Impact analysis of sea level rise on the future fate of small coral islands: the case of Hurasdhoo Island in the Maldives

The small coral islands of the Maldives face an imminent threat of disappearance in the 21st century due to rising sea levels. This study evaluated the projected shrinkage of Hurasdhoo, a coral island with a radius of approximately 91 meters, under future sea-level rise scenarios. The analysis utilized ten years of Sentinel-2 satellite imagery and employed a Line Tracking Method (LTM) designed to optimally extract the closed shoreline curve around the island. The results indicated that the representative radius of the beach land area decreased by an average of 21.88 centimeters per year, with a standard deviation of 2.27 meters. The mean radius retreat rate, calculated at 1° intervals along a baseline centered on the island, was found to be 19.19 centimeters per year, with a standard deviation of 10.83 meters. This variability was attributed to a mean annual center shift of 5.67 meters. Under two Shared Socioeconomic Pathway scenarios (SSP2-4.5 and SSP5-8.5), projections suggest that by 2100, Hurasdhoo may lose 53% and 72% of its surface area, respectively. By 2150, expected losses could reach 83% and complete inundation (100%), respectively. These estimates were derived from the relationship between sea-level rise and shoreline retreat for a circular coral island, modeled using Bruun's rule within a cylindrical coordinate framework. This study demonstrates that the LTM, specifically developed for small closed perimeters like coral islands, can effectively distinguish land from sea. Furthermore, the findings indicate that smaller islands are particularly vulnerable to sea-level rise, highlighting the need for timely technical and institutional measures to monitor and mitigate these vulnerabilities.