Canterbury does not have 70% of New Zealand’s freshwater, it has 12%

By Waiology 29/10/2012 5

By Daniel Collins

In the Christchurch Press today there is an article about the race to irrigate Canterbury. In it is the following statement:

“Canterbury had 70 per cent of New Zealand’s fresh water resource, and 34 per cent of its hydro-generation capacity.”

Unfortunately the 70% is an error that has appeared in the past and it is timely to make a correction and provide some other statistics that describe water resources in Canterbury more generally.

Canterbury has about 12% of New Zealand’s freshwater. This number is obtained from a Statistics NZ report, written by NIWA, on the water stock accounts of New Zealand.

To check for yourself, download the two Excel files from the Statistics NZ website, calculate the annual average of “Outflow to sea and net abstraction” for both Canterbury and the country as a whole, and divide one by the other.

This error has already been noted by the Christchurch Press in an article from March 2010.

For a fuller picture, here are some more useful statistics, from the Ministry of the Environment’s 2010 water allocation snapshot compiled by Aqualinc Research:

    Canterbury’s percent of national water consents (number): 30%
    Canterbury’s percent of national irrigation consents (number): 35%
    Canterbury’s percent of national annual consumptive allocation (m3/yr): 19%
    Canterbury’s percent of national annual consumptive allocation, discounting Southland’s Manapouri hydro scheme (m3/yr): 46%
    Canterbury’s percent of national irrigation allocation (m3/yr): 62%
    Canterbury’s percent of national consented irrigated area (ha): 63%

And from the Canterbury Water Management Strategy:

    Canterbury’s percent of national water allocation (m3/yr): 58%
    Canterbury’s percent of national irrigated area (ha): 70%

5 Responses to “Canterbury does not have 70% of New Zealand’s freshwater, it has 12%”

  • Regional democracy factoid:
    Canterbury has 0% of New Zealand’s regional council democracy.

  • Well spotted. The Press do print corrections, so it might be worth bringing the error to their attention. The subject is fraught enough without adding major errors into the mix.

  • The Canterbury and national water permit allocation data need to be treated and reported carefully. The Aqualinc report does not for example, appear take account of some major Canterbury water permits specifying that they can not be exercised concurrently with some other water permits. Therefore it is likely that the reported Canterbury allocation figures are an over-estimate. It’s not clear how widespread these types of resource consent conditions are so its not possible to conclude whether or not this is a regionally consistent issue.

  • Yes, the consents database and the Aqualinc report based on it are imperfect. And so the resulting numbers will have errors, much like any data really. Going through the database in detail recently, I have noticed a number of other discrepancies, large and small. But they are still the best indication we have of gross allocation at this stage, and no-one has yet sought to quantify their errors or uncertainties. Even with these errors, certain conclusions will be robust, such as some relative rankings (e.g., “We’re #1!”). And as for regional variation in these uncertainties or errors, I very much expect them to be inconsistent.

    Another important fact to remember, when all’s said and done on the consents database, is that they are consents for allocation, not actual use. [DC]

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