Sea Level Rise Models Overlook Rainfall Impacts on Coastal Cities

Strategic Insights -

Researchers at the University of Hawai'i at Manoa have discovered that existing sea level rise models for coastal cities often overlook the impacts of rainfall on infrastructure, which can lead to severe flooding and contamination of stormwater inlets. A study published in Scientific Reports found that by 2050, large rain events combined with sea level rise could cause flooding severe enough to disrupt transportation and contaminate stormwater inlets across 70% of Waikiki on O'ahu, Hawai'i. The researchers developed a computer model of the Waikiki storm drainage system and installed sensors to record water depth during rain events, which revealed that rainfall is the dominant driver of drainage backflow until sea level rises two feet.

Key Takeaways:

  • Existing sea level rise models for coastal cities often overlook the impacts of rainfall on infrastructure.
  • By 2050, large rain events combined with sea level rise could cause flooding severe enough to disrupt transportation and contaminate stormwater inlets across 70% of Waikiki on O'ahu, Hawai'i.
  • Rainfall is the dominant driver of drainage backflow until sea level rises two feet.
  • The dominant driver of drainage backflow is high tidal levels once four feet of sea-level rise is reached.
  • Over 75% of the storm drainage system in Waikiki is connected to the Ala Wai Canal, which is known to be heavily contaminated.
  • Accounting for precipitation, the study determined that 100% of the outfalls of the Waikiki storm drainage system will fail by 2050, causing backflow of potentially contaminated water.
  • The research highlights the importance of incorporating rainfall and drainage infrastructure into coastal flood models to better understand how drivers of coastal flooding change over time.
  • Management practices aimed at reducing rainfall runoff will help minimize compound flooding in the short-term, but management to reduce tidal backflow is urgently needed.
  • The study contributes to the growing body of knowledge warning of present and near future climate challenges that will affect transportation, recreation, and accessibility in Waikiki.

Statistics:

  • 70% of Waikiki on O'ahu, Hawai'i will experience flooding severe enough to disrupt transportation and contaminate stormwater inlets by 2050.
  • 75% of the storm drainage system in Waikiki is connected to the Ala Wai Canal, which is known to be heavily contaminated.
  • 100% of the outfalls of the Waikiki storm drainage system will fail by 2050, causing backflow of potentially contaminated water.
  • 2 feet of sea-level rise: rainfall is the dominant driver of drainage backflow.
  • 4 feet of sea-level rise: high tidal levels become the dominant driver of drainage backflow.

Sources:

  • Chloe Obara, lead author of the study, Department of Earth Sciences at the UH Manoa School of Ocean and Earth Science and Technology (SOEST).
  • Chip Fletcher, study co-author, director of the Coastal Research Collaborative, and Dean of SOEST.
  • University of Hawai'i at Manoa, Scientific Reports, "Incorporating rainfall and drainage infrastructure into coastal flood models: A case study of Waikiki, O'ahu, Hawai'i."