Development of a World-Wide Database of Atoll Morphometrics

Abstract

Small Island Nations are at considerable risk of climate change impacts from sea-level rise to coral acidification to increasing cyclone intensity; understanding how they will change in the coming century is vital for climate mitigation and resiliency. Atoll morphometrics are calculated for 3,795 motu and 593 reef flats on 154 atolls. The total land (motu) area is 1,836.55 km 2 with a total reef flat area of 7,387.43 km 2 . A consistent methodology to classify, segment, and calculate morphometrics is used. Composites are created for 4 years (2015)(2016)(2017)(2018), and are classified into motu, reef flat, open water/lagoon via unsupervised classification. Morphometrics are computed for each motu and reef flat of the atoll in python, creating a database of atolls and their associated morphometrics. Consistency in processing removes spatial and user bias, enabling a better understanding of geographic patterns of atolls. We identify trends in atoll, motu, and reef flat formations. The average atoll reef flat width is 850 ± 817 m and the average motu width is 263 ± 210 m. Distinct differences in the distribution of motu can be seen on a regional scale in French Polynesia, while globally, wider reef flats with larger motu are found closest to the equator. Globally there is a consistent reef flat width in front of large motu (> 10 km length) of 188 ±156 m. Our atoll morphometric database creates a baseline of current atoll characteristics that can be expanded upon in the future and used for evaluating temporal changes to atoll islands.