Historical area and shoreline change of reef islands around Tarawa Atoll, Kiribati

Abstract

Low-lying reef islands on atolls appear to be threatened by impacts of observed and anticipated sea-level rise. This study examines changes in shoreline position on the majority of reef islands on Tarawa Atoll, the capital of Kiribati. It investigates short-term reef-island area and shoreline change over 30 years determined by comparing 1968 and 1998 aerial photography using geographical information systems. Reef islands have substantially increased in size, gaining about 450 ha, driven largely by reclamations on urban South Tarawa, accounting for 360 ha (~80 % of the net change). Widespread erosion and high average accretion rates appear to be related to disjointed reclamations. In rural North Tarawa, most reef islands show stability, with localised changes in areas such as embayments, sand spits and beaches adjacent to, or facing, inter-island channels. Shoreline changes in North Tarawa are largely influenced by natural factors, whereas those in South Tarawa are predominantly affected by human factors and seasonal variability associated with El Niño—Southern Oscillation (ENSO). However, serious concerns are raised for the future of South Tarawa reef islands, as evidence shows that widespread erosion along the ocean and lagoon shorelines is primarily due to human activities and further encroachment onto the active beach will disrupt longshore sediment transport, increasing erosion and susceptibility of the reef islands to anticipated sea-level rise. Appropriate adaptation measures, such as incorporating coastal processes and seasonal variability associated with ENSO when designing coastal structures and developing appropriate management plans, are required, including prohibiting beach mining practices near settlements.

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Acknowledgments

This study was undertaken during tenure of an AusAID scholarship by N.B. We are grateful to Schlencker Mapping for access to the photography and photogrammetry; we appreciate the support of the Government of Kiribati. Radiocarbon age analyses were undertaken under Grant AINGRA10073 from the Australian Institute of Nuclear Science and Engineering (AINSE). We appreciate the constructive comments from the reviewers and editors of this special issue.

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Correspondence to Colin D. Woodroffe.

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Handled by John E. Hay, Ibaraki University, Japan.

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Biribo, N., Woodroffe, C.D. Historical area and shoreline change of reef islands around Tarawa Atoll, Kiribati. Sustain Sci 8, 345–362 (2013). https://doi.org/10.1007/s11625-013-0210-z

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Keywords

  • Atoll
  • Sea-level rise
  • Shoreline change
  • Tarawa Atoll
  • Kiribati