Climate Update 38 - August 2002

28 March 2007 - 11:15am

Science Centres: Climate

August

Climate

River flows

Soil moisture

Three-month outlook

Checkpoint

Backgrounder

August
Climate Update is a summary each month of New Zealand's climate, including soil moisture and river flows. August 2002 – Number 38 July’s climate: Wet in the north; low rainfalls in the south. July’s river flows: July streamflows high in the north Soil moisture levels: Some east coast South Island soils were drier than normal at the end of July. Three month outlook: Generally warmer than average, but winter’s typical cold outbreaks at times. Checkpoint: How well are we doing with our predictions? Backgrounder: Satellites assist frost mapping. This issue of the Clima

Backgrounder
Backgrounder 2002 rainfall to date Large areas of New Zealand have received near normal rainfall. Parts of Waikato and Bay of Plenty, and the north and southwest of the South Island have been drier than average. Total rainfalls for 1 January to 31 July 2002. Update on the SOI The mean Southern Oscillation Index (SOI) for July was -0.8, with the three month average now at -1.0. A moderate El Niño is now in place, but its affect on New Zealand climate during spring is expected to be weaker than in 1997-98.

Checkpoint
Outlook and outcome – May to July 2002 Rainfall was as forecast for many areas. It was higher than predicted in parts of the east of the North Island, and over coastal south Otago and Southland. Air temperatures were as expected in all regions except the south and west of the South Island, where they were higher than predicted. River flows were above what was expected in much of the North Island, and in Buller and Southland.

Climate
New Zealand Climate Wet in the north; dry in the south Rainfall in northern and eastern North Island regions was well above normal, with Napier recording more than double its July average. Flooding occurred at Te Awamutu on 5 July, Te Kuiti and Mangakino on 8 July, Kaukapakapa on 11 July, and Mercer on 12 July when the Waikato River flooded farmland already saturated by weeks of wet weather.

Three-month outlook
The outlook for August to October 2002 An El Niño event in the tropical Pacific is now in place, but its duration and magnitude still remain uncertain. It is likely to be much weaker than the 1997–98 event, when there was lower than normal rainfall in many east coast areas, and severe drought in some localities. El Niños are typically, but not always, associated with below average temperatures and more frequent southwesterly winds over New Zealand.

River flows
New Zealand River Flows July streamflows high in the north July flows were above normal for most of the North Island and normal to below normal for the South Island.

Soil moisture
Soil moisture on 31 July Some east coast South Island soils were drier than normal at the end of July, particularly in Marlborough and south Canterbury. Elsewhere in the South Island, and in most of the North Island, soil moisture levels were near field capacity. Soil moisture deficit in the pasture root zone at the end of July (right) compared with the deficit at the same time last year (centre) and the long term end of July average (left). The analysis is done for an average soil type where the available water capacity is taken to be 150 mm.