Irrigated land area

  • Image, farm numbers and farm size

    Irrigation is used to support land use, particularly in areas with low or seasonal rainfall. Irrigation can improve the productivity of land for farming activity, and support amenity or recreational land uses within urban environments. Irrigation can also alter the natural character of our landscapes (eg change dry land to greener and wetter land), and can increase nutrient (phosphorus and nitrogen) run-off and leaching into waterways. We report on the total area of irrigated land and irrigation systems in New Zealand.

    We classified Irrigated land area as supporting information.

    Key findings

    Trend not assessed

    In 2017, irrigated land covered 3.0 percent (794,440 ha) of New Zealand’s land area.

    • The majority of irrigated land was in Canterbury (63.8 percent or 507,420 ha).
    • Other regions with large irrigated land areas were: Otago (11.7 percent or 93,080 ha), Marlborough (4.0 percent or 31,420 ha), Hawke’s Bay (3.6 percent or 28,800 ha), Waikato (3.0 percent or 23,740 ha), and Manawatu-Wanganui (3.0 percent or 23,710 ha).
    • Nearly 70 percent of irrigation was spray irrigation (69.9 percent or 555,520 ha).
    • Drip or micro irrigation was more likely to be used in regions with horticulture land. The regions with the largest area of drip or micro irrigation were Marlborough (25,310 ha), Hawke’s Bay (14,180 ha), Tasman (5,520 ha), and Gisborne (4,060ha).
    Figure 1
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    Figure 2

    Note: Nelson region is not included due to its small size. Mapping accuracy is higher in regions with a medium to high visual contrast between irrigated and non-irrigated land. Low contrast areas are: Waikato, Tasman, Northland, Auckland, Bay of Plenty, West Coast, and Taranaki.

    Drip/micro systems are commonly used for viticulture, fruit, and vegetable growing. Spray and flood systems are commonly used for agricultural farming. ‘Unknown’ includes systems that were difficult to identify; this was largely in the low and moderate contrast regions.

    Figure 3

     

    Definition and methodology

    Irrigation information comes from a spatial map showing the extent of irrigated land for all New Zealand. The spatial dataset includes farmland and urban land (eg golf courses). Irrigated land area was mapped using:

    • aerial photographs
    • multispectral satellite analysis of Normalised Difference Vegetation Index (a remote-sensing measurement of whether an image contains live green vegetation) imagery during summer (mostly January to March)
    • resource consent records of current irrigation consents
    • property boundary extents (from land ownership and title data from Land Information New Zealand).

    The most up-to-date data were used, ranging from 2013 to 2017 depending on source. Most of the mapping was completed in 2017, and typically represents the year of the most recent aerial/ satellite imagery dataset which could be one or two years earlier (see Dark et al., 2017).

    Accuracy of the mapping varies between regions. In some areas, identifying irrigated land and irrigation system type is difficult due to the lack of visual contrast between irrigated and non-irrigated land. In regions where contrast is medium to high, the mapping accuracy is higher. High contrast areas are: Canterbury, Otago, and Marlborough. Medium contrast areas are: Hawke’s Bay, Manawatu-Wanganui, Southland, Wellington, and Gisborne. Low contrast areas are: Waikato, Tasman, Northland, Auckland, Bay of Plenty, West Coast, and Taranaki. For 15.5 percent of the irrigated area, the irrigation system type was mapped as ‘unknown’.

    Land used for short-rotation cropping may not be identifiable as irrigated if no crop was actively growing when the aerial photo or imagery was taken. Accuracy may vary due to uncertainty about a property’s irrigation system capacity (litres of water per second per hectare), which can result in a whole property being mapped as irrigated when only part of the property can be irrigated at any one time.

    Irrigation system types were identified from high resolution aerial or satellite photos (preferably 0.5m pixel or less). The system type was estimated by considering factors such as visual sighting of travelling irrigators, marking on the ground, or irrigation patterns. Except for the Canterbury region and the Takaka catchment in Tasman district, the national spatial dataset was created without any primary-sector verification.

    We used the following groupings for irrigation system types: spray (pivot, lateral, roto-rainer, linear boom, K-line/Long lateral, solid set, gun, and side-roll); flood systems (border dyke and wild flooding); and micro or drip irrigation.

    When cross-referenced with irrigation data from the 2012 Agricultural Production Census (APC), the total mapped area of irrigated land for most regions was consisently higher than the agricultural census figures. Overall, there was 10 percent more irrigated area in the spatial dataset, which can be attributed to the population frames being different (ie the APC only includes land used for primary production).

    The total land area of New Zealand used is 26.7 million hectares, which excludes water bodies such as inland lakes, harbours, and inlets.

    Data quality

    We classified Irrigated land area as supporting information.

    Relevance

    Image, Indirect relevance. This case study is a indirect measure of the ‘Resource use and management and other human activities’ topic.

    Accuracy

    Image, Medium accuracy. The accuracy of the data source is of LOW-MEDIUM quality.

    See Data quality information for more detail.

    References

    Dark, A, Birendra, KC, & Kashima, A (2017). National Irrigated Land Spatial Dataset: Summary of methodology, assumptions and results. Retrieved from www.mfe.govt.nz.

    Published 19 April 2018

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