In 2012 a detailed examination of sea-level trends, vertical land movement, storminess, and the ocean wave climate in the Chagos Archipelago (Dunne et al., 2012) concluded that the Chagos islands had experienced a relatively stable physical environment over the last 20 years. Rates of sea-level rise had not been larger than the generally-accepted rate of up to 2mm yr−1 for 20th century global-average sea-level rise, and there was no evidence of any change in the magnitude or frequency of waves (wind and swell), such that the impacts on the islands (erosion and inundation) had not increased.
Update Summary
This update extends the Diego Garcia tide gauge record and the altimetry sea-level regional maps to the most recently available data (31 August 2014). It also examines periods of extreme high water at Diego Garcia in the last 10 years.
The datum shift in the Diego Garcia record which occurred when the tide gauge was replaced in 2003 still remains unresolved by the gauge owners, the University of Hawaii Sea Level Center. This precludes the earlier record (1988 – 2000) from being combined with the post-2003 data.
The recent tide gauge record is still too short (11 years) for meaningful trend analysis. Unsurprisingly it is still not possible to detect any long term trend in either the monthly or daily data.
The satellite altimetry data now extend to 21 years (1993 – 2014). Consistent with the earlier analysis it shows a pattern of higher rates of sea-level rise in the southern part of the region (70-74oE and 4-9oS), decreasing northwards. Significant linear trends can now be detected at Peros Banhos and Salomon (3.18 ± 1.14 mm yr-1 (± SE) p=0.0054) and Diego Garcia (3.83 ± 1.68 mm yr-1 p=0.0277). These are higher rates compared to 2012.
There is no evidence that extreme values (the highest tides) are increasing at a faster rate than mean sea level.
At Diego Garcia, high tides that have been observed to lead to flooding in certain areas (e.g., at the Donkey Gate on the western arm of the atoll) have occurred 64 times since 2004, the majority prior to 2012. There is no evidence of a higher frequency of occurrence, nor that annual maximum spring-tide levels have increased in the last 10 years.
A recent study of regional sea-level change over the last century suggests that Chagos sea level rose by about 6 mm yr-1 during the first half of the 20th Century (1901-1949) decreasing to 2 mm yr-1 in the latter half (1950-1999).
Richard Dunne
4 March 2015
The full update is available as a PDF - downloadable from below
Page last updated: 1 December 2020