Climate change projections for the Manawatu-Whanganui region

Map of Manawatu-Whanganui region. This page provides an overview of how the climate in the Manawatu/Whanganui 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 1.1˚C warmer by 2040 and 0.7˚C to 3.1˚C warmer by 2090.

By the end of the century, the Manawatu-Whanganui is projected to have from 7 to 47 extra days per year where maximum temperatures exceed 25˚C. The number of frosts could decrease by around 6 to 17 per year by 2090. 

Rainfall

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

Seasonal projections show winter rainfall increasing by 6 to 10 per cent in Whanganui and 7 to 16 per cent in Taumaranui by 2090. 

According to the most recent projections, the Manawatu-Whanganui region is not expected to experience a significant change in the frequency of extreme rainy days as a result of climate change.

Snowfall

A reduction in the number of snow days experienced annually is projected throughout New Zealand, including the Central Plateau.

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 regions. Places that currently receive snow are likely to see increasing rainfall as snowlines rise to higher elevations due to rising temperatures.

Wind

The frequency of extremely windy days in the Manawatu-Whanganui region is not likely to change significantly by 2090. There may be an increase in westerly wind flow during winter and north-easterly wind flow during summer.

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. 

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, the region could expect*:

Spring

  • 0.6°C to 2.7°C temperature rise
  • 1 per cent less to 3 per cent more rainfall in Whanganui
  • No change to 5 per cent more rainfall in Taumaranui

Summer

  • 0.7°C to 3.3°C temperature rise
  • No change to 3 per cent more rainfall in Whanganui
  • 2 per cent more rainfall in
  • Taumaranui across the range of scenarios

Autumn

  • 0.7°C to 3.2°C temperature rise
  • 5 per cent less to 2 per cent more rainfall in Whanganui and Taumaranui

Winter

  • 0.7°C to 3.2°C temperature rise
  • 6 to 11 per cent more rainfall in Whanganui
  • 7 to 16 per cent more rainfall in Taumaranui

*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 Manawatu-Whanganui by 2090?

Flooding – More heavy rainfall will increase the risk of flooding which could become up to four times as frequent by the end of the century. This could have large implications for areas already prone to river flooding such as the Manawatu and Rangitikei flood plains and Whanganui City.

Drought – By 2090, the time the Manawatu spends in drought could range from minimal change through to more than double compared to 1995. More frequent droughts are likely to lead to water shortages, increased demand for irrigation and increased risk of wild fires. Droughts are likely to increase in both intensity and duration.

Erosion and landslides – The possibility of drier average conditions and more intense rainfall at times could lead to increased problems with erosion, landslides and sedimentation in rivers. Areas already at high risk include the hill country within the Ruapehu district, the north-eastern Whanganui district, the central Rangitikei district and the eastern Tararua district.

Coastal hazards – Sea-level rise and increased storminess will increase the impacts of high tides and storm surge on coastal erosion and flooding and make groundwater aquifers near the coast more vulnerable to salt-water intrusion.

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

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

Find out more 

Chapter 9 - Natural hazards (Horizons regional policy statement) [Horizons Regional Council website]

Reviewed:
30/06/16