La Nina set to return

In pastoral farming in NZ the weather gods determine the success or otherwise of the season, with spring rains often most critical to build feed supplies.

Farmers manage this spring surplus by conserving into supplementary feed, or saving in situ for future deficits over a hot dry summer. Operators in dry areas have become adept at developing  systems that adjust with the climates unpredictability, using flexible stocking rates classes of stock that can be sold quickly, and forage species that cope in drier years.

As climate science has developed, predictions have become more accurate and NIWA's seasonal outlook is helpful in farmer planning for the season ahead. One climate commentator believes this La Nina weather pattern generally is favourable for most pastoral farmers, with warm summers but often characterised with rain bursts to keep soil moisture levels reasonable.

How valuable do you think these long term predictions are, and do they influence your medium term management decisions?

The NIWA National Climate Centre’s outlook for late spring and early summer, October to December 2011, indicates that seasonal rainfall is likely to be normal or below normal in all regions reports Scoop.Soil moisture levels and river flows are likely to be below normal in all regions of the country, except for the west and south of the South Island where normal or below normal soil moisture levels are likely. The Centre notes that soils are already drier than normal for this time of year in north Canterbury, MacKenzie country and Central Otago, as well as parts of the North Island.

Temperatures for October-December are likely to be average or above average in the North Island and northern South Island, and near average in the rest of the South Island. La Niña conditions are redeveloping in the tropical Pacific, and the event is expected to build through spring and continue over the summer season, according to the NIWA National Climate Centre. The outlook states that mean sea level pressures during the October-December period as a whole are likely to be above normal across New Zealand, with weaker westerlies over the country.

Temperature: For the October – December period as a whole, air temperatures are likely to be average or above average in the North Island and in Nelson-Marlborough. For the remainder of the South Island, temperatures are likely to be near average. Sea surface temperatures near New Zealand are expected to be close to normal or slightly above normal through the period.

Rainfall, soil moisture, and river flows: The National Climate Centre says that late spring-early summer rainfall is likely to be normal or below normal for all regions of New Zealand. Soil moisture levels and river flows are likely to be below normal everywhere, except for the west and south of the South Island where normal or below normal soil moisture levels are likely. Soils are already drier than normal for this time of year in north Canterbury, MacKenzie country and central Otago, as well as parts of the North Island.

There has been a major shift in the consensus from global climate models which predict El Niño-Southern Oscillation conditions. The majority of these models are now forecasting further development of La Niña patterns over spring and a continuation through the summer of 2011/12. At this early stage, we cannot be confident about the intensity of the event.