Sustained coral reef growth in the critical wave dissipation zone of a Maldivian atoll

Sea-level rise is expected to outpace the capacity of coral reefs to grow and maintain their wave protection function, exacerbating coastal flooding and erosion of adjacent shorelines and threatening coastal communities. Here we present a new method that yields highly-resolved direct measurements of contemporary reef accretion on a Maldivian atoll reef rim, the critical zone that induces wave breaking. Results incorporate the suite of physical and ecological processes that contribute to reef accumulation and show growth rates vary from 6.6 ± 12.5 mm.y−1 on the reef crest, and up to 3.1 ± 10.2 mm.y−1, and −0.5 ± 1.8 mm.yr−1 on the outer and central reef flat respectively. If these short-term results are maintained over decades, the reef crest could keep pace with current sea-level rise. Findings highlight the need to resolve contemporary reef accretion at the critical wave dissipation zone to improve predictions of future reef growth, and re-evaluate exposure of adjacent shorelines to coastal hazards.

A systematic review of blue carbon as an approach for Eco-DRR: current gap and future research

Blue carbon ecosystems (BCEs), such as wetlands, marshes, mangroves, and seagrasses, warrant increased attention for their abilities to protect life, property, and environments locally and globally. BCEs serve as both buffers reducing coastal hazards and carbon sinks storing ‘blue’ carbon in aquatic plant life and soils. While research exists on BCE functions and benefits, their global diversity necessitates a collection of localized research investigating the unique dynamics and histories of distinct BCEs. The historic degradation of coastal ecosystems proves the need for purposeful, well-informed, sustainable ecosystem management to conserve and restore BCEs. We conducted a systematic literature review to understand the existing body of research on synergies between BCEs and ecosystem-based disaster risk reduction (Eco-DRR). We investigated how prior research employed various research methods, discussed key aspects of sustainable land management, and considered geographic locations and scales. We discovered localized case studies have incredible insights on the efficacy of BCEs along with context-specific strategies for sustainable ecosystem management. However, as these case studies are not plentiful and are concentrated in North America and Asia, they do not account for the diversity of BCEs. We suggest increased support for localized research on the benefits and implementation of BCEs as Eco-DRR measures.

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.

Climate Change Induced Coastline Change Adjacent to Small Tidal Inlets

The many thousands of small tidal inlets (STIs), and their adjacent coastlines, are almost certain to be affected by climate change in multiple ways, due to their behaviour being closely linked to both oceanic and terrestrial drivers such as riverflow, sea level, and ocean waves, all which are projected to change over the 21st century. Development of risk informed adaptation strategies for these highly utilized and inhabited inlet-interrupted coast zones requires projections of both alongshore average coastline recession and alongshore variability in coastline position along the coast under future forcing conditions, the latter being an aspect that has not received much attention to date. Here, a combination of a process-based morphodynamic model (Delft3D) and the reduced complexity coastline model (SMIC), concurrently forced with tides, waves, riverflows, and sea level rise, is used to investigate both of these phenomena at STI-interrupted coasts. The models are here applied to schematised conditions representing two systems in Sri Lanka, representing two of the three main Types of STIs: Negombo lagoon – permanently open, locationally stable inlet (Type 1), and Kalutara lagoon – permanently open, alongshore migrating inlet (Type 2). Results indicate that, under a high emissions climate scenario following RCP 8.5, by end-century, the coastline adjacent to the Type 1 STI may experience an alongshore average recession as large as 200 m, and that the alongshore variability in coastline position may be up to twice that at present. The Type 2 STI is projected to experience an alongshore average coastline recession of about 120 m, and up to a 75% increase in alongshore variability in coastline position by end-century, relative to the present. Thus, both the alongshore average coastline recession and the increase in the alongshore variability in coastline position are greater at the Type 1 STI, compared to at the Type 2 STI. These findings highlight the importance of accounting for both alongshore average coastline recession and future changes in alongshore variability in coastline position when assessing coastal hazards and risk on inlet-interrupted coasts to adequately inform climate adaptation strategies.

Estimating population and urban areas at risk of coastal hazards, 1990–2015: how data choices matter

The accurate estimation of population living in the low-elevation coastal zone (LECZ) – and at heightened risk from sea level rise – is critically important for policymakers and risk managers worldwide. This characterization of potential exposure depends on robust representations not only of coastal elevation and spatial population data but also of settlements along the urban–rural continuum. The empirical basis for LECZ estimation has improved considerably in the 13 years since it was first estimated that 10 % of the world's population – and an even greater share of the urban population – lived in the LECZ (McGranahan et al., 2007a). Those estimates were constrained in several ways, not only most notably by a single 10 m LECZ but also by a dichotomous urban–rural proxy and population from a single source. This paper updates those initial estimates with newer, improved inputs and provides a range of estimates, along with sensitivity analyses that reveal the importance of understanding the strengths and weaknesses of the underlying data. We estimate that between 750 million and nearly 1.1 billion persons globally, in 2015, live in the ≤ 10 m LECZ, with the variation depending on the elevation and population data sources used. The variations are considerably greater at more disaggregated levels, when finer elevation bands (e.g., the ≤ 5 m LECZ) or differing delineations between urban, quasi-urban and rural populations are considered. Despite these variations, there is general agreement that the LECZ is disproportionately home to urban dwellers and that the urban population in the LECZ has grown more than urban areas outside the LECZ since 1990. We describe the main results across these new elevation, population and urban-proxy data sources in order to guide future research and improvements to characterizing risk in low-elevation coastal zones (https://doi.org/10.7927/d1x1-d702, CIESIN and CIDR, 2021).

Progress or Regress? A Systematic Review on Two Decades of Monitoring and Addressing Land Subsidence Hazards in Semarang City

Land subsidence is a major cause of environmental degradation. It increases the exposure of global sea level rise-related disasters in coastal cities lying on young sediment. Ample monitoring, adaptation, and mitigation measures have been taken to tackle the impact of such coastal hazards for decades in Semarang City. However, to date, land subsidence still has a negative impact on people’s quality of life. This brings us to the question of whether the measures are progressing towards better management or going to the opposite side. This paper is aimed to answer that question through an extensive literature review using PRISMA Guidelines to 125 scholarly articles and quantitative supporting analysis. We found that land subsidence is overlooked. Although the monitoring measures are progressing towards better technology utilization, it was not properly integrated into mitigation and adaptation measures. Instead of investing more on developing better urban water management, groundwater extraction still became the preferred water source. Thus, there is a major shift needed with regard to urban activities that need to pay more heed to the environment.

A systematic review of blue carbon as an approach for Eco-DRR: current gap and future research

Blue carbon ecosystems (BCEs), such as wetlands, marshes, mangroves, and seagrasses, warrant increased attention for their abilities to protect life, property, and environments locally and globally. BCEs serve as both buffers reducing coastal hazards and carbon sinks storing ‘blue’ carbon in aquatic plant life and soils. While research exists on BCE functions and benefits, their global diversity necessitates a collection of localized research investigating the unique dynamics and histories of distinct BCEs. The historic degradation of coastal ecosystems proves the need for purposeful, well-informed, sustainable ecosystem management to conserve and restore BCEs. We conducted a systematic literature review to understand the existing body of research on synergies between BCEs and ecosystem-based disaster risk reduction (Eco-DRR). We investigated how prior research employed various research methods, discussed key aspects of sustainable land management, and considered geographic locations and scales. We discovered localized case studies have incredible insights on the efficacy of BCEs along with context-specific strategies for sustainable ecosystem management. However, as these case studies are not plentiful and are concentrated in North America and Asia, they do not account for the diversity of BCEs. We suggest increased support for localized research on the benefits and implementation of BCEs as Eco-DRR measures.

Vulnerable Territories: The Perpetually Shifting Edge

<p>New Zealand’s coastline is rapidly receding. The increased threat of rising sea levels continues to erode the shore line causing extensive and irreparable damage to thousands of coastal properties, often dismantling communities and the kiwi dream of living near the ocean. With global temperatures continuing to rise, all of our coastal communities are at risk. The current measure of response to this issue is through managed retreat, the removal and relocation of all ‘at risk’ buildings in coastal hazard zones. While this approach is successful in preserving the physical structures, it remains an undesirable solution that forces homeowners to abandon their community and the coastline for the safety of higher ground. The retreat is hampered among debate within the effected regions as the forced detachment of long standing communities often results in the loss of ‘sense of place’ that living within a coastal community enables. This thesis proposes that Haumoana in Hawkes Bay offers the fitting location to introduce an alternative coastal community model that actively responds to the impending hazards whilst retaining the societal poetics. Situated just south of the nearby communities of Te Awanga and Haumoana, two of the most at-risk coastal regions in New Zealand that are currently facing the prospect of dismantlement. The site was specifically chosen due to the fact that erosion is predicted to diminish half its usable land over the next century, this thesis will investigate the potential risks to the respective coastline, the role that this would play in an adaptive community, and the possible design options that can respond and enhance a future sustainable landscape. This thesis argues that a coastal community can be designed to actively adapt and respond to the threat of erosion rather than being dismantled through retreat; that by adopting design principles that protect the land on which they are placed, the coastal hazards of the region can be lessened; and that an adaptive community model can be achieved whilst retaining the ‘sense of place’ that coastal community’s exhibit. The thesis proposes that this can be achieved by incorporating and reinforcing natural features of the coast into the architectural design at various scales; accommodating for, and adapting to the imminent threat of erosion; and by invoking principles of sustainable design in company with adaptive planning and resilient design, thereby pushing the standards of coastal planning beyond typical practice.</p>

Vulnerable Territories: The Perpetually Shifting Edge

<p>New Zealand’s coastline is rapidly receding. The increased threat of rising sea levels continues to erode the shore line causing extensive and irreparable damage to thousands of coastal properties, often dismantling communities and the kiwi dream of living near the ocean. With global temperatures continuing to rise, all of our coastal communities are at risk. The current measure of response to this issue is through managed retreat, the removal and relocation of all ‘at risk’ buildings in coastal hazard zones. While this approach is successful in preserving the physical structures, it remains an undesirable solution that forces homeowners to abandon their community and the coastline for the safety of higher ground. The retreat is hampered among debate within the effected regions as the forced detachment of long standing communities often results in the loss of ‘sense of place’ that living within a coastal community enables. This thesis proposes that Haumoana in Hawkes Bay offers the fitting location to introduce an alternative coastal community model that actively responds to the impending hazards whilst retaining the societal poetics. Situated just south of the nearby communities of Te Awanga and Haumoana, two of the most at-risk coastal regions in New Zealand that are currently facing the prospect of dismantlement. The site was specifically chosen due to the fact that erosion is predicted to diminish half its usable land over the next century, this thesis will investigate the potential risks to the respective coastline, the role that this would play in an adaptive community, and the possible design options that can respond and enhance a future sustainable landscape. This thesis argues that a coastal community can be designed to actively adapt and respond to the threat of erosion rather than being dismantled through retreat; that by adopting design principles that protect the land on which they are placed, the coastal hazards of the region can be lessened; and that an adaptive community model can be achieved whilst retaining the ‘sense of place’ that coastal community’s exhibit. The thesis proposes that this can be achieved by incorporating and reinforcing natural features of the coast into the architectural design at various scales; accommodating for, and adapting to the imminent threat of erosion; and by invoking principles of sustainable design in company with adaptive planning and resilient design, thereby pushing the standards of coastal planning beyond typical practice.</p>

Coastal Vulnerability Assessment Based on Multi-Hazardous Events. Case study: Northwestern Coastline of Guinea-Bissau (NC-GB)

Guinea-Bissau coastlines are found highly vulnerable to coastal hazards, and this vulnerability will likely increase under future climate changes scenarios. In addition, the multi-hazardous assessment studies have not yet been conducted to clarify the status of vulnerability index to coastal hazards. Therefore, we integrated eight bio-geophysical parameters and elaborate a comprehensive Coastal Vulnerability Index to coastal hazards, stablish the rate of sea-level rise and determine the role of coastal habitats in protecting the shorelines in the Northwestern Coastline of Guinea-Bissau, by using the GIS and Coastal Vulnerability Index of InVEST Model. The study found that, out of 87 km of the studied coastlines, nearly 45 km lie in high to very-high vulnerability index. 17 km are found in a moderate vulnerability index and 25 km are found at low to very-low vulnerability index. The main responsible for high vulnerability registered in Zone-B were the wind and wave exposure, as this coastline is highly exposed to sea. The other reason was the storm surge and sea-level that rises 8.79/year, motivated by low coastal elevation. Mangrove ecosystem that are largely found in Zone-A, play very important role in protecting shoreline from coastal hazards with value 0.61, followed by forest and sand dune that are found mostly in Zone-C with 0.49 and 0.4 respectively, and saltmarsh that are relatively found in Zone-B with value 0.32. These findings can assist coastal managers in cost-effective adaptation plans, provide a scientific basis for sustainable coastal management and guidance for ecological conservation in coastal regions.