Second dry summer for North
Climate figures for February highlight how parts of the North Island are having their second dry summer in a row, but scientists say the reason for the lack of rain in 2014 is different to the cause of last summer’s drought.
Niwa’s February climate summary, published today, said much of the North Island had well below normal rainfall during the month, except for eastern Northland and the coast south of Hawke’s Bay.
Many places in the South Island also had well below normal rainfall, particularly areas from south Canterbury through central Otago and northern Southland.
No rainfall at all was recorded for Ohakune, compared to the February average of 84.6mm, while Paeroa had just 12 per cent of its normal February rainfall with 10mm, Auckland Airport had its fourth driest February with 11mm or 15 per cent of normal, and Taumarunui had its second-equal driest February with 9mm or 9 per cent of normal.
Hamilton had just 17 per cent of normal rainfall with 12mm, while Christchurch actually had 120 per cent of normal with 52mm, and Wellington had 68 per cent of normal with 48mm.
Despite the widespread low rainfall, Niwa said soil moisture deficits were not as extensive as those a year ago in the 2013 drought - one of New Zealand’s most extreme on record.
Niwa did say the deficits may be as severe as 2013 in isolated regions, with soil moisture levels lowest, compared to normal for this time of year, in the Waikato, Waitomo and Taupo districts.
Having two dry summers in a row did happen from time to time, but it was also "not inconsistent" with the type of weather patterns being projected for later in the century as an effect of climate change, Niwa principal climate scientist Dr Andrew Tait said.
While in some areas, such as Waikato, many dairy farms were irrigated, being able to use irrigation depended on being able to take water from rivers and the ground.
"Even dairy farming might find it hard to continue current practices if we get these dry periods much more frequently," Tait said.
The dry conditions this summer tended to be a mainly January and February event, whereas last summer’s drought had started as early as October 2012 and had intensified from January to March.
Being drier for longer last summer had added a range of extra pressures, which he did not think were present in most places this year, Tait said.
The mechanisms leading to the dry conditions were also different this summer from last year.
"Last year’s dry conditions really were associated with a lot more anti-cyclones over the country than we normally would have, giving sunny, warm days with no rain.
"Whereas January and February this year ... it’s been more of a wind direction change, where there hasn’t been as many westerlies as we would normally get. So particularly western areas of the North Island haven’t been getting the rain they normally would," Tait said.
The Niwa summary said February had been characterised by unusually high pressure to the south of New Zealand, and unusually lower pressures to the northeast.
That resulted in a predominantly southeast wind flow over the country for the month, contributing to the abnormally dry conditions in western and central areas of the North Island. In contrast, rainfall had been higher than normal for some eastern coastal sections of the North Island.