Paradise In Peril

By Kristen Pope

With sandy beaches, sparkling turquoise waters, winding seaside roads, and swaying palm trees, Hawaii seems like paradise. But the idyllic archipelago could face severe repercussions from a lurking threat: climate change. Hawaii is one of the states most at risk.

Tourists flock to Hawaii to enjoy a tropical setting for their romantic honeymoon or family getaway. In 2016, 8.9 million people visited, spending $15.6 billion. But the changing climate is threatening the state, and it could have a huge impact on visitors and its 1.4 million residents, not to mention its wildlife and fragile ecosystems.

Planners and government officials have begun work to meet the challenges presented by climate change — sea-level rise, coastal erosion, flooding, increased storm damage, and groundwater inundation, among others — a difficult task in a state where the places facing the most danger are also the most desirable and most expensive real estate on the islands. Coastal development is rampant and much of Hawaii is built up near the shoreline.

Hawaii has taken some steps to address these threats, and the state legislature has undertaken efforts to map a sustainable path forward with the passage of the Hawai‘i Climate Adaptation Initiative Act, known as Act 83. As noted in the law itself: "Hawaiʻi is one of the few coastal states that has not adopted a statewide climate adaptation plan, yet is among the most vulnerable."

Act 83 created the Interagency Climate Adaptation Committee, which includes representatives from numerous state agencies, counties, planning departments, and other stakeholders. The committee's first task is to put together a Sea Level Rise Vulnerability Assessment and Adaptation report, due at the end of 2017.

"We know for sure that sea level has risen six to eight inches in the last century and that it's going to continue to rise and accelerate," says Sam Lemmo, the administrator for the Office of Conservation and Coastal Lands and cochair of the interagency committee. "... The consequences could be catastrophic because a lot of our communities are located [in] low-lying coastal areas."

Elsewhere in the Pacific, some small islands have already become submerged, forcing residents to relocate. In the Solomon Islands, five islands are completely underwater; six others have lost large pieces of land to the ocean, destroying villages and forcing people to move. On Nuatambu Island, 11 homes were destroyed, along with half its inhabitable area. (For more on the relocation of coastal communities, see "Before It's Too Late," Planning, August/ September.)

It doesn't appear that Hawaii is in quite that degree of peril — yet. But according to researchers, the global mean sea level could rise one foot by mid-century, and 2.5 to 6.2 feet by 2100.

Paul Kirshen, PhD, professor of climate adaptation at University of Massachusetts Boston's School for the Environment, provides some perspective: "Here in Boston, if the sea level goes up six feet ... then the elevation, the height of that water, is going to be equivalent to the height of a 100-year storm. That means twice a day, we would have flooding equivalent to a 100-year storm."

Assessing risk

Hawaiian agencies are modeling maps of the sea-level rise exposure area to assess places that could be affected by coastal erosion, seasonal flooding, inundation, wave effects, and interactions with the groundwater table. They are also assessing economic impacts — threats to property and structures and infrastructure including roads, communications, water systems, government facilities, and schools. The Interagency Climate Adaptation Committee will analyze this data and make recommendations.

Already, several major concerns are clear:

GROUNDWATER INUNDATION. Rising seas mean a rising water table. Groundwater in low-lying coastal plains rests just a few feet below the ground's surface. That water can leech above ground, and even if it doesn't, rising water tables can wreak havoc on underground infrastructure such as electrical lines, sewer systems, and underground pipes. Drinking water wells can also face increased levels of salinity. "When the groundwater table reaches the land's surface, that's a wetland, and you can't have wetlands in the middle of urban areas like Waikiki and downtown Honolulu," says Chip Fletcher, PhD, associate dean for academic affairs and professor of geology and geophysics at the School of Ocean and Earth Science and Technology, University of Hawaii at Manoa. "Obviously, this is going to require an enormous amount of planning, long-term planning as well as, I would argue, short-term planning."

"Groundwater inundation, and the storm drain flooding that will accompany it, will require high-resolution mapping of the problem," Fletcher says. "One area may be very vulnerable to flooding while next door the threat is less. In a nutshell, these threats are not simple, and they each are accompanied by a set of research and engineering needs."

Hawaii is currently using duckbill check valves to restrict water flow in some places. One-way tidal valves, like the type currently being used in South Florida, could also help. They allow water to exit to the ocean but not enter from it.

Miami Beach is also working to combat flooding by raising its streets and installing 80 pump stations. In the longer term, planners are looking to create resilience and use structural design to mitigate the effects of sea-level rise. (See "Miami Beach Readies for Sea-Level Rise," News, February 2015.) Another major concern is the potential for more frequent and severe El Niño years, which climate change models predict. This phenomenon is associated with very warm ocean waters in the equatorial Pacific and can lead to severe weather as well as a lessening of Hawaii's famous trade winds.

In 2015, a very strong El Niño year, record-setting rainfall occurred for 11 days in Honolulu, causing flash flooding and high waves that impacted coastal highways and eroded beaches. However, the year also included nine months of very little rain, and 25 days of record-setting heat that put a strain on electrical systems due to high air conditioning use. It was also a very active hurricane season that year, with 15 tropical cyclones, topping the previous record of 11 storms (in both 1992 and 1994). A typical year sees four or five of the storms.

King tides, which are extreme high tides, normally occur several times a year, but their frequency and severity are also increasing, with water levels remaining six inches above predicted levels for over a year.

This has led to ocean waters swamping roadways, parking lots, beaches, and decks. People have even found fish swimming down city streets.

"We are heavily impacted whenever there is a strong El Niño year," says Fletcher.

BEACH EROSION. Coastal erosion is also a pressing worry, along with the potential for cliff collapse. "We have an erosion model which projects that if sea levels rise as much as three feet, we could see as much as 200 feet of erosion," Fletcher says. "Eroding the shoreline 200 feet back is going to threaten houses, highways, in fact, entire blocks of houses."

Sea walls can be constructed to help protect structures, at a cost: The beaches on their seaward side disappear into the ocean. Chronic erosion already affects 70 percent of Hawaii's beaches.

"The Waikiki region in particular is host to Hawaii's premier resort hub where beaches are crucial to the state's tourism economy," the paper notes. "Yet the degraded state of beaches has caused surveyed visitors to indicate their reluctance to return."

One potential solution is beach nourishment, where offshore sand is collected and placed on the beach. However, it's a pricey endeavor. A 2012 beach nourishment project at Royal Hawaiian Beach at Waikiki cost $2.9 million.

ROADS AT RISK. Many of Hawaii's roads are built very close to the ocean and have beautiful views — but they are in danger, which could severely impact communities. "The roads are critical," Lemmo says. "They connect communities, business centers, emergency services."

Planners have options, though all are expensive. They could raise the roads in place, allowing the shoreline to pass underneath. Armoring existing roads, and adding a seawall or other fortification — which would mean sacrificing beaches — could help, though rising groundwater and overtopping waves make this likely only a temporary solution. Another option is to move the roads inland, and potentially raise them. But communities are typically located landward of the roads, leaving few places to relocate the roads without destroying homes and businesses.

To adapt or retreat?

The state has a lot of tough decisions to make, and those decisions will affect both residents and visitors. Tourism is crucial to Hawaii; it makes up a quarter of its economy. Waikiki Beach alone brings in $2 billion a year in visitor spending. Declining ecosystems, eroding beaches, bleached coral reefs, and threatening storms may keep visitors away. Rising temperatures will also create a health threat for residents, especially the young, elderly, and infirm.

While scientists and planners are using the best information available to formulate their plans, the uncertainty about the extent and speed of sea-level rise is making it difficult to plan a response. Planners must decide whether to adapt or retreat, but like many coastal communities on the mainland, they lack complete information.

"With smaller levels of sea-level rise, say one or two feet, we could change building codes in the coastal zone and require that all future development have freeboard underneath," Fletcher says, referring to the practice of raising structures above the ground so that flooding flows beneath the lowest part of a house without causing massive damage. Likewise, building codes can require that homes be built to withstand hurricane force winds.

Paul Kirshen of the University of Massachusetts says a multihazard approach is crucial when planning, incorporating factors such as extreme precipitation, rising temperatures, and sea-level rise, which may interact and cause additional issues.

However, without certainty of what will happen, planners and decision makers have to make their best guesses about the future. "It's not easy from a planning perspective," he says.

Addressing flooding with the Ala Wai Canal

One potential project that could help alleviate the effects of climate change is the Ala Wai Canal Project in Honolulu, which will address runoff, sea-level rise, and damage from flash floods and other severe storms. The two-mile-long canal was originally built in the 1920s to drain wetlands and allow Waikiki to develop, but improvements are needed to reduce flood risk, including constructing debris and retention basins, debris catchment systems, and concrete floodwalls alongside the canal.

"The fear is that if you get a massive storm event, all these tributaries will fill up with water and drain down to Ala Wai Canal and the canal will overtop and essentially flood out this area of Honolulu," says Michael Wyatt, Ala Wai Canal project manager for the U.S. Army Corps of Engineers. "It's one of the most urbanized areas in the state." The area contains 3,000 structures that would be in danger in the event of a 100-year flood — with a potential for $318 million in damages.

The project would cost $350 million and require an act of Congress to authorize federal funding for two-thirds of the cost. State and local governments would have to shoulder their share and acquire private property, possibly through eminent domain. If approved, it could take quite some time for the project to come to fruition, but it could protect the Ala Wai Watershed, and the state's tourism industry, from the catastrophic effects of major flooding.

Home owners and home buyers are also becoming increasingly concerned about the proximity of their homes to the rising oceans. Being close to the water was once the main criteria people looked for, but now potential owners are opting for properties farther back from the water line and inquiring about how high properties are above the sea level, how well they are protected from storm surges, and about homes' emergency protection features. Rising flood insurance costs are also a concern.

Moving residents further inland and "retreating" from the areas most severely impacted by sea-level rise is another option. One idea in Hawaii is for the Legacy Land Conservation Program to purchase land to prevent development. The agency's current annual $4 to $6 million budget won't go far with pricey coastal lands.

However, as sea-level rise erodes and undermines beachfront properties, Chip Fletcher of the University of Hawaii notes that owners may be more likely to sell for a lower price. He also suggests trading low-lying coastal lands for higher-elevation state lands might be a possibility.

In Boston, Kirshen is involved with a study examining financing options for climate change adaptations, including special taxation areas, public-private partnerships, revolving loan mechanisms, and federal funding. Most federal funding is available after a disaster, though pre-hazard planning and mitigation funds are starting to become available.

But even after receiving funding after a disaster, it can take many years to implement changes. Kirshen notes that infrastructure renewal cycles, typically 20 to 100 years, are good opportunities to implement climate change adaptations, such as rebuilding a road to be more climate change resilient. But he emphasizes the importance of addressing climate change and making necessary infrastructure changes soon.

"Every study that I've carried out and every study that I've seen shows that the benefits of adapting to rising seas and coastal flooding over a 20 to 30 year period far exceeds the cost of adaption," he says. Adaptation is extremely cost-effective along the coastal zone. There's really no excuse for not doing it. You either pay now or you pay a lot more later on."

When Hawaii's Interagency Climate Adaptation Committee releases their findings at the end of the year, planners and officials will have a better idea of just what the future holds for the Aloha State and how planners can work to help Hawaiian communities build resiliency and meet the challenges ahead.

Kristen Pope is a freelance writer and editor in Jackson, Wyoming.

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Resources

"What Climate Change Means for Hawaii": tinyurl.com/ydxglqmt.

Hawai‘i Climate Adaptation Portal: climateadaptation.hawaii.gov.

Climate Change in Hawai'i, Pacific Islands Climate Partnership: tinyurl.com/y9tvsvyu.

Coastal Geology Group, University of Hawai'i at Manoa: soest.hawaii.edu/coasts.

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