Physical impacts of climate change on coral reef islands

Due to their low-lying nature, coral reef island nations such as Maldives, Tuvalu, Kiribati, Marshall Islands (combined population > 1M) are widely acknowledged to be amongst the most vulnerable countries to climate change. It is widely assumed that the islands will become increasingly uninhabitable through this century, threatening their very existence.

However, such considerations ignore the ability of the islands to morphologically adjust to rising sea level and increased flooding frequency. Recent physical and numerical modelling carried out by the University of Plymouth has suggested, however, that coral reef islands can respond morphologically to rising sea levels by vertical accretion through overwash processes.

Island drowning is only the inevitable outcome of sea-level rise for islands where coastal structures, such as seawalls, have essentially cut-off the reef island from sediment supply from the reef platform and are preventing overwash from occurring, and/or where ecological processes have closed down and there are no new sediment supplies delivered to islands.

This GCRF project takes a case study approach to develop a transferable modelling capability of the physical impacts of climate change on coral reef islands to help formulate transformative methodologies for climate change adaptation strategies.

The case study site is a small populated island in the Maldives. Hydrodynamic and topographic data collected during an extensive field campaign will be used for numerical modelling the physical impacts of climate change, particularly sea-level rise and enhanced storminess, on the island and the consequences for long-term habitability. The impacts of different forcing scenarios and efficacy of various adaptation strategies will also be explored.

The research team will work closely together with national and local government authorities, the Maldives National University and a coastal consultancy. Capacity building amongst the partners is critical to the success of the project.

A key outcome of the project is the formulation of a methodology to serve as a 'blue print' for assessing vulnerability of small coral reef islands to the physical impacts of climate change and exploring implications of different climate change adaptation strategies.

Workflow components include: (1) identification of appropriate extreme wave and water level conditions and sea-level rise scenarios; (2) development of a digital elevation model of a small coral reef island based on relatively low-cost sea-, air- and land-based survey methods; (3) acquisition of field data set of water level, waves and groundwater table to validate and calibrate a hydrodynamic model (XBeach) for modelling wave transformation across reef platforms; (4) assessment of future risk of coastal flooding and island inundation using XBeach for a variety of sea-level and wave forcing scenarios; and (5) evaluation of various adaptation strategies to mitigate risk of coastal flooding and identify pathways to extend future habitability.

Benefits and impacts of the project

  • 6 The generalised methodology with workflow components can be applied by government agencies and coastal consultancies companies to any small coral reef island to help them increase resilience to climate change.
  • H The output of this project can also contribute to the design of resilient artificial (resort) islands to enhance future commercial viability of sustainable tourism in the Maldives, which in turn will support local communities through employment.
  • J Local community will have insight into future risk of coastal flooding and island inundation, and will be empowered to make decisions about their own future occupation and land use on the island.
  • m Knowledge transfer and capacity building amongst the project partners will enable them identify and implement more sustainable ways for small coral reef islands to adapt to the physical impacts of climate change.