Local-Scale Variations in Atoll Island Vulnerability to Flooding and Inundation: Fongafale, Tuvalu

Abstract

Atoll islands are generally low-lying, with maximum elevations of 3-5 m above mean sea level and are considered to be under threat to flooding by climate induced sea level rise. The aim of this research was to improve our understanding of local scale variations to vulnerability in an atoll island setting. Few studies have examined the spatial temporal vulnerability of atoll islands at local scales. This study provides insights into the variation in vulnerability to flooding and local scale impacts associated with climate induced rising sea level and local impacts. Elevation and structural data collected on Fongafale, Tuvalu, over a two week period was analysed in an inundation model to show the susceptibility of flooding to land and structures. Results of island inundation analysis show that elevation data combined with the analysis of human activities has provided new insights into the dimensions of atoll island vulnerability. Reconstruction of the island over a 110 year period displayed substantial land cover modification to the island with increase in structural and population densities on Fongafale, which further increases vulnerability to flooding. An assessment of the effects of flooding caused by future sea level projections based on IPCC scenarios was conducted. Results show that by 2100, 61% of the island and 38% of structures will be susceptible to flooding under the King high tide scenario. Spatially, flooding occurs in the basin of the central section and borrow pit in the south section of the island. As sea level continues to rise, flooding on Fongafale will become extensive towards the lagoon ridge. Under storm surge conditions, flooding will become widespread. Results indicate that a Category Three storm surge would flood the entire island and 96% of structures. In the event of a storm surge coinciding with King high tide, it will only take a Category One storm surge to flood the entire island. Cross sections highlight the substantial variation in morphology on Fongafale, which affects the spatial susceptibility to flooding of the island. In general, the morphology can be distinguished by high ocean and lagoon ridges and a central depression. Consequently, the vulnerability to flooding on Fongafale is a result of local factors (population increase, human modifications) and global issues (rising sea level and increasing storm frequency). Should the worst-case scenario occur and flooding frequencies increase, the community of Fongafale will have no option but to migrate or resettle.