Climate Update 66 - December 2004

December

Climate

River flows

Soil moisture

Three-month outlook

Checkpoint

Backgrounder

Backgrounder

Backgrounder
Measuring drought

Irrigating near Luggate, Central Otago.

Potential evapotranspiration deficit (mm) that is likely to be equalled or exceeded once every 20 years.

Drought is often hard to quantify, and its severity and duration affect different enterprises in different ways.
One way of measuring drought is to calculate the amount of water typically available for a particular purpose, and then estimate the reduction in water available for that purpose during low rainfall seasons.
For example, we can estimate the amount of water that is 'consumed' during normal pasture growth

Checkpoint

Outlook and outcome – September 2004 to November 2004
Rainfall was normal to below normal in the north and east of the North Island, as predicted. Higher rainfalls than forecast occurred in the west and southwest of the South Island, and it was drier than predicted in the northeast of the South Island.
Air temperatures were lower than predicted in Waikato, and in the east of the North Island and north of the South Island.
Streamflows were below normal in the northern North Island, and normal in the southwest of the North Island, as predicted.

December

Climate Update is a summary each month of New Zealand’s climate, including soil moisture and river flows.
December 2004 – Number 66
November’s climate: November air temperatures higher than average overall.
November’s river flows: Low streamflows in the north and east of the North Island.
Soil moisture levels: Low rainfall in the North Island and north of the South Island.
Three-month outlook: A tendency for drier conditions in the north and east of the country ranging to wetter in the west and southwest.

Climate

New Zealand Climate
Mild; dry in the north and east
November was a mild month, with warmer than normal conditions, particularly in the South Island. The national average temperature of 14.3 °C was 0.6 °C above the historical average.
Rainfall was 50% of average in Northland, Auckland, parts of Hawke’s Bay, and along the Kaikoura coast and North Canterbury.
For more information on the climate in November, visit the climate summaries page at www.niwa.co.nz/ncc/cs/mclimsum_04_11
 
Percentage of average rainfall for November 2004 (recording sites shown with dots).

River flows

River flows
North Island flows low in some areas
Streamflows were below normal in the north and east of the North Island and the northern South Island. Elsewhere, streamflows were near normal, with a trend to above normal in some South Island alpine catchments.

Percentage of average November 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: dry spots developing
End of November soil moisture levels were lower than normal in much of Northland, and in Hawke’s Bay, Marlborough, and Kaikoura. Elsewhere, moisture conditions were near normal.
 
Soil moisture deficit in the pasture root zone at the end of November (right) compared with the deficit at the same time last year (centre) and the long-term end of November average (left). The analysis is done for an average soil type where the available water capacity is taken to be 150 mm.