Our climate is changing

Climate change is expected to affect when, where and how much rainfall, snowfall and drought occur. This may change the amount of water in our soils and in glaciers, lakes, rivers, and groundwater.

The frequency of extreme weather events is expected to increase.

The flows, mixing and temperature of water in lakes, rivers and groundwater are also projected to change.

Climate change is likely to affect river flows

Computer models can be used to predict future changes in river flows across the country.

These models show that river flows are likely to:

  • increase on the west coast of the South Island and in rivers that drain the eastern side of the Southern Alps.
  • decrease on the east coast of the North and South Islands, and in Waikato and Northland but these predictions are less certain.

Find out more in Our freshwater 2020 report

Projected change in mean annual river flows between 1990 and 2090

Figure 16. Map.
Hawke's Bay rivers include the largest decreases. Central Otago rivers include the largest increases. Increased westerly airflow brings more rain to the West Coast. Flows in major Alps-fed rivers increase even as shorter neighbouring rivers become drier.

Image: NIWA, 2016. Adapted from Collins 2013

Figure 16. Map.
Hawke's Bay rivers include the largest decreases. Central Otago rivers include the largest increases. Increased westerly airflow brings more rain to the West Coast. Flows in major Alps-fed rivers increase even as shorter neighbouring rivers become drier.

Image: NIWA, 2016. Adapted from Collins 2013

Changes to water mixing in lakes are being observed

Lake water moves around and mixes up naturally to keep a lake healthy. There has been less mixing of water layers in lakes in recent decades. This issue is expected to get worse as the climate warms.

Mixing of water layers is an important process as it:

  • moves nutrients within lakes
  • replenishes the oxygen dissolved in deeper water
  • affects what types of species can live in a particular lake.  

Find out more in Our freshwater 2020 report

Water mixing in lakes: today and in a warmer future

Climate change and lake health. Infographic.
Today: lake waters are mixing once a year. Warmer future: partial or no mixing in a year.
Climate change and lake health. Infographic.
Today: lake waters are mixing once a year. Warmer future: partial or no mixing in a year.

Likely impacts of climate change on freshwater species

Impacts on location of some freshwater species

Climate change is likely to shift where some freshwater species can be found. Warmer temperatures could cause species to be found further south, but be lost from their northern habitats. 

Impacts on some native fish that migrate to the sea and back

Water temperature influences their growth. Drought affects the survival of their eggs and the ability of hatched larvae to move downstream. Floods can wash out and destroy eggs that are laid in the vegetation beside a waterway

Changes in ecological communities and interactions between species

Climate change is likely to cause major changes in ecological communities and interactions between species. The extent of these changes is unknown. Climate change could also make ecosystems and organisms more susceptible to other stresses like pollution and fire.

Impacts on freshwater species and habitats in estuaries, lagoons and wetlands 

Estuaries, lagoons and wetlands are especially sensitive to climate change. They are exposed to changes in freshwater flows as well as rising sea levels.

Coastal erosion and rising seas (which moves salt water into freshwater environments) may cause these ecosystems and their diverse habitats to be reduced or lost. Even small changes in salinity (saltiness) can affect freshwater species and habitats. 

Find out more in Our freshwater 2020 report

Climate change could make some other issues affecting our freshwater worse

Extreme weather events caused by climate change are likely to increase pollution, erosion and sediment in our waterways. 

Droughts related to climate change could also put pressure on water supplies. Communities and infrastructure that depend on rain to supply drinking water may be at risk of running out.

Find out more in Our freshwater 2020 report

Find out more

Climate change is affecting freshwater in Aotearoa New Zealand - Our freshwater 2020 report

Climate change - facts and science from Our atmosphere and climate 2020 report

Impacts of changing river flows

Actions you can take to help look after our freshwater