Climate change freshwater impacts assessments

New Zealand’s climate is changing – and so are our  freshwaters. These changes  reflect a global pattern of  increasing temperatures and  shifting precipitation regimes, and are likely to alter freshwater supply and demand, aquatic ecosystems and natural  hazards. This means we can no longer rely solely on the past to guide freshwater management into the future; we must account for potential climate-change impacts.

Many of the decisions water users and planners make now will have implications for decades to come.  The National Policy Statement for Freshwater Management requires regional councils to take account of “reasonably foreseeable impacts of climate change".

Read the National Policy Statement for Freshwater Management 

NIWA is leading the way in understanding and helping New Zealanders prepare for these changes.

NIWA's climate change impacts assessments

Climate change impact assessments are the product of a series of linked computer models that encapsulate the physics, chemistry and biology of the atmosphere and water cycle. They start with representative scenarios of global climate change, ranging from slight to extreme warming. Using the global climate models that have been vetted for New Zealand, we downscale the projected climatic conditions to provide high-resolution projections across the country. These, in turn, are used to drive hydrological models of snow, glaciers, rivers, soil and groundwater. Projections can be made over different time periods, allowing us to chart the impact of climate change over time.

We can also estimate when the future changes in the freshwater system are likely to become detectable in hydrological records by comparing the modelled trend with natural variability. In a similar way, we can also estimate when the changes may become significant in terms of freshwater management. This is an important consideration in adaptive management and long-term planning or investment decisions.

Applications of climate-change impact assessments include:

  • water allocation limit setting
  • flood and drought mitigation
  • water storage siting and sizing
  • conservation management
  • municipal water supply
  • hydropower potential.

NIWA’s modelling tools can be tailored to provide the following assessments:

  • mean monthly and annual river flows
  • groundwater recharge and base flow
  • low flows and reliability of supply
  • mean annual flood and flood percentiles
  • extreme rainfalls and precipitation deficits
  • frequency of ecological disturbance
  • timing of freshwater impacts and detectability
  • uncertainty and risk.

Communicating the science

Working with you, we can provide tailor-made solutions addressing your needs. These include technical reports for specific locations, regional or policy contexts and implications, stakeholder summaries designed for different communication channels, or assistance in direct community outreach.

Examples of NIWA modelling tool outputs

Precipitation change projections. Precipitation annual average change 2080 - 2099, using average of 12 GCMs A1B emission scenario (MfE 2008). Click on the image to enlarge it.

Seasonal and annual average mean flow change and associated range of change for Awanui River (Collins, 2011). The cnages are presented for the reference period 1980 - 1999, mid-century 92003 - 2049) and end of century 92080 - 2099). Click on image to enlarge it.

Analytical results showing one river's montly flows. Change in mean monthly flows for the period 2030 - 2039 using average of 12 GCMs A1B emission scenario. Reference taken as mean monthly flow over the period 1980 - 1999.

For more information on NIWA's climate change freshwater impacts assessments contact: 

Daniel Collins
Phone: 03 343 8033

Christian Zammit
Phone: 03 343 7879