[ Revised 25 November 2017 with deletion of Christchurch ]
Published data were used to analyse the long-term annual temperature trends at four locations located in the New Zealand region. Stations selected were located in New Zealand and Australia.
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 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 93 years to 132 years of complete annual data. The earliest record, at Hokitika, commenced in 1867.
The plots shown below are of the annual mean temperatures at each of the four 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 four 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 1940.
ANNUAL MEAN TEMPERATURE TRENDS FOR INDIVIDUAL STATIONS
Lord Howe Island (Australia) 1915-2015
Norfolk Island (Australia) 1925-2015
Hokitika (New Zealand) 1867-2015
Chatham Islands (New Zealand) 1878-2011
DISCUSSION AND COMMENTS
- The data analysed was limited to that which were available on the KNMI website.
- The annual mean temperature trend-lines for the four stations in Australia and New Zealand all showed weak cyclical patterns.
- Except for Chatham Islands, the stations generally had a Lows around 1920-1930 and a High or plateau around 2000.
- All of the stations showed increasing trend-lines since around 1920-1930.
- Chatham Islands was an exception with a fairly steady increase of about 0.7 deg C between ~1900 and ~2000, but with indications of a plateau since around 1990.
- The increase in temperature from ~1940 to ~2010 was generally 0.2-0.5 deg C.
- The trend-lines for the four stations were all weakly cyclical.
- Threeof the stations showed a Low in the trend-line around 1920-1930 and a High or plateau around 2000-2010.
- Chatham Islands was an exception having a fairly steady increase for a Low around 1900 to a High plateau around 2000.
- The temperature rise between around 1940 and around 2010 was generally 0.2-0.5 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.