with John Maunder
Monthly rainfalls for Tauranga have been recorded at several recording sites during the last 118 years.
From January 1898 to December 1904, the observation site was described as 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 Rd, in Judea; from October 1940 to January 1941 the site was at Te Puna; and from February 1941 to now, the site is Tauranga 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.
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.
This should be coupled 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 graph below shows the annual rainfalls at Tauranga from the period 1898-2017.
The long-term average rainfall for Tauranga for the calendar year is 1300 mm, ranging from a low of 747 mm in 2002, to a high of 2049 mm in 1962.
For comparison, the rainfall for the last year, 2017 was 1687 mm, compared with 1302 mm in 2016, and 842 mm in 2015. Although 2017 appeared to be very wet, the last two months of the year were quite dry so that in total 2017 was only the ninth wettest year on record.
Since 1898, there have been only five years with a rainfall of less than 900 mm, they are 1914, 1982, 1993, 2002, and 2015.
And there's only been four years with a rainfall of more than 1800 mm; they are the two consecutive years of 1916 and 1917, plus 1938 and 1962.
The ten wettest years on record are: 1962 which had 2049 mm or 57 per cent above of the long-term average, while 1917 had 1985 mm or 52 per cent above average. Also, 1916 had 1941 mm or 49 per cent above average, plus 1938 (1817 mm), 1920 (1789 mm), 1956 (1777 mm), 1979 (1730 mm), 2011 (1696 mm), 2017 (1687 mm), and 2005 (1682 mm).
In chronological order, these wettest years occurred in 1916, 1917, 1920, 1935, 1938, 1956, 1962, 1979, 2005, 2011 and 2017.
In contrast, the 11 driest years on record are: 2002 (747 mm or 48 per cent below the long-term average), 1914 (773 mm or 41 per cent below the long-term average), 1982 and 2015 (842 mm or 36 per cent below the long-term average), plus 1993 (863 mm), 1906 (950 mm), 1919 (962 mm), 1997 (978 mm), 1973 (989 mm), 1986 (991 mm), and 1999 (1002 mm).
In chronological order, these driest years occurred in 1906, 1914, 1919, 1973, 1982, 1986, 1993, 1997, 1999, 2002, and 2015.
The average rainfall in Tauranga for the 50 years 1911-60 was 1365 mm, compared with the average rainfall for the 50 years 1961-2010 of 1263 mm. This indicates a decrease of 100 mm over the last 50 years compared with the previous 50 years.
For further information on a range of weather/climate matters see: https://sites.google.com/site/climatediceandthebutterfly/