Sunshine hours

  • Image, Sunshine hours.

    Sunshine is essential for our mental and physical well-being and plant growth. It is also important for tourism and recreation.

    The patterns of cloud cover are changing as our climate changes. As storm tracks and sub-tropical dry zones shift poleward, less cloud cover and more sunshine is expected in the future in the mid-latitudes where New Zealand is located.

    We classified Sunshine hours as a case study.

    Key findings

    Sunshine hours increased at almost all selected sites throughout New Zealand from 1972 to 2016.

    • Of 30 sites, 27 showed an increasing trend in total annual sunshine hours, while three showed no determinable trend. Trends were assessed at the 95 percent confidence level.
    • For the most recent three-year period (2014–16), compared to normal:
      • sunshine hours were near average (96–100 percent of normal) or above average (> 104 percent of normal) for most of New Zealand.

      • southern Fiordland had lower sunshine hours (88–96 percent of normal).
    • On average, from 1972 to 2016, most of the country received between 1,672 and 2,098 hours of sunshine each year.

    Figure 1

    Annual average sunshine hours and trends 1972–2013 and anomaly 2014–2016 for 30 stations – interactive map

    Map, Average annual sunshine hours and trends 1972–2016 and anomaly 2014–2016 for 30 stations.

                                                                                                                                                                                                        Source: NIWA
    Note: Anomaly sunshine hours are calculated as the percent difference between the 2014–16 three-year average and the normal (1981–2010) 30-year average.

    Definition and methodology

    Sunshine hours is a measure of the amount of direct sunshine a site receives. It can also be thought of as a proxy for the general level of cloudiness at a given location. Surrounding terrain or buildings that cast shadows on the instrument will also affect the amount of direct sunshine recorded.

    NIWA extracted data for sunshine hours from the Climate Database for all stations with data (approximately 90 stations across the country) for the particular year. NIWA then interpolated the data to create a regular 500m resolution grid of average annual sunshine hours for each year from 1972 to 2016. Missing data were infilled using Virtual Climate Station Network data (NIWA, nd). Be cautious when interpreting interpolated data because interpolation accuracy is affected by stations opening or closing over time, station density, and terrain complexity. The type of instrument used for recording sunshine hours may change over time which could also influence results. Data are for a calendar year (January–December).

    NIWA calculated percent of normal sunshine hours by comparing interpolations of the annual average for each year to the long-term average for 1981–2010. The most recent three-year average (2014–16) percent of normal annual sunshine hours was created by averaging the three individual year interpolations. We used a three-year average to account for inter-annual variability while providing information on recent conditions.

    Coordinates for each of the 30 sites (corresponding with the same 30 sites used for some of our other measures, eg growing degree days) were obtained from NIWA and imported to a geographic information system. The number of sunshine hours from NIWA’s interpolation was obtained at each of the 30 sites for each year. Note that these values should be viewed with some caution as they are interpolated rather than measured values.

    Decreasing cloud cover and increasing sunshine is expected in the future in the mid-latitudes where New Zealand is located, with storm tracks and subtropical dry zones shifting poleward (Norris et al, 2016). 

    Data quality

    We classified Sunshine hours as a case study.

    Relevance

       This case study 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.

    References

    NIWA (nd). Virtual climate station data and products. Retrieved 29 May 2017 from www.niwa.co.nz.

    Norris, JR, Allen, RJ, Evan, AT, Zelinka, MD, O’Dell, CW, & Klein, SA (2016). Evidence for climate change in the satellite cloud record. Nature, 536(7614), 72–75. http://doi.org/10.1038/NATURE18273.

    Archived pages

    See Sunshine hours (archived October 2017).

     

    Updated 19 October 2017

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