Table 2.1: Main features of New Zealand climate change projections for 2040 and 2090
(**** Very confident, *** Confident, ** Moderate confidence, * Low confidence)
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| Climate variable | Direction of change | Magnitude of change | Spatial and seasonal variation |
|---|---|---|---|
Mean temperature |
Increase (****) |
All-scenario average 0.9°C by 2040, 2.1°C by 2090 (**) |
Least warming in spring (*) |
Daily temperature extremes (frosts, hot days) |
Fewer cold temperatures and frosts (****), more high temperature episodes (****) |
Whole frequency distribution moves right (see section 2.2.3) |
See section 2.2.3 |
Mean rainfall |
Varies around country, and with season. Increases in annual mean expected for Tasman, West Coast, Otago, Southland and Chathams; decreases in annual mean in Northland, Auckland, Gisborne and Hawke’s Bay (**) |
Substantial variation around the country and with season (see section 2.2.2) |
Tendency to increase in south and west in the winter and spring (**). Tendency to decrease in the western North Island, and increase in Gisborne and Hawke’s Bay, in summer and autumn (*) |
Extreme rainfall |
Heavier and/or more frequent extreme rainfalls (**), especially where mean rainfall increase predicted (***) |
No change through to halving of heavy rainfall return period by 2040; no change through to fourfold reduction in return period by 2090 (**) [See note 2] |
Increases in heavy rainfall most likely in areas where mean rainfall is projected to increase (***) |
Snow |
Shortened duration of seasonal snow lying (***), rise in snowline (**), decrease in snowfall events (*) |
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Glaciers |
Continuing long-term reduction in ice volume and glacier length (***) |
Reductions delayed for glaciers exposed to increasing westerlies |
|
Wind (average) |
Increase in the annual mean westerly component of windflow across New Zealand (**) |
About a 10% increase in annual mean westerly component of flow by 2040 and beyond (*) |
By 2090, increased mean westerly in winter (> 50%) and spring (20%), and decreased westerly in summer and autumn (20%) (*) |
Strong winds |
Increase in severe wind risk possible (**) |
Up to a 10% increase in strong winds (> 10m/s, top 1 percentile) by 2090 (*) |
|
Storms |
More storminess possible, but little information available for New Zealand (*) |
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Sea level |
Increase (****) |
At least 18–59 cm rise (New Zealand average) between 1990 and 2100 (****) See Coastal Hazards and Climate Change manual (MfE 2008) |
See Coastal Hazards and Climate Change manual (MfE 2008) |
Waves |
Increased frequency of heavy swells in regions exposed to prevailing westerlies (**) |
See Coastal Hazards and Climate Change manual (MfE 2008) |
|
Storm surge |
Assume storm tide elevation will rise at the same rate as mean sea-level rise (**) |
See Coastal Hazards and Climate Change manual (MfE 2008) |
|
Ocean currents |
Various changes plausible, but little research or modelling yet done |
See section 2.2.9 |
|
Ocean temperature |
Increase (****) |
Similar to increases in mean air temperature |
Patterns close to the coast will be affected by winds and upwelling and ocean current changes (**) |
Note 1: Further guidance on values suggested for preliminary scenario analyses of potential climate change effects is provided in Table 5.1.
Note 2: Changes in the return period of heavy rainfall events may vary between different parts of the country, and will also depend on the rainfall duration being considered. See section 2.2.4 for further discussion.
