Matheen, N. and Kench, P.S., 2024. Morphological response of coral reef islands to the 2019 extreme positive Indian Ocean Dipole event.

The influence of the Indian Ocean Dipole (IOD) on winds, waves, and water levels has been studied in considerable detail, but the effect of these anomalous IOD-induced metocean conditions on coastal zones has so far received limited attention. This study analyses the impact of IOD events on the morphological response of coral reef islands by undertaking a case study of five islands in the Maldivian archipelago during the 2019 extreme positive IOD (pIOD) event. A 6-year dataset of shorelines before, during, and after the pIOD event was analysed to establish the magnitude of year-on-year variability and seasonal oscillation trends in the shorelines and thereby identify variability induced by the pIOD event. The results indicate a departure in the shorelines beyond the magnitude of the year-on-year variability during the mature phase of the pIOD event (September–November 2019) and a substantial change in the morphodynamics of the shoreline in the months immediately following the end of the pIOD event (November 2019–April 2020). It was identified that the anomalous metocean conditions during the pIOD event caused a change in the seasonally oscillating shoreline buffer around the island, with potential implications on medium-term island change and overall stability for the vegetated island core. The results showed that it took up to 2 years after the end of the pIOD event for the shorelines to return to their pre-pIOD state.

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