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Last updated: December 2011
Supporting report: Projected climate and river flow for the Waimakariri catchment for 2040s and 2090s
Name of Applicant Group: Environment Canterbury
Contact person: Dr Tim Davie
Address: PO Box 345, Christchurch 8140
Telephone: 03 372 7084
CIF funding: $25,000 excl GST
Proposed start date: 1 July 2010
Proposed finish date: 31 May 2011
Related website links: http://www.canterburywater.org.nz
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 objective of this project is to inform the strategic planning process by answering the following key questions:
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.
The objective of this project was to inform the strategic planning process for water allocation in Canterbury by answering the following key questions:
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 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.
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:
There are two reports available from this project:
Project has started with initial work on modelling climate change scenarios.