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2 Projections of future New Zealand climate change

Key points:

  • The best estimates of New Zealand temperatures are for an expected increase of about 1°C by 2040, and 2°C by 2090. However owing to the different emission scenarios and model climate sensitivities, the projections of future warming cover a wide range: 0.2–2.0°C by 2040 and 0.7–5.1°C by 2090.

  • Projected rainfall and wind patterns show a more marked seasonality than was evident in models used in the IPCC Third Assessment, 2001. Westerlies are projected to increase in winter and spring, along with more rainfall in the west of both the North and the South Island and drier conditions in the east and north. Conversely, the models suggest a decreased frequency of westerly conditions in summer and autumn, with drier conditions in the west of the North Island and possible rainfall increases in Gisborne and Hawke’s Bay.

  • Other changes expected are: decreased frost risk, increased frequency of high temperatures, increased frequency of extreme daily rainfalls, decreased seasonal snow cover, and a possible increase in strong winds.

  • Temperature rise is expected to speed up. The rate of temperature increase from these projections is expected to be higher than a linear extrapolation of the historical New Zealand temperature record for the 20th century.

  • Projected New Zealand climate changes are based on results from 12 global climate models, with additional information on extremes and other physical climate elements provided from a regional climate model.

2.1 Introduction

This chapter outlines the changes in New Zealand’s climate that are expected to result from global human-induced emissions of greenhouse gases and aerosols. Most of the projections are based on results from General Circulation Model simulations prepared for the IPCC Fourth Assessment, 20079. Model changes are statistically downscaled10 to provide spatial detail over New Zealand.

Human-induced climate change should be considered within the context of the natural variability of the climate system, and this aspect is discussed in chapter 3. Chapter 5 provides advice on typical changes that local government should take into account when assessing risk. Appendix 2 provides technical details on the General Circulation Models used and the scaling applied to generate future projected ranges that appear in the tables of this chapter. Appendix 3 gives further information on topics such as the downscaling approach, the level of agreement (or otherwise) between the model projections, and changes in extreme precipitation.

Projected values of a particular climate element for use in an impacts assessment are available from Tables 5.1 and 5.2 of chapter 5. Those tables provide guidance on values for use in scenario analyses, and refer users back to particular parts of the current chapter.

Climate is often thought of as only the long-term averages of weather elements, but it actually also includes the range of likely values and the occurrence of extremes. Indeed, it is recognised that the largest impacts of climate change will probably be felt through changes in these extremes. Changes in extremes cannot be reliably derived directly from General Circulation Model outputs, owing to the coarse spatial resolution of the models. However, as illustrated in Box 2.1, small changes in average values (for example, in average annual temperature) can result in large changes in the frequency with which climate extremes occur (for example, for frosts and very high temperatures, and similarly for heavy rainfall, floods and drought). Thus, projections of changes in the average value of a climate element can also help us estimate how the frequency of extremes might change, although this might require additional assumptions about the shape of the distribution. Information on the distribution of daily extremes for New Zealand’s future climate can now be supplemented with simulations by the NIWA regional climate model. This model is currently run at a 30-km grid spacing over New Zealand, which is an improvement in resolution over the typical global model (100- to 300-km spacing). Computational constraints mean that the regional model can presently be run only from a single global model (ukmo_hadcm3, see Appendix 2) and for a limited number of emissions scenarios.

2.1.1 Global climate scenarios

Predictions of future climate depend on projections of future concentrations of greenhouse gases and aerosols. These depend on projections of emissions which, in turn, depend on changes in population, economic growth, technology, energy availability, and national and international policies. The IPCC developed 40 different future emissions pathways or scenarios11 as a basis for projecting future climate changes. These SRES scenarios formed the basis of much of the climate projection work done for the IPCC’s Third and Fourth Assessments.

Figure 2.1 indicates a range of possible future global temperatures, and reflects the range of plausible emissions scenarios and the range of General Circulation Model predictions for given scenarios. The scenario labelled ‘A1B’, which gives an intermediate level of warming by the end of the century, has more General Circulation Model output data available than any other scenario, and is the scenario used to derive most of the projections discussed in this manual. To cover the full spread across all the IPCC emission scenarios, New Zealand projections from the A1B scenario were rescaled using the known differences on the global scale between the A1B and other scenarios (this gives the vertical grey bars in Figure 2.1).

The IPCC made subtle changes between the Third and Fourth Assessment Reports in the way it expressed the climate projections. The Third Assessment Report stated12: “The globally averaged surface temperature is projected to increase by 1.4 to 5.8°C over the period 1990 to 2100.” These results are for the full range of 40 SRES scenarios, based on a number of climate models. In the Fourth Assessment Report, the projections were expressed as changes between 1980–1999 and 2080–2099, and projections were given separately for six illustrative scenarios (see Appendix 2) that spanned the range of all 40 SRES scenarios. For each of the six scenarios, a best estimate was provided, as well as the likely range. The full range in global temperature increase over the six illustrative scenarios used in the Fourth Assessment Report was 1.1–6.4°C.

Figure 2.1: IPCC multi-model temperature projections for selected scenarios. The grey bars to the right show the range in global warming for the scenarios we have used in this manual.

This figure illustrates historic global average temperatures from 1900 to 2000, and from 2000 to 2100 a range of possible future global temperatures, which reflect the range of plausible emissions scenarios and the range of Global Climate Model predictions for given scenarios. 3 SRES scenarios are each represented by a solid lineshowing an increase in temperature to a maximum of 3.6 degrees Celsius.. These are shown as continuations of the 20th century simulations. Coloured shading is included to denote the ± standard deviation range of individual model annual averages.

The full range in global temperature increase over the six illustrative scenarios of the AR4 was 1.1 to 6.4 degrees Celsius expressed as changes between 1980-1999 and 2080-2099.

Note: Solid lines are multi-model global averages of surface warming (relative to 1980–1999) for scenarios B1, A1B and A2, shown as continuations of the 20th century simulations. The coloured shading denotes the ±1 standard deviation range of individual model annual averages. The grey bars at right indicate the best estimate (solid horizontal line within each grey bar) and the ‘likely range’ for all six SRES illustrative scenarios. Source: IPCC 2007a (figure SPM.5).

The SRES scenarios cover the key greenhouse gases (carbon dioxide, methane, nitrous oxide and CFCs) and the sulphate aerosols. They do not account for explicit climate change policy actions to reduce greenhouse gas emissions, such as might be taken under the Kyoto Protocol. However, some scenarios assume a reduction in world population after a mid-century peak, and the rapid and widespread introduction of clean and resource-efficient technologies. The SRES scenarios also do not account for any unexpected climate ‘surprises’, such as increased methane emissions from permafrost melting or undersea methane clathrates.13

Box 2.1: Small changes in average conditions can lead to large changes in the frequency with which extremes occur

Local impacts of climate are likely to depend more on changes in the frequency of extreme events (such as heavy rainfall, drought or very high temperatures) than on changes in average conditions. However, these two aspects of climate – averages and extremes – are closely connected. The figure below is a simplified illustration of how a small change in average conditions can lead to a large change in the frequency with which extremes occur. (In the real world, the curves will not be so smooth or symmetrical.)

Suppose the dashed line represents the current frequency of hourly temperatures over a year, and the heavy line a possible future distribution. The shaded area under a curve represents how often temperatures occur above a particular threshold (orange, red) or below a threshold (blue).

Suppose that in this case the cold area (blue) represents hourly temperatures below freezing, the orange area represents temperatures above 30°C, the red area represents temperatures above 35°C, and the change in mean (average) temperature shown by the arrow is 3°C. So, in this case, an apparently modest change in average temperature is accompanied by a total cessation of frosts, occurrence of higher temperatures than hitherto experienced (red area) and a substantial increased frequency of temperatures above 30°C.

This relationship between averages and extremes has important implications for adaptation (as noted by Warrick 2002). For example, a particular farming operation might already be well adapted to temperatures ranging between –2°C and 30°C, and able to cope occasionally with temperatures between 30°C and 35°C. While the changes in the mean temperature lie well within the ‘autonomous’ (easily coped with) adaptation region, changes into the red area are outside the ‘coping’ region and damage occurs. This example is overly simplistic (in the real world the shape, width and height of the curve might also change), but it serves to illustrate the importance of extremes.

The figure illustrates how two aspects of climate - average and extreme temperatures - are closely connected. The horizontal axis is temperature, and the vertical axis is probability of occurrence.

In this simplified example, normally distributed frequency distribution curves of temperatures for present and future climates display the extremes in the distributions by shading areas as representing portions of the curves that are below freezing and above 30 degrees Celsius.

For a 3 degree Celsius shift in the average temperature, a future climate could expect a total cessation of frosts, and an increased frequency of high and very high temperatures than previously experienced under the current climate.

Figure Box 2.1: Effect of climate change on average and extreme temperatures. The horizontal axis represents temperature (Source: figure 4.1–IPCC Synthesis Report, IPCC 2001b). Note that the horizontal axis is not to scale, and the diagram is illustrative only.

2.1.2 Downscaling to New Zealand

To identify likely future climate changes across New Zealand, projected changes from General Circulation Models are statistically downscaled. This method is used to translate the coarse-scale information available from General Circulation Models to the local scale. Historical observations are used to develop regression equations that relate local climate fluctuations to changes at the larger scale. These historical observations are then replaced in the regression equations by the modelled changes to produce the fine-scale projections (see Appendix 3 for more information). Downscaled changes were prepared for a 0.05 degrees latitude and longitude grid (approximately 5 km by 4 km) covering New Zealand.

The New Zealand downscaled projections follow the approach of the Fourth Assessment Report. That is, changes are relative to 1980–1999, which we abbreviate as ‘1990’ for convenience. Changes are calculated for two future periods: 2030–2049 (‘2040’) and 2080–2099 (‘2090’). Thus, the New Zealand projections are for changes over time periods of 50 and 100 years from the baseline climate (centred on 1990). Figure 2.2 provides a schematic for the time horizons of the climate projections. Also shown in Figure 2.2, for reference, are the averaging periods referred to as the ‘2030s’ (2020–2049 average) and the ‘2080s’ (2070–2099 average) used in the previous edition of this Guidance Manual.

Figure 2.2: Schematic of time horizons for climate projections.

The figure illustrates how the time periods used in this publication and in the previous edition are related to each other. The base year, referred to as 1990, is actually the average of the years 1980 to 1999. The 50-year projections are referred to as being for 2040 but are really the expected average for the period 2030 to 2049 (whereas in the earlier edition they were 45-year projections, for the period 2020 to 2049). The 100-year projections, referred to as being for 2090, are really the expected average for the period 2080 to 2099 (whereas in the earlier edition they were 95-year projections, for the period 2070 to 2099).

Note: Curve (blue line) shows a smoothly varying climate parameter, such as temperature or sea level, relative to a base level defined as the average over 1980–1999 (first horizontal red line; ‘1990’). Future 20-year averages are indicated by the other red lines at 2040 (2030–2049 average) and 2090 (2080–2099). Dotted orange lines show projection horizons used in the previous Guidance Manual (Ministry for the Environment 2004), identified as the ‘2030s’ (2020–2049 average) and the ‘2080s’ (2070–2099 average).

Councils may also be interested in projections for other decades during the 21st century. Initial projections for these non-tabulated decades can be obtained by interpolating linearly between the values for 1990, 2040 and 2090. For example, a projection for 2050 (relative to 1990) would be the change at 2040 plus 20% of the change between 2040 and 2090. Different start dates (eg, council data more recent than 1999) could also be accommodated by linear interpolation, although it is important to use a time average rather than an individual year.

Downscaling is applied to the projections obtained from 12 General Circulation Models when emissions follow the A1B middle-of-the-road emissions scenario (Figure 2.1). A range of possible values for each climate variable (temperature, rainfall, etc) is provided. The range for each variable reflects not only the range of greenhouse gas futures represented by the six SRES illustrative scenarios, but also the range of climate model predictions for individual emission scenarios. The other five SRES emissions scenarios are catered for by re-scaling the A1B results for New Zealand according to the ratio of global temperature increases, as documented in the IPCC Fourth Assessment Report (see Appendix 2 for details).

Like the IPCC, we are unable to indicate whether any one emission scenario is more likely than another, but do provide the average across all models and all emission scenarios. The extreme ends of the ranges may be slightly less likely than the central values, since they generally result from the one climate model that gives the most extreme projection, rather than reflecting the consensus from a number of models. Eliminating the most extreme models as outliers causes little change to the average from the remaining models, but can, on occasion, greatly reduce the range of the projected changes (see Appendix 3).

2.2 Projections for New Zealand

Table 2.1 summarises the main features of these New Zealand climate projections. More detail on the changes is given in the figures and tables later in this chapter. Quantitative estimates of the changes in parameters relevant to local government functions and services, and advice on how to construct relevant scenarios to estimate the importance of those changes, are given in chapter 5 (specifically Tables 5.1 and 5.2).

Each estimate in Table 2.1 is the best current scientific estimate of the direction and magnitude of change a given climate variable could undergo. The degree of confidence placed by NIWA scientists on the projections is indicated by the number of stars in brackets:

**** Very confident, at least 9 out of 10 chance of being correct. Very confident means that it is considered very unlikely that the estimate will be substantially revised as scientific knowledge progresses.

*** Confident.

** Moderate confidence, which means that the estimate is more likely than not to be correct in terms of indicated direction and approximate magnitude of the change.

* Low confidence, but the best estimate possible at present from the most recent information. Such estimates could be revised considerably in the future.

Hence, a higher degree of caution should be employed where investment decisions are based on the low-confidence estimates.

Table 2.1: Main features of New Zealand climate change projections for 2040 and 2090. (**** Very confident, *** Confident, ** Moderate confidence, * Low confidence)

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 (*)

   

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 (*)

   

Sea level

Increase (****)

At least 18–59 cm rise (New Zealand average) between 1990 and 2100 (****) See CoastalHazards 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 CoastalHazards and Climate Change manual (MfE 2008)

 

Storm surge

Assume storm tide elevation will rise at the same rate as mean sea-level rise (**)

See CoastalHazards 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.

The following sections, along with material in Appendix 3, provide more detail on the projected changes summarised in Table 2.1.

2.2.1 Mean temperature

Downscaled projections of the changes in mean temperature14 over New Zealand are shown in Table 2.2 (for 2040) and Table 2.3 (for 2090), and in Figure 2.3 (changes in annual average temperature) and Figures 2.4–2.5 (seasonal changes).

The tables indicate the range not only across the models analysed, but also across the various emissions scenarios. The A1B projections were rescaled by the quoted IPCC global temperature changes to cover the other five illustrative scenarios. The values given in Tables 2.2 and 2.3 are averages over all grid points within each regional council region.

The figures depict the pattern of temperature change as an average over 12 climate models for the A1B emissions scenario15. There is considerable pattern variation among the climate models, so we also present changes in the annual average for each of the 12 models separately (Figures A3.2 and A3.3 in Appendix 3).

Averaging over all models and all six illustrative emissions scenarios gives a New Zealand-average warming of 0.2–2.0°C by 2040 and 0.7–5.1°C by 2090. For just the A1B scenario alone, the projected warming is 0.3–1.4°C by 2040 and 1.1–3.4°C by 2090, with a 12-model average (or ‘best estimate’) of 0.9°C and 2.1°C for 2040 and 2090, respectively. For comparison, the IPCC quotes a best estimate of 2.8°C for the global temperature increase by 2090 under the A1B scenario, with a likely range of 1.7–4.4°C. The projected New Zealand temperature changes are in all cases smaller than the globally averaged changes for the corresponding SRES scenarios (see also Table A2.1 in Appendix 2).

The pattern of warming in the annual average is fairly uniform over the country, although slightly greater over the North Island than the South. Also, the warming accelerates with time under this emissions scenario: ie, the 2090 warming is more than twice the 2040 warming. Figures 2.4 and 2.5 map projected seasonal mean changes at 2040 and 2090 for the A1B scenario. In the summer and autumn seasons, the North Island and northwest of the South Island show the greatest warming, whereas in the winter season the South Island has the greatest warming. Spring shows the least warming of all seasons. Further discussion of agreement between the various models can be found in Appendix 3 (section A3.3 and Figures A3.2 and A3.3).

Table 2.2: Projected changes in seasonal and annual mean temperature (in °C) from 1990 to 2040, by regional council area. The average change, and the lower and upper limits (in brackets), over the six illustrative scenarios are given.

  Summer Autumn Winter Spring Annual

Northland

1.1 [ 0.3, 2.7]

1.0 [ 0.2, 2.9]

0.9 [ 0.1, 2.4]

0.8 [ 0.1, 2.2]

0.9 [ 0.2, 2.6]

Auckland

1.1 [ 0.3, 2.6]

1.0 [ 0.2, 2.8]

0.9 [ 0.2, 2.4]

0.8 [ 0.1, 2.2]

0.9 [ 0.2, 2.5]

Waikato

1.1 [ 0.2, 2.5]

1.0 [ 0.3, 2.7]

0.9 [ 0.2, 2.2]

0.8 [ 0.0, 2.0]

0.9 [ 0.2, 2.4]

Bay of Plenty

1.0 [ 0.3, 2.5]

1.0 [ 0.3, 2.7]

0.9 [ 0.1, 2.2]

0.8 [ 0.0, 2.1]

0.9 [ 0.2, 2.4]

Taranaki

1.1 [ 0.2, 2.4]

1.0 [ 0.2, 2.6]

0.9 [ 0.1, 2.2]

0.8 [ 0.0, 2.0]

0.9 [ 0.2, 2.3]

Manawatu-Wanganui

1.1 [ 0.2, 2.3]

1.0 [ 0.2, 2.6]

0.9 [ 0.2, 2.2]

0.8 [ 0.0, 1.9]

0.9 [ 0.2, 2.2]

Hawke’s Bay

1.0 [ 0.2, 2.5]

1.0 [ 0.3, 2.6]

0.9 [ 0.1, 2.2]

0.8 [ 0.0, 2.0]

0.9 [ 0.2, 2.3]

Gisborne

1.0 [ 0.2, 2.6]

1.0 [ 0.3, 2.7]

0.9 [ 0.1, 2.2]

0.8 [ 0.0, 2.1]

0.9 [ 0.2, 2.4]

Wellington

1.0 [ 0.2, 2.2]

1.0 [ 0.3, 2.5]

0.9 [ 0.2, 2.1]

0.8 [ 0.1, 1.9]

0.9 [ 0.3, 2.2]

Tasman-Nelson

1.0 [ 0.2, 2.2]

1.0 [ 0.2, 2.3]

0.9 [ 0.2, 2.0]

0.7 [ 0.1, 1.8]

0.9 [ 0.2, 2.0]

Marlborough

1.0 [ 0.2, 2.1]

1.0 [ 0.2, 2.4]

0.9 [ 0.2, 2.0]

0.8 [ 0.1, 1.8]

0.9 [ 0.2, 2.1]

West Coast

1.0 [ 0.2, 2.4]

1.0 [ 0.2, 2.1]

0.9 [ 0.2, 1.8]

0.7 [ 0.1, 1.7]

0.9 [ 0.2, 1.8]

Canterbury

0.9 [ 0.1, 2.2]

0.9 [ 0.2, 2.2]

1.0 [ 0.4, 2.0]

0.8 [ 0.2, 1.8]

0.9 [ 0.2, 1.9]

Otago

0.9 [ 0.0, 2.4]

0.9 [ 0.1, 1.9]

1.0 [ 0.3, 2.1]

0.7 [ 0.0, 1.8]

0.9 [ 0.1, 1.9]

Southland

0.9 [ 0.0, 2.4]

0.9 [ 0.1, 1.9]

0.9 [ 0.2, 2.0]

0.7 [-0.1, 1.7]

0.8 [ 0.1, 1.9]

Chatham Islands

0.8 [ 0.2, 1.9]

0.9 [ 0.2, 2.0]

0.9 [ 0.1, 2.3]

0.7 [ 0.1, 1.8]

0.8 [ 0.2, 1.9]

Note 1: This table covers the period from 1990 (1980–1999) to 2040 (2030–2049), based on downscaled temperature changes for 12 global climate models, re-scaled to match the IPCC global warming range for six illustrative emission scenarios (B1, A1T, B2, A1B, A2 and A1FI). Corresponding maps (Figures 2.3, 2.4) should be used to identify sub-regional spatial gradients.

Note 2: If the seasonal ranges are averaged, the resulting range is larger than the range shown in the annual column, because of cancellation effects when summing over the year.

Note 3: Projected changes for the 15 regional council regions were the result of the statistical downscaling over mainland New Zealand. For the Chatham Islands, the scenario changes come from direct interpolation of the General Circulation Model grid-point changes to the latitude and longitude associated with the Chathams.

Table 2.3: Projected changes in seasonal and annual mean temperature (in °C) from 1990 to 2090, by regional council area. The average change, and the lower and upper limits (in brackets), over the six illustrative scenarios are given.

  Summer Autumn Winter Spring Annual

Northland

2.3 [ 0.8, 6.6]

2.1 [ 0.6, 6.0]

2.0 [ 0.5, 5.5]

1.9 [ 0.4, 5.5]

2.1 [ 0.6, 5.9]

Auckland

2.3 [ 0.8, 6.5]

2.1 [ 0.6, 5.9]

2.0 [ 0.5, 5.5]

1.9 [ 0.4, 5.4]

2.1 [ 0.6, 5.8]

Waikato

2.3 [ 0.9, 6.3]

2.2 [ 0.6, 5.6]

2.1 [ 0.5, 5.2]

1.8 [ 0.3, 5.1]

2.1 [ 0.6, 5.6]

Bay of Plenty

2.2 [ 0.8, 6.2]

2.2 [ 0.6, 5.6]

2.0 [ 0.5, 5.2]

1.8 [ 0.3, 5.1]

2.1 [ 0.6, 5.5]

Taranaki

2.3 [ 0.9, 6.1]

2.2 [ 0.6, 5.3]

2.1 [ 0.5, 5.1]

1.8 [ 0.3, 4.9]

2.1 [ 0.6, 5.3]

Manawatu-Wanganui

2.3 [ 0.9, 6.0]

2.2 [ 0.6, 5.3]

2.1 [ 0.5, 5.0]

1.8 [ 0.3, 4.9]

2.1 [ 0.6, 5.3]

Hawke’s Bay

2.1 [ 0.8, 6.0]

2.1 [ 0.6, 5.3]

2.1 [ 0.5, 5.1]

1.9 [ 0.3, 5.1]

2.1 [ 0.6, 5.4]

Gisborne

2.2 [ 0.8, 6.2]

2.2 [ 0.6, 5.6]

2.0 [ 0.5, 5.2]

1.9 [ 0.3, 5.2]

2.1 [ 0.6, 5.5]

Wellington

2.2 [ 0.9, 5.7]

2.1 [ 0.6, 5.1]

2.1 [ 0.6, 5.0]

1.8 [ 0.3, 4.8]

2.1 [ 0.6, 5.2]

Tasman-Nelson

2.2 [ 0.9, 5.6]

2.1 [ 0.6, 5.1]

2.0 [ 0.5, 4.9]

1.7 [ 0.3, 4.6]

2.0 [ 0.6, 5.0]

Marlborough

2.1 [ 0.9, 5.6]

2.1 [ 0.6, 5.0]

2.1 [ 0.6, 5.0]

1.8 [ 0.3, 4.8]

2.0 [ 0.6, 5.1]

West Coast

2.2 [ 0.9, 5.3]

2.1 [ 0.7, 5.0]

2.1 [ 0.6, 4.9]

1.7 [ 0.4, 4.5]

2.0 [ 0.7, 4.9]

Canterbury

2.1 [ 0.8, 5.2]

2.1 [ 0.7, 4.9]

2.2 [ 0.8, 5.1]

1.8 [ 0.4, 4.7]

2.0 [ 0.7, 5.0]

Otago

2.0 [ 0.7, 4.8]

2.0 [ 0.8, 4.6]

2.2 [ 0.8, 4.8]

1.7 [ 0.5, 4.3]

2.0 [ 0.8, 4.6]

Southland

2.0 [ 0.7, 4.7]

2.0 [ 0.8, 4.6]

2.1 [ 0.8, 4.7]

1.6 [ 0.5, 4.1]

1.9 [ 0.8, 4.5]

Chatham Islands

1.9 [ 0.8, 4.6]

2.1 [ 0.6, 4.9]

2.0 [ 0.3, 4.5]

1.8 [ 0.3, 4.6]

2.0 [ 0.5, 4.7]

Note 1: This table covers the period from 1990 (1980–1999) to 2090 (2080–2099), based on downscaled temperature changes for 12 global climate models, re-scaled to match the IPCC global warming range for six illustrative emission scenarios. Corresponding maps (Figures 2.3, 2.5) should be used to identify sub-regional spatial gradients.

Note 2: If the seasonal ranges are averaged, the resulting range is larger than the range shown in the annual column, because of cancellation effects when summing over the year.

Note 3: Projected changes for the 15 regional council regions were the result of the statistical downscaling over mainland New Zealand. For the Chatham Islands, the scenario changes come from direct interpolation of the General Circulation Model grid-point changes to the latitude and longitude associated with the Chathams.

2.2.2 Rainfall patterns

Downscaled rainfall projections are shown in Figure 2.3 (changes in annual average) and Figures 2.6 and 2.7 (seasonal changes), and in Table 2.4 (for 2040) and Table 2.5 (for 2090). Maps of the changes in annual average rainfall given by individual models are presented in Appendix 3.

There are often systematic variations in the projected rainfall within regional council regions (for example, wetter in the west and drier in the east for Canterbury). Thus, it is not very useful to tabulate averages for each region as was done for temperature. Instead, rainfall projections have been tabulated for specific places. Councils may need to carefully examine these regional gradients in rainfall changes, when considering issues related to river levels. For example, in coastal Canterbury, rainfall is projected to decrease, but large alpine-fed rivers could have increased flows because of greater rainfall in the headwaters.

Tables 2.4 and 2.5 give the estimated range in precipitation change over the six illustrative SRES scenarios, for selected sites within each region. The average change over all 12 models and six scenarios is also given. Two sites per region (for Canterbury, three sites) are included in the tables whenever there is a marked spatial variation across a region. Figure 2.2 maps the projected annual mean precipitation change for the A1B scenarios for the period from 1990 to 2040 and 2090. Figures 2.6 and 2.7 show the seasonal projections, again as an average over the 12 models for just the A1B scenario. As might be expected, there is much more spatial structure in the rainfall changes than in the temperature changes, and also a larger spread between models. For most sites, rainfall can show either an increase or a decrease, depending on which model is chosen. Appendix 3 gives further discussion on the level of model agreement.

The annual average rainfall change has a pattern of increases in the west (up to 5% by 2040 and 10% by 2090) and decreases in the east and north (exceeding 5% in places by 2090). Figures 2.6 and 2.7 show that this annual pattern of being wetter in the west and drier in the east is driven by that pattern occurring in the winter and spring seasons. In summer and autumn, the pattern is quite different. Indeed, for the North Island in particular, the pattern is reversed, with it being drier in the west and wetter in the east (although the percentage changes are smaller than for the winter and spring seasons, and winter has the largest total precipitation). These distinct seasonal differences are a new result, not apparent in the smaller sample of models used in the previous edition of this Manual. There is still a lot of variability between models, although some regions show more agreement between models than others on the sign of the projected precipitation change (see Appendix 3 for further discussion).

Figure 2.3: Projected changes in annual mean temperature (in °C) and in annual mean rainfall (in %), relative to 1990: average over 12 climate models for A1B emission scenario. Note the different temperature scales for 2040 and 2090.

This figure shows four maps of New Zealand, giving projected changes over New Zealand in annual mean temperatures in degrees Celsius and in precipitation in percent relative to 1990 for 2040 and 2090 from the twelve-model averages.

For 2040 the projected changes in mean annual temperature for New Zealand range from 0.8 degrees (South-Westland and Stewart Island) to 1.0 degrees (Canterbury-Kaikoura and most of the North Island). For 2090 the projected changes in temperature range from 1.8 degrees (Stewart Island) to 2.2 degrees (most of the north of the South Island, and most of the North Island).

For 2040 the projected changes in mean annual precipitation for New Zealand range from an increase of 7.5 percent (West Coast of the South Island) to a decrease of 5 percent (along a thin coastal strip from Kaikoura north to East Cape, and in Northland). For 2090 the projected changes in precipitation range from an increase of over 10 percent (West Coast of the South Island) to a decrease of 7.5 percent (in patches along the coastal strip from Kaikoura north to East Cape, and in Northland).

Figure 2.4: Projected changes in seasonal mean temperature (in °C), for 2040 relative to 1990: average over 12 climate models for A1B emission scenario.

This figure shows four seasonal maps of projected changes in mean temperature (in degrees Celsius) over New Zealand for 2040 relative to 1990 (twelve model average) for the A1B scenario.

For summer, Stewart Island and Southland show an increase in seasonal mean temperature of up to 0.85 degrees, with greater increases of up to 1.1 degrees projected for the north-west of the South Island.  Much of the North Island is also expected to show increases of up to 1.1 degrees.  Increases over 1.1 degrees are expected for Waikato and northern Taranaki.

For autumn, a similar distribution of temperature increases to summer is shown but with a lower maximum of around 1.05 degrees.

For winter, increases in seasonal mean temperature of 0.8 to 1.0 degrees are expected over much of the country with the maximum changes, of over 1.1 degrees, in the Southern Alps.

For spring, seasonal mean temperature is projected to increase in the North Island, north of the South Island and Canterbury by 0.75 to 0.85 degrees. The rest of South Island is expected to increase by up to 0.75 degrees.

Figure 2.5: Projected changes in seasonal mean temperature (in °C), for 2090 relative to 1990: average over 12 climate models for A1B emission scenario.

This figure shows four seasonal maps of projected changes in seasonal mean temperature (in degrees Celsius) over New Zealand for 2090 relative to 1990 (twelve model average) for the A1B scenario.

For summer, Stewart Island shows a 1.8-1.9 degree increase in seasonal mean temperature, increasing to up to 2.4 degrees in the north-west of the South Island. In the North Island, an increase of up to 2.2 degrees along the east coast from the Wairarapa to East Cape is shown, with over 2.3 degrees west of the ranges and over 2.4 degrees in Waikato-King Country.

For autumn, the map shows an increase in seasonal mean temperature of up to 2 degrees in Stewart Island, with greater increases of up to 2.3 degrees as we head towards north-west of the South Island. Increases of 2.1 to 2.3 degrees are expected over the North Island.

For winter, seasonal mean temperature is expected to increase by 1.8 to 2.3 degrees over much of the country with the maximum changes, of over 2.4 degrees, in the Southern Alps.

For spring, seasonal mean temperature is expected to increase in the North Island, north of the South Island and Canterbury by 1.8 to 2.0 degrees. In the  rest of the South Island increases of up to 1.8 degrees are projected, with up to 1.7 degrees expected for South-Westland.

Figure 2.6: Projected changes in seasonal mean rainfall (in %), for 2040 relative to 1990: average over 12 climate models for A1B emission scenario.

This figure shows four seasonal maps of projected changes in seasonal mean rainfall (in percentage) over New Zealand for 2040 relative to 1990 (twelve model average) for the A1B scenario.

For summer, increases in seasonal mean rainfall of 2.5 to 5 percent are projected for the eastern North Island from East Cape down through the Wairarapa and for patches down the east coast of the South Island. Increases of up to 7.5 percent are expected for the Hawkes Bay and Gisborne. Slight decreases are projected in the west of the North Island, north-west of the South Island, and parts of Southland. Little change is seen elsewhere.

For autumn, increases in seasonal mean rainfall of 2.5 to 5 percent are projected for most places, with slight increases of 0 to 2.5 percent in Southland and Northland, Auckland and Waikato.

For winter, marked increases in seasonal mean rainfall are expected in the West with Southland and the West Coast increasing by over 10 percent, and Kapiti and Taranaki increasing by 5 to 7.5 percent. Decreases are projected in the east, with Canterbury and Hawkes Bay decreasing by more than -7.5 percent, Northland decreasing around -5 percent, and Bay of Plenty decreasing between 0 to -2.5 percent.

For spring, significant increases in seasonal mean rainfall are projected in the West with Southland and the West Coast increasing by 5 to 7.5 percent, and Kapiti and Taranaki increasing by 0 to 2.5 percent. Decreases are expected in the east, with Canterbury decreasing by 0 to -2.5 percent, Northland decreasing by around -5 percent, the Bay of Plenty decreasing by -5 to -7.5 percent, and Hawkes Bay decreasing more than -7.5 percent.

Figure 2.7: Projected changes in seasonal mean rainfall (in %), for 2090 relative to 1990: average over 12 climate models for A1B emission scenario.

This figure shows four seasonal maps of projected changes in seasonal mean rainfall (in percentage) over New Zealand for 2090 relative to 1990 (twelve model average) for the A1B scenario.

For summer, the map shows increases in seasonal mean rainfall of up 10 percent in Hawkes Bay and parts of the East Cape. Smaller increases of up to 7.5 percent are projected in most parts of Marlborough and Canterbury, the Wairarapa and southern Bay of Plenty. Decreases of up to -5 percent are shown in the east of the North Island and Kapiti region, the northern West Coast and parts of Southland. Smaller decreases over Stewart Island, the Waikato Region and south Westland are projected.

For autumn, increases of up to 7.5 percent in seasonal mean rainfall are projected for Marlborough, Canterbury, Otago, Westland, Western Bay of Plenty, and from East Cape down through Hawkes Bay and the Wairarapa. Decreases of up to -5 percent are shown for Northland, Waikato, Wanganui,  most of the central North Island and the region around the northern end of the Southern Alps.

For winter, marked increases in seasonal mean rainfall are projected, particularly in the west, with the West Coast of the South Island, Southland, parts of Taranaki, Manawatu and the Waikato increasing by over 10 percent. Decreases in the east of up to -7.5 percent in Northland and from East Cape down through Hawkes Bay and the Wairarapa are expected, as well as down the east coast of the South Island as far as Canterbury. Smaller decreases in the Bay of Plenty and parts of the Waikato are shown.

For spring, marked increases in seasonal mean rainfall of over 10 percent are projected for the West Coast of the South Island and Southland. Smaller increases of up to 5 percent are expected for Otago, the north-west of the South Island and most of Taranaki and the Manawatu. Marked decreases of more than -7.5 percent are shown in Northland, Auckland, Coromandel, East Cape, Hawkes Bay and parts of the Wairarapa. Smaller decreases in the central North Island and Marlborough/Canterbury regions are expected.

Table 2.4: Projected changes for selected stations within each regional council area in seasonal and annual precipitation (in %) from 1990 to 2040. Lower and upper limits are shown in brackets.

Region: Location

Summer

Autumn

Winter

Spring

Annual

Northland: Kaitaia
Whangarei

1 [–15, 20]

–0 [-14, 16]

–5 [–23, 1]

–6 [–18, 4]

–3 [–13, 5]

1 [–14, 23]

1 [–15, 33]

–9 [–38, –1]

–9 [–25, 3]

–4 [–16, 7]

Auckland: Warkworth
Mangere

1 [–16, 20]

1 [–13, 22]

–4 [–22, 2]

–6 [–18, 6]

–3 [–13, 5]

1 [–17, 20]

1 [–14, 17]

–1 [–10, 5]

–5 [–15, 10]

–1 [–10, 6]

Waikato: Ruakura
Taupo

1 [–18, 19]

2 [–13, 10]

1 [ –4, 8]

–2 [–10, 13]

0 [ –6, 6]

3 [–16, 28]

3 [ –9, 16]

1 [ –4, 7]

–3 [–10, 12]

1 [ –5, 8]

Bay of Plenty: Tauranga

2 [–16, 25]

3 [–12, 25]

–4 [–16, 2]

–5 [–18, 7]

–1 [–10, 8]

Taranaki: New Plymouth

0 [–20, 18]

3 [ –8, 13]

2 [ –2, 9]

0 [ –8, 16]

2 [ –3, 9]

Manawatu-Wanganui: Wanganui
Taumarunui

–1 [–21, 13]

3 [ –8, 10]

5 [ –3, 15]

1 [–10, 15]

2 [ –3, 10]

0 [–19, 19]

2 [–10, 13]

7 [ 0, 17]

2 [–12, 19]

3 [ 0, 13]

Hawke’s Bay: Napier

4 [–33, 38]

5 [–14, 42]

–13 [–34, –1]

–7 [–17, 3]

–3 [–14, 14]

Gisborne: Gisborne

3 [–26, 33]

4 [–18, 46]

–11 [–30, –2]

–9 [–21, 3]

–4 [–15, 14]

Wellington: Masterton
Paraparaumu

2 [–17, 25]

4 [ –8, 32]

–6 [–20, 4]

–1 [ –8, 10]

–1 [ –7, 9]

0 [–21, 13]

4 [ –3, 14]

4 [ –1, 13]

2 [ –5, 14]

2 [ –3, 10]

Tasman-Nelson: Nelson

4 [–14, 27]

5 [ –2, 19]

1 [ –4, 9]

0 [ –8, 9]

2 [ –3, 9]

Marlborough: Blenheim

3 [–16, 25]

4 [ –4, 24]

–1 [–10, 7]

–1 [ –7, 10]

1 [ –5, 9]

West Coast: Hokitika

0 [–22, 19]

3 [–11, 18]

11 [ 1, 24]

5 [ –1, 18]

5 [ –2, 20]

Canterbury: Christchurch
Hanmer
Tekapo

2 [–15, 22]

5 [–10, 30]

–8 [–30, 7]

–1 [ –8, 9]

–1 [–10, 9]

2 [–16, 25]

4 [ –5, 19]

–7 [–26, 6]

0 [ –6, 12]

–1 [ –8, 7]

1 [–16, 16]

2 [–12, 10]

8 [ –1, 19]

6 [ –3, 17]

4 [ 0, 13]

Otago: Dunedin
Queenstown

1 [–11, 13]

2 [ –9, 10]

3 [–10, 13]

2 [ –5, 11]

2 [ –4, 9]

1 [–16, 20]

2 [–15, 23]

16 [ 2, 38]

8 [ –3, 21]

7 [ 1, 22]

Southland: Invercargill

–1 [–15, 22]

2 [–17, 22]

10 [ 2, 30]

7 [ –3, 22]

4 [ –2, 19]

Chatham Islands

–2 [–10, 10]

4 [ –7, 29]

4 [–10, 43]

3 [ –8, 19]

3 [ –5, 23]

Note 1: This table covers the period from 1990 (1980–1999) to 2040 (2030–2049), based on downscaled precipitation changes for 12 global climate models, re-scaled to match the IPCC global warming range for six indicative emission scenarios. Corresponding maps (Figures 2.3, 2.6) should be used to identify sub-regional spatial gradients.

Note 2: If the seasonal ranges are averaged, the resulting range is larger than the range shown in the annual column, because of cancellation effects when summing over the year.

Note 3: Projected changes for the 15 regional council regions were the result of the statistical downscaling over mainland New Zealand. For the Chatham Islands, the scenario changes come from direct interpolation of the General Circulation Model grid-point changes to the latitude and longitude associated with the Chathams. 

Table 2.5: Projected changes for selected stations within each regional council area in seasonal and annual precipitation (in %) from 1990 to 2090. Lower and upper limits are shown in brackets.

Region: Location

Summer

Autumn

Winter

Spring

Annual

Northland: Kaitaia
Whangarei

–1 [–26, 21]

–3 [–22, 11]

–8 [–32, 2]

–11 [–33, 8]

–6 [–22, 5]

0 [–20, 19]

1 [–27, 26]

–12 [–45, –0]

–16 [–45, 1]

–7 [–28, 2]

Auckland: Warkworth
Mangere

–2 [–31, 20]

–1 [–20, 12]

–4 [–24, 5]

–12 [–33, 6]

–5 [–19, 6]

–1 [–33, 20]

–2 [–21, 12]

–1 [–12, 9]

–9 [–30, 11]

–3 [–13, 9]

Waikato: Ruakura
Taupo

–1 [–34, 18]

–1 [–24, 10]

3 [ –7, 15]

–4 [–23, 16]

–1 [–11, 11]

4 [–19, 30]

1 [–16, 9]

3 [ –8, 15]

–5 [–23, 13]

1 [ –7, 10]

Bay of Plenty: Tauranga

2 [–20, 23]

2 [–15, 16]

–3 [–16, 8]

–9 [–32, 12]

–2 [–12, 5]

Taranaki: New Plymouth

–2 [–38, 15]

1 [–18, 15]

6 [ –6, 20]

–1 [–17, 21]

1 [–10, 11]

Manawatu-Wanganui: Wanganui
Taumarunui

–3 [–42, 12]

–1 [–20, 12]

8 [–5, 25]

–0 [–16, 23]

1 [–11, 11]

–1 [–36, 18]

–2 [–25, 12]

13 [ 1, 36]

1 [–16, 26]

3 [ –7, 15]

Hawke’s Bay: Napier

9 [–46, 52]

5 [–14, 25]

–16 [–45, –1]

–13 [–38, 9]

–4 [–20, 11]

Gisborne: Gisborne

5 [–38, 41]

4 [–25, 27]

–13 [–41, 1]

–16 [–42, 7]

–5 [–22, 8]

Wellington: Masterton
Paraparaumu

4 [–28, 32]

3 [ –7, 13]

–7 [–28, 2]

–4 [–20, 16]

–2 [–15, 7]

–1 [–38, 16]

2 [–12, 14]

9 [ 0, 26]

2 [–15, 26]

3 [ –7, 14]

Tasman-Nelson: Nelson

6 [–13, 30]

5 [ –4, 18]

6 [ –2, 19]

–1 [–20, 19]

4 [ –3, 14]

Marlborough: Blenheim

5 [–15, 28]

5 [ –5, 16]

1 [–14, 9]

–1 [–18, 20]

2 [ –7, 13]

West Coast: Hokitika

–1 [–44, 32]

3 [–28, 26]

21 [ 5, 52]

8 [–11, 46]

8 [ –5, 31]

Canterbury: Christchurch
Hanmer
Tekapo

3 [–17, 25]

6 [ –6, 20]

–11 [–41, 10]

–2 [–15, 25]

–2 [–14, 16]

4 [–25, 32]

3 [ –7, 15]

–10 [–34, 6]

–1 [–13, 29]

–2 [–14, 15]

2 [–30, 31]

0 [–16, 17]

18 [ 5, 41]

10 [ –6, 47]

8 [ 0, 29]

Otago: Dunedin
Queenstown

0 [–29, 19]

2 [–11, 16]

7 [–16, 24]

6 [ –1, 32]

4 [ –9, 23]

1 [–38, 37]

2 [–32, 20]

29 [ 7, 76]

15 [ –5, 50]

12 [ –2, 34]

Southland: Invercargill

–2 [–44, 27]

2 [–31, 19]

18 [ 1, 51]

13 [ 0, 47]

7 [–12, 29]

Chatham Islands

–3 [–20, 16]

4 [–14, 29]

8 [–16, 67]

6 [–14, 45]

4 [–11, 35]

Note 1: This table covers the period from 1990 (1980–1999) to 2090 (2080–2099), based on downscaled precipitation changes for 12 global climate models, re-scaled to match the IPCC global warming range for 6 indicative emission scenarios. Corresponding maps (Figures 2.3 and 2.7) should be used to identify sub-regional spatial gradients.

Note 2: If the seasonal ranges are averaged, the resulting range is larger than the range shown in the annual column, because of cancellation effects when summing over the year.

Note 3: Projected changes for the 15 regional council regions were the result of the statistical downscaling over mainland New Zealand. For the Chatham Islands, the scenario changes come from direct interpolation of the General Circulation Model grid-point changes to the latitude and longitude associated with the Chathams.


9  Meehl et al 2007.

10  Mullan et al 2001a.

11 IPCC Special Report on Emissions Scenarios: Nakicenovic and Swart 2000. See also Appendix 1.

12  IPCC 2001a.

13 Clathrates, also called ‘gas hydrates’, are crystalline solids that look like ice, and that occur when water molecules form a cage-like structure around smaller ‘guest molecules’ such as methane. Clathrates occur naturally in cold environments, such as the deep ocean.

14  ‘Mean’ temperature is the average of daily minimum and maximum temperatures. Simulations by NIWA’s regional climate model suggest that minimum and maximum temperatures both increase at very nearly the same rate, and so no distinction between them is made for New Zealand temperatures.

15  Note that in this 2008 edition of the Guidance Manual, the maps are specific to a single SRES emissions scenario (A1B), unlike in the previous edition where changes were scaled to cover all SRES scenarios. However, the Tables (2.2 and 2.3) do incorporate the full range of projected changes.