Impacts of sea-level rise and wave inundation in the Tongariki Complex, Rapa Nui

Abstract

Sea-level rise (SLR) threatens both modern assets and the irreplaceable, tangible heritage of past coastal settlements. Assessment of SLR inundation on coastal cultural sites has been a topic of growing interest but the distribution of research is globally uneven and particularly scarce in Pacific Islands. Using XBeach in 2D non-hydrostatic mode we simulate the wave environment under future SLR scenarios in the Tongariki Complex, Rapa Nui, to estimate the extent of wave- and SLR-induced inundation. We model the extent of SLR-induced flooding at current mean higher high water and SLR scenarios of 1.2 m and 3 m. Wave modeling is accomplished using 1-yr and 100-yr swell event return periods. We find that cultural assets are within the reach of wave run-up at current sea level and the number of assets impacted could triple by 2100. Particularly, we estimate that the iconic Ahu Tongariki, part of the Rapa Nui National Park UNESCO world heritage site, could be reached by seasonal waves as soon as 2080 under a High SLR scenario (1.2 m SLR). The results suggest urgency for SLR-related assessments in other coastal cultural sites in the Rapa Nui National Park and encourage community consultation for adaptation and mitigation efforts.