3/10/2021 Annual and seasonal rainfall wprdipe24/browse_for_stats/environment/environmental-reporting-series/environmental-indicators/Home/Atmosphere-and-climate/annual-rain.aspx 1/3 Annual and seasonal rainfall Rain is vital for life – it supplies the water we need to drink and to grow our food, keeps our ecosystems healthy, and supplies our electricity. New Zealand’s mountainous terrain and location in the roaring forties mean rainfall varies across the country. Changes in rainfall amount or timing can significantly affect agriculture, energy, recreation, and the environment. For example, an increase or decrease of rainfall in spring can have marked effects on crops or fish populations. Climate models project rainfall to increase during winter and spring in the west of both the North and South islands, with drier conditions in the east and north. In summer, wetter conditions are projected in the north and east of both islands. We classified Annual and seasonal rainfall as a national indicator. Key findings Some areas in New Zealand have experienced changes in seasonal rainfall since 1960. At the 95 percent confidence level, between 1960 and 2016, 8 of 30 locations experienced changes in the amount of spring rainfall. Five sites in the northern and central North Island had decreased rainfall (Kerikeri, Whangarei, Tauranga, Taupo, Rotorua). In contrast, two sites in the southwest of the North Island (Whanganui, Waiouru) and one in the south of the South Island (Invercargill) had increased rainfall. Between 1960 and 2016, at the 95 percent confidence level, 4 of 30 locations showed a trend in winter rainfall (New Plymouth, Wellington, and Whangarei decreased and Milford Sound increased), and three locations showed trends in summer rainfall (Dunedin and Kerikeri increased while Dannevirke decreased). No trend was apparent in autumn rainfall for any location. On average, winter is the wettest season for most of the country except for the southern half of the South Island, where most rain falls during summer. In general, the South Island experiences more consistent average rainfall across seasons, but greater variability in annual totals, as the wettest and driest areas of the country are both in the South Island. Figure 1 Seasonal trends (1960-2016) and seasonal average rainfall (1981-2010) – interactive map HOME Environmental Indicators > Home > Atmosphere and climate > Annual and seasonal rainfall Related co Access data fi Precipitation d Related indica Rainfall intens Soil moisture a Water physica evapotranspira Related links Our atmosphe Environment A Climates chan Zealand Our future clim Climate summ National and r Marine Land Fresh water Atmosphere and climate Air ABOUT BROWSE BY TOPIC MORE IN THE SERIES
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3/10/2021 Annual and seasonal rainfall
wprdipe24/browse_for_stats/environment/environmental-reporting-series/environmental-indicators/Home/Atmosphere-and-climate/annual-rain.aspx 1/3
Annual and seasonal rainfall
Rain is vital for life – it supplies the water we need to drink and to grow our food, keeps ourecosystems healthy, and supplies our electricity. New Zealand’s mountainous terrain and location inthe roaring forties mean rainfall varies across the country. Changes in rainfall amount or timing cansignificantly affect agriculture, energy, recreation, and the environment. For example, an increase ordecrease of rainfall in spring can have marked effects on crops or fish populations.
Climate models project rainfall to increase during winter and spring in the west of both the North andSouth islands, with drier conditions in the east and north. In summer, wetter conditions are projected inthe north and east of both islands.
We classified Annual and seasonal rainfall as a national indicator.
Key findings
Some areas in New Zealand have experienced changes in seasonal rainfall since 1960.
At the 95 percent confidence level, between 1960 and 2016, 8 of 30 locations experienced changesin the amount of spring rainfall. Five sites in the northern and central North Island had decreasedrainfall (Kerikeri, Whangarei, Tauranga, Taupo, Rotorua). In contrast, two sites in the southwest ofthe North Island (Whanganui, Waiouru) and one in the south of the South Island (Invercargill) hadincreased rainfall.
Between 1960 and 2016, at the 95 percent confidence level, 4 of 30 locations showed a trend inwinter rainfall (New Plymouth, Wellington, and Whangarei decreased and Milford Sound increased),and three locations showed trends in summer rainfall (Dunedin and Kerikeri increased whileDannevirke decreased). No trend was apparent in autumn rainfall for any location.
On average, winter is the wettest season for most of the country except for the southern half of theSouth Island, where most rain falls during summer.
In general, the South Island experiences more consistent average rainfall across seasons, butgreater variability in annual totals, as the wettest and driest areas of the country are both in theSouth Island.
Figure 1
Seasonal trends (1960-2016) and seasonal average rainfall (1981-2010) – interactive map
HOME
Environmental Indicators > Home > Atmosphere and climate > Annual and seasonal rainfall
Related co
Access data fiPrecipitation d Related indicaRainfall intensSoil moisture aWater physicaevapotranspira Related linksOur atmospheEnvironment AClimates chanZealandOur future climClimate summNational and r
MarineLandFresh waterAtmosphere and climateAir
ABOUT BROWSE BY TOPIC MORE IN THE SERIES
3/10/2021 Annual and seasonal rainfall
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Source: NIWA
Figure 2
Average total annual rainfall, 1972–2016 – interactive map
Source: NIWA
Definition and methodology
Annual rainfall is the total accumulated rainfall in a year, using daily rainfall estimates from rain gaugesat 30 locations across New Zealand. We calculate average seasonal rainfall by aggregating dailyrainfall estimates by site for each meteorological season of the year: summer = December (of previousyear)-January-February, autumn = March-April-May, winter = June-July-August, and spring =September-October-November. For the 30-year period 1981–2010, rainfall normals (averages) for eachseason were calculated for comparison purposes. Annual and seasonal rainfall is highly variable anddepends on short-term weather patterns and long-term climate oscillations such as the El NiñoSouthern Oscillation, Interdecadal Pacific Oscillation, and Southern Annular Mode, which may all beinfluenced by a warming climate.
NIWA interpolated annual and seasonal rainfall totals, measured at climate station locations acrossthe country, to create a regular 500m resolution grid of average seasonal rainfall from 1981 to 2010and annual rainfall for each year from 1972 to 2016. Missing data were infilled using Virtual ClimateStation Network data (NIWA, nd). Although the interpolations cover the entire land area of NewZealand, accuracy is lowest where station density is low and terrain is complex (Tait et al, 2006; Tait etal, 2012; Tait & Turner, 2005).
3/10/2021 Annual and seasonal rainfall
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NIWA also provided daily rainfall data from 1960 to 2016 for each of 30 regionally representativeclimate stations (note that the time series for nine stations started later than 1960: Auckland, 1962;Gore, 1971; Hokitika, 1963; Kerikeri, 1981; Masterton, 1992; Queenstown, 1968; Rotorua, 1963; Taupo,1976; Whangaparaoa, 1986). These data were used to assess seasonal rainfall trends. Criteria used toselect the 30 regionally representative climate stations are that the station must currently be open andbe likely to remain open for the foreseeable future; have a long record of reliable, good-quality data; belocated near a large city (eg at an airport site) so is representative of the climate where many people inthe region live. One station per region is to be selected, but if deemed necessary, two or three stationsmay be selected to represent a large region.
Data quality
We classified Annual and seasonal rainfall as a national indicator.
Relevance
This national indicator is a direct measure of the ‘Climate' topic.
Accuracy
The accuracy of the data source is of high quality.
See Data quality information for more detail.
References
NIWA (nd). Virtual climate station data and products. Retrieved 29 May 2017 from www.niwa.co.nz.
Tait, A, Henderson, R, Turner, R, & Zheng, X (2006). Thin plate smoothing spline interpolation of dailyrainfall for New Zealand using a climatological rainfall surface. International Journal of Climatology,26(May 2006), 2097–2115.
Tait, A, Sturman, J, & Clark, M (2012). An assessment of the accuracy of interpolated daily rainfall forNew Zealand. Journal of Hydrology New Zealand, 51(1), 25–44.
Tait, A & Turner, R (2005). Generating multiyear gridded daily rainfall over New Zealand. Journal ofApplied Meteorology, 44(9), 1315–1323. http://doi.org/10.1175/JAM2279.1.
Archived pages
See Annual rainfall (archived October 2017).
Updated 30 January 2018
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