CIF Project - Implications of Climate Change to Canterbury Water Management Strategy

Grant No: 10/02

Last updated: December 2011

Final report

Supporting report: Projected climate and river flow for the Waimakariri catchment for 2040s and 2090s

Contact details

Name of Applicant Group: Environment Canterbury
Contact person: Dr Tim Davie
Address: PO Box 345, Christchurch 8140
Telephone: 03 372 7084
Email: tim.davie@ecan.govt.nz

Project details

Status: Finished
CIF funding: $25,000 excl GST
Proposed start date: 1 July 2010
Proposed finish date: 31 May 2011
Region: Canterbury
Related website links: http://www.canterburywater.org.nz

Project description

The proposed project is part of work being undertaken by Environment Canterbury to assess the potential impact of climate change on the region’s water resources and contributes to the Canterbury Water Management Strategy.  The geographical scope of the proposed project is the Canterbury Plains, from the Rakaia River to the Ashley River catchment foothills.

The issue/opportunity

The objective of this project is to inform the strategic planning process by answering the following key questions:

  • What would be the effect on irrigated agriculture in Selwyn and Waimakariri Districts of projected changes in climate if no new infrastructure was developed?
  • Will current infrastructure options based on water storage in the Lees Valley continue to be hydrologically viable given projected changes in climate?
  • In what ways might the Canterbury Water Management Strategy need to change given the projected changes in climate?

The context/background

Irrigation development in most of Canterbury has reached the limit of what is feasible, in the absence of additional bulk water storage.  If climate change is consistent with current projections, irrigable area may need to shrink by about 10 percent to maintain current water allocation policy outcomes.  The other major water issue facing Canterbury is the effect of rural and urban land-use-change and intensification on water quality in our groundwater systems, and groundwater dependent streams.  The degree of contaminant loading on groundwater that is acceptable, and therefore the nature, scale and intensity of land-uses that are environmentally sustainable, depends (inter alia) on complex interactions between lowland stream water quality, recharge contaminated by land-use activities, comparatively clean groundwater recharge from upland rivers, and the location and depth of water supply bores.   Projected changes in climate are very likely to change the nature of these interactions and thus affect the nature, scale and intensity of land-uses that are environmentally sustainable.

Current water management strategy development is constrained by the paucity of information on the potential effects of climate change on the quantity and quality of water flows in our surface and groundwater systems.

Methods

  1. Define the climate change scenarios on which this project will be based.  It is proposed that the scenarios will be based on the combination of IPCC4 emissions scenario and GCM that provided the “mid-range” projection used by Aqualinc and NIWA in relation to the Rangitata Catchment.  There will be three scenarios – historical baseline, one set in the 2040’s and the other in the 2090’s.
  2. Develop daily river flow time series data for the Waimakariri and Ashley Catchments for 2040’s and 2090’s climate scenarios
  3. Develop daily rainfall and potential evapotranspiration time series for each grid point of the NIWA Virtual Climate Network covering the Canterbury Plains from Rakaia to Waipara.
  4. Develop Baseline, 2040’s and 2090’s irrigation demand and land-surface recharge time series for the area potentially irrigable within the project boundary.
  5. Quantify the hydrological performance of water storage infrastructure planned to serve the area from the Rakaia River north to and including the Ashley Catchment, for each of the Baseline, 2040’s and 2090’s climate scenarios.
  6. Quantify the potential effects of climate change on groundwater recharge with and without storage-based irrigation on the upper plains in the 2040’s and 2090’s.
  7. Assess and describe the implications of the projected changes in climate on infrastructure requirements and the viability of current proposals and concepts, and the management of water allocation (which impacts on infrastructure requirements).
  8. Assess and describe the implications of projected changes in climate on the current water management strategy.
  9. Report on the findings of the project via a written project report and presentations to the Mayoral Forum, the water strategy steering group, and key stakeholders.

Project Update: October 2011

The objective of this project was to inform the strategic planning process for water allocation in Canterbury by answering the following key questions:

  • What would be the effect on irrigated agriculture in Selwyn and Waimakariri Districts of projected changes in climate if no new infrastructure was developed?
  • Will current infrastructure options based on water storage in the Lees Valley continue to be hydrologically viable given projected changes in climate?
  • In what ways might the Canterbury Water Management Strategy need to change given the projected changes in climate?

The study took the outputs from global climate models (GCMs) as inputs to a hydrological model which was used to create a time series of river flows in the Waimakariri and Ashley Rivers. The time series were created for a range of climate scenarios. The flow time series was then used as input to an assessment of proposed water storage infrastructure for Lees Valley

The GCM rainfall and evaporation outputs were also used as input to an irrigation demand model which provided a time series of water demand across the Canterbury Plains. The water demand time series was then compared to the available water under different climate options and the implications of the projected changes in climate on infrastructure requirements and the viability of current proposals and concepts were then assessed.

The potential effects of climate change on groundwater recharge with and without storage-based irrigation on the upper plains in the 2040's and 2090's was quantified.

  • The assessment shows that with the different climate change scenarios:
  • Dry-land agriculture will become increasingly tenuous because of the increasing frequency of drought days and of water-stress days.
  • Average annual irrigation water use will increase significantly. The eighty percentile annual irrigation water use will increase, but not to the same degree.

The Lees Valley storage option will remain hydrologically feasible, providing a modest reduction in demand is achieved – reducing canal seepage losses is a technically feasible means of doing so.

Net land surface recharge volumes per unit area reduce; the degree of reduction varies across land use type (un-irrigated, irrigated from rivers, irrigated from groundwater). The reduction for land irrigated from rivers is less than for un-irrigated land. The reduction for land irrigated from groundwater is substantially greater than either of the other land use types.

There is an infinite number of approaches to achieving and maintaining Water Management Strategy goals with respect to irrigated area increase and to enhancing lowland streamflows through manipulating land surface recharge. Common to all of these approaches is increasing the amount of land surface recharge through increasing river supplied irrigation, or direct injection, or both.


Project Update: June 2011

The effects of a mid-range 2040’s and 2090’s climate scenario on hydrological parameters of importance to agriculture in North Canterbury have been assessed. The assessment shows that:

  • Dry-land agriculture will become increasingly tenuous because of the increasing frequency of drought days and of water-stress days.
  • Average annual irrigation water use will increase significantly.
  • The Lees Valley storage option of the Canterbury Water Management Strategy will remain hydrologically feasible, providing a modest reduction in demand is achieved – reducing canal seepage losses is a technically feasible means of doing so.
  • Net land surface recharge volumes per unit area reduce; the degree of reduction varies across land use type (un-irrigated, irrigated from rivers, irrigated from groundwater).
  • There are many different approaches to achieving and maintaining Canterbury Water Management Strategy goals with respect to irrigated area increase and to enhancing lowland stream flows through manipulating land surface recharge.
  • These approaches could include increasing the amount of land surface recharge through increasing river supplied irrigation, or direct injection, or both.

There are two reports available from this project:


Project Update: October 2010

Project has started with initial work on modelling climate change scenarios.

 

Last Updated: 16 December 2011

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