Countdown to 2050. That is just 25 years away, and researchers are flagging that sea level rise and the flood risk are not something to ignore.
This week, University of Hawaiʻi researchers will meet with the mayor about their findings. Their work was published last month in Scientific Reports. It cautioned that Waikīkī’s storm drain system, which empties into the Ala Wai Canal, could fail sooner than people think.
Chip Fletcher is the dean of the School of Ocean Earth Science and Technology, known as SOEST. Fletcher, Chloe Obara and Shellie Habel have long studied the very real threat facing communities. HPR featured Habel’s work with groundwater inundation in Waikīkī earlier this year.
Interview highlights
On the threat of sea level rise
CHIP FLETCHER: Sea level rise is real. We've been measuring it by satellite for 30 years. During that time, the rate of global sea level rise has doubled, in fact, a little bit more than that. And the melting of ice and the thermal expansion of the ocean are — up until a week or two ago — the major components driving sea level rise. But a paper came out a week ago telling us that the human use of aquifers, aquifer water on continents, and then discharging that water into the oceans now is a greater source of water to the oceans than the melting of all the ice in the world. That was pretty stunning. … So my point is that sea level rise is essentially a permanent condition. It's not something that will stop once we manage to stop emitting greenhouse gases. It's not something that will stop, for instance, when global warming stops, it's going to continue. And so all of our government agencies, all of our communities, need to think very hard about this, because it's going to cause flooding of many different types, and it's going to be unrelenting, accelerating and inevitable at this point.
On research work
CHLOE OBARA: The work that me and my colleagues did was essentially looking at the condition of the storm drainage network in Waikīkī, and then applying different scenarios of climate, be it sea level rise or rainfall events, and just understanding when we can expect to see failure and where across Waikīkī we'll see failure. We found that by 2050 or between 2050 and 2060, which is when we expect to see 2 feet of sea level rise, that's when we're going to start to see really significant failure or flooding at a lot of the inlets in Waikīkī. … When I was walking across Waikīkī to install the sensors we used, we found interesting things in some of the drainage occasionally, boogie boards or discolored water, and we don't know exactly what's going on underground, those are some clues that potentially contaminants are entering the drainage system, and that's something that we just need to be aware of. And so that is a consideration with this modeling. Anywhere that we have water backflowing, where we know that drainage system is connected to the Ala Wai, there is potential for contaminants in that water. We installed 10 sensors throughout Waikīkī, and those were continuously monitoring the water level. And so we used that to both calibrate and validate our results to make sure that we were accurately modeling those water levels as we projected forward into the future. … We placed two transects from the Ala Wai to inland, essentially looking at the gradient of where we see the title signature. And we found that we did see a tidal water level change in every single sensor moving inland, even into the center of Waikīkī. And then we also placed sensors in western Waikīkī, because we know that's an area that is projected to see effects of sea level rise.
On drainage failure
SHELLIE HABEL: We really do need to look at drainage failure and how Ala Wai exacerbates that, because the Ala Wai is basically an estuary, so it's influenced by things like the tide and by rainfall. So the confluence of that. And about three-quarters of our drainage system drains into the Ala Wai. So once it reaches a certain level, it can start backflowing through parts of the city. And that's concerning, because we all know that Ala Wai waters aren't clean. So the Ala Wai includes things like urban contaminants, sewage, all sorts of pathogens. And so it is really concerning that with big rainfall events, water from the Ala Wai could be getting into the city now, and with sea level rise, that could be a more chronic condition.
On possible solutions
CHLOE OBARA: An example that I cited was the Miami Beach area, and they have a very similar condition to what we're seeing in Waikīkī, where they are a very low-lying coastal urban area, and one of the solutions that they've looked to is pumping their drainage. So instead of relying on gravity to root storm water into the ocean or into the Ala Wai, we could consider some sort of pumping mechanism. … Anything we can do to relieve some of the pressure on the storm drain system would be helpful, whether that's green infrastructure or permeable pavement. So there's a lot of small-scale solutions that, on a parcel-by-parcel level, folks can look at too to help address this problem.
This story aired on The Conversation on Aug. 18, 2025. The Conversation airs weekdays at 11 a.m. Hannah Kaʻiulani Coburn adapted this interview for the web.
