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Impacts: Canterbury’s changing climate

2013 storm damage to pine plantation image: Sonny Whitelaw

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Canterbury’s changing climate

Summary

Home > Climate wiki > Impacts > Canterbury’s climate is changing

Summary

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 atmospheric rivers, and resulting precipitation (rain, hail, snow) reaching the West Coast and parts of Southland and atmospheric rivers.

This increases the risks of flooding from rivers that originate in the Southern Alps. 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, however will also be subject to flooding (Fig. 1 Canterbury’s main rivers, Figs. 4, 5 & 6). The natural hydrology of braided rivers has been destroyed or confined (virtually all Canterbury rivers), and the pace is accelerating.

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) (there has been a verified 10% increase globally since 2003), compounding the effect of more frequent and intense droughts.

This also increases the risk of wildfires, especially in plantation forests and areas where wetlands have been removed (most of Canterbury). 

As heat and moisture are key drivers of weather, by continuing to add greenhouse gases into the atmosphere, we are increasing the risk of more frequent and more powerful extreme weather events including marine heatwaves, hailstorms, more powerful windstorms and tornadoes, and more frequent and intense flooding both rivers and from rainfall

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 (NIWA based on

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)

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