The influence of corals, coral reef morphology, and climate change on waves and wave-driven water levels along reef-lined coasts

The unprecedented 0.3 m rise in sea level in the central and western Pacific Ocean over the past two decades far exceeds best estimates of vertical coral-reef accretion rates. Although absolute rates of sea-level rise and projected 2100 global sea levels are still under deliberation, the existing data and predictive models consistently suggest that eustatic sea level will be considerably higher by the end of the century, which will have a profound impact on reef-lined tropical coasts. To understand how sea-level rise and climate change may impact reef-lined coastal areas, a calibrated and validated numerical model, XBeach, was used to examine the effects of different coral reef characteristics, such as coral coverage and reef morphology, on potential coastal hazards caused by wave-driven flooding and how these effects may be altered by projected climate change. Model results suggest that coasts fronted by relatively narrow reefs with steep fore reef slopes (~1:10 and steeper) and deeper, smoother reef flats are expected to experience the largest incident and infragravity waves heights and highest wave runup. Both sea-level rise and coral degradation are projected to increase incident and infragravity wave heights and wave-driven runup. Rising sea levels and climate change will reduce the ability of coral reefs to mitigate wave-driven flooding in the future, leading to more frequent, persistent, and extreme marine flooding and overwash on coastal communities and the natural resources on which they depend.