The report says tropical islands are experiencing rapid sea level rise at a higher rate than anywhere else in the world.
The study, carried out in the Marshall Islands, is the first of its kind to focus on the hazard of wave-driven over wash and its impact on freshwater availability. It projected the impact of sea-level rise and wave-driven flooding on atoll infrastructure, as well as freshwater availability under a variety of climate change scenarios.
The study was commissioned by the US. Defence Department because many of these atoll islands are home to American military sites. The scientists used climate projections with weather and wave modelling to study the impacts of rising seas.
The authors predict that at current greenhouse gas emission rates, there will be “annual wave-driven over washes” of most atoll islands by the mid-21st century. They say this annual flooding will result in the islands becoming uninhabitable, due to frequent damage to infrastructure and the inability of freshwater aquifers to recover between over wash events.
The report’s current projections indicate these effects will be “amplified” in the tropics, where sea level rise will be greater than the global average.
“The tipping point when potable groundwater on the majority of atoll islands will be unavailable is projected to be reached no later than the middle of the 21st century,” says US Geological Survey geologist and lead author of the new report, Curt Storlazzi.
Most atolls in the Cook Islands have limited land available for habitation, as well as water and food sources. Most have ecosystems that are also vulnerable to seawater inundation also. Wave impacts can be caused by events such as passing tropical storms and cyclones, but can also occur as “blue sky events” due to large, remotely generated swell, the report says
“Such information is key to assessing multiple hazards and prioritising efforts to reduce risk and increase the resiliency of atoll islands’ communities around the globe” Storlazzi says.
“Sea level rise will exacerbate the impact of large waves on atolls’ coral reefs, by reducing wave breaking at the reef crest. This will increase the water level over the reef flat, which will allow for larger waves to reach the shoreline.