Scientist turns detective on NZ temperature records
A NIWA climate scientist is awaiting a ruling from the World Meteorological Organisation (WMO) on whether New Zealand’s coldest recorded temperature will be accepted as an official world weather extreme.
Gregor Macara has submitted a detailed report to the WMO about a temperature of -25.6°C recorded at Ranfurly, Central Otago on 17 July, 1903.
The WMO is currently considering the report and if accepted, the Ranfurly observation would become the coldest recorded temperature for the Oceania region.
Mr Macara conducted a lengthy investigation on the temperature recording, which included hunting through the newspaper archives of the Otago Daily Times (ODT), Southland Times, Tuapeka Times and the Mt Ida Chronicle.
“It wasn’t the kind of scientific research I am used to, but I was trying to find out what the weather conditions were in the lead up to this coldest temperature observation. Temperatures like this don’t occur in isolation in New Zealand, you need a specific sequence of weather events.”
Mr Macara looked at July news articles and discovered there was a massive snow storm throughout the South Island on July 10. In the days immediately following, the skies cleared under a high pressure system and enabled the temperatures to drop drastically.
A report in the ODT on 18 July said: The 2.10pm train from Dunedin to Ida Valley could not get beyond Middlemarch, as on arrival at the latter station it was found that no water could be got for the engine, the water in the tanks having been frozen into one solid mass.
Three days later on 21 July the ODT reported: Beef and mutton are frozen, and can only be cut with a saw or chopper, a knife being of no use. Turnips, potatoes and milk are also frozen, and the ink in the post office is in a similar state.
The -25.6°C temperature was recorded at Eweburn Nursery, where a plantation of pine trees had been established, on a form headed Meteorological Return (3rd Class Station).
Mr Macara said unfortunately there was quite a lack of station information, especially when it came to the instruments used and observation procedures employed.
“We can’t be 100% certain of the instruments accuracy given there’s no indication they were verified at the time, but on the balance of evidence there’s no real reason to doubt it did get so cold.”
The WMO keeps an official, unbiased list of world weather extremes and has a set of procedures to verify and certify records. It is expected to release its decision on the Ranfurly temperature early in the New Year.
In the meantime, Mr Macara is now working on second report for the WMO. This one is on New Zealand’s highest temperature of 42.4°C recorded at Rangiora on 7 February, 1973.
Currently the WMO lists 42.2°C recorded at Tuguegarao, Philippines, on 29 April, 1912 as the highest ever recorded Oceania temperature.
Mr Macara says the temperature investigations have been very interesting.
“It is important to maintain reliable records of weather and climate extremes as they can be used as indicators of climate variability and change.”
World weather extremes according to WMO official records
- Highest temperature: 56.7°C, 10 July, 2013 at Furnace Creek Ranch, California
- Lowest temperature: -89.2°C, 21 July, 1983 at Vostok, Antarctica
- Greatest 60 minute rainfall: 305mm, 22 June, 1947 at Holt, Missouri
- Greatest 12-month rainfall: 26.47m, August 1860 to July 1861 at Cherrapunji, India
- Heaviest hailstone: 1.02kg, 14 April, 1986 at Gopalganj district, Bangladesh
- Maximum wind gust: 407.16km/h, 10 April, 1996 at Barrow Island, Australia