A recent round of federal funding cuts included the termination of a $3 million grant from the Office of Naval Research to the University of �鶹��ý at ����ԴDz�. The grant, awarded to Chip Fletcher, interim dean of the (SOEST), supported the (CRC), which provided data and high-resolution modeling of sea level rise impacts, heat exposure and precipitation extremes—critical tools that inform decisions made by state and county agencies, urban planners, infrastructure designers, and emergency managers.

“The loss of federal funding for �鶹��ý’s climate and sea level rise research will have devastating consequences for the state’s ability to plan, adapt and protect its people and resources,” said Fletcher.

“The models we develop and their supporting databases underpin key pieces of �鶹��ý’s climate legislation and coastal permitting regulations, including assessments of flood risk, groundwater inundation, coastal erosion, coastal construction setbacks and public safety. Without sustained federal investment, �鶹��ý will lose its capacity to provide accurate climate projections tailored to island topography, severely hampering our preparedness for compound hazards such as king tides, rain-at-high-tide flooding and storm-driven flooding.”

CRC employed 15 people, including graduate students, climate researchers, policy experts and geospatial analysts. To prepare for and adapt to the growing threats related to climate change in �鶹��ý and the Pacific region, this team gathered data and developed new modeling tools that reduce vulnerabilities to community and infrastructure on the island of Oʻahu.

Specifically, the CRC team has been modeling the impacts of sea level rise including flooding, coastal erosion, drainage failure, wave impacts at higher sea level and groundwater pollution with higher sea level.

Data guides land management, policies

Various state laws and policies rely on CRC data and models: construction setbacks on Maui, Kauaʻi, and Honolulu; mandatory disclosure of sea level rise impacts in real estate transactions; Special Management Area designations on Maui and Oʻahu; Kauai County sea level rise constraint district; and the required analysis of sea level rise impacts in state Environmental Policy Act, including environmental impact statements and environmental assessment permits.

“The loss of these data systems will undermine the scientific foundation of climate resilience policies, stall progress on community adaptation, and increase the vulnerability of coastal populations, public infrastructure, and cultural heritage,” Fletcher emphasized. “Maintaining federal support is not just about sustaining science—it is about safeguarding �鶹��ý’s future.”

—By Marcie Grabowski

Oʻahu’s sandy beaches are at risk. New research from the (CRC) at the University of �鶹��ý at ����ԴDz� determined that 81% of Oʻahu’s coastline could experience erosion by 2100, with 40% of this loss happening by 2030. These forecasts of shoreline erosion are more extreme than previous studies indicated for Oʻahu. The study was published in .

“Our findings reiterate the already observed threat of coastal erosion as a hazard to sea level rise in �鶹��ý,” said Richelle Moskvichev, geospatial modeler at CRC in the UH ����ԴDz� (SOEST) and lead author of the study. “In rapidly eroding areas, communities may see damage to roads, homes or underground infrastructure. Shorelines along the north shore and east side of Oʻahu that are backed with hard-armoring, such as seawalls, could experience total beach loss.”

Creating erosion predictions

To create erosion predictions, the team of researchers used a computer model that incorporates about 30 years of satellite imagery, as well as aerial and drone imagery. The new model also directly accounts for the seasonal movement of sand. For example, when large swells arrive in the winter on Oʻahu’s north shore, sand is transported from one part of the beach to another.

Given prior modeling efforts, the team’s own survey observations and anecdotal evidence from residents, the researchers expected to see erosion predicted for many sandy beaches around Oʻahu.

“By including additional satellite data and seasonal modeling, our forecasts show that erosion will increase by nearly 44% above our previous estimates in the short-term, meaning that we anticipate more severe erosion sooner,” said Moskvichev.

Coastal erosion can limit beach access, damage fragile ecosystems and infrastructure, and destroy homes.

“This study provides an update on potential areas of shoreline change around Oʻahu, and can inform long-term development planning for coastal communities and infrastructure of the island,” said Chip Fletcher, interim dean of SOEST, director of CRC, and senior author of the study. “This UH-led research provides science-backed data to those who create local adaptation strategies, and ultimately to those most affected by the forecasted hazards. With improved forecasting for erosion hazard zones around the coast, communities, planners and policymakers can create targeted mitigation and adaptation efforts.”

The research team plans to expand their modeling efforts to the other Hawaiian Islands so that similar predictions are accessible to planners and communities on all islands. Additionally, they plan to use the results in conjunction with other hazard predictions, such as flooding and groundwater inundation, to analyze overlapping locations and timing of risk to communities.

Nearly $1 million was appropriated to the (�鶹��ý Sea Grant) for the development of a beach and dune management plan for the North Shore of Oʻahu, specifically focusing on the area between Sunset Beach and Sharks Cove.

An important component of the project is community engagement and outreach so that the outcomes and pilot demonstration projects are aligned with community values, concerns and needs. In addition to developing the beach and dune management plan, pilot projects focusing on public infrastructure such as beach access stairs and decks will be discussed.

“This effort serves as a significant coastal management action plan reflecting the values and priorities of the North Shore community,” said Dolan Eversole, �鶹��ý Sea Grant’s coastal management specialist and project lead. “In addition to the development of recommendations for site-specific beach and dune management practices, the plan will establish the scientific, environmental, and economic foundation for future evaluation of appropriate adaptation strategies for this critically important resource.”

Gov. Josh Green signed , which provided the funding in a ceremony held at the �鶹��ý State Capitol on July 8. The ceremony included 16 bills that expand the state’s efforts to preserve �Ჹ�ɲ���ʻ��’s natural resources and foster sustainable tourism. While HB2248 focuses on ��ʻ�����’s North Shore, the bill serves as an important coastal management, adaptation planning, and community engagement model for coastal communities within and outside of �鶹��ý struggling with sea-level rise and other coastal hazards.

“These bills represent significant steps forward in safeguarding �Ჹ�ɲ���ʻ��’s environment and promoting responsible tourism,” said Green.

�鶹��ý Sea Grant will have 1.5 years to develop the recommendations for increased conservation of the beach and dune area. It will draw on similar community-based beach and dune management plans that it developed for Maui County, Kailua Beach Park on Oʻahu, Windward Oahu Tourism Assessment and the �鶹��ý Dune Restoration Manual.

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—By Cindy Knapman

A provides predictions of coastal flooding in West Maui under various scenarios of sea-level rise and a range of wave events for community members, property owners, businesses, as well as state and county officials. The West Maui Wave-Driven Flooding With Sea Level Rise tool was created by researchers at the (PacIOOS) based at the University of �鶹��ý at Mānoa.

The combination of high sea levels and large swells can result in significant coastal erosion, damage to infrastructure and properties, and land-based sedimentation that impairs coastal water quality. �鶹��ý has experienced an increase in wave plus tide-driven flooding in recent years, and these events are expected to grow in numbers and duration due to sea-level rise and changing wave energies.

“Along with other planning tools, we hope these scenarios that are tailored for West Maui will be useful to inform land use planning,” said Tara Owens, co-investigator on the grant that funded this work and extension specialist with .

The public is invited to learn about this new tool on August 30, 4–5 p.m. to receive log-in information.

Factors impacting West Maui

The water level—and the associated risk of coastal flooding—in West Maui is impacted by several factors that are included in the flooding product: daily tidal cycles, long-term sea-level rise, moderate to large wave events, and the slowly-oscillating ocean sea level height around Maui (caused in part by El Niño). PacIOOS, based at UH ��ā�ԴDz�’s , created the new West Maui Wave-Driven Flooding With Sea Level Rise tool by adopting a next-generation modeling approach to combine these factors and augment the annual high wave flooding model represented in the .

In addition to chronic coastal erosion leading to severe damage of properties, wave overtopping and flooding also pose a major safety concern to infrastructure, in particular to Honoapiʻilani Highway, the major access corridor to West Maui.

“Coastal managers and planners in �鶹��ý rely on science-based information that can support decision making,” said County of Maui Coastal Planner Jim Buika. “This scenario-based tool is powerful because it is locally specific and easy to use. It can guide us to promote sustainable land use and environmental protection.”

The wave flooding tool and a related in West Maui were developed by PacIOOS through a collaborative effort led by the Coastal Hazards Group in the Department of Oceanography at UH Mānoa, and funded by the National Oceanic and Atmospheric Administration grant “” (award #NA17NOS4730143).

–By Marcie Grabowski

To address the impacts of climate change on Oʻahu, the (�鶹��ý Sea Grant) is highlighting efforts its experts are conducting around the island to tackle issues surrounding sea-level rise, coastal erosion and inland flooding.

On a field trip to ��ʻ�����’s North Shore and Māpunapuna organized by �鶹��ý Sea Grant on July 29, UH students and visiting fellows witnessed the impacts of climate change in �鶹��ý.

Shellie Habel, a coastal geologist and extension faculty at �鶹��ý Sea Grant, led and organized the site visit and extended opportunities for the five participants to learn more about coastal resilience and planning activities.

“It’s really important that these participants see present day impacts of sea-level rise because they will be contributing to environmental management as part of their future careers,” said Habel. “Today we observed the manifestation of impacts in the form of erosion and drainage related inland flooding, which are often not intuitively associated with sea-level rise.”

Participants saw firsthand the coastal erosion that is taking place at Rocky Point. Homeowners are using shoreline hardening measures to help save their homes, but Habel said that was only a short-term solution to what will become a dire problem as climate change and sea-level rise continue in the future.

“Visiting the North Shore and Māpunapuna reminded me of the extremely difficult challenges that �鶹��ý faces as sea-level rise and blue sky flooding gets more frequent and harder to manage,” said Cuong Tran, a graduate student in UH ��ā�ԴDz�’s urban and regional planning program in the and 2022 Grau Fellow. “To adapt to the climate crisis, we all must work together and be able to make tough decisions. I am optimistic that we will find creative solutions through the collaborative efforts put in by government, institutional and community partners.”

• See more UH News stories on climate change.

Challenging the next generation of leaders

Participants were given the opportunity to ask questions and engage in dialogue with Habel. She challenged them to brainstorm innovative solutions as they become the next generation of environmental managers who will continue to address the challenges of climate change.

“I’m extremely grateful to Shellie for taking time to bring us to see the endangered site on the North Shore—seeing these situations in person evokes such a visceral response that inspires me to continue in this field (environmental policy/administration) and to foster the relationships that need to exist in order for us to protect coastlines and coastal communities,” said Sarah Chin, a visiting 2022 Rappa Fellow from Columbia University.

The field trip included a quick stop through ��ʻ�����’s industrial district in Māpunapuna to see the effects of inland flooding in low-lying areas. King tides and higher water levels are becoming more frequent and provide a snapshot of the future and what could eventually become commonplace.

“It is crazy to see the erosion on the North Shore and the inland flooding in Māpunapuna because those sites are indicators of how sea-level rise will impact the island,” said Joel Burgess, a third year law student at UH ��ā�ԴDz�’s and 2022 Rappa Fellow. “The biggest takeaway for me is that climate change is already here, so we cannot afford to waste any more time to take action.”

The reactive and piecemeal approach historically used to manage beaches in �鶹��ý has failed to protect them, according to a by researchers in the at the University of �鶹��ý at Mānoa (SOEST). The study also found that if policies are not changed, as much as 40 percent of all beaches on Oʻahu could be lost before mid-century.

In an era of rising sea-level, beaches need to migrate landward, otherwise they drown. Beach migration, also known as shoreline retreat, causes coastal erosion of private and public beachfront property. Shoreline hardening, the construction of seawalls or revetments, interrupts natural beach migration—causing waves to erode the sand, accelerating coastal erosion on neighboring properties, and dooming a beach to drown in place as the ocean continues to rise.

The team of scientists, led by graduate researcher Kammie Tavares in SOEST’s , assessed the shoreline around Oʻahu that would be most vulnerable to erosion under three scenarios of sea-level rise—all estimated to occur around mid-century.

Shoreline hardening and beach loss

They identified the location and severity of risk of shoreline hardening and beach loss, and a potential timeline for the increase in erosion hazards. The most threatened properties fall into an “administrative erosion hazard zone,” an area likely to experience erosion hazards and qualify for the emergency permitting process to harden the shoreline.

“By assessing computer models of the beach migration caused by 9.8 inches (0.25 meters) of sea-level rise, an amount with a high probability of occurring before mid-century, we found that emergency permit applications for shoreline hardening to protect beachfront property will substantially increase,” said Tavares.

According to co-author Tiffany Anderson, assistant researcher in the Department of Earth Sciences, “We determined that almost 30 percent of all present-day sandy shoreline on Oʻahu is already hardened, with another 3.5 percent found to be so threatened that those areas qualify for an emergency permit today. Our modeling indicates that, as sea-level rises about 10 inches (0.25 meters) by mid-century, an additional nearly eight percent of sandy shoreline will be at risk of hardening—meaning at that point, nearly 40 percent of ��ʻ�����’s sandy beaches could be lost in favor of hardened shorelines.”

“In another , we showed that accelerated erosion on neighboring properties, called flanking, usually leads to additional shoreline hardening, and condemns entire beaches,” said co-author Chip Fletcher, associate dean and professor in SOEST. “It is clear that management decisions made today, and during the careers of most of today’s natural resource managers, will be critical in determining if future generations will inherit a healthy shoreline, or one that has been ruined by seawalls, and other types of shoreline hardening.”

Continue reading on .

–By Marcie Grabowski

The first construction project in Waikīkī Beach in 50 years, which marks the beginning of a new era of renewal and recovery, started with the replacement of the Royal Hawaiian groin. Built in 1927, the original curving cement wall was built to prevent erosion. The new rock groin is replacing the old one with a similar role and function but is much more robust, providing a more stable beach and will be followed by more beach improvement projects including additional beach sand over the next several years.

The replacement groin is designed to maintain the approximate beach width of the 2012 Waikīkī Beach maintenance shoreline nourishment project. No enlargement of the beach or additional sand nourishment is involved in this project.

During this project, the (�鶹��ý Sea Grant) played an essential role in providing technical project management and coastal science and policy support to the (WBSIDA) which serves as a public private partnership with the state paying for 50 percent of the $1.5 million project cost.

The project began in early May and is expected to be completed in late July. Originally scheduled for September 2020 to avoid the busy summer season, it was accelerated after the COVID-19 pandemic shut everything down and presented a once-in-a-lifetime opportunity to do heavy construction without interfering with hotel or recreational beach activities.

Dolan Eversole, the Waikīkī Beach management coordinator with �鶹��ý Sea Grant, coordinated with stakeholders and agencies involved and conducted regular project oversight and environmental monitoring, while also serving as technical project oversight on behalf of the Department of Land and Natural Resources (DLNR).

“This project improves the resilience of this beach and will stabilize an extremely important and valuable natural resource,” said Eversole. “Stabilizing the beach system will also reduce the amount of sand migrating offshore which can cause problems for the coral reefs and surf sites if unmanaged.”

The Royal Hawaiian groin was more than 90-years-old and at risk of failure due to deterioration. Structural engineers determined it was leaking sand and contained large voids, cracks, bowing and no apparent internal reinforcement. Its failure would have resulted in the destabilization and eventual loss of more than 1,700 feet of sandy shoreline located east of the groin.

• Related UH News story: UH Sea Grant called on to help save Waikīkī Beach, June 17, 2019

The new structure was built around the remnants of the old vertical wall groin and constructed in an L-shaped design. The replacement groin serves to stabilize the beach in the western end of the Royal Hawaiian and will mitigate the extreme seasonal beach erosion which has become more frequent recently in that area.

“Looking ahead, we are actively working with the DLNR on an Environmental Impact Statement (EIS) and master plan for Waikīkī Beach that includes resilient design features that account for future sea-level rise and the acceleration of beach erosion, this type of planning for future conditions is a crucial part of designing and supporting resilient communities and economies and demonstrates the successful partnership that has developed between UH, the WBSIDA and the DLNR,” said WBSIDA President Rick Egged.

A successful partnership

The important UH partnership with WBSIDA and the DLNR to improve and manage Waikīkī Beach has proved to be successful. �鶹��ý Sea Grant continues to provide scientific and technical support and outreach to a wide variety of Waikīkī stakeholders and government officials. �鶹��ý Sea Grant also conducts regular outreach, education and policy review for issues such as climate change, sea-level rise, coastal erosion, beach and reef management and now economic recovery.

“The University of �鶹��ý plays a key role in serving as a respected neutral broker of coastal science and beach management policy and practice,” said Eversole. “The community in Waikīkī can access all kinds of information and ask questions through the extension and outreach provided by the university. It also serves in an important role conducting environmental and economic research, science, engineering and coastal management policy to better observe and provide information that assists decision-makers in improving the management of the area.”

Additional details on the Royal Hawaiian Groin project can be found at .

—By Sarah Hendrix

A global tendency for future sea levels to become more variable this century as oceans warm, due to increasing greenhouse gas emissions was identified by a team of researchers at the University of �鶹��ý at Mānoa (SOEST). Sea-level variability alters tidal cycles and enhances the risks of coastal flooding and erosion beyond changes associated with sea-level rise.

Sea-level rise is occurring as Earth warms due to two main factors: melting of land-based ice such as glaciers and ice sheets, and the expansion of seawater as it warms—termed thermal expansion. Previously unknown was whether the rate of thermal expansion, which accelerates with warming, will also affect the variability of sea level.

In a , a team led by Matthew Widlansky, associate director of the , assessed future sea-level projections from global climate models. The team found that while future sea-level variability changes are uncertain in many locations, nearly all of the 29 models they analyzed agreed on an overall tendency for the variability to increase on seasonal-to-interannual timescales.

“Whereas it is well understood that the rate of global mean sea-level rise will accelerate with future warming, in part due to the oceans expanding faster at higher temperatures, it was previously unexplored how this nonlinear thermal expansion property of seawater will affect future sea-level variability,” said Widlansky.

“Following thermodynamic laws, sea-level variability increases in a warmer climate because the same temperature variations, for example related to the seasonal cycle, cause larger buoyancy and sea-level fluctuations,” added Fabian Schloesser, a researcher at the UH Sea Level Center who collaborated on the study.

In places where changes due to ocean thermodynamics and other climate variability processes align, the team found the largest increases in future sea-level variability.

Coastal flooding occurs increasingly often due to a combination of slowly rising sea levels and ocean variability. The new findings therefore further emphasize the importance of sea-level monitoring and forecasting.

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–By Marcie Grabowski

The results of a collaborative research project led by a graduate student at the have been , a website where the public can find information and tools to understand and address climate risks. The case study also has been published regionally on the .

The UH Hilo study examines shoreline migration on �鶹��ý Island and combines historic aerial photos, current drone imagery and topographic surveys to discover coastal changes around �鶹��ý Island. The project is being used by county planners and policymakers to develop a more comprehensive and effective coastal development plan.

The published case study, “,” is co-authored by Scott Laursen, program specialist at the , and Bethany Morrison, a planner on land use with the County of �鶹��ý who collaborated on the research.

“We do not have adequate knowledge of �鶹��ý Island’s shoreline to be able to assess and adapt to the vulnerabilities from sea level rise and related hazards,” Morrison explained. “The goals of this project will help us to address these challenges. More specifically, �鶹��ý County will have a first phase of shoreline change rates and sea-level rise projections for three different types of shorelines.”

In May 2018, the research team presented their findings to the county planning department, which administers planning regulations for the entire island and provides technical advice to the mayor, planning commission and county council. Based on analyses at Hāpuna, Honoliʻi and Kapoho, the team suggested ways the county could use scientific data to create place-based setbacks.

“Directly involving local professional networks within every stage of the scientific method roots research products within the place-based experiences of these natural and cultural resource managers,” Laursen explains in an email. “[This] increases the probability that these products will be utilized.”

Looking to the future and the uncertainty associated with climate change, the combined results of the completed study will be used to develop policies that are increasingly adaptive to present and future coastal change.

—By Susan Enright

If Waikīkī Beach completely eroded, the state could lose more than $2 billion in visitor spending and related economic revenues each year, according to an economic impact analysis report by the and at the .

Waikīkī Beach, formerly the residence and playground of �鶹��ý’s king and high chiefs, became the “playground of the Pacific” in the early- to mid-1900s, and remains the most iconic landmark in the state today, drawing millions of visitors to the islands each year.

Now the main stretch of Waikīkī Beach is in danger of completely eroding, and the report found that if the concrete wall (groin) that was built in 1927 in front of the Royal Hawaiian fails, visitors wiil stop flocking to Waikīkī. The state Legislature recently allocated $13 million to reconstruct the Royal Hawaiian groin and a new temporary sandbag groin at Kuhio Beach fronting the Duke Kahanamoku statue. The appropriation will also be used for beach improvement projects outlined in the draft Waikīkī Beach Master Plan.

The �鶹��ý Department of Land and Natural Resources (DLNR) in partnership with �鶹��ý Sea Grant and the Waikīkī Beach Special Improvement District Association (WBSIDA) are developing the master plan. The plan relies heavily on input from the Waikīkī Beach Community Advisory Committee.

An effective partnership

“�鶹��ý Sea Grant has been serving in a technical and scientific advisory role to the Waikīkī Beach Special Improvement District since it was created in 2015,” said Dolan Eversole, Waikīkī Beach management coordinator and a coastal processes specialist with �鶹��ý Sea Grant. “It has also been collaborating with DLNR and WBSIDA in the development of the beach improvement projects in Waikīkī and assisting with community outreach. This advisory role has proven to be a very effective partnership with local, state and nonprofits, and has demonstrated success in helping to inform the decision-making process for such high-profile improvement projects in Waikīkī.”

While the master plan has an expected completion date of 2021, three project priority areas (Halekulani, Royal Hawaiian and Kuhio Beach cells) emerged, with projects ranging from beach restoration using offshore sand pumped to shore, adding or restoring existing beach stabilizing structures and relocating sand back to its initial point of origin.

—By Cindy Knapman

A picture of Keawaʻula Bay with a clear sky, light blue water and green mountains of the Waiʻanae range is on the screen as Kammie Tavares began her presentation at the (GES) Symposium, the culminating event of her bachelor’s of science degree at the . She described her favorite memory there—watching sunsets and playing in the sand with her brothers while her parents prepared dinner on the grill. She grew up in Waiʻanae and always felt a deep connection to the Mākaha-Keawaʻula coast.

After starting her degree program, Tavares realized beaches are important not just personally but also ecologically, culturally and economically. Despite the importance of beaches, coastal development is an ongoing major issue. Shoreline hardening, the construction of seawalls to protect beachfront development from erosion, paradoxically causes narrowing and loss of beach in adjacent areas.

For her project, Tavares and her advisor, Professor Chip Fletcher, hypothesized that the number of coastal structures considered threatened by coastal erosion, and whose owners may consider hardening the shore, will increase as sea level rises. She used a computer model to project the erosion risk with a sea level up to three-feet higher than present day, and then calculated the length of developed shoreline on Oʻahu that will be considered threatened based on current state policies.

Initial results show that just one foot of sea-level rise has drastic implications for the future of beaches on Oʻahu and coastal development. Tavares’ findings accentuate that the time to act is now.

“Beaches are dynamic environments, and most beaches in �鶹��ý, especially here on Oʻahu, are trapped by development near the shore,” said Tavares. “Retreating from the shore provides the space needed for natural coastal changes and provides our best chance for beach preservation. Let’s free the beach.”

To conclude her presentation, Tavares takes the audience back to Keawaʻula except, this time, her niece and nephew are playing in the sand. They and future generations are her motivation in this project. For her, protecting beaches is important to ensure that future generations have the opportunity to make memories of their own.

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—By Marcie Grabowski

In honor of Emeritus Professor E. Gordon Grau, former visionary director of the , a unique graduate student fellowship has been launched in his name.

The E. Gordon Grau Coastal and Marine Resource Management Fellowship Program will provide talented students focusing on coastal or marine science, policy or management the unique opportunity to obtain relevant policy experience in �鶹��ý.

The two-year paid fellowship will place early-career professionals with municipal, state or federal host agencies to receive hands-on experience transferring science to management and policy.

Said Darren T. Lerner, �鶹��ý Sea Grant’s director who took the helm when Grau retired, “He has not only transformed the Sea Grant College Program here in our state, but has contributed to the dramatic reshaping of Sea Grant nationally, reflecting the understanding that the problems we face in the ocean and on our coasts are in large part due to our activities on land.”

For the , see the Sea Grant website.

—By Cindy Knapman

By including models of dynamical physical processes such as erosion and wave run-up, a team of researchers from the and the state determined that �鶹��ý land areas vulnerable to future sea-level rise may be double what was previously estimated.

The .

“It’s important that we identify land areas vulnerable to sea level-related hazards because, if left unmanaged, flooding, wave inundation and erosion will continue to encroach upon coastal lands that are typically heavily developed,” said , study co-author and associate dean and earth sciences professor at the UH ����ԴDz� (SOEST). “Preparing for these effects will be very costly and take a long time to implement. With these results, stakeholders of all types are now able to establish empirically based adaptation policies.”

Previously, a widely used approach for assessing impacts of sea level rise was the “bathtub” model, in which a static sea-level surface is projected onto a terrain model.

“The bathtub method provides a good first look at low-lying flood-prone areas, but underestimates the full extent of potential damage due to sea level rise, particularly on �鶹��ý‘s high-energy coasts,” said lead researcher , a faculty member in the at SOEST.

As sea level rises, several processes are at work. Coastal erosion results in permanent land loss, but is also essential for preserving beaches; annual wave flooding rapidly escalates past a critical point; and groundwater inundation and storm-drain backflow create new wetlands and cause urban flooding. These render coastal protection insufficient as an adaptation strategy.

Developing a more realistic prediction

“Our more comprehensive assessment reveals important realities that can be overlooked with other methods,” said Fletcher. “Critically, the ‘bathtub’ approach alone ignores 35–54 percent of the total land area exposed to one or more of these hazards, depending on location and sea level rise scenario.”

The team also found that typical elevations of �鶹��ý‘s low-lying coastal plains create thresholds of flood levels, above which rapid increases in flooding occur. As sea level rises, coastal lands are exposed to higher flood depths and water velocities.

The prevalence of low-lying coastal plains leads to a rapid increase in land exposure to hazards when sea level exceeds a critical elevation of about 1 to 2 feet, depending on location.

The team had identified this phenomenon in previous research and named it a “critical point.”

“Additionally, a large portion of lands at risk of flooding is not in direct proximity to the shoreline,” said Anderson. “Instead, they are low-lying areas where sea-level rise causes the groundwater table to rise up to the surface. These areas can be located one to two miles inland from the coastline.”

Preparing for the future

The modeling presented in this study was conducted to support the creation of the �鶹��ý Sea Level Rise Vulnerability and Adaptation Report, which is the basis for further government planning initiatives.

Anderson and team are currently incorporating rainfall into the computer model to determine how sea level-related flooding might be exacerbated during rainfall events that occur during high tides. , also located within SOEST, and Tetra Tech Inc. are helping to guide state and county agencies in considering this new data in future planning.

—By Marcie Grabowski

New research from scientists at the and the �鶹��ý brings into clearer focus just how dramatically �鶹��ý beaches might change as sea level rises in the future.

Chronic erosion dominates the sandy beaches of �鶹��ý, causing beach loss as it damages homes, infrastructure and critical habitat. Researchers have long understood that global sea level rise will affect the rate of coastal erosion.

For the study published this week in Natural Hazards, the research team developed a simple model to assess future erosion hazards under higher sea levels—taking into account historical changes of �鶹��ý shorelines and the projected acceleration of sea level rise reported from the (IPCC). The results indicate that coastal erosion of �鶹��ý’s beaches may double by mid-century.

“Business as Usual” leads to double erosion

Like the majority of �鶹��ý’s sandy beaches, most shorelines at the 10 study sites on Kauaʻi, Oʻahu and Maui are currently retreating. If these beaches were to follow current trends, an average 20 to 40 feet of shoreline recession would be expected by 2050 and 2100, respectively.

“When we modeled future shoreline change with the increased rates of sea level rise (SLR) projected under the IPCC’s “business as usual” scenario, we found that increased SLR causes an average 16–20 feet of additional shoreline retreat by 2050, and an average of nearly 60 feet of additional retreat by 2100,” said Tiffany Anderson, lead author and post-doctoral researcher at the UH Mānoa .

“This means that the average amount of shoreline recession roughly doubles by 2050 with increased SLR, compared to historical extrapolation alone. By 2100, it is nearly 2.5 times the historical extrapolation. Further, our results indicate that approximately 92 percent and 96 percent of the shorelines will be retreating by 2050 and 2100, respectively, except at Kailua, Oʻahu which is projected to begin retreating by mid-century.”

Preparing for the future

The model accounts for accretion of sand onto beaches and long-term sediment processes in making projections of future shoreline position. As part of ongoing research, the resulting erosion hazard zones are overlain on aerial photos and other geographic layers in a geographic information system to provide a tool for identifying resources, infrastructure and property exposed to future coastal erosion.

“This study demonstrates a methodology that can be used by many shoreline communities to assess their exposure to coastal erosion resulting from the climate crisis,” said Chip Fletcher, associate dean at the School of Ocean and Earth Science and Technology and co-author on the paper.

Mapping historical shoreline change provides useful data for assessing exposure to future erosion hazards, even if the rate of sea level rise changes in the future. The predicted increase in erosion will threaten thousands of homes, many miles of roadway and other assets in �鶹��ý. Globally the asset exposure to erosion is enormous.

“With these new results government agencies can begin to develop adaptation strategies, including new policies, for safely developing the shoreline,” said Anderson.

To further improve the estimates of climate impacts, the next step for the team of researchers will be to combine the new model with assessments of increased flooding by waves.

The research was sponsored by the �鶹��ý Department of Land and Natural Resources and the U.S. Geological Survey .

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—By Marcie Grabowski

Sea-level rise has been isolated as a principal cause of coastal erosion in �鶹��ý. Differing rates of relative sea-level rise on the islands of Oʻahu and Maui remain as the best explanation for the difference in island-wide shoreline trends (that is, beach erosion or accretion) after examining other influences on shoreline change including waves, sediment supply and littoral processes, and anthropogenic changes.

Researchers from the and the state recently published a paper showing that sea-level rise is a primary factor driving historical shoreline changes in �鶹��ý and that historical rates of shoreline change are about two orders of magnitude greater than sea-level rise. .

Knowing that sea-level rise is a primary cause of shoreline change on a regional scale allows managers and other coastal zone decision-makers to target sea-level rise impacts in their research programs and long-term planning. This study is confirmation that future sea-level rise is a major concern for decision-makers charged with managing beaches.

“It is common knowledge among coastal scientists that sea-level rise leads to shoreline recession,” said Brad Romine, coastal geologist with the . “Shorelines find an equilibrium position that is a balance between sediment availability and rising ocean levels. On an individual beach with adequate sediment availability, beach processes may not reflect the impact of sea-level rise. With this research, we confirm the importance of sea-level rise as a primary driver of shoreline change on a regional to island-wide basis.”

Globally averaged sea-level rose at about 2 mm per year over the past century. Previous studies indicate that the rate of rise is now approximately 3 mm per year and may accelerate over coming decades. The results of the recent publication show that sea-level rise is an important factor in historical shoreline change in �鶹��ý and will be increasingly important with projected sea-level rise acceleration in this century. “Improved understanding of the influence of sea-level rise on historical shoreline trends will aid in forecasting beach changes with increasing sea-level rise,” said Charles Fletcher, associate dean and professor of geology and geophysics at SOEST.

Results of island-wide historical trends indicate that Maui beaches are significantly more erosional than beaches on Oʻahu. On Maui, 78 percent of beaches eroded over the past century with an overall (island-wide) average shoreline change rate of 13 cm of erosion per year, while 52 percent of Oʻahu beaches eroded with an overall average shoreline change rate of 3 cm of erosion per year.

“The research being conducted by SOEST provides us with an opportunity to anticipate sea-level rise effects on coastal areas, including �鶹��ý’s world famous beaches, coastal communities and infrastructure. We hope this information will inform long-range planning decisions and allow for the development of sea-level rise adaptation plans,” said , administrator, .

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An assessment of coastal change over the past century has found 70 percent of the beaches on the islands of Kauaʻi, Oʻahu and Maui are undergoing longterm erosion, according to a report released by the and the U.S. Geological Survey.

Scientists from UH����ā�ԴDz�’�� and USGS studied more than 150 miles of island coastline and found the average rate of coastal change was 0.4 feet of erosion per year from the early 1900s to 2000s.

Of the three islands, Maui beaches experienced the highest rates and greatest extent of beach erosion, with 85 percent of beaches eroding. Erosion is the dominant trend on all three islands with 71 percent of beaches eroding on Kauaʻi and 60 percent of beaches eroding on Oʻahu.

Researchers used historical data sources such as maps and aerial photographs to measure shoreline change at more than 12,000 locations. This analysis of past and present trends of shoreline movement is designed to allow for future repeatable analyses of shoreline movement, coastal erosion and land loss.

“Over a century of building along the Hawaiian shoreline, without this sort of detailed knowledge about shoreline change, has led to some development that is located too close to the ocean,” said Charles Fletcher, UH Mānoa geology and geophysics professor and lead author. “A better understanding of historical shoreline change and human responses to erosion may improve our ability to avoid erosion hazards in the future.”