Weather Eye with John Maunder

Monthly rainfalls for Tauranga have been recorded at several recording sites over the last 114 years.

From January 1898 to December 1904, the observation site was the Tauranga Harbour, from November 1904 to April 1907 the site was described as simply ‘Tauranga', from January 1910 to December 1923 the site was Waikareao in Otumoetai, from January 1924 to September 1940 the site was at 148 Waihi Road in Judea, from October 1940 to January 1941 the site was at Te Puna, and from February 1941 to the present, the site is Tauranga Airport.

C.S Thompson of the former New Zealand Meteorological Service computed a homogeneous rainfall series for Tauranga appropriate to the current recording site at the airport.

The methodology use in adjusting the older sites to the current observing site is published in the NZ Meteorological Service Miscellaneous Publication No 180 in 1984.

Although adjusting rainfall observations from one site to another is not without its difficulties, it is considered that the homogeneous rainfall series described here is a fair and true record of what the rainfall would have been if the current observation site (Tauranga Airport) had been used since 1898, with the understanding that although standard accepted methodologies have been used, any adjustments are only estimates of what would have occurred if the location of the rainfall records had always been in the same place with the same surroundings and the same or similar recording gauge.

In terms of climate change, (such as: is it getting wetter or drier, or warmer or colder?) the methodology used in computing an ‘official' set of climate observations is very important as otherwise erroneous conclusions may be drawn.

The long-term average rainfall for Tauranga for the calendar year is 1300mm, ranging from a low of 747mm in 2002, to 2049mm in 1962.

For comparison, the rainfall for the past year, 2011, was 1696mm, which made it the ninth wettest year since observations began in 1898.

Since 1898, there have been only three years with a rainfall of less than 1000mm (1993, 1982, 2002), and only three years with a rainfall over 1800mm (1938, 1917, 1916).

The 10 wettest years on record are: 1962 (156% of the long term average), 1916 (147%), 1917 (143%), 1938 (138%), 1920 (136%), 1956 (135%), 1971 (133%), 1979 (131%), 2011 (129%), and 2005 (128%).

In chronological order these wettest years occurred in 1916, 1917, 1920, 1938, 1956, 1962, 1971, 1979, 2005 and 2011.

In contrast the 10 driest years on record are: 2002 (57% of the long term average), 1915 (59%), 1982 (64%), 1993 (66%), 1906 (72%), 1919 (73%), 1997 (74%), 1973 (75%), 1986 (75%), and 1999 (76%).

In chronological order these driest years occurred in 1906, 1915, 1919, 1973, 1982, 1986, 1993, 1997, 1999, and 2002.

A graph of the rainfalls for Tauranga for 1898-2011 shows little long-term change although the last three decades have shown some tendency towards drier years, with five of the driest 10 years occurring during the last 30 years.

However, two of wettest 10 years have occurred during the last decade.

Dr John Maunder is a retired climate scientist now living in Tauranga. He was President of the Commission for Climatology of the World Meteorological Organization (WMO) from 1989 to 1997. Over the last 60 years he has written four books and has been involved in the ‘weather business' in various countries, including New Zealand, Australia, Canada, USA, Ireland, Switzerland, and the UK.

For further information, Google ‘Dr John Maunder' or email [email protected]