Atoll islands can grow taller naturally when storm waves wash sand and coral debris across them, a process that could help them keep pace with rising seas. Current forecasts predict most atoll islands will be uninhabitable by mid-century, but these models treat the islands as static landforms that simply drown as water rises. The models ignore overwash—the storm-driven process that deposits sediment onto island surfaces, allowing them to build upward. This project will fill that gap by measuring overwash in the field (in the Maldives and Pacific) and in a massive wave flume, then using the data to build realistic computer models of how islands actually respond to sea-level rise. If the models work, they could transform adaptation planning for the hundreds of thousands of people living on atoll islands. Instead of building expensive sea walls or relocating entire communities, island governments could manage sediment transport—for example, by maintaining healthy reef systems that supply the sand and gravel needed for natural island building. The tools would let communities test which strategies keep islands habitable longest, buying decades of time.
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Due to their low-lying nature, coral atoll islands are widely acknowledged to be amongst the most vulnerable environments to climate change. Most of them are predicted to be uninhabitable by the mid-21st century because of sea-level rise. However, these forecasts are based on relatively simple hydrodynamic models that consider the islands immobile, whereas, when overwashed during storms, the islands can vertically accrete due to sediment deposition. Repeated overwash can enable atoll islands to keep up with rising sea level. This potentially provides opportunities for island communities to prolong habitability through innovative adaptation strategies, instead of having to construct expensive coastal defences or traumatically relocate to regions with no flood risk. It is generally accepted that overwash is key to atoll island survival, but further research is required to increase our quantitative understanding of overwash processes and transform the enhanced insights into practice by developing management tools. The overarching aim of this project is therefore to 'revolutionise our capability to model the physical impacts of sea-level rise on atoll islands to aid in the formulation, development and implementation of transformative climate-change adaptation strategies for atoll island communities'. We will conduct ground-breaking laboratory experiments in the Delta Flume and unprecedented field measurements in the Maldives and Pacific where we will measure overwash processes and their impacts. We will use these unique data sets to develop, calibrate and validate hydro- and morphodynamic numerical models. An innovative modelling framework will then be used to evaluate the role of the various processes involved in atoll island response to sea-level rise. Finally, the modelling tools will be deployed to enable atoll island communities to implement adaptation strategies that maximise opportunities for continued habitation.
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