New Zealand national climate summary 2011: A year of extremes.
The year 2011 will be remembered as one of extremes. Sub-tropical lows during January produced record-breaking rainfalls. The country melted under exceptional heat for the first half of February. Winter arrived extremely late – May was the warmest on record, and June was the 3rd-warmest experienced. In contrast, two significant snowfall events in late July and mid-August affected large areas of the country. A polar blast during 24-26 July delivered a bitterly cold air mass over the country. Snowfall was heavy and to low levels over Canterbury, the Kaikoura Ranges, the Richmond, Tararua and Rimutaka Ranges, the Central Plateau, and around Mt Egmont. Brief dustings of snow were also reported in the ranges of Motueka and Northland. In mid-August, a second polar outbreak brought heavy snow to unusually low levels across eastern and alpine areas of the South Island, as well as to suburban Wellington. Snow also fell across the lower North Island, with flurries in unusual locations further north, such as Auckland and Northland. Numerous August (as well as all-time) low temperature records were broken between 14 – 17 August. And torrential rain caused a State of Emergency to be declared in Nelson on 14 December, following record-breaking rainfall, widespread flooding and land slips.
Annual mean sea level pressures were much higher than usual well to the east of the North Island in 2011, producing more northeasterly winds than usual over northern and central New Zealand. The northeasterly winds resulted in above average annual temperatures and well above normal rainfall for the northeast North Island and the north of the South Island.
The large-scale climate setting was primarily driven by a very strong La Niña event at the start of 2011, which eased to neutral in winter, but redeveloped to moderate levels during spring.
Mean annual temperatures were above average (between 0.5°C and 1.2°C above the long-term average) in the northeast of the North Island, and over the north of the South Island. Mean annual temperatures were generally near average (within 0.5°C of the long-term average) elsewhere. The nation-wide average temperature for 2011 was 12.8°C, 0.3°C above the 1971–2000 annual average, using NIWA's seven-station temperature series which begins in 1909. 2011 was the 17th warmest year since 1909, based on this 7-station series.
In broad terms, six months of the year were wetter than normal and two were drier than normal. Four months were mixed, with large geographical differences between very wet regions and areas of extreme dryness. Annual rainfall totals for 2011 as a whole were above normal (more than 120 percent of annual normal) in parts of: Northland, Auckland, Coromandel, Bay of Plenty, Nelson, and Central Otago; as well as around New Plymouth, Napier, Wanganui and Palmerston North. In contrast, it was a relatively dry year (with annual rainfall totals between 50 and 79 percent of annual normal) for the Kaikoura Coast and Canterbury, as well as much of Fiordland and Westland. Elsewhere, annual rainfall was in the near normal range (80 to 119 percent of normal).
Above normal sunshine was observed in central North Island, and for much of western and southern South Island (with annual sunshine totals between 110 and 125 percent of normal). Parts of Wellington region received below normal (between 75 and 90 percent of normal) sunshine totals for 2011. Elsewhere, sunshine totals were generally close to the annual normal.
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For media comment, please contact:
Dr James Renwick, NIWA Principal Scientist, Climate Variability & Change Tel: mobile (021) 178 5550, office DDI (04) 386 0343
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