The outlook for Canterbury – New Zealand climate solutions

How will climate change affect us?

(Image: Sonny Whitelaw)

Canterbury’s changing climate

Preface

Information on this page is primarily taken from these two reports (PDFs):

- National Risk Assessment ‘NCCRA’ (MfE, August 2020)
- Climate change projections Canterbury (NIWA, Feb. 2020)

These projections on this page use 2013/2014 IPCC Assessment Report scenarios. The ‘outlook’ maps are limited to RCP8.5 (worst case scenario) because: “Stage 1 of this NCCRA used projections based on RCP8.5, a high greenhouse gas emissions scenario. This is assumed to be a plausible upper level of risk. It supports the identification of the most significant climate-related risks, analysed in Stage 2 of the assessment.” (page 36) …and because real-world events are outpacing several projections, which in turn has prompted this disclaimer: “More extreme scenarios are possible, and the sensitivity of the climate system remains uncertain.” (op cit)

It is strongly recommended that the snapshots below are read in the context in which the above reports are written, particularly in light of climate tipping points now being breached.

The current and future climate of the Canterbury region

“All aspects of the climate of Canterbury are dominated by the influence of the Southern Alps on the prevailing westerly airflows. These prevailing westerlies result in a steep precipitation gradient eastward from the western ranges. Five main climate zones can be distinguished in Canterbury:

The plains, with prevailing winds from the north-east and south-west, low rainfall, and a relatively large annual temperature range by New Zealand standards.
The eastern foothills and southern Kaikoura Ranges, with cooler and wetter weather, and a high frequency of north-west winds.
The high country near the main divide, with prevailing north-west winds, abundant precipitation, winter snow and some glaciers particularly towards the south.
Banks Peninsula and the coastal strip north of Amberley, with relatively mild winters, and rather high annual rainfall with a winter maximum.
The inland basins and some sheltered valleys, where rainfall is low with a summer maximum, and diurnal and annual temperature ranges are large.

Although north-west winds are not frequent on the plains they are an important consideration, due to the exceptional evaporation that occurs on north-westerly days. Irrigation is necessary in most parts of the plains during the growing season due to the relatively low rainfall received there.”– NIWA

Fig. 1: Canterbury’s main rivers (Image: BRaid).

Warmer oceans around New Zealand means there’s more water vapour over the water. Warmer air carries more moisture so winds are able to pick up more moisture as they cross the Tasman, leading to more precipitation (rain, hail, snow) reaching the West Coast and parts of Southland.

This increases the risks of flooding from rivers that originate in the Southern Alps. However, rivers that begin life in the foothills to the east of the main divide, will likely have less rain and dry out more often and for longer periods. (Fig. 1 Canterbury’s main rivers, Figs. 4, 5 & 6).

Stronger dryer nor’westerlies combined with higher air temperatures (Fig. 2; current average and Fig. 3 projected under RCP8.5.) leads to a greater number of dry days (Fig. 7), less snow (Fig. 10), and greater evapotranspiration (Fig. 11), compounding the effect of more frequent and intense droughts.

The risk of forest fires, especially in plantation forests and areas where wetlands have been removed (most of Canterbury) and the natural hydrology of braided rivers has been destroyed or confined (virtually all Canterbury rivers), is also increasing.

As heat and moisture are key drivers of weather, by continuing to add greenhouse gasses into the atmosphere, we are increasing the risk of more frequent and more powerful extreme weather events including destructive hailstorms, more powerful windstorms and tornadoes, and more frequent and intense flooding both, rivers and from rainfall and on the coast, rising sea levels.

Average current temperatures

Fig. 2: Modelled annual mean temperature average 1986-2005. Results are based on dynamical downscaled projections using NIWA’s Regional Climate Model. Resolution of projection is 5km x 5km. (Image: NIWA)

Projected temperature increases

Fig. 3: Projected annual mean temperature changes under an RCP8.5 climate change scenario. Time periods: 2031- 2050 (left) and 2081-2100 (right). Changes are relative to 1986-2005 average (Fig. 2), based on the average of six global climate models. Results are based on dynamical downscaled projections using NIWA’s Regional Climate Model. Resolution of projection is 5km x 5km. (Image: NIWA)

Current mean rainfall

Fig. 4: Modelled annual mean rainfall average 1986-2005. Results are based on dynamical downscaled projections using NIWA’s Regional Climate Model. Resolution of projection is 5km x 5km. (Image: NIWA)

Current mean number of dry days

Fig. 5: Modelled annual number of dry days average 1986-2005. Results are based on dynamical downscaled projections using NIWA’s Regional Climate Model. Resolution of projection is 5km x 5km. (Image: NIWA)

Projected changes to rainfall

Fig. 6: Projected annual mean rainfall changes under RCP8.5 climate change scenarios. Time periods: 2031-2050 (left) and 2081-2100 (right). Changes are relative to 1986-2005 average (Fig. 4) based on the average of six global climate models. Results are based on dynamical downscaled projections using NIWA’s Regional Climate Model. Resolution of projection is 5km x 5km. (Image: NIWA)

Projected changes in the number of dry days

Fig. 7: Projected annual mean number of dry days under RCP8.5 climate change scenarios. Time periods: 2031-2050 (left) and 2081-2100 (right). Changes are relative to 1986-2005 average (Fig. 5) based on the average of six global climate models. Results are based on dynamical downscaled projections using NIWA’s Regional Climate Model. Resolution of projection is 5km x 5km. (Image: NIWA)

Current mean number of snow days

Fig. 8: Modelled annual mean snow days 1986-2005. Results are based on dynamical downscaled projections using NIWA’s Regional Climate Model. Resolution of projection is 5km x 5km. (Image: NIWA)

Current mean evapotranspiration

Fig. 9: Modelled evapotranspiration deficit accumulation (mm) average1986-2005. Results are based on dynamical downscaled projections using NIWA’s Regional Climate Model. Resolution of projection is 5km x 5km. (Image: NIWA)

Projected changes in the number of snow days

Fig.10: Projected mean number of snow days under RCP8.5 climate change scenarios. Time periods: 2031-2050 (left) and 2081-2100 (right). Changes are relative to 1986-2005 average (Fig. 8) based on the average of six global climate models. Results are based on dynamical downscaled projections using NIWA’s Regional Climate Model. Resolution of projection is 5km x 5km. (Image: NIWA)

Projected evapotranspiration deficit accumulation

Fig.11: Projected annual potential evapotranspiration deficit (PED) accumulation changes under RCP8.5 climate change scenarios. Time periods: 2031-2050 (left) and 2081-2100 (right). Changes are relative to 1986-2005 average (Fig. 9) and should be added to those baseline figures to get the final projected figure. The figures in this and all graphs are based on the average of six global climate models. Results are based on dynamical downscaled projections using NIWA’s Regional Climate Model. Resolution of projection is 5km x 5km. (Image: NIWA)

Explainers

Representative Concentration Pathways (RCPs):

The represent the concentration of greenhouse gasses in the atmosphere based on how these gasses retain heat.

Heat is measured in watts per metre squared, written as W⋅m⁻²
In most graphs and models, the numbers 2.6, 4.5, 6.0, and 8.5 are W⋅m⁻². However, the term ‘W⋅m⁻²‘ is implied, and the four units are written instead as four scenarios that will likely result if that much heat is in the atmosphere: RCP2.6 being the lowest amount of heat and RCP8.5 being the most. Hence, the ‘RCP8.5’ scenario is the ‘worst case’ scenario.
In some graphs and reports (not on this website), the numbers are written without a decimal place: RCP26, RCP85 etc.
These scenarios are based on models for the 2013 IPCC Fifth Assessment Report. They were developed in the years leading up to this report, so the data is at least 7 years old. Limitations and shortcomings are outlined here (this website).
More recent research and real-world observations indicate that the RCP8.5 scenario may be conservative.
Improved earth systems climate modelling is now underway that will help inform the IPCC Sixth Assessment Report due in 2022.

References and further reading

IPCC Sixth Assessment Reporting (AR6)
Ministry for the Environment: First national climate change risk assessment for New Zealand
NIWA/ECan : Climate change projections for Canterbury
NIWA: Climate change for students
Deep South Science Challenge (NZ): Will your property become uninsurable?
Deep South Science Challenge (NZ): Planning for coastal adaptation
Deep South Science Challenge (NZ): Extreme weather, climate change & the EQC
Deep South Science Challenge (NZ): How should the risks be shared?
Deep South Science Challenge (NZ): Earth System Modelling and Predictions
2019 UN Environment Programme: Emissions Gap Report
2019: WMO Statement on the State of the Global Climate in 2019, World Meteorological Organisation, WMO-No. 1248
2014 IPCC 5th assessment Report AR5: Australasia
2013/2014 IPCC 5th Assessment Report AR5 (full)

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