University of Hawaiʻi at Mānoa researchers revealed that Waikīkī is facing a fundamental shift in flood hazards as sea levels rise—transitioning from a flooding that is driven primarily by rainfall to events increasingly dominated by tidal processes. The team identified two key pathways that will become more significant with sea-level rise, both of which will increase public exposure to sewage-contaminated waters. The study was published in .

“Our findings make clear that current flood management strategies for Waikīkī are incomplete,” said Kayla Yamamoto, climate modeling analyst at the in the 东精影业 Mānoa (SOEST). “Most planning focuses on surface damage and economic loss from storms, but largely ignores the contamination dimension. Our results show that contaminated flooding will become more frequent, more extensive, and eventually a daily occurrence rather than a storm-driven one. There are currently no effective management strategies in place to address this.”

Simulating future scenarios

The team used an open-source, physics-based flood model to simulate how multiple flood sources interact in Waikīkī. The team used an advanced flood model that, unlike previous models, integrates all sources of flooding—rain, tides, underground water behavior, and storm drains—to provide a single, complete view of the hazard

“What we found is that during extreme rainfall like we鈥檝e been experiencing, high tides and elevated water levels in the Ala Wai can combine to create conditions where contaminated water flows back into low-lying streets and sidewalks,” said Shellie Habel, study co-author and coastal geologist with the Coastal Research Collaborative and . “As sea level rises, it will take less extreme rainfall and tides to cause similar flooding in the future.”

The two key pathways they identified were: storm drain backflow, where polluted water from the Ala Wai Canal is forced into streets and public spaces in Waikīkī through drainage systems, and groundwater emergence, which brings sewage and other contaminants from aging and leaking sewage infrastructure to the surface.

The model simulations show that storm drain backflow is projected to occur even when there is no rainfall:

• 1 foot of sea-level rise: Storm drain backflow occurs during extreme tides, even without rain.
• 2 feet of sea-level rise: Storm drain backflow occurs during moderate daily tidal conditions.
• 4 feet of sea-level rise: Groundwater emergence (bringing sewage to the surface) begins to occur without rain.

Researchers compared their model simulations against tide gauges, canal water level sensors, groundwater monitoring wells, and photographs of street-level flooding during three real recent storm events, including a major 50-year Kona storm in December 2021, a moderate storm in April 2023, and a five-year Kona storm in May 2024.

Implications for Waikīkī, beyond

The Ala Wai Canal is one of the most polluted waterways in Hawaiʻi, containing sewage, heavy metals and pathogens such as Vibrio and MRSA. Exposure to these waters is a documented risk, with MRSA infections linked to Hawaiʻi waters already contributing to an estimated 200 deaths per year in the state. Because Waikīkī is a primary economic engine where residents and visitors are in constant contact with coastal waters, the anticipated flooding represents a growing public health and environmental crisis.

Many coastal cities around the world rely on estuarine waterways to drain their stormwater, and face the same combination of aging infrastructure, rising seas and contaminated waters.

“Our modeling framework is transferable, and we hope this study serves as a wake-up call to modernize stormwater and wastewater infrastructure, integrate contamination risk into coastal flood planning, and build early warning systems before these thresholds are crossed,” Yamamoto said.

More than 2 trillion gallons of water鈥攅nough to fill 3 million Olympic-sized swimming pools鈥攊nundated 贬补飞补颈驶颈 in March. The accumulated rainfall over 14 days reached as high as 3,000% of normal historical levels for this time of year, culminating in a destructive 鈥渞ain bomb鈥� over 翱驶补丑耻. Through the University of 贬补飞补颈驶颈鈥檚 贬补飞补颈驶颈 Mesonet and the 贬补飞补颈驶颈 Climate Data Portal, researchers captured the scale of these back-to-back Kona low systems, mapping localized threats and providing crucial data on the state’s severe flooding.

Between March 1 and March 23, statewide rainfall averaged 18.25 inches鈥攎ore than 2.6 times the standard March average of 6.85 inches.

While the first storm (March 10鈥�16) brought hurricane-force wind gusts of 135.4 mph to 贬补飞补颈驶颈 Island and up to 62 inches of rain to Maui, the second Kona storm between March 19 and 23 triggered a new wave of devastation. The second storm dumped up to 61 inches of rain in localized areas, producing destructive floods across eastern and central 惭辞濒辞办补驶颈, West Maui and 翱驶补丑耻.

Communities such as Waialua and Haleiwa on 翱驶补丑耻鈥檚 north shore experienced devastating inundation. 贬补飞补颈驶颈 Mesonet stations highlighted the widespread intensity of the storm: the 碍补驶补濒补 station recorded the island’s highest two-day rainfall of roughly 22 inches, including 19.67 inches in a 24-hour period beginning the evening of March 19. Almost simultaneously, the nearby 碍补濒补丑别驶别 Ridge station above Waimea Valley recorded 9.75 inches in 24 hours.

惭腻苍辞补, Palolo flash floods

As the two-week rainy period neared its end, an intense, localized atmospheric event struck 惭腻苍辞补 and Palolo valleys on March 23. Honolulu Mayor Rick Blangiardi described it as a 鈥渃lassic rain bomb,鈥� heavy rain caused by a stationary storm cell. This 鈥渞ain bomb,鈥� over 惭腻苍辞补 and Palolo valleys, dropped 2 to 4 inches of rain per hour.

Six 贬补飞补颈驶颈 Mesonet stations in the Nu驶uanu-惭腻苍辞补 area recorded between 3.5 and 6.5 inches of rain, the majority of which fell within a three-hour window. Falling on already saturated ground, this turned streams into raging torrents and triggered significant flash floods.

The 贬补飞补颈驶颈 Mesonet, a statewide network of state-of-the-art weather stations, is proving to be a critical source of weather information, especially valuable during extreme events.

鈥淲e are building the mesonet to serve multiple purposes, including research, resource management, support for farmers and ranchers, and others,鈥� said Thomas Giambelluca, 贬补飞补颈驶颈 Mesonet project lead, and former director of the 东精影业 Water Resources Research Center. 鈥淏ut, providing data when and where it is most needed before and during extreme events like floods and wildfires, might be its most important purpose. Mesonet data will make us better prepared for future events by improving weather forecasts and enabling emergency managers to plan for and respond to extremes.鈥�

For University of Hawaiʻi at Mānoa PhD student Brian Gorberg, the devastating Kona low storms weren’t just an academic research topic—they were a recurring nightmare that inundated his home three times in less than four weeks. Renting the bottom bedroom of a home in Waialua on Oʻahu’s north shore, Gorberg witnessed the final and most severe flood send an 8-foot wall of water through his place.

After experiencing two recent floods that ruined his belongings, Gorberg was seeking refuge at a friend’s house down the street when the third flood hit. The flash flooding was catastrophic, acting like a “dam spillway” through his neighborhood. The water destroyed his Jeep Patriot given to him by his dad, caused a neighboring house to spin off its foundation, and trapped another neighbor in neck-deep water.

“I got woken up by a giant wave,” Gorberg said. “I assumed the worst because I study hydrology. I assumed the dam failed and I knew I had to get out of the watershed. So, I drove all the way to the evacuation site. I actually ran up the hill because I didn’t believe the evacuation site was safe enough.”

Flooding expertise proved critical

Gorberg’s academic background proved critical during the floods. As an student in the and working with the under advisor Chris Shuler, his expertise allowed him to understand the mechanics of the disaster. During the floods, Gorberg spent hours walking through his neighborhood trying to warn residents ahead of the rising waters.

Gorberg鈥檚 current research work is to create high-end, reproducible flood models and stage height maps to better protect local communities. Working alongside undergraduate students Chiara Duyn, Megan Wong and Anne Dominique, Gorberg created a that provides residents with transparent, scenario-based flood information.

While the app and Gorberg鈥檚 maps currently focus on Windward 翱驶补丑耻 watersheds such as Kāneʻohe, the underlying flood models are designed to be reproducible, and Gorberg aims to eventually expand this mapping to any flood zone across Hawaiʻi. The flood maps simulate exact inundation levels when local streams breach their banks at incremental heights—such as 12, 13 or 14 feet—allowing communities to visualize their risk and prepare for an approaching storm.

Reflecting on the tools he is building, Gorberg emphasized the urgent need for better preparedness in Hawaiʻi.

“Every stream gauge in the mainland has these maps. It’s not fair that Hawaiʻi doesn’t have it, especially considering these events,“ Gorberg said. ”And because there are graduate students like myself who have created this… that’s like the missing link in Hawaiʻi that would honestly solve this event, or would have been different if we had those maps.”

In the wake of historic flooding on Oʻahu鈥檚 North Shore, University of Hawaiʻi at 惭腻苍辞补 (JABSOM) students continue to provide care where it鈥檚 urgently needed. On March 23, JABSOM鈥檚 Houseless Outreach and Medical Education (H.O.M.E.) Project—a student-run initiative that provides free healthcare to unsheltered and underserved communities—set up an on-site clinic at Waialua Elementary, treating 25 patients with a team of 16 student volunteers under the guidance of faculty.

“We鈥檝e been seeing a wide range of patients. We鈥檝e seen a fair amount with wounds and infections, probably from the storm water,” said Jill Omori, H.O.M.E. Project director.

Other patients sought care for back pain, joint pain and eye infections, conditions that can worsen when access to routine care is disrupted.

“We also saw people with GI (gastrointestinal) problems because of the contaminated water, but also just regular medical issues like hypertension or diabetes that still need to be controlled,” Omori said.

Student dedication and rural health disparities

The clinic weaves hands-on care into the JABSOM curriculum, but Omori said the majority of the students today came on their own time.

“A lot of times, the students come down to the North Shore and do service projects here and there,” Omori said. “But something like this really hits home for them. It鈥檚 really nice for them to be able to give back to the community this way.”

Second-year medical student Michael Ajimura saw that impact firsthand.

“A lot of people weren鈥檛 able to get care because of the past few days of flooding, as well as those who were injured helping out or because of the flooding,” Ajimura said. “Just being able to help them has been really rewarding. When we say that we care for the community, it鈥檚 everyone. Being out here is fulfilling, and it鈥檚 something a lot of the students are more than willing to do.”

The response also highlighted the broader issue of rural health in Hawaiʻi, which is exacerbated during a disaster.

“Rural health doesn鈥檛 just mean the neighbor islands,” Omori said. “Waialua is a great example of a rural community right here on Oʻahu. They have some of the same problems that other rural communities have, even without storms. I think it just emphasizes some of the rural health disparities and the need for more equitable care.”

As recovery continues on the North Shore, JABSOM鈥檚 H.O.M.E. Project plans to hold a pop-up clinic every day during the week of March 23. They will either be at Waialua District Park or at Haleiwa Beach Park. .

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