{"id":234958,"date":"2026-05-26T11:26:41","date_gmt":"2026-05-26T21:26:41","guid":{"rendered":"https:\/\/www.hawaii.edu\/news\/?p=234958"},"modified":"2026-05-27T16:50:32","modified_gmt":"2026-05-28T02:50:32","slug":"native-forests-protect-honolulu-from-flooding","status":"publish","type":"post","link":"https:\/\/www.hawaii.edu\/news\/2026\/05\/26\/native-forests-protect-honolulu-from-flooding\/","title":{"rendered":"Native forests could help protect Honolulu from flooding"},"content":{"rendered":"Reading time: <\/span> 2<\/span> minutes<\/span><\/span>
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Parking lot in Mānoa<\/span> Valley following the March 23, 2026 storm (Photo credit: Conrad Newfield)<\/figcaption><\/figure>\n

A significant reduction in flood damage and erosion across urban Honolulu can be achieved by protecting native forests and controlling invasive species in the Ala Wai watershed, according to a new interdisciplinary study by researchers at the University of Hawaiʻi<\/span> at Mānoa<\/span> and state and community partners released May 26.<\/p>\n

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Broken logs in and near streams following the March 23, 2026 floods in Mānoa<\/span> (Photo credit: Conrad Newfield)<\/figcaption><\/figure>\n

The research examined how invasive species such as albizia and miconia affect flooding in the Makiki, Mānoa<\/span> and Pālolo<\/span> watersheds. Researchers found that unmanaged spread of the invasive plants over the next decade could nearly double expected annual flood damages from $68 million to $134 million.<\/p>\n

The study was released following the March 23 flash flooding in Mānoa<\/span> that overtopped Woodlawn Bridge, flooded homes and left mud across parts of the valley, including Noelani Elementary School. Researchers said healthy native forests act like a natural sponge by slowing stormwater runoff and stabilizing steep slopes. Invasive species can weaken those protections by increasing erosion and clogging streams with fallen trees and debris.<\/p>\n

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The research team combined hydrological monitoring data with land cover and economic modeling to measure the impacts of watershed management efforts led by the Koʻolau<\/span> Mountains Watershed Partnership and the Oʻahu<\/span> Invasive Species Committee.<\/p>\n

“The results show decreased streamflow for a given rainfall amount in Makiki and Mānoa<\/span>, where albizia and miconia were detected and removed most often,” the authors wrote, noting that runoff reductions were observed within just a few years of invasive species removal.<\/p>\n

The study also projected that unchecked invasive species growth would more than double annual Ala Wai Canal dredging costs from about $1.4 million to $3 million because of increased sediment runoff. Researchers said the findings highlight the need for long-term funding to support watershed protection and invasive species management programs across Hawaiʻi<\/span>.<\/p>\n

Project team members:<\/p>\n

    \n
  • Yu-Fen Huang (NREM<\/abbr>)<\/li>\n
  • Yinphan Tsang (NREM<\/abbr>)<\/li>\n
  • Leah Bremer (Institute for Sustainability and Resilience, 糖心视频ERO<\/abbr>, WRRC<\/abbr>)<\/li>\n
  • Conrad Newfield (ISR<\/abbr>, 糖心视频ERO<\/abbr>)<\/li>\n
  • Emma Yuen (Department of Land and Natural Resources–Forestry and Wildlife)<\/li>\n
  • Kimberly Burnett (糖心视频ERO<\/abbr>)<\/li>\n
  • Nathan DeMaagd (NREM<\/abbr>, 糖心视频ERO<\/abbr>)<\/li>\n
  • Jean Fujikawa (Oʻahu<\/span> Invasive Species Committee)<\/li>\n
  • Nate Dube (Oʻahu<\/span> Invasive Species Committee)<\/li>\n
  • Erin Bishop (Oʻahu<\/span> Invasive Species Committee)<\/li>\n
  • Serene Smalley (Koʻolau<\/span> Mountains Watershed Partnership)<\/li>\n<\/ul>\n

    Read the entire report on 糖心视频ERO<\/abbr>\u2019s website<\/a>.<\/p>\n

    糖心视频ERO<\/abbr> is housed in 糖心视频<\/abbr> Mānoa<\/span>\u2019s College of Social Sciences<\/a>.<\/p>\n