4. Discussion
It is important to note that the order of the list is based on aggregate
farmgate GDP generated from the supply of irrigation water from the particular
waterbody. Water use information is not available to calculate the marginal
return from each additional unit of water. Other criteria such as value added
per hectare irrigated or by cubic metre of water used should also be considered.
It is also important to note that the values identified for current irrigation
exist alongside the other values from those waterbodies identified in other
reports within the Waters of National Importance study. In the same way, the
potential for irrigation from waterbodies may be able to be realised without the
loss of other values or indeed may create other benefits for those values.
Irrigation benefit is not necessarily (but may be) gained at the expense of
other values.
The estimate of total value of each waterbody is likely to be conservative for
the following reasons:
1. Gross margin analysis does not account for fluctuations in output over time.
Downside fluctuations are likely to be greater under a dryland scenario than
under irrigation.
2. The benefits of irrigation of parts of farms are not accounted for (e.g.,
growing fodder crops to support the stock carried on the rest of the farm). If
they were, it would have the effect of further increasing the value of
irrigation.
Of these qualifiers, the first has been taken into account to a degree in
assuming that some land uses would not occur without irrigation. Even so, the
fluctuations in dryland pastoral incomes are demonstrably larger than for
irrigated areas (Butcher 200011).
The second is difficult to demonstrate, although evidence of the value of
partially irrigating properties is supported by farm consultants.
The relative importance of each waterbody for irrigation compared to each other
is unlikely to change, but the absolute values calculated in this study are
subject to a number of assumptions that must be more closely examined when the
next stage of the project compares values.
11 Regional Economic Impacts of the 1997-1999 Canterbury Drought, Butcher Partners Ltd and Agriculture NZ, Feb 2000, MAF Technical Paper 00/18.
Contact for Enquiries
Water Programme of Action
Ministry for the Environment
PO Box 10-362
Wellington
or
Water Programme of Action
Ministry of Agriculture and Forestry
PO Box 2526
Wellington
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