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By Daniel Collins

Federated Farmers released their election year manifesto last week. In the press release, President Bruce Wills said:

“Water storage represents New Zealand’s strategic ace. Water storage removes the annual lottery all New Zealanders face from La Niña, El Niño or a changing climate. Our rainfall is plentiful but we miss opportunities with most of it washing out to sea.’

The ‘annual lottery’ relates to the chance that any particular year or growing season turns into a drought*. This risk is heightened during La Nina or El Nino, depending on where in NZ you are, and is likely to heighten further as the climate warms.

Water storage can help alleviate these costly shortfalls in supply, but it is no panacea.

Water storage (i.e., using a reservoir) helps by storing up water throughout the year, or perhaps just the wet season, making it available for use in the growing season. With 80% of NZ’s precipitation flowing to the sea, there may seem to be ample water. But this water is not equally available around NZ. Where water is plentiful, such as on the West Coast, irrigation typically isn’t in as much demand.

Furthermore, just as droughts come with a cost, so too do reservoirs. Large reservoirs cost a lot to build, and while small farm-scale dams may be cheaper they are actually more expensive to develop, in terms of $/m3. Moreover, changes to a river’s flow means that costs may also be incurred by the aquatic biodiversity, recreational opportunities, natural character, and cultural assets of the river system and even the coast.

As David Schiel (University of Canterbury) and Clive Howard-Williams (NIWA) wrote last December:

‘… there are no free lunches when it comes to major extractions of water: benefits in one place have downstream consequences somewhere else.’

So while water storage can help agricultural production it can also hinder other aspects of NZ life, and is thus not a panacea for water resource management. Where the balance is to be struck is a value judgment (not a scientific one), which is made all the more difficult by the diversity of opinions NZers have about their freshwaters.

* Droughts are actually more predictable than the lottery.