Patterns of island change and persistence offer alternate adaptation pathways for atoll nations

Abstract

Sea-level rise and climatic change threaten the existence of atoll nations. Inundation and erosion are expected to render islands uninhabitable over the next century, forcing human migration. Here we present analysis of shoreline change in all 101 islands in the Pacific atoll nation of Tuvalu. Using remotely sensed data, change is analysed over the past four decades, a period when local sea level has risen at twice the global average (~3.90 ± 0.4 mm.yr−1). Results highlight a net increase in land area in Tuvalu of 73.5 ha (2.9%), despite sea-level rise, and land area increase in eight of nine atolls. Island change has lacked uniformity with 74% increasing and 27% decreasing in size. Results challenge perceptions of island loss, showing islands are dynamic features that will persist as sites for habitation over the next century, presenting alternate opportunities for adaptation that embrace the heterogeneity of island types and their dynamics.

Rethinking the Limits of Climate Change Adaptation

“…While several massive bleaching events have been documented in many places in recent times (Nurse et al 2014), new studies are beginning to explore the feasibility of coral preservation and transplantation (Yamamoto and Esteban 2014). On the other hand, 4 decades' worth of remotely sensed data regarding the shoreline changes of all 101 islands of Tuvalu show a net increase in land area of the country as a whole, despite the fact that its local SLR was twice as much as the global average within that period (Kench, Ford, and Owen 2018). Similar results have been found by studies conducted in the 29 islands of Funafuti Atoll as well as 12 different atolls in central and western Pacific .…”

A global assessment of atoll island planform changes over the past decades

“…Tuvalu is the only atoll country for which a complete assessment of areal change has been conducted (in this case showing land area stability; Kench et al, ). Consequently, no final conclusion on change in land area can be drawn for other atoll countries and territories.…”

Masked Shoreline Erosion at Large Spatial Scales as a Collective Effect of Beach Nourishment

“…Along low-lying coasts at passive tectonic margins around the world, sea-level rise should, on average, drive net long-term shoreline erosion over large spatial scales (>10 2 km; FitzGerald et al, 2008;Passeri et al, 2015). Coastal erosion is not necessarily an inevitable consequence of sea-level rise: A variety of natural, dynamic physical factors can influence positive and negative changes in shoreline position over decades to centuries (Cooper & Pilkey, 2004;FitzGerald et al, 2008;Kench et al, 2018;Komar & Holman, 1986;Nicholls & Cazenave, 2010;Passeri et al, 2015;Wong et al, 2014;Zhang et al, 2004). For example, isostacy (regional flexure of the Earth's crust) can exacerbate relative sea-level rise, such as through sediment loading at a major river delta (Syvitski et al, 2009), or effect relative sea-level fall, through long-term rebound after an ice sheet (Dyke et al, 1991;Lambeck & Chappell, 2001;Shennan et al, 2000).…”

“…Sediment supply, type, and whether littoral sediment comes from one or a combination of fluvial, offshore, or local (e.g., soft cliff) sources can differentially affect shoreline position (FitzGerald et al, 2008), even within the same littoral cell (Willis & Griggs, 2003). Ecological feedbacks by which coastal vegetation (e.g., marshes and mangroves) or coral systems trap, retain, and create sediment may use relative sea-level rise to drive shoreline advance (Kench et al, 2018;Kirwan & Megonigal, 2013). Regional wave climates (multiannual to multidecadal distributions of deep-water wave height and direction of travel) reshape coastal planforms by setting up gradients in wave-driven alongshore sediment flux that drive transient spatial patterns of erosion and accretion over large spatial scales (~10 1 -10 2 km; Ashton & Murray, 2006a, 2006bLazarus, Ashton, et al, 2011;Lazarus et al, 2012).…”