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Projections of New Zealand's Climate

The Ministry for the Environment and the National Institute for Water and Atmosphere (Niwa) have published projections for New Zealand climate to 2120, addressing expected changes to New Zealand’s climate under different scenarios. It draws heavily on climate model simulations from the Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report.

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The following is an unedited copy from the executive summary of the Projections report

Projected overall changes for New Zealand are similar to those from the previous assessment published in 2008.

The mid-range estimate for projected New Zealand temperature change is for an expected increase are listed. The possible range is given in brackets.

  • 0.8°C (0.2-1.7°C) by 2040,
  • 1.4°C (0.1–4.6°C) by 2090, and
  • 1.6°C (0.3–5.0°C) by 2110, relative to the 1986–2005 period.

Projected changes in rainfall show a marked seasonality and variability across regions. It is very likely that for winter and spring there will be an increase in rainfall for the west of both the North and South Islands, with drier conditions in the east and north.

This is a robust prediction both in 2040 and 2090, caused by the westerly winds over New Zealand increasing during these seasons. For summer it is likely that there will be wetter conditions in the east of both islands, with drier conditions in the west and central North Island.

This table is a copy of table 1- "Main features of New Zealand climate change projections" from the summary section of the projections report. 

Climate variable
Direction of change
Magnitude of change
Spatial and seasonal variation
Mean temperature
Progressive increase with concentration.
Only for RCP2.6 does warming trend peak and then decline.
By 2040, from +0.7°C [RCP2.6] to +1.0°C [RCP8.5].
By 2090, +0.7°C to +3.0°C.
By 2110, +0.7°C to +3.7°C.
Warming greatest at higher elevations. Warming greatest summer/autumn and least winter/spring.
Minimum and maximum temperatures
As mean temperature.
Maximum increases faster than minimum. Diurnal range increases by up to 2°C by 2090 (RCP8.5).
Higher elevation warming particularly marked for maximum temperature.
Daily temperature extremes: frosts
Decrease in cold nights (minimum temperature of 0°C or lower).
By 2040, a 30% [2.6] to 50% [8.5] decrease.
By 2090, 30% [2.6] to 90% [8.5] decrease.
Percentage changes similar in different locations, but number of days of frost decrease (hot day increase) greatest in the coldest (hottest) regions.
Daily temperature extremes: hot days
Increase in hot days (maximum temperature of 25°C or higher).
By 2040, a 40% [2.6] to 100% [8.5] increase.
By 2090, a 40% [2.6] to 300% [8.5] increase.
Mean precipitation
Varies around the country and with season. Annual pattern of increases in west and south of New Zealand, and decreases in north and east.
Substantial variation around the country.
increasing in magnitude with increasing emissions.
Winter decreases: Waikato, Gisborne, Hawke’s Bay and Canterbury.
Winter increases: Nelson, West Coast, Otago and Southland.
Spring decreases: Auckland, Northland and Bay of Plenty.
Daily precipitation extremes: dry days
More dry days throughout North Island, and in inland South Island.
By 2090 [8.5], up to 10 or more dry days per year (~5% increase).
Increased dry days most marked in north and east of North Island, in winter and spring.
Daily precipitation extremes: very wet days
Increased extreme daily rainfalls, especially where mean rainfall increases.
More than 20% increase in 99th percentile of daily rainfall by 2090 [8.5] in South West of South Island. A few percentage decrease in north and east of North Island.
Increase in western regions, and in south of South Island. Decrease in extremes in parts of north and east of North Island.
Snow
Decrease.
Snow days per year reduce by 30 days or more by 2090 under RCP8.5.
Large decreases confined to high altitude or southern regions of the South Island.
Drought
Increase in severity and frequency.
By 2090 [8.5], up to 50mm or more increase per year, on average, in July–June PED.
Increases most marked in already dry areas.
Circulation
Varies with season.
Generally, the changes are only a few hectopascals, but the spatial pattern matters.
More northeast airflow in summer. Strengthened westerly's in winter.
Extreme wind speeds
Increase.
Up to 10% or more in parts of the country.
Most robust increases occur in southern half of North Island, and throughout the South Island.
Storms
Likely poleward shift of mid-latitude cyclones and possibly also a small reduction in frequency.
More analysis needed.
 
Solar radiation
Varies around the country and with season.
Seasonal changes generally lie between -5% and +5%.
By 2090 [8.5], West Coast shows the largest changes: summer increase (~5%) and winter decrease (5%).
Relative humidity
Decrease.
Up to 5% or more by 2090 [8.5], especially in the South Island.
Largest decreases in South Island in spring and summer.

  

Climate extremes

This is a brief summary from the sections in the 2016 projections report that address climate extremes.

As seasonal mean temperature increases, so the an increase in high temperatures (day 25°C) extremes is expected. Similarly low temperature extremes (nights 0°C) are expected to decrease. 

Hot days increase and cold days decrease everywhere.

By 2090 under RCP8.5, Southland is projected to have as many hot days as Northland does in the current climate (about 24 per year). The change in cold days is a decrease of about 50% (2090, RCP 2.6) to between a 70-80% reduction in the South Island (2090, RCP 8.5).

Extreme rainfall is likely to increase in most areas, with the largest increases being seen in areas where mean rainfall is also increasing, such as the West Coast.

Drought severity is projected to increase in most areas of the country, except for Taranaki-Manawatu, West Coast and Southland. Although these last two findings on extremes are not new, they are more robust because of more detailed regional information compared to the 2008 assessment, made possible through the inclusion of the latest regional climate modelling results.

What are extremes

Extreme events are the initial and consequential physical phenomena of a weather or climate event. 

Climate variables, such as temperature, have distributions based on the frequency or probabilities of occurrence. Extreme events are have a lower probability of occurrence. Extreme events matter as small changes on the mean of a climate parameter, such as a 2​°C mean temperature increase, can result in increased probabilities of occurrence at the extremes of the distribution. This is best expressed in the figure below from SREX (p. 41).

Implicit in managing extreme events is the presumption that extreme events are proportionally more damaging that normal weather events, so even a small increase in occurrence can significantly negatively impact businesses, people and communities.

Where simultaneous extreme occurrences occur with more than one climate variable then the impacts can be magnified, e.g. increased extreme rainfall with extreme winds causing land slips.

 

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