While overwhelming efforts have been made to investigate coastal land use changes, few studies have simultaneously explored urban growth dynamics and its interaction with the coastal hazards. This paper applied the cellular automaton-based SLEUTH model to calibrate historical urban growth pattern from 1974 to 2013 in Bay County coastal areas, Florida. Three scenarios of urban growth – historical trend, compact development, and urban sprawl – up to 2080 were predicted by applying the calibrated SLEUTH model. To assess the effects of different policies, we developed three excluded layers – no regulations, flooding-risk mitigation, and conservational/agricultural land protection – and evaluated how different urban growth scenarios were oriented under these policies. Eventually, flooding maps were overlaid with future urban areas, and the exposure of different urban growth patterns to sea level rise induced flooding was examined. The findings suggest that if coastal cities expand in a compact manner, areas vulnerable to flooding will increase compared with historical trend and urban sprawl scenarios. With respect to policies, if no regulations are implemented, on average the flooded area in 2080 would be more than 25 times under flooding-risk mitigation. The joint model can serve as a decision support tool to assist city officials, urban planners, and hazard mitigation planners in making informed decisions. The visualization results can be also useful in public outreach regarding coastal communities' increasing risk to flooding enhanced by sea level rise.

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Climate Change Preparedness: Comparing Future Urban Growth and Flood Risk in Amsterdam and Houston

Sustainability ◽

10.3390/su11041048 ◽

2019 ◽

Vol 11 (4) ◽

pp. 1048 ◽

Cited By ~ 6

Author(s):

Youjung Kim ◽

Galen Newman

Keyword(s):

Land Use ◽

The Netherlands ◽

Sea Level Rise ◽

Sea Level ◽

Urban Growth ◽

Land Use Planning ◽

Flood Risk ◽

Urban Areas ◽

Land Use Changes ◽

Transformation Model

Rising sea levels and coastal population growth will increase flood risk of more people and assets if land use changes are not planned adequately. This research examines the efficacy of flood protection systems and land use planning by comparing Amsterdam in the Netherlands (renown for resilience planning methods), with the city of Houston, Texas in the US (seeking ways of increasing resilience due to extreme recent flooding). It assesses flood risk of future urban growth in lieu of sea level rise using the Land Transformation Model, a Geographic Information Systems (GIS)-based Artificial Neural Network (ANN) land use prediction tool. Findings show that Houston has currently developed much more urban area within high-risk flood-prone zones compared to Amsterdam. When comparing predicted urban areas under risk, flood-prone future urban areas in Amsterdam are also relatively smaller than Houston. Finally, the increased floodplain when accounting for sea level rise will impact existing and future urban areas in Houston, but do not increase risk significantly in Amsterdam. The results suggest that the protective infrastructure used in the Netherlands has protected its future urban growth from sea level rise more adequately than has Houston.

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Shoreline Changes in Tuban District in East Java Caused by Sea Level Rise Using Bruun Rule and Hennecke Methods

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.862.34 ◽

2017 ◽

Vol 862 ◽

pp. 34-40 ◽

Cited By ~ 2

Author(s):

Marita Ika Joesidawati ◽

Suntoyo

Keyword(s):

Sea Level Rise ◽

Sea Level ◽

Least Square Method ◽

Sandy Beaches ◽

Coastal Areas ◽

Least Square ◽

Shoreline Retreat ◽

Shoreline Changes ◽

Bruun Rule ◽

Starting Point

Changes in the shoreline setback is a major threat of coastal areas dominated by sandy beaches and coastal lowlands. The impacts of sea level rise itself will be greatly felt by coastal regions in the island nations, such as Indonesia. Tuban is one of northern coastal areas in East Java, which includes the areas where the condition of beaches damaged. Thus, it is necessary to investigate the characteristics of beaches in Tuban, and how much the sea level rise occurs in Tuban district as well as the extent of its influence on the shorelines of Tuban. The calculation of sea level rise was predicted using the Least Square Method with tidal data of Semarang city in 1985-2014 which was later adopted as the tidal of Tuban, and the sea level rise at the beaches in Tuban, which was estimated at 0,024 meter annually by implementing the equation of y = 0.002x + 0.751. In the year of 2050 and 2100, the rise of the sea level reaches 2.55 m and 3.54 m respectively. The most appropriate method used is the Hennecke method, with the error value of 0.27%. The error value of Hennecke method is smaller than the error value of Bruun Rule method, which reaches 0.38%. Using Hennecke method, the prediction of the shoreline changes in Tuban with the starting point of the year of 2008 shows that the average shoreline retreat in the year of 2050 is about 94.71 meters and in 2100 is about 234.2 m. However, by using the method of Bruun Rule, the average shoreline retreat in the year of 2050 is about 161.27 m, and in the year of 2100 is about 349.16 m. The adaptation strategies that can be conducted to minimize the impacts are (i) protective pattern, (ii) accommodative pattern, and it is better to have a Strategic Area Construction Plan.

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Grid-based global coastal zone datasets for coastal impact analysis

10.5194/egusphere-egu2020-18584 ◽

2020 ◽

Author(s):

Daniel Lincke

Keyword(s):

Land Use ◽

Sea Level Rise ◽

Sea Level ◽

Coastal Zone ◽

Urban Areas ◽

Impact Analysis ◽

Rocky Shores ◽

Management Options ◽

Elevation Model ◽

Natural Boundaries

Global coastal impact and adaptation analysis in the context of climate change induced sea-level rise needs precise and standardized datasets. Here, such datasets and their construction are presented. Starting from a high-resolution global digital elevation model, the coastline is extracted with taking into account river mouths and lagoons taken from a global surface water dataset. The global low-elevation coastal zone (LECZ) is derived by determining all grid cells hydrological connected to the coastline. Recent surge-data is combined with sea-level rise scenarios to partition the global LECZ into local floodplains. Latest socio-economic and land-use data is used to partition and classify these local floodplains. As local impacts and adaptation responses are not spatially uniform, but depend on a range of conditions including: i) biophysical conditions such as natural boundaries between floodplains (e.g. hills, rocks, etc.) and coastal geomorphology (e.g. sandy versus rocky shores), ii) technical conditions such as existing flood protection infrastructure (e.g. dike rings in the Netherlands), and ii) socio-economic conditions such as administrative boundaries, land use and urban extent (e.g. rural versus urban areas), latest land-use, beach and wetland datasets are used to partition the coastline of each floodplain into a network of coastline segments which can be used for assessing local shoreline management options. The generated datasets contain about 1.6 million km of coastline distributed over 87,600 islands. The LECZ comprises 3.14 million km&#178; and partitioning this LECZ with surge and sea-level rise data into floodplains for coastal impact modelling finds about 221,800 floodplains with at least 0.05 km&#178; area.

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Coastal Flooding in the Balearic Islands During the Twenty-First Century Caused by Sea-Level Rise and Extreme Events

Frontiers in Marine Science ◽

10.3389/fmars.2021.676452 ◽

2021 ◽

Vol 8 ◽

Author(s):

Pau Luque ◽

Lluís Gómez-Pujol ◽

Marta Marcos ◽

Alejandro Orfila

Keyword(s):

Sea Level Rise ◽

Sea Level ◽

Storm Surges ◽

Coastal Flooding ◽

Sandy Beaches ◽

Balearic Islands ◽

First Century ◽

Shoreline Retreat ◽

Mean Sea Level ◽

Recreational Services

Sea-level rise induces a permanent loss of land with widespread ecological and economic impacts, most evident in urban and densely populated areas. Potential coastline retreat combined with waves and storm surges will result in more severe damages for coastal zones, especially over insular systems. In this paper, we quantify the effects of sea-level rise in terms of potential coastal flooding and potential beach erosion, along the coasts of the Balearic Islands (Western Mediterranean Sea), during the twenty-first century. We map projected flooded areas under two climate-change-driven mean sea-level rise scenarios (RCP4.5 and RCP8.5), together with the impact of an extreme event defined by the 100-year return level of joint storm surges and waves. We quantify shoreline retreat of sandy beaches forced by the sea-level rise (scenarios RCP4.5 and RCP8.5) and the continuous action of storm surges and waves (modeled by synthetic time series). We estimate touristic recreational services decrease of sandy beaches caused by the obtained shoreline retreat, in monetary terms. According to our calculations, permanent flooding by the end of our century will extend 7.8–27.7 km2 under the RCP4.5 scenario (mean sea-level rise between 32 and 80 cm by 2100), and up to 10.9–36.5 km2 under RCP8.5 (mean sea-level rise between 46 and 103 cm by 2100). Some beaches will lose more than 50% of their surface by the end of the century: 20–50% of them under RCP4.5 scenario and 25–60% under RCP8.5 one. Loss of touristic recreational services could represent a gross domestic product (GDP) loss up to 7.2% with respect to the 2019 GDP.

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Single Extreme Strong Sequence Can Offset Decades of Shoreline Retreat by Sea-level Rise

10.21203/rs.3.rs-805900/v1 ◽

2021 ◽

Author(s):

Mitchell Harley ◽

Gerd Masselink ◽

Amaia Ruiz de Alegría-Arzaburu ◽

Nieves Valiente ◽

Tim Scott

Keyword(s):

Sea Level Rise ◽

Sea Level ◽

Coastal Erosion ◽

Sediment Budget ◽

Positive Contribution ◽

Volume Changes ◽

Shoreline Retreat ◽

Quantitative Understanding ◽

The Uk

Abstract Extreme storms cause extensive beach-dune erosion and are universally considered to enhance coastal erosion due to sea-level rise (SLR). However, extreme storms can also have a positive contribution to the nearshore sediment budget by exchanging sediment between the lower and upper shoreface and/or between adjacent headlands, potentially mitigating adverse SLR impacts. Here we use three high-resolution morphological datasets of extreme storm-recovery sequences from Australia, the UK and Mexico to quantify the nearshore sediment budget and relate these episodic volume changes to long-term coastal forecasts. We show that sediment gains over the upper shoreface and beach were very significant (58-140 m3/m) and sufficient to offset decades of predicted shoreline retreat due to SLR, even for an upper SSP5-8.5 scenario. It is evident that increased confidence in shoreline predictions due to SLR relies fundamentally on robust quantitative understanding of the sediment budget, in particular any long-term contribution of sediment transport from outside the nearshore region.

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An examination of land use impacts of flooding induced by sea level rise

Natural Hazards and Earth System Science ◽

10.5194/nhess-17-315-2017 ◽

2017 ◽

Vol 17 (3) ◽

pp. 315-334 ◽

Cited By ~ 8

Author(s):

Jie Song ◽

Xinyu Fu ◽

Yue Gu ◽

Yujun Deng ◽

Zhong-Ren Peng

Keyword(s):

Land Use ◽

Sea Level Rise ◽

Sea Level ◽

Urban Growth ◽

Flood Mitigation ◽

Coastal Hazards ◽

Land Use Impacts ◽

Study Region ◽

Sea Levels ◽

Modeling Uncertainties

Abstract. Coastal regions become unprecedentedly vulnerable to coastal hazards that are associated with sea level rise. The purpose of this paper is therefore to simulate prospective urban exposure to changing sea levels. This article first applied the cellular-automaton-based SLEUTH model (Project Gigalopolis, 2016) to calibrate historical urban dynamics in Bay County, Florida (USA) – a region that is greatly threatened by rising sea levels. This paper estimated five urban growth parameters by multiple-calibration procedures that used different Monte Carlo iterations to account for modeling uncertainties. It then employed the calibrated model to predict three scenarios of urban growth up to 2080 – historical trend, urban sprawl, and compact development. We also assessed land use impacts of four policies: no regulations; flood mitigation plans based on the whole study region and on those areas that are prone to experience growth; and the protection of conservational lands. This study lastly overlaid projected urban areas in 2030 and 2080 with 500-year flooding maps that were developed under 0, 0.2, and 0.9 m sea level rise. The calibration results that a substantial number of built-up regions extend from established coastal settlements. The predictions suggest that total flooded area of new urbanized regions in 2080 would be more than 25 times that under the flood mitigation policy, if the urbanization progresses with few policy interventions. The joint model generates new knowledge in the domain between land use modeling and sea level rise. It contributes to coastal spatial planning by helping develop hazard mitigation schemes and can be employed in other international communities that face combined pressure of urban growth and climate change.

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Climate Change and Man-made Interventions, as Destabilizing Factors of the Coastal Zone: Some Examples of Coasts and Coastal Wetlands in Urban, Peri-Urban Areas and Natural Parks in Greece

International Journal of Environment and Climate Change ◽

10.9734/ijecc/2019/v9i1130144 ◽

2019 ◽

pp. 616-642

Author(s):

Aristeidis Mertzanis ◽

Asimina Mertzani

Keyword(s):

Climate Change ◽

Sea Level Rise ◽

Sea Level ◽

Urban Areas ◽

Coastal Erosion ◽

River Mouth ◽

Coastal Development ◽

Aerial Photographs ◽

Rapid Urbanization ◽

Natural Parks

The consequences of man-made interventions, Climate Change and future Sea-level rise upon some coastal plains of Greece are examined. Many urban, peri-urban areas and Natural Parks, in low elevation coastal zones in Greece are experiencing or are at risk of Sea-level rise, storm surges, water and soil pollution, saline water intrusion (salinity), coastal erosion and shoreline retreat, floods, and droughts. Sea-level rise could erode and inundate coastal ecosystems and disrupt wetlands, Urban and peri-Urban areas. Characteristic examples of these are the protected wetlands that exist in Greece such as those in the Delta and the river mouth areas of the Sperchios, Alfeios, Arachthos, Louros, and Inois rivers, and the small town of Tolo. Man-made interventions affect the coastal wetland ecosystems, Urban and peri-Urban areas under study. At the same time, an important factor of the destabilization of the ecological balance is the Climate Change and the expected sea-level rise. The main anthropogenic degradation and stresses on the under investigation areas, in recent decades, includes wetland draining, exsiccation of lagoons and lakes, river engineering works, dam construction, intensification and development of agriculture projects, sand mining from riverbeds and beaches, construction of motorways, construction of harbor structures, such as harbors, jetties, seawalls, groins, and breakwaters, rapid urbanization processes, holiday home building and tourist facilities, massive tourism and intense coastal development, water pollution, human-induced land subsidence (uncontrolled water abstraction from surface and underground water tables), and removal of coastal vegetation. Satellite images, maps and systematic in situ observations, integrated with the direct digitizing on the basis of different aged aerial photographs was adopted to estimate the coastal erosion and accretion rates in recent decades (1945-2019) in the areas, under study.

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When the Tides Come, Where Will We Go?: Modeling the Impacts of Sea Level Rise on the Greater Boston, Massachusetts, Transport and Land Use System

Transportation Research Record Journal of the Transportation Research Board ◽

10.3141/2653-07 ◽

2017 ◽

Vol 2653 (1) ◽

pp. 54-64 ◽

Cited By ~ 3

Author(s):

Yafei Han ◽

P. Christopher Zegras ◽

Victor Rocco ◽

Michael Dowd ◽

Mikel Murga

Keyword(s):

Land Use ◽

Sea Level Rise ◽

Sea Level ◽

Urban Areas ◽

Inner Core ◽

Extreme Event ◽

Transport Model ◽

System Response ◽

Transit System ◽

Short Run

For coastal urban areas, an increase in flooding is one of the clearest climate change threats. The research presented in this paper demonstrates how a land use–transport model can be used to forecast the short- and longer-term impacts of a potential 4-ft sea level rise in greater Boston, Massachusetts, by 2030. The short-term scenario represents the immediate transport system response to inundation, which provides a measure of resiliency in the case of an extreme event, such as a storm surge. In the short run, the results reveal that transit captive users will suffer more. Transit, in general, displays less resiliency, at least in part because of the center city’s vulnerability and Boston’s radial transit system. Trip distances would modestly decrease, and average travel speeds would go down by more than 50%. Rail transit ridership would be decimated, and overall transit usage would go down by 66%. The longer-term scenario predicts how households and firms would prefer to relocate in the so-called new equilibrium when more than 10 mi2 of land disappears and the transport network inundations become permanent. Assuming no supply constraints, new residential growth centers would emerge on the peripheries of the inundated zones, primarily in the inner-core suburbs. Some regional urban centers and traditional industrial towns would boom. Firms would be hit harder, because of their heavy concentration in the inner core; firm relocation would largely follow households. Transit usage would again be decimated, but walking trips would increase. Results, however, should be viewed as cautious speculation.

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Projections and uncertainties of sandy beach loss due to sea level rise at the European scale

10.5194/egusphere-egu2020-10149 ◽

2020 ◽

Author(s):

Panagiotis Athanasiou ◽

Ap van Dongeren ◽

Alessio Giardino ◽

Michalis Vousdoukas ◽

Roshanka Ranasinghe ◽

...

Keyword(s):

Spatial Variation ◽

Sea Level Rise ◽

Sea Level ◽

Input Data ◽

Large Scale ◽

Satellite Images ◽

Sandy Beaches ◽

Land Loss ◽

Shoreline Retreat ◽

The Impact

Climate change driven sea level rise (SLR) is expected to rise with even higher rates during the second half of the present century. This will exacerbate shoreline retreat of sandy coasts, which comprise one third of the global coastline. Sandy coasts have high touristic and ecological value while they are the first level of defense against storms, protecting valuable infrastructures and buildings. Therefore, in recent years, large scale risk assessments are considered useful tools for the guidance of policy makers to identify high risk hotspots.&#160; Reliable input data at this scale are required in order to make useful estimations. Among others, crucial data to assess the impact of SLR on shoreline retreat are the detection of different coastal types and, in particular, of sandy erodible beaches, and the nearshore slope, which is usually assumed to be uniform.The important issue of input data uncertainty and spatial variation and consequent impact on predictions has been so far ignored in most large-scale studies. Estimates of shoreline retreat are however very sensitive to the variation in these inputs. Here we quantify SLR driven potential shoreline retreat and consequent land loss in Europe during the 21st century by employing different combinations of geophysical datasets for (a) the location of sandy beaches and (b) their nearshore slopes. For the estimation of the shoreline retreat, the Bruun Rule is used, which offers a suitable approach for a first approximation of erosion impacts at large scales. Sea level rise projections associated with the moderate-emission- mitigation-policy (RCP4.5) and the high-end, business-as-usual scenario (RCP8.5) are used as boundary conditions. The location of sandy beaches is determined from two different datasets. One is based on manual visual estimation from satellite images and the other on automatic detection from satellite images using machine learning techniques. For nearshore slopes we apply the commonly used constant slope assumption of 1:100 and a newly produced global dataset which captures the spatial variation of coastal slopes.With this approach, we create four different combinations for each SLR scenario, for which we estimate and compare land loss at EU, country and NUTS3 regional level. We find that the land loss estimations for each combination can differ significantly, especially at the regional and local level. At the European or country level, even though differences in total land loss projections can be significant, they can be concealed by the spatial aggregation of the results. Using data-based spatially-varying nearshore slope data, a European averaged median shoreline retreat of 97 m (54 m) is projected under RCP 8.5 (4.5) by year 2100, relative to the baseline year 2010. This retreat would translate to 2,500 km2 (1,400 km2) of land loss. A variance-based global sensitivity analysis indicates that the uncertainty associated with the choice of geophysical datasets can contribute up to 45% (26%) of the variance in land loss projections for Europe by 2050 (2100).

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