Climate change projections for the West Coast region

Map of West Coast region. This page provides an overview of how the climate in the West Coast region is likely to change into the future and what implications this has for the region.

Projections of climate change depend on future greenhouse gas emissions, which are uncertain. There are four main global emissions scenarios ranging from low to high greenhouse gas concentrations. This page presents regional projections as a range of values from a low emissions to a high emissions future.

The projected changes are calculated for 2031–2050 (referred to as 2040) and 2081–2100 (2090) compared to the climate of 1986–2005 (1995).

Temperature

Compared to 1995, temperatures are likely to be 0.7˚C to 1.0˚C warmer by 2040 and 0.6˚C to 3.0˚C warmer by 2090.

By 2090, the West Coast is projected to have up to 30 extra days per year where maximum temperatures exceed 25˚C. The number of frosts could decrease by around 7 to 18 days per year.

Rainfall

Rainfall will vary locally within the region. The largest changes will be for particular seasons rather than annually.

The West Coast is expected to become wetter, particularly in winter and spring. Winter rainfall in Hokitika is projected to increase by 8 to 29 per cent by 2090.
According to the most recent projections, extreme rainy days are likely to become more frequent throughout the West Coast region by 2090 under the highest emissions scenario.

Wind

The frequency of extremely windy days in the West Coast by 2090 is likely to increase by between 2 and 5 per cent. Changes in wind direction may lead to an increase in the frequency of westerly winds over the South Island, particularly in winter and spring.

Storms

Future changes in the frequency of storms are likely to be small compared to natural inter-annual variability. Some increase in storm intensity, local wind extremes and thunderstorms is likely to occur.

Snowfall

The West Coast region is likely to experience significant decreases in seasonal snow. By the end of the century, the number of snow days experienced annually could decrease by as much as 30-40 days in some parts of the region. The duration of snow cover is also likely to decrease, particularly at lower elevations.

Less winter snowfall and an earlier spring melt may cause marked changes in the annual cycle of river flow in the region. Places that currently receive snow are likely to see a shift towards increasing rainfall instead of snowfall as snowlines rise to higher elevations due to rising temperatures. So for rivers where the winter precipitation currently falls mainly as snow and is stored until the snowmelt season, there is the possibility for larger winter floods.

Glaciers

Overall glacier ice mass has decreased by 25 per cent over the last 60 years in New Zealand, and is expected to continue to do so into the future. Some of our most iconic glaciers (such as Franz Josef) have advanced in recent times. This is a result of more precipitation falling at their glacier heads. Whether these glaciers continue to advance into the future will depend on the balance between increased melting due to warmer temperatures and increased precipitation in the mountains. For example, one climate modelling study suggests the Franz Josef glacier may retreat approximately 5 km and lose around 38 per cent of its mass by 2100.

Sea-level rise

New Zealand tide records show an average rise in relative mean sea level of 1.7 mm per year over the 20th century. Globally, the rate of rise has increased, and further rise is expected in the future.

The Ministry for the Environment provides guidance on coastal hazards and climate change, including recommendations for sea level rise, see Preparing for coastal change: A guide for local government in New Zealand.  An updated edition is due for release in 2017.

Impacts by season

By 2090, seasonally the region could expect*:

Spring
  • 0.6°C to 2.5°C temperature rise
  • 4 to 9 per cent more rainfall in Hokitika

Summer

  • 0.6°C to 3.2°C temperature rise
  • 2 to 4 per cent more rainfall in Hokitika

Autumn

  • 0.7°C to 3.1°C temperature rise
  • 2 to 5 per cent more rainfall in Hokitika

Winter

  • 0.7°C to 3.1°C temperature rise
  • 8 to 29 per cent more rainfall in Hokitika

*Projected changes are relative to 1995 levels. The values provided capture the range across all scenarios. They are based on scenario estimates and should not be taken as definitive. For more information, see the full report on climate projections.

What could this mean for the West Coast?

Coastal hazards – Coastal roads and infrastructure may face increased risk from coastal erosion and inundation, increased storminess and sea-level rise.

Flooding and landslides – More heavy rainfall will increase the risk of flooding, erosion and landslides, which is already high in many parts of the region. Many West Coast communities are located along narrow coastal and river strips beneath mountain ranges, leaving them exposed to increased risks of storms, flooding and landslides.

Biosecurity – Warmer, wetter conditions could increase the spread of pests and weeds.

Agriculture – Warmer temperatures, a longer growing season and significantly fewer frosts could provide opportunities to grow new crops and farmers might benefit from faster growth of pasture and better growing conditions. However, these benefits may be limited by negative effects of climate change such as increased flood risk or greater frequency and intensity of storms.

The Ministry for Primary Industries website and associated Climate Cloud website have more information on the regional impacts of climate change on agriculture.

Reviewed:
30/06/16