This section reports on a range of climate variables that together give a picture of the current and changing state of New Zealand’s climate. The longest record reported in this section is for land-surface temperature, with data back to 1909 (NIWA, 2010). For the 30 sites we report on, measurement of most other variables started in the 1960s or early 1970s – once all sites were reporting regular data for that variable. A wealth of data, collected over many decades, allows us to monitor and detect natural climate variability, long-term trends, and the human contribution to such trends.
2016 was our warmest year since at least 1909.
New Zealand’s annual average land-surface temperature (measured 1.3 metres above the ground) has increased 1 degree Celsius since 1909, when measurements first began. This is consistent with the lower end of the global average increase of land temperature over a similar period (1–1.2 degrees Celsius from 1880 to 2012) due to the moderating influence of our oceanic location.
From 1909 to 2016, our annual average temperature was 12.3 degrees Celsius.
Our five warmest years occurred in the last 20 years, with 2016 the warmest. Globally, 19 of the 20 warmest years occurred within the last 20 years. The more variable and more moderate recent warming over New Zealand reflects the moderating influence of our oceanic location (NIWA, nd-b) (see figure 8).
Note: The unusual drop in temperature from 1992 to 1993 is a result of the volcanic eruption at Mount Pinatubo in the Philippines.
This graph shows annual average temperature, 1909–2016. Visit the MfE data service for the full breakdown of the data.
We can expect temperatures to continue increasing, with warming unabated to 2100 and beyond unless the world follows a low-emissions path that includes removing some carbon dioxide presently in the atmosphere (Ministry for the Environment, 2016) (see New Zealand’s future climate and climate risks and Appendix: Climate change projections for New Zealand).
Frost and warm days
Between 1972 and 2016, the number of frost days decreased at 10 of 30 measurement sites.
Frost days are days when the minimum air temperature is 0 degrees Celsius or lower, while warm days are days when the maximum air temperature is higher than 25 degrees Celsius. Climate models project fewer cold and more warm extremes in the future (see Appendix: Climate change projections for New Zealand).
Over the 45 years between 1972 and 2016, the number of frost days decreased at 10 of the 30 measured sites and increased at 1 site, while no trend was apparent at the other 19 measured sites around New Zealand. The number of warm days increased at 8 and decreased at 1 of the 30 measured sites. No trend in warm days was apparent at 21 sites (figure 9).
Growing degree days
Our increasing temperatures have resulted in a greater number of growing degree days across the country between 1972 and 2016.
Growing degree days measure heat accumulation, which can be used to predict plant, and subsequently, animal growth. For example, they can be used to predict when certain flowers will bloom or insects will emerge from dormancy. Growing degree days count the total number of degrees Celsius the average temperature each day is above a base temperature, commonly a threshold of 10 degrees Celsius.
We are experiencing a greater
number of growing degree days
across the country. (Photo: NIWA)
Plant and animal cycles are interdependent across the food chain. Small changes, for example, in the timing of insect reproduction, can mean that species further up the food chain miss out on a crucial food source. The greater the change in timings, the more pressure species further up the food chain experience. In extreme cases, some species are threatened with extinction.
Sunshine is important for plant growth and our mental and physical well-being, as well as benefiting tourism and recreation. However, it can also increase our risk of skin damage (see UV sunlight and health).
From 1972 to 2016, sunshine hours increased at 27 of 30 locations around New Zealand (see figure 10). On average, most places around the country received between around 1,700 and 2,100 hours of sunshine each year. The increase in sunshine hours is because of reduced cloud cover (Liley, 2009).
Cloud distribution patterns in the atmosphere appear to be changing globally, with increasing greenhouse gas concentrations a major driver for this change (Norris et al, 2016). The changing patterns are consistent with storm tracks shifting towards the poles and subtropical dry zones expanding. As a result of these changes, we can expect less cloud cover and more sunshine over New Zealand (Norris et al, 2016).
This graph shows annual average sunshine hours and trends in sunshine hours, 1972–2016. Visit the MfE data service for the full breakdown of the data.
The impacts of high or low rainfall can be positive or negative. Rainfall is a valuable source of water for crops and gardens, as well as a generator of hydroelectricity. However, rainfall can restrict some recreational activities and has serious impacts when it leads to flooding, or when a lack of it leads to drought.
Annual and seasonal rainfall
Between 1960 and 2016, winter rainfall in Whangarei, Wellington, and New Plymouth decreased while summer rainfall in Dunedin and Kerikeri increased.
Annual and seasonal rainfall are highly variable and depend on short-term weather patterns and long-term climate oscillations such as El Niño Southern Oscillation, the Interdecadal Pacific Oscillation, and the Southern Annular Mode.
Geographically, annual average rainfall varies from less than 400 millimetres in places like Central Otago to over 4,000 millimetres in mountainous areas such as the Tararua range, and even more in the Southern Alps (an average of over 6,000 millimetres has been recorded at Milford Sound).
Rainfall also varies seasonally, with more rain in winter than in summer for most of the country except the southern half of the South Island, where most rain falls in summer. Despite no clear trend in annual rainfall, seasonal rainfall in some locations showed trends (see figure 11). For example, between 1960 and 2016, winter rainfall in Whangarei, Wellington, and New Plymouth decreased while summer rainfall increased in Dunedin and Kerikeri.
Climate models project that rainfall is very likely to increase on average over winter and spring in the south of the South Island and west of both the North and South islands (see Appendix: Climate change projections for New Zealand). Meanwhile, drier average conditions are expected in the east and north. In summer, wetter conditions are likely in the north and east of both islands (Ministry for the Environment, 2016).
Intense rainfall events
Between 1960 and 2016, the proportion of intense annual rainfall events increased in Napier and Timaru.
Changes in the frequency, intensity, spatial extent, duration, and timing of weather and climate extremes are expected to result from a changing climate (IPCC, 2012). Some reasons for this are well understood. For example, the natural global water cycle is intensifying as the atmosphere warms. This leads to increased evaporation, which may worsen droughts but may also increase the
frequency of intense rainfall events because
a warmer atmosphere can hold more water.
This graph shows average seasonal rainfall (1981–2010) and seasonal rainfall trends (1960–2016). Visit the MfE data service for the full breakdown of the data.
For most of New Zealand, there is no clear evidence that intense rainfall events have changed between 1960 and 2016. However, there were trends at some locations (see figure 12):
- the proportion of annual rainfall occurring in intense events (in the 95th percentile) decreased at 4 of 30 locations (Auckland, New Plymouth, Rotorua, and Taupō) and increased at two (Napier and Timaru)
- the annual maximum one-day rainfall amounts decreased at 4 of 30 locations (Auckland, Hamilton, Taupō, and New Plymouth) and increased at two (Timaru and Dunedin).
As the climate changes, the number of intense rainfall events is expected to increase over most of the country (except for Northland and Hawke’s Bay), with up to a 20 percent increase of events possible in the south of the South Island (Ministry for the Environment, 2016) (see Appendix: Climate change projections for New Zealand).
The extent to which a specific individual event is influenced by increasing greenhouse gas concentrations is difficult to determine. Many factors combine to produce a specific event, and because such events are rare, there are usually only a few examples of past events for any given location (Herring et al, 2016).
So far, published studies have identified increasing greenhouse gas concentrations contributing to two recent New Zealand flooding events: 2011 – a flood in Golden Bay (Dean et al, 2013); and 2014 – a flood in Northland (Rosier et al, 2015). These studies indicate that, while such events might have happened in the absence of high greenhouse gas emissions, they were more extreme than they would have been without the warming caused by additional greenhouse gases in the atmosphere.
Between 1972 and 2016, the frequency and magnitude of extreme wind decreased at about one-third of sites across New Zealand.
Wind is a valuable source of renewable energy, but strong gusts can damage property and trees and cause havoc for transport, communications, and power.
Average annual maximum wind gusts using data between 1972 and 2016 showed Wellington, Invercargill, and Gore were the windiest populated centres in the country, while Reefton, Gisborne, and Queenstown were the least windy.
In this report, we analysed extreme wind using two statistics: the number of days each year with a maximum wind gust in the 99th percentile and the annual highest maximum gust.
Between 1972 and 2016, the frequency and magnitude of extreme wind decreased at about one-third of sites across New Zealand (see figure 12). Over this period, the number of days a year with a gust that is extreme for that location decreased at 10 of 30 sites (Whangarei, Hamilton, Tauranga, Rotorua, Napier, Wellington, Blenheim, Christchurch, Timaru, and Dunedin) and increased at two sites (New Plymouth and Queenstown). New Plymouth also experienced an increase in highest maximum wind gusts.
Projections indicate climate change may alter the occurrence of extreme wind events, with the strength of extreme winds expected to increase over the southern half of the North Island and the South Island, especially east of the Southern Alps (Ministry for the Environment, 2016) (see Appendix: Climate change projections for New Zealand).
This graph shows trends in extreme wind (1972–2016) and intense rainfall (1960–2016). Visit the MfE data service for the full breakdown of the data.
Box 4 Māori ways of knowing the weather and climate
He tau hāwere tētahi, he tau tukuroa tētahi
One is a season of plenty, another a season of famine
This whakataukī (proverb) reflects Māori familiarity with natural climate variations. It is a reminder of the unpredictability of growing seasons and the importance of preparing for a poor season or extreme weather event (Kanawa, 2010).
Māori knowledge of the climate and weather can be traced back to the learnings of their Polynesian ancestors. Alongside a sophisticated system for navigating by the stars, the long sea voyages of Polynesian mariners required intimate familiarity with ocean currents and prevailing weather patterns. On arriving in New Zealand, these first peoples soon found that coconut, breadfruit, and other tropical staples did not grow well in our temperate climate, requiring them to test and quickly adopt new horticultural and food storage methods (Anderson, 2013).
Since those early days, Māori have developed an extensive set of biophysical indicators (using mathematics, physics, chemistry, and biology to study how living organisms function) that help to forecast local weather and climate conditions (see table 2). The indicators are most useful to the iwi and location they evolved in, but some are shared more widely (King et al, 2005).
See Understanding local weather and climate using Māori environmental knowledge for a more extensive table of indicators.
Observations of greater variability in traditional climate indicators
In a 2005 study by Te Kūwaha o Taihoro Nukurangi, Māori reported greater countrywide variability in climate conditions, including indicators for weather forecasting, for example, earlier tree flowering and increasingly variable and less predictable winds (King et al, 2005). Such variability raises questions about how long these Māori weather and climate indicators will remain reliable in forecasting.
New research that builds on this work is currently underway through the Vision Mātauranga science programme as part of the Deep South National Science Challenge (see Vision Mātauranga).