Extreme wind

  • Image, Occurence of potentially daming winds.

    Steady wind can be an important resource, but strong gusts can damage property, topple trees, and disrupt transportation, communications, and electricity. Extreme wind events can occur with frontal weather systems, around strong convective storms such as thunderstorms, and with ex-tropical cyclones. Projections indicate climate change may alter the occurrence of extreme wind events, with the strength of extreme winds expected to increase over the southern half of the North Island and the South Island, especially east of the Southern Alps, and decrease from Northland to Bay of Plenty. Monitoring can help us gauge the potential of, and prepare for, such events.

    We classified Extreme wind as a case study.

    Key findings

    Between 1972 and 2016, trends in the frequency and magnitude of extreme wind decreased at some sites across New Zealand. However, missing records for some stations and unavailable data across the time period for all sites mean these results should be treated with caution.

    • The highest maximum wind gust in a given year for the 23 sites with enough data to assess a trend, at the 95 percent confidence level:
      • decreased at nine sites – six in the South Island (Blenheim, Hokitika, Christchurch, Timaru, Dunedin, Invercargill); three in the North Island (Tauranga, Whangarei, Wellington)

      • increased for one site (New Plymouth).

    • Wellington had the largest average annual highest maximum wind gusts (averaging 142 km/hr from 1972 to 2016) of all locations with six or more years of data, much higher than the second windiest location, Invercargill (118 km/hr).
    • The number of days per year with a gust that is extreme for that location (ie annual number of days with a maximum gust in the 99th percentile) for the 23 sites with enough data to assess a trend, at the 95 percent confidence level:
      • decreased at 10 sites – six in the North Island (Whangarei, Hamilton, Tauranga, Rotorua, Napier, Wellington); four in the South Island (Blenheim, Christchurch, Timaru, Dunedin).

      • increased at New Plymouth and Queenstown.

    • For sites with records back to 1972, Timaru had the most days with an extreme wind event in a year (18 days in 1988).

    Figure 1

    Extreme wind trends, 1972–2016 – Interactive map

    Map, Extreme wind trends, 1972–2016.

                                                                                                                                                                                                Source: NIWA

    Table 1

    Location Years of data (year records began)  Average annual highest maximum wind gust (km/hr) Highest annual total days p99 exceeded (year)
    Wellington 43 (1972) 142 11 (1977)
    Invercargill 45 (1972) 118 12 (1988)
    Gore 30 (1987) 115 10 (1998)
    Lake Tekapo 13 (2004) 111 12 (2006)
    Dunedin 30 (1982) 104 13 (1995)
    New Plymouth 37 (1972) 103 10 (2016)
    Christchurch 45 (1972) 101 15 (1972)
    Dannevirke 9 (2008) 101 6 (2011)
    Napier 41 (1974) 99 12 (1988)
    Tara Hills 17 (1997) 99 10 (1997)
    Auckland 21 (1995) 98 8 (2002, 2014)
    Hokitika 43 (1972) 96 9 (1975)
    Blenheim 28 (1972) 96 14 (1972, 1975)
    Timaru 45 (1972) 96 18 (1988)
    Whangarei 41 (1974) 94 15 (1976)
    Rotorua 42 (1973) 94 8 (1988, 2012)
    Nelson 26 (1972) 93 10 (1987)
    Tauranga 43 (1974) 92 11 (1975)

    Whanganui

    20 (1997) 89 10 (2004)
    Taupo 34 (1982) 88 10 (1985, 2004)
    Kerikeri 6 (2010) 88 11 (2011)
    Hamilton 33 (1979) 88 13 (1980)
    Queenstown 24 (1972) 86 11 (2014)
    Gisborne 43 (1972) 81 10 (1996)
    Reefton 8 (2002) 60 7 (2002, 2004, 2010)
    Note: Only sites with six or more years of data are included in the table.
    Source: NIWA

    Definition and methodology

    We analysed extreme wind using two statistics: the number of days per year with a maximum wind gust in the 99th percentile and the annual highest maximum gust.

    The number of days with a maximum gust in the 99th percentile provides information on the frequency of extreme wind events. Percentiles are obtained from all available daily maximum wind gust data. On average, the 99th percentile daily maximum wind gust will be exceeded on approximately 3.6 days per year. Therefore, annual counts higher than this indicate more days than usual with very strong wind gusts recorded; annual counts lower than 3.6 indicate fewer strong wind gust days than usual. By using a percentile threshold we can identify events that are extreme for a particular location. Some places are naturally subject to stronger winds than others, so vegetation can become ‘wind-hardened’ and may have a higher tolerance to high wind gusts (eg a 100 km/hr wind gust may be damaging at one location, but not at another). Using a relative threshold accounts for these differences and better captures extreme wind gust occurrences.

    The highest maximum gust per year and the average annual highest maximum wind gust both provide information on the magnitude of extreme wind events.

    Data are available for 30 climate stations. Wind speeds are highly variable over space and time and are strongly influenced by local terrain. Where observations are missing, data are infilled from a nearby station (usually within 500m). In some cases, no suitable station data were available to infill missing wind gust data so some gaps in the wind data series at some locations remain. Therefore, the results reported should be treated with caution.

    Criteria used to select the 30 regionally representative climate stations are that the station must currently be open and be likely to remain open for the foreseeable future; have a long record of reliable, good-quality data; be located near a large city (eg at an airport site) so is representative of the climate where many people in the region live. One station per region is to be selected, but if deemed necessary, two or three stations may be selected to represent a large region.

    Global climate change may alter the occurrence of extreme wind events (Seneviratne et al, 2012). According to climate projections, the strength of extreme winds may increase over the southern half of the North Island and the South Island, especially east of the Southern Alps and decrease from Northland to Bay of Plenty (Ministry for the Environment, 2016).

    Data quality

    We classified Extreme wind as a case study.

    Relevance

       This case study is a direct measure of ‘Climate’ topic.

    Accuracy

       The accuracy of the data source is of medium quality.

    See Data quality information for more detail.

    References

    Ministry for the Environment (2016). Climate change projections for New Zealand: Atmosphere projections based on simulations undertaken for the IPCC 5th assessment (PDF, 4MB). Retrieved from www.mfe.govt.nz.

    Seneviratne, S, Nicholls, N, Easterling, D, Goodess, C, Kanae, S, Kossin, J,… Zhang, X (2012). Changes in climate extremes and their impacts on the natural physical environment. In Field, CB, Barros V, Stocker, TF, Qin, D, Dokken, DJ, Ebi, KL,… Midgley, PM (Eds), Managing the risks of extreme events and disasters to advance climate change adaptation, 109–230. Cabridge: Cambridge University Press.

    Archived pages

    See Occurrence of potentially damaging wind (archived October 2017).

    Published 19 October 2017

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