New Study Documents Our Vulnerability to Sea Level Rise

By Ruby Pap

The sea level rise exposure area (SLR-XA) is made up of passive flooding, annual high wave flooding, and coastal erosion. Image courtesy of DLNR/OCCL Tetra Tech

By now many of you have probably seen in the conventional press that the long awaited Hawai‘i Sea Level Rise Vulnerability and Adaptation Report has been released (http://climateadaptation.hawaii.gov/). On Kaua‘i, with 3.2 feet of sea level rise, more than 900 structures and 5,760 acres of land could be chronically flooded, costing us $2.6 billion. Three thousand and four hundred residents could be displaced, putting new meaning to the term, “housing crisis.”

The report made public in December by the state Department of Land and Natural Resources recommends we plan for 3.2 feet of sea level rise now, but be ready to adjust that projection upward due to continually evolving science (see my column last December, “Let’s Get on the Same Page with Sea Level Rise”). Beyond these dire headlines, I’m interested in helping folks interact with the report in a meaningful way. So here goes.

Potential economic loss to Po‘ipū from 3.2 feet of sea level rise. Photo courtesy of PACIOOS

First of all, if you are a visual person and like playing with maps, the online Hawai‘i Sea Level Rise Viewer (Viewer) is the way to go (http://www.pacioos.hawaii.edu/shoreline/slr-hawaii/). Brought to you by the Pacific Islands Ocean Observing System (PACIOOS), the viewer allows you to zoom to anywhere in the state and view sea level rise exposure (SLR-XA) for different SLR projections (0.5 to 3.2 feet). The SLR-XA is made of three different types of hazards exacerbated by sea level rise: Passive Flooding, Annual High Wave Flooding, and Coastal Erosion.

This is what planning and science geeks have been waiting for, and I am very grateful it is finally here. For years, we knew the impacts of SLR (to properties, structures, etc.) could not be accurately estimated because we were limited to using passive models for flooding provided by the National Oceanic and Atmospheric Administration (NOAA). While the NOAA data was a great first cut at identifying vulnerable communities, we needed a tool to see the increased erosion and wave inundation that would result from SLR. Scientists from the University of Hawai‘i School of Ocean and Earth Science and Technology (SOEST) have been working hard to create the models, and the Viewer provides a great user friendly interface for them. The Viewer also has other data layers that are useful, such as geology and land use.

SLR-XA at 3.2 feet for Kapa`a town, including coastal erosion (red line). Many areas of the town would become flooded including sections of Kuhio Highway, causing a peninsula effect. Photo courtesy of PACIOOS

Ok, so now that we have a better idea of our exposure to sea level rise, the report and Viewer take it a step further to examine our vulnerability. Vulnerability is defined as, “the degree to which a system is susceptible to, and unable to cope with, adverse effects of climate change, including climate variability and extremes.” Vulnerability in the SLR-XA is assessed as the estimated potential permanent loss of land and structures and displaced people from the exposure to SLR (see my first paragraph for summary statistics). Geographic Information System (GIS) data from county, state and federal agencies were used, including county tax parcel and building footprint data. You can turn on and off the vulnerability layers on the Viewer, providing a powerful first look at your community’s vulnerability.

In my mind, in order to make choices on how to adapt, the next step is for communities to ground through this information and identify their own vulnerabilities. Conducting community-based vulnerability assessments that examine threatened assets (such as roads) and anything else the community values is an essential next step.

This column would be incomplete if I didn’t note the report’s gaps. There is no modeling of SLR impacts above 3.2 feet. Some studies project SLR upwards of 6 feet and even 8 feet by 2100 if the world does nothing to curb its greenhouse gas emissions. The report acknowledges this, and you can read my December 2017 column about uncertainties with projections. The 3.2-feet estimate is still a good target to plan for, but we should all be ready to revise our plans and estimates upwards. You can go to the NOAA SLR Viewer to glimpse passive flooding at six feet SLR: https://coast.noaa.gov/digitalcoast/tools/slr.

Also, the SLR-XA does not include impacts from less frequent high wave events from hurricanes, tropical cyclones and tsunamis with sea level rise. Moving forward with adaptation, it will be important for communities to discuss their vulnerabilities to this event based flooding. Kaua‘i certainly has had its fair share of hurricanes and thus significant local knowledge in this area.

All in all, hats off to the state Legislature that mandated the report, as well as DLNR, UH, PACIOOS, and the countless other partners involved with the effort! We certainly have our work cut out for us.

• Ruby Pap is a Coastal Land Use Extension Agent at University of Hawai‘i Sea Grant College Program. She can be reached at rpap@hawaii.edu.