Annual Climate Summary 2015

The year 2015 was sunny for most of New Zealand, and drier than normal for some of the country.

Overview

Annual mean sea level pressures for 2015 were higher than normal in the Tasman Sea and lower than normal to the south of New Zealand. This pressure set-up produced more south-westerlies than normal over the country. October was particularly extreme: the mean westerly winds over the southern half of the South Island in October 2015 were the strongest since records began in 1941[1].

Rainfall 

Yearly rainfall in 2015 was below normal (50-79% of the annual normal) in Northland, Tasman, Nelson and Canterbury, as well as for parts of eastern Waikato, Bay of Plenty, Gisborne and Wellington.  Rainfall was in the near normal (within 20% of the annual normal) range for the remainder of New Zealand. 

Soil moisture

Below normal soil moisture levels prevailed for the majority of the country through January and February. By the end of July, soil moisture levels had returned to near normal levels for much of the country with the exception of Hawke’s Bay, Wairarapa and eastern parts of Canterbury and north Otago. Soil moisture levels around the country began to decrease again in October and as of 1 January 2016, soil moisture levels were below normal for the time of year for the entire country with the exception of the Auckland region and Coromandel where levels were near normal.

Temperature

Annual temperature was near average (within 0.5°C of the annual average) across much of the country.  However, above average (+0.51 to 1.20°C above the annual average) temperature was recorded in isolated locations in the Bay of Plenty and Queenstown Lakes district. 

Sunshine

2015 was a very sunny throughout the country. Above normal (110-125% of the annual normal) to well above normal (> 125% of the annual normal) sunshine was recorded for much of the South Island as well as northern and eastern parts of the North Island. Several locations observed their highest annual sunshine total on record.

El Niño Southern Oscillation (ENSO)

Positive conditions prevailed for much of the year with an El Niño event officially declared in June. The El Niño continued to intensify throughout the second half of the year becoming a key climate driver for New Zealand. By many measures this El Niño developed into one of the strongest since 1950.

Rainfall 

As a whole, annual rainfall totals for 2015 were below normal (50-79% of the annual normal) in Northland, Tasman, Nelson and Canterbury as well as parts of eastern Waikato, Bay of Plenty, Gisborne and Wellington – a pattern aided by El Niño. Rainfall was in the near normal (within 20% of the annual normal) range for the remainder of New Zealand. It was the driest year on record for Kaitaia and Kerikeri which recorded 75% and 63% of their normal annual rainfall, respectively. There were no high total rainfall records or near-records set in 2015.

Soil moisture levels 

The dryness, in terms of rainfall, was also reflected in soil moisture levels throughout the year. 2015 started off very dry with below normal soil moisture levels observed for the majority of the country through January and February. It was particularly dry in central and north Otago, Canterbury and Marlborough. As a result, a drought was officially declared in those areas on 12 February. By the end of July, soil moisture levels had returned to near normal levels for much of the country with the exception of Hawke’s Bay, Wairarapa and eastern parts of Canterbury and north Otago. With the intensification of El Niño, soil moisture levels around the country began to decrease again in October and as of 1 January 2016, soil moisture levels were below normal for the time of year for the entire country; the exceptions were the Auckland region and district of Thames-Coromandel, where soil moisture levels were near normal.

Temperatures 

Temperature-wise, 2015 as a whole was near average across much of the country (within 0.5°C of the annual average). Despite this, several extreme temperature events occurred throughout the year and new records set. Most notably, -21°C was recorded at Tara Hills on 24 June which became the fourth temperature ever recorded in the country.

Sunshine 

2015 was a very sunny year with above normal (110-125% of the annual normal) to well above normal (greater than 125% of the annual normal) sunshine recorded for much of the South Island and northern and eastern parts of the North Island. Nine locations around the country experienced their sunniest year on record with several more experiencing near-record sunshine hours.

Temperature series 

The two warmest months in 2015 in terms of the 7-station temperature series were January (+1.1°C) and March (+1.0°C), due to enhanced north-easterly airflow. September was very cold (0.8°C below the September average[2]) with the ‘most southerly’[3] September airflow for over 20 years (since 1994). The nation-wide average temperature for 2015 was 12.7°C (0.1°C above the 1981–2010 annual average), using NIWA’s seven-station temperature series which begins in 1909.  2015 was the 27th-warmest year since 1909, based on this seven-station series.


[1] Based on the Trenberth “Z2 Index” derived from the Christchurch minus Campbell Island pressure difference.

[2] Note all temperature, rainfall and sunshine anomalies reported in this document are relative to the 1981-2010 average/normal.

[3] Based on the Trenberth “M1 Index” derived from the Hobart minus Chatham Island pressure difference.

Download 

Download the 2015 New Zealand Annual Climate Summary [PDF 1.7MB]