As scientists warn of a merciless rise in sea level that could render more than 25,000 acres of statewide land uninhabitable this century, Kauai County planners are plotting new rules to defend homes and businesses from a watery demise.

The Kauai Planning Department submitted a draft ordinance to the County Council this month that would mitigate the intensifying effects of climate change by requiring owners to hoist up new construction on stilts in areas susceptible to impacts from a projected 3.2-foot increase in sea level. The proposed mandate would also apply to rebuilds where the cost of improvements to a structure equals or exceeds 50% of the market value.

If the County Council adopts the ordinance and the mayor signs off on it, Kauai would follow Boston in becoming one of the nation’s first municipalities to regulate construction based on the future impacts of two menacing symptoms of sea level rise: passive flooding and annual high-wave run up.

The county’s conservative shoreline setback rules already account for many of the projected effects of coastal erosion. But no entity in Hawaii currently regulates construction to protect buildings from the projected depths of these two other flood hazards.

“This is for structures where, within the lifetime of the structure, it’s going underwater if it’s not built at elevation,” said Kauai Planning Director Ka’aina Hull.

For residential buildings, the lowest floor, including basements, would need to be elevated at least 2 feet above the highest projected sea level rise flood elevation, as calculated by the authors of the seminal 2017 Hawaii Sea Level Rise Vulnerability and Adaptation Report and mapped by Kauai County planners. Nonresidential structures would need to be raised at least one foot above this flood water marker.

Existing buildings in these vulnerable coastal areas would not be affected by the proposal, except for rebuilds.

“Having to elevate a structure can be a little bit more expensive,” Hull said. “In some cases, it can actually be cheaper. But where it will absolutely, hands down, be more expensive is for those who have existing structures and want to do a substantial repair or improvement that would constitute a rebuild. Those structures do need to be elevated and that’s where we anticipate the biggest pushback.”

A majority of the properties that the ordinance seeks to regulate already have to be built on stilts for insurance purposes. But insurance companies make flood risk determinants based on historical data, not the future effects of climate change. Kauai’s proposed ordinance would impose elevation requirements on some properties for the first time because it considers sea level rise projections through the year 2100.

Hull emphasized that while it’s probably not a good idea to build in the affected areas, the county is not proposing to take away property rights. Rather, he said the goal of the ordinance is to ensure that any new structures there can accommodate flood waters that scientists say are indisputably coming.

Dire predictions have so far done little to dampen a feverish demand for Hawaii coastal real estate. Hawaii Life CEO Matt Beall said that while new regulations tend to reduce the number of interested buyers looking at a property, Kauai’s pronounced real estate supply and demand imbalance will likely offset any influence of the proposed ordinance toward lowering property values.

“The more complicated it gets, the narrower the buyer pool gets,” Beall said. “It’s hard to say how much that impacts value because it’s already a zero sum game, meaning permanently and forever the demand outweighs the supply, always, no matter what. Everyone wants to be here and there’s only so much of it to go around — period.”

Beall points out that even after the devastating Hanalei flood in April 2018 — the greatest rain event recorded in the nation’s history — property values skyrocketed in the north shore surf town wedged between waterfall-laced mountains and a half moon-shaped bay.

“All that destruction might have dragged the buyer pool down, and maybe it did change the overall value, but the rate of increase is so high that it’s really hard to detect it,” he said.

Rising Groundwater Tables And Big Wave Events

Over the next century, rising seas are expected to unleash numerous distinct flooding hazards, including coastal erosion, passive flooding and annual high-wave flooding.

The Hawaii Sea Level Rise Viewer maps out the danger zone affected by this trio of hazards and concludes that rising seas threaten to cause $19 billion in property losses and displace 20,000 residents, possibly as soon as 2060.

This data informed the passage of the nation’s first real estate disclosure law earlier this year that requires Hawaii property sellers to disclose whether their land is expected to be destroyed or damaged by sea level rise. It also is being used in shoreline setback ordinances either adopted or under debate in Kauai, Maui and Honolulu counties.

But Kauai’s proposed ordinance to require stilts for some new construction marks the first time that the pioneering climate change research would be used to regulate the style of building.

“It’s different than the setback, which says where you’re allowed to build,” said Hawaii climate scientist Chip Fletcher. “What Kauai is doing is saying how you’re going to build, and that’s something new. This application of the data will save money because it’s designed to reduce damage during flooding, as well as building resilience in our communities.”

It’s also the first time that a Hawaii government entity is seeking to regulate construction based on passive flooding and annual high-wave run up — two hazards expected to rear up from time to time.

Kauai already has one of the most conservative shoreline setback ordinances in the nation and, for the most part, Hull said it addresses concerns about coastal erosion. But it doesn’t mitigate hazards from passive flooding, such as rising coastal water tables and drainage problems, or annual high-wave run up — the farthest inland that big waves are expected to reach at least once a year.

A house built on stilts to avoid a deluge is a necessary step toward climate resilience, Hull said. But it shouldn’t be mistaken for a magic solution to the full menu of climate change-induced flooding hazards that the island’s homes and businesses are expected to face.

That’s because while sea level rise is projected to have destructive impacts, the increasing intensity and frequency of storms — another climate change-related hazard — has so far proved to be the island’s most difficult challenge.

In Hawaii, the influence of climate change on rainfall is still being studied. Scientists haven’t figured out yet how to predict major precipitation events, such as the record-setting rainstorm in April 2018 that triggered a dozen landslides on Kauai’s north shore, wrecking more than 500 homes and causing $180 million in damage.

“With the data that we have right now, these are the kinds of regulations we can create,” Hull said. “So while this is a step in the right direction, we need to be clear it’s not going to address what happened in Hanalei and other parts of Kauai during the rain bomb. That was just a monumental amount of water that dropped from the sky in a 24-hour period.”

Civil Beat’s coverage of climate change is supported by the Environmental Funders Group of the Hawaii Community Foundation, Marisla Fund of the Hawaii Community Foundation and the Frost Family Foundation.