Water physical stocks: precipitation and evapotranspiration

  • Image, Water physical stocks.

    Precipitation and evapotranspiration (the loss of water by evaporation and transpiration from plants) are important components of the water cycle. They influence the amount of water available for our forests and crops and contribute to river, lake, and aquifer levels. Our water stocks are important for sustaining natural ecosystems and supporting our economy and lifestyles.

    We classified Water physical stocks: precipitation and evapotranspiration as a national indicator.

    Key findings

       Indeterminate trend

    From 1995 to 2014, precipitation across New Zealand varied annually by a maximum of +16 to a minimum of -14 percent of average.

    • On average, New Zealand receives 550 billion cubic metres of precipitation a year.
    • In 2012, total precipitation was 14 percent less than average. This was largely because the Southland and West Coast regions, which generally receive 40 percent of total precipitation, received 23 percent (50 billion cubic metres) less than average.
    • The average annual outflow to sea is around 80 percent of total precipitation.
    • Evapotranspiration accounts for most of the remaining precipitation (around 19 percent).
    • Precipitation showed a decreasing trend, but it is not statistically significant.
    Note: Outflow to sea includes water abstracted/discharged for hydroelectric generation.

    Definition and methodology

    Information on how much water is gained through precipitation and lost through evapotranspiration summarises the surface component of the water stocks of New Zealand. We derived this from a combination of direct measurement and modelled data.

    The data revise and update three previous reports on surface water information. NIWA reran the national TopNet model from July 1994 to June 2014, extended the records of lake volume change and hydroelectric generation water use from recording authorities, and extended the national ice and glacier accounts. A year runs from 1 July to 30 June and is referred to by the year at the end of the period (eg the 1995 year runs from 1 July 1994 to 30 June 1995).

    The data cover 11 components of the water stocks:

    • precipitation
    • inflows from rivers (regional scale only)
    • evapotranspiration
    • abstraction by hydro-generation companies
    • discharges by hydro-generation companies
    • outflows to sea from surface water
    • outflows to other regions (regional scale only)
    • net change in lakes and reservoirs
    • net change in soil moisture
    • net change in snow
    • net change in ice.

    Currently, we do not have sufficient readily available data to quantify the actual volumes of water abstracted for irrigation, industrial use, municipal and domestic use, livestock use, and geothermal electricity production. However, we are able to report on water use for hydropower. This water use highlights climate’s important role for our economy and society.

    Data quality

    We classified Water physical stocks: precipitation and evapotranspiration as a national indicator.

    Relevance

       This national indicator is a direct measure of the ‘Climate’ topic.

    Accuracy

       The accuracy of the data source is of high quality.

    See Data quality information for more detail.

    Supporting information

    Change in glacier ice volume

    Archived pages

    See Water physical stocks: precipitation and evapotranspiration (archived October 2017).

     

    Updated 19 October 2017

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