Thursday, 11 January 2007
Severe winter snowstorms
Floods, wind storms, destructive tornadoes
Variable temperatures, yet sunny overall
Erratic and sometimes extreme, New Zealand’s climate for 2006 will probably be most remembered for one of the severest winter snowstorms in decades, a very windy spring, and a cold start to summer late in the year. So it may surprise people to hear that 2006 was also very sunny in the southeast of the South Island, and generally sunny in many other regions.
"The year was marked by too little rain in some places and too much in others", says NIWA Principal scientist Dr Jim Salinger. Extreme climatic events continued, with severe snowstorms, floods, destructive tornadoes, and windstorms. Excessive winter rainfall produced severe flooding in the Wairarapa, but it was very dry for the year in Otago. Of the main centres, Dunedin was dry and sunny, while Wellington and Christchurch were very wet.
"The year saw a swing from a La Niña to an El Niño climate pattern. The first quarter of the year was dominated by weak La Niña-like characteristics in the equatorial Pacific, and frequent troughs of low pressure often over New Zealand. From September onwards weak–moderate El Niño conditions in the tropical Pacific had developed, with a noticeable increase in windiness, and more frequent south westerlies than normal over the country."
"There were numerous heavy rainfall events during 2006, about 18 of which produced floods. Notable snowfall events occurred on nine occasions, mainly in high country areas from mid-autumn to late winter, with ski areas having an extended season. Other climate extremes included a summer heat-wave, four tornado incidents, three severe hailstorms, and many damaging windstorms", said Dr Salinger.
The year in review
The year began with significant soil moisture deficits in the north and east of the North Island and eastern South Island, which persisted in these regions until March. A 3–day heat wave in Central Otago with temperatures reaching 36°C occurred at the end of January.
March was cold, and an ex-tropical cyclone produced high rainfall in the north of the North Island.
Flood-producing rainfall events occurred in north and east Otago and in the Hauraki-Coromandel region during April. As a result the month’s rainfall was very high in these regions. Rainfall in north and east Otago totalled 300–400 percent (three to four times) of normal, and totals in the Hauraki-Coromandel region were at least 200 percent (two times) of normal. It was the 8th warmest April on record. May produced well above average rainfall in the north of the North Island, and east of the South Island, with low rainfall in parts of the south of the South Island.
Two severe winter snowstorms accompanied by bitterly cold conditions, and later heavy frost contributed to a particularly cold June. Temperatures were 2°C below average in some regions. It was much sunnier than normal in all western and southern regions, with record high June totals in the north of the North Island, and coastal Otago.
In contrast, July was warmer than June, going against the usual trend. It was very wet in the south and west of the North Island, with twice the normal rainfall in Wairarapa with flooding. July was rather settled in other areas with rainfall totals a mere 25 percent (a quarter) to 50 percent (half) or less of normal in the north of the North Island and Otago.
High rainfall continued in August in the south and west of the North Island, but it was dry in much of the South Island, and extremely sunny in the south.
September was a month of climate extremes with record low rainfall and high mean temperatures at many locations. Rainfall was low throughout much of New Zealand, especially in the east with some locations recording 10 percent (one tenth) or less of normal rainfall. In some areas temperatures were 2°C above average, with windy conditions in the south.
It was windier than usual over most of the South Island and southern half of the North Island in October with several locations in Marlborough and Otago recorded their windiest October in over a decade.
November produced stormy westerlies over the South Island: it was particularly warm in the east of the North Island, yet cold in the southwest of the South Island. Significant soil moisture deficits existed in Northland and central Marlborough by the end of the year. December ended the year on a cool note, with one of the coldest Decembers in the last 60 years.
The most significant extreme event of the year was the winter snowfall event over the night of 11/12 June in Canterbury, especially in the south, with snow settling to sea level. This was severe with snow settling to depths of 75-90cm around Fairlie and Burkes Pass, almost 40cm in Ashburton, and more than 20cm in Timaru, some remaining in some inland areas until the 27th. Extended power cuts occurred throughout much of South Canterbury, due to broken power lines and poles. The roofs of several buildings also collapsed, due to the weight of snow. Many motorists were stranded in the snow, and many roads closed.
The worst flooding events during 2006 were those of 25/26 April in Otago and 4–6 July in Wairarapa. In the Otago flood, rivers ran extremely high, and much of the Taieri Plains including Mosgiel were flooded, with some evacuations. Flood waters also affected the towns of Oamaru and Waitati. The Wairarapa flood occurred during a three day period of high rainfall, also affecting Wanganui and Wellington. This resulted in high rivers and severe surface flooding throughout much of southern Wairarapa, with substantial landslips in parts of Wanganui and Wellington. There were evacuations in parts of southern Wairarapa. Martinborough was isolated by the floodwaters, with surface flooding in Greytown and Carterton. Many roads were closed by flooding or landslips. In the Wanganui region, the settlement of Mangamahu was isolated by the collapse of a river bridge (with damages estimated at $10 million). 125 people were evacuated from Whangaehu, and Turakina.
Windstorms occurred on 13 separate occasions, and in October days with strong gusty winds were more frequent than average over much of the South Island and over the southern North Island, especially in the east, with near or record number of windy days (gusts to at least 60 km/h). Four tornadoes were reported, one damaging 20 houses in Greymouth.
Records for the year
NIWA analyses of month-by-month records and preliminary end of year data show:
- The highest annual mean temperature recorded for the year was 15.8 °C recorded at Kaitaia.
- The highest recorded extreme temperature of the year occurred during a heat-wave in Central Otago toward the end of January. Alexandra recorded maximum temperatures of 36 °C for three consecutive days from the 27–29th (unheard of in their historical record, commencing in 1930).
- The lowest air temperature for the year was -14.0 °C recorded at both Tara Hills, Omarama on 14 June and Fairlie on 28 June. The minimum air temperatures were –10 °C or lower in parts in inland South Canterbury and/or North Otago, on nine days between 14 and 29 June.
- April was the warmest since 1978.
- June was the equal coldest (with 1992) since 1972.
- September was the 3rd warmest on record.
- December was one of the coldest since 1945, approximately equal with Decembers 1946 and 2004.
- The highest recorded wind gust for the year was 180 km/h was recorded from the northwest, at Southwest Cape (Stewart Island) on 2 September, a new record for a wind gust at that site. Mean wind speeds reached 128 km/h.
- The driest rainfall recording locations were Alexandra in central Otago with 266 mm of rain for the year, followed by Clyde with 286 mm.
- Of the regularly reporting gauges, the Cropp River gauge in Westland, inland in the headwaters of the Hokitika River, recorded the highest rainfall with a 2006 annual total of 11370 mm.
- Dunedin was easily the driest of the five main centres with 641 mm and Wellington the wettest with 1579 mm. Hamilton received 1155 mm, Auckland 1263 mm, and Christchurch 884 mm.
- Nelson was the sunniest centre in 2006, recording 2580 hours, followed by Blenheim with 2528 hours, and Tauranga with 2507 hours. Auckland was the sunniest of the five main centres with 2189 sunshine hours, followed closely by Christchurch (2169 hours), and Wellington (2159 hours). Dunedin recorded 1960 hours, and Hamilton 1996 hours.
Prevailing climate patterns – a change from La Niña like conditions early in the year to an El Niño in spring with more southwesterlies
The weak La Niña-like characteristics that occurred in the equatorial Pacific during the first quarter of the year were accompanied by more frequent troughs of low pressure over New Zealand from January to May. From September onwards a weak-moderate El Niño had developed and persisted for the remainder of the year. It was noticeably windy over New Zealand, with winds being were much more frequent from the southwest during the second half of the year. The overall mean sea level pressure pattern for 2006 showed more frequent winds from the southwest over the whole of New Zealand, along with troughs of low pressure to the south east of the country. Warmer than normal sea temperatures around New Zealand disappeared over winter, and were much cooler than normal at the end of the year.
Well below normal rainfall in parts of Otago, high rainfall in Wairarapa, Wanganui, Wellington, and Canterbury
2006 was much drier than average (with totals less than 75 percent of normal) throughout parts of Central Otago and the Awatere Valley in Marlborough; Clyde in Central Otago recording its driest year in more than 20 years, with only 286 mm for the year. Rainfall was also below average (75 to 90 percent of normal) in parts of Northland, Coromandel, North Taranaki, Buller, Nelson, Marlborough, north and east Otago, and South Westland. However, rainfall was well above average (at least 125 percent of normal) in parts of Wairarapa, Wanganui, Wellington, and Canterbury, and at least 110 percent of normal in Taupo, Manawatu, Kapiti, North Westland, and coastal areas of Southland. Wellington recorded its wettest year since the late 1970s. Rainfall was near normal elsewhere.
Extremely low annual rainfall, for the year 2006, was measured at:
|Location||2006 rainfall (mm)||Percentage Of normal||Year Records began||Comments|
|Awatere Valley||486||73||2001||Well below normal|
|Raoul Island||948||61||1938||3rd lowest|
High annual rainfall, for the year 2006, was measured at:
|Location||2006 rainfall (mm)||Percentage of normal||Year Records began||Comments|
|East Taratahi||1150||137||1973||2nd highest|
|Wellington, Kelburn||1579||126||1900||3rd highest|
|Wanganui, Spriggens Park||1149||130||1890||Well above normal|
|Christchurch, Gardens||884||135||1864||Highest since 993 mm in 1986|
Alexandra, in Central Otago, was the driest of the sites where NIWA records rainfall, with only 266 mm (73% of average), followed by Clyde with 286 mm (69% of average). Of the regularly reporting rainfall stations, the wettest location in 2006, for which rainfall data are presently available was the Cropp River gauge in Westland, inland in the headwaters of the Hokitika River, with an annual total of 11370 mm. Milford Sound’s rainfall totalled 6853 mm (101% of average).
Of the five main centres, Dunedin was the driest with 641 mm (80% of average) and Wellington the wettest with 1579 mm (126% of average). Hamilton received 1155 mm (99% of average), Auckland 1263 mm (102% of average), and Christchurch 884 mm (135% of average).
2006 temperatures: above normal in the northeast of both islands, below normal in many inland areas
The national average temperature in 2006 was 12.4 °C, 0.2 °C below the 1971 &38211; 2000 normal. Thus, 2006 ended up very close to the 1971-2000 normal, as a consequence of very warm months (April, September) offsetting some very cold months (March, June, December).
Temperatures were above normal (by about 0.3 °C) in the northeast of both islands, in regions like Gisborne, as well as parts of Marlborough and Nelson. However, they were at least 0.5 °C below average in inland South Canterbury and parts of King Country, and at least 0.3 °C below average in parts of Northland, Wairarapa, Buller, Westland, Otago, and inland areas of Southland. The warmest local was Kaitaia, with a mean temperature for the year of 15.8 °C (0.2 °C above normal).
For New Zealand as a whole, there were three warmer than normal months (April, May, and September), and three cooler than normal months (March, June, and December). All other months had mean temperatures close to the climatological average. March with a mean temperature of 14.2°C (1.5 °C below normal) was the coldest since 1992, April with 14.6 °C (1.2 °C above normal) was the warmest since 1981, June with 7.3 °C (1.2 °C below normal) was coldest since 1972, and September with 11.6 °C (1.2 °C above normal) was the warmest since 1988, and 3rd warmest nationally since reliable records commenced in the 1860s. December was the coolest since 2004 (1.9°C below normal) and one of the coldest in the last 60 years.
More sunshine than normal over much of the south island and in the north east of the north island
Sunshine hours were more than 110 percent of normal in Bay of Plenty, Southland, coastal Otago, and inland South Canterbury, with Invercargill recording its sunniest year on record. Totals were at least 105 percent of normal in many South Island regions, as well as Northland, Auckland, and Gisborne. Sunshine hours were near normal elsewhere. Nelson was the sunniest centre in 2006, recording 2580 hours, followed by Blenheim with 2528 hours, and then Tauranga with 2507 hours.
Near or record high sunshine hours for the year 2006 were:
|Location||2006 Sunshine (hours)||Normal (hours)||Departure from normal||Records Began||Comments|
|Kaitaia Observatory||2264||2098||+8%||1985||2nd highest|
|Tauranga Airport||2507||2250||+11%||1932||2nd highest|
|Invercargill||1853||1609||+15%||1932||Highest on record|
|Hokitika Airport||2036||1860||+9%||1964||3rd highest|
2006 climate in the five main centres
Dunedin was by far the driest, and Wellington easily the wettest. Dunedin was the coldest, and Auckland the sunniest of the main centres. Rainfall was below average in Dunedin, well above average in Wellington and Christchurch, and near average in the other main centres. Temperatures were below average in Wellington, and near average in the other main centres. Sunshine totals were near average in Hamilton, and above average in the other main centres. Dunedin recorded its 2nd sunniest year on record.
2006 climatological statistics for the five main centres:
|Location||2006 Mean temp.(°C)||Dep. from normal (°C)||2006 rainfall (mm)||% of normal||2006 Sunshine (hours)||% of normal|
|Auckland||15.1||-0.2||Near normal||1263a||102||Near normal||2189||109||Above normal|
|Hamilton||13.5||-0.2||Near normal||1155||99||Near normal||1996||100||Near normal|
|Wellington||12.5||-0.3||Below normal||1579||126||Well above normal||2159||105||Above normal|
|Christchurch||12.0||-0.2||Near normal||884||135||Well above normal||2169b||103||Above normal|
|Dunedin||11.1||0.0||Near normal||641||80||Below normal||1960||123||2nd highest|
a Owairaka b Christchurch Airport
Climate Summary for 2006 (PDF 134 KB)
For further information, please contact:
Dr Jim Salinger – Principal Scientist, Climate
NIWA National Climate Centre – Auckland
Phone +64 9 375 2053
Stuart Burgess – Climatologist
NIWA National Climate Centre – Wellington
Phone +64 4 386 0569
Geoff Baird – Communications Manager
Phone +64 4 386 0543
Acknowledgement of NIWA as the source is required.