'Seven-station' series temperature data
NIWA's long-running 'seven-station' series shows NZ's average annual temperature has increased by about 1 °C over the past 100 years.
Mean annual temperature for New Zealand, calculated from NIWA's 'seven-station' series. This series uses climate data from seven geographically representative locations. The data are adjusted to take account of factors such as different measurement sites (Mullan et al 2010). The blue and red bars show the difference from the 1981-2010 average. The black line is the linear trend over 1909 to 2015 (0.92 ± 0.26°C/100 years).
Locations in the "seven station" series
The series has been derived from seven locations:
These locations were chosen because they provide broad geographical coverage and long records (with measurements started at all sites by 1908).
How the 'seven-station' series is constructed
For each location, temperature records from a number of local sites have been merged together to form a long time series. When merging different temperature records like this, it is necessary to adjust for climatic differences from place-to-place, or even changes in exposure or instrumentation at the same site. If no adjustments are made, significant biases could be introduced. For example, the longest record in the country comes from Dunedin, with climate readings taken at six sites throughout its history.
Our new analysis confirms the warming trend
The last overall review of the seven station adjustments was performed in 1992. In 2010, as a result of increased interest in the series, NIWA re-analysed the adjustments for the seven locations.
The key result of this revisiting is that the New Zealand-wide warming trend is almost exactly the same as in our previous assessment. In other words, either approach gives an accurate trend result. So without a doubt, on the basis of the 'seven-station' series, New Zealand did indeed get about 0.9°C warmer over the course of last one hundred years.
The pattern of warming is also consistent with changes in sea surface temperature and prevailing winds.
In terms of the detail, the re-analysis concluded that some sites have warmed more than previously calculated, and other sites warmed less, but these variations between the old and new series are within the margin of error.
The overview document below discusses the revision of the 'seven-station' series in more detail.
The adjusted data
The spreadsheet below contains the adjusted data used to compile the 'seven-station' series.
In this file, you will find:
- annual average temperature for each location, and for the 7 locations combined
- annual anomaly (difference from the 1981-2010 average) for each location, and for the 7 locations combined.
Note, also, that:
- similar Excel files can be obtained from NIWA (through email@example.com) for the annual minimum temperatures and maximum temperatures for the 7-station series
- the anomalies were previously calculated relative to the 1971-2000 average, but are now given relative to the updated 1981-2010 climatological average. This does not alter the actual site temperatures or the trend, only the anomaly.
- a change has been to one of the Hokitika adjustments since the 2010 Review report.
Schedule of adjustments
NIWA has documented its analysis for each of the 7 locations, including all the station offsets used to merge temperature records for each place.
Scientific references about the temperature series adjustment process, and the internationally accepted best practice approaches to adjusting raw climate data to accurately calculate temperature trends, can be found here.
Download a combined report
A PDF is available here which includes the overview and the reports for each of the seven stations. Each of these documents is available separately by following the other links on this page.
Changes to this page
Over time NIWA has added new material to this section and refined the way that it is presented. For transparency these changes are detailed here.