Response of reef island shorelines to seasonal climate oscillations: South Maalhosmadulu atoll, Maldives

The Maldives experience seasonal shifts in monsoon winds from the west‐northwest to northeast. The morphologic response of reef island beaches and shorelines to these predictable shifts in climate was examined on eight islands in South Maalhosmadulu Atoll based on global positioning system surveys of island shoreline planform in January and June 2002 and February 2003. Surveys show that islands exhibit large gross changes (31–120% of beach area) in shoreline position between seasons. Such changes reflect large reversals in sediment flux of 9–23 × 103 m3 on a biannual basis driven by seasonal reversals in wind and wave conditions. Annual net change is small (2–15%), suggesting islands spatially exhibit a dynamic equilibrium. An island oscillation index (Io) is defined that describes the spatial extent of shoreline change around islands. Island shape (ellipticity, e) is found to be positively correlated with Io in the expression Io = 1.021e − 0.275, suggesting island shape is a better indicator of the susceptibility of island shorelines to morphological change than wave energy exposure.