UPDATED 2 September 2017 with the addition of Dzaoudzi.
Published data were used to analyse the long-term annual temperature trends at five locations located in the Indian ocean. Stations selected were located in Mayotte, Mauritius and Seychelles.
The data used were all from the website of KNMI (the Royal Netherlands Meteorological Institute). Only raw data were used (ie as originally recorded, without any adjustments). Data were only used from stations located in rural areas or in small towns so as to avoid the possible influence of urbanisation on the temperatures.
The periods of the data ranged from 46 years to 101 years of complete annual data. The earliest record, at Seychelles International Airport, commenced in 1895.
The plots shown below are of the annual mean temperatures at each of the five locations. On each plot a polynomial “best fit” trendline has been added. It should be noted that the trendlines near each extremity (ie near the start and end of the records) are quite sensitive to individual data points, whereas trendlines within the main body of the record are much more stable and reliable.
COMPARISON OF TRENDLINES
Annual Mean Temperature Trends
[ The basis of these trendlines can be seen from the analyses for the five individual stations – see next section. ]
Annual Mean Temperature Residual Trends
[ The individual trend-lines have been adjusted by constant amounts to be approximately zero at the trend-lines in 1970.
ANNUAL MEAN TEMPERATURE TRENDS FOR INDIVIDUAL STATIONS
Dzaoudzi (Mayotte) 1951-2015
Seychelles International Airport (Seychelles) 1895-2015
Agalega (Mauritius) 1951-2015
St Brandon (Mauritius) 1951-2015
Plaisance (Mauritius) 1951-2010
DISCUSSION AND COMMENTS
- The data analysed was limited to that which were available on the KNMI website.
- The annual mean temperature trend-lines for all five stations showed weak cyclical patterns.
- Seychelles IAP was the only station with records prior to 1951 and had cyclical Highs around 1910 and 1970 and a Low around 1940.
- All of the stations showed increasing trend-lines since around 1970, and particularly since around 2000.
- The increase in temperature from ~1970 was generally 0.5-1.0 deg C.
- The trend-lines for the five stations were all weakly cyclical.
- There was an increase in the temperature trend since around 1970, and particularly since around 2000.
- There was no evidence at any of the stations of a peak in the temperature trend in around 2000.
- The temperature rise between around 1970 and around 2010 was generally 0.5-1.0 deg C.
This article was written by Brian Gunter of Narooma, NSW. In his previous life Brian was an engineering hydrologist involved over many years in the analysis of rainfall and river flow data for the planning of water resources projects in Australia, Asia and Africa. In recent years he has been one of the Marine Rescue NSW (previously Royal Volunteer Coastal Patrol) volunteer weather observers who operate the Narooma station for the Bureau of Meteorology.