To island nations, sea level rise (SLR) is an existential threat. An insidious and often hidden consequence of SLR is groundwater inundation (GWI), which reduces the unsaturated zone causing flooding, enhanced corrosion, and reduced service life of buried utilities. In the Pacific, SLR may reach 0.6–2.5 m by the end of century, and on Tutuila, American Samoa (AS), apparent SLR is five times the global average, making adaptation planning critically important. This study addresses the climate impact-knowledge-gap regarding AS' infrastructure by combining a numerical groundwater model with buried and surface utility data to map where adaptation efforts should be prioritized. Rigorous studies of GWI are few, and this study is the first to model this phenomenon in the South Pacific. The model estimates that 70 km or 45% of the buried water, electrical, and sewer lines will be inundated, and 28% of present-day roads, 13.6% of buildings, and 20% of water-booster stations will be permanently flooded under a 2.4-m SLR scenario with a climate following the RCP4.5 trajectory. These effects are often overlooked by or unknown to policy and decision makers, therefore building awareness of GWI will help managers in AS and in other island communities to prioritize holistic adaptation actions.

  • Groundwater inundation (GWI), a lesser known consequence of sea level rise (SLR) threatens buried infrastructure in island nations.

  • American Samoa faces significant inundation of buried (45%) and surface (28%) infrastructure at 2.4-m SLR.

  • This study, the first of its kind in the South Pacific, helps prioritize areas most vulnerable to GWI and emphasizes the need for climate adaptation in island communities.

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