Climate Update 70 - April 2005

April

Climate

River flows

Soil moisture

Three-month outlook

Checkpoint

Backgrounder

April

Climate Update is a summary each month of New Zealand’s climate, including soil moisture and river flows.
April 2005 – Number 70
March’s climate: March temperatures above average in the north.
March’s river flows: Low stream flows in the northern North Island and normal in most other locations.
Soil moisture levels: High rainfalls in the Wairarapa.
Three-month outlook: A mostly warm autumn, with average to above average rainfall likely in the northern North Island.

Backgrounder

Backgrounder
More fog than usual in Wellington

Fog hours - February

Fog hours - March

Fog hours per year

Major disruptions to the operation of Wellington Airport occurred in February and March. Although fog is not unusual at this time of year, there was more fog around this year than normal.
Fog typically forms when moist air comes into contact with a cool surface. The air cools and condenses into visible water droplets.

Checkpoint

Outlook and outcome – January 2005 to March 2005
Rainfall was as forecast in the north and southwest of the North Island, and in north Canterbury, Central Otago, and Southland. It was wetter than predicted elsewhere in the east, and lower than predicted elsewhere in the west.
Air temperatures were lower than forecast in parts of the North Island, but generally average or below average as predicted in the South Island.
Streamflows were normal to above normal in much of the North Island, apart from Hawke’s Bay and the east coast where they were below normal.

Climate

New Zealand climate in March 2005
March was unsettled, with above average rainfall over much of the North Island, especially Wairarapa. However, drier and sunnier than average conditions occurred in Northland, Auckland, Waikato, and Coromandel.
It was warmer than normal in the North Island and in Nelson, while temperatures were mostly near average elsewhere.

Three-month outlook

The outlook for April 2005 to June 2005
Over the next three months, atmospheric pressures at mean sea level are expected to be lower than their historical average to the west of New Zealand, with more northerly flows than usual over the country. Sea surface temperatures around New Zealand are expected to be near or above average.
Mean three-month air temperatures are expected to be near or above historical averages in all districts.
Mean rainfalls are likely to be near normal in all districts, but may be above normal in the northern North Island.

River flows

River flows
Low flows in northern New Zealand
Stream flows were below normal in the northern North Island and above normal in the southern North Island, the northern South Island, and the southwest of the South Island. Near normal flows occurred elsewhere.

Percentage of average March streamflows for rivers monitored in national and regional networks. The contributing catchment area above each monitoring location is shaded. NIWA field teams, regional and district councils, and hydro-power companies are thanked for providing this information.

Soil moisture

Soil moisture levels recover in many areas
During March, soil moisture levels in central and eastern parts of the North Island, in the north and east of the South Island, and in much of Otago recovered to normal or above normal conditions. Most recovery occurred late in the month. Northland soils remained relatively dry during the month.
 
Soil moisture deficit in the pasture root zone at the end of March (right) compared with the deficit at the same time last year (centre) and the long-term end of March average (left).