Here’s what Hawai‘i could lose from sea level rise

Sea levels are rising, and they have been for over two hundred years.

“Global mean sea level has risen about 8–9 inches (21–24 centimeters) since 1880, with about a third of that coming in just the last two and a half decades,” said Rebecca Lindsay, National Oceanic and Atmospheric Administration.

So we lose a little bit of beach here and there--what’s the big deal? Once we lose our beaches, our roads will start to erode if they are not completely underwater already.

Losing roads prevents people from getting place to place: home, work, school, local businesses. But the problem is much more significant than that. The dissolution of a road also entails the loss of power lines, transporting food into a region and a laundry list of other things.

It is estimated that the sea level around Hawai’i will rise 6 inches within the next 12 years.

However, sea level is not the only factor that Sea level rise is not the only factor we should take into account. Rising sea level coupled with a high tide, a storm surge or a tsunami could very possibly be bad news.

That is where University of Hawai’i researchers Oceana Francis, Linqiang Yang, Harrison Togia and Gleb Panteleev come in.

Using 20 years worth of data, they assessed the vulnerability of coastal areas (i.e. roads) on O’ahu, Moloka’i and Maui in anticipation of what could happen. The report is titled, “Development of an Ocean Hazards Classification Scheme for Projecting Future Scenario Vulnerability Ranking on Coastal Built Infrastructure,” and was funded by the state Department of Transportation. It was published on January 13.

“Essentially what we do is we take the range of measurements that we can find for our islands or for our study area and then we break them down into measures of hazard,” Togia said. “The OHCS, the classification scheme is really meant to give us a really..., antiquated in some ways, but just a regional picture of how ocean processes overlap to create hazard.”

He added that they looked at historical sea level rise, projected sea level rise, mean tidal ranges, annually occurring peak wave periods and data from other sources such as the NOAA.

Tides are generally not a threat to coastal areas.

“They do have some level of influence in sediment transport, basically how long the shore is at some times of the year and how short it is at other times of the year--a lot of these seasonal changes,” Togia said. “But it doesn’t impact the shore as far as erosion or degradation of the infrastructure, really at all.”

“We try and determine its (the tide’s) impact on other systems,” he continued. “We look at, well what happens when we get high tide mixed with say, a high rain event and then we get flooding.”

Due to Hawaiʻi’s unique location in the Pacific, the islands experience less sea level rise than the global average. Sea level rise will be an issue for the island chain eventually.

“It will be. Everywhere it will be,” Togia said.

Storm surge (a.k.a. hurricanes) and tsunamis are the more immediate threats to Hawaiʻi’s coastal areas. Those events are more likely to inundate them.

“What people don’t realize is that roads are also kind of the guidelines for electrical posts,” Togia said.  “They’re also the guidelines for natural gas and a lot of the resources and infrastructure that govern life on the island. Inundation affects that because it decreases access.”

Building rock walls as a temporary means of protecting roads from encroaching ocean water is very shortsighted.

The beach is “actually a much more robust safety system than a wall. A wall has a limited cutoff.”  The wall is useless once the water overcomes it.

“A beach evolves. A beach changes,” Togia said. “It moves inland, it moves out to sea, it grows, it shrinks and it is actually the most robust barrier we have to storm surge and tsunamis--the best thing you can literally have to protect yourself is a beach or some type of mangrove field or natural habitat.”