Soil water balance - a quick guide to droughts.
The soil water balance is a method of calculating how much rain or irrigation water in a given soil depth is used by plants, or is lost through drainage or by surface runoff.
Climate Update 73 - July 2005
Outlook and outcome – April 2005 to June 2005
Rainfall was near normal as predicted in parts of the North Island, but lower than expected in the north and west of the North Island and much of the South Island.
Air temperatures were above average in the north of the country, and near average in much of the South Island, as was predicted, but lower than expected in the east and south of the country.
Streamflows were above normal to normal on the east coast of the North Island and in the south of the South Island, and below normal elsewhere.
The outcome maps shown here give the t
Climate Update is a summary each month of New Zealand’s climate, including soil moisture and river flows.
July 2005 – Number 73
June’s climate: cold southerlies over the North Island and dry conditions in much of the South Island.
June’s river flows: Localised high river flows contrasted with very low flows in much of the South Island.
New Zealand climate in June 2005
New Zealand experienced frequent cold southerlies in June, especially over the North Island. Air temperatures were lower than normal in the east and south of the country. Christchurch Airport recorded –6.1 °C on 25 June, the lowest temperature for 30 years.
It was sunny and dry along the east coast of the South Island.
The outlook for July 2005 to September 2005
In contrast to June’s southerly conditions, a return to wind flows of average variability over New Zealand is expected for the rest of winter. Enhanced westerly flows are likely to the south of the country.
Expected conditions are mapped below. Air temperatures are expected to be near or above average in all regions.
Regional flow contrasts
Strong regional contrasts in June streamflows were seen, with both high and low streamflows in both islands. In the North Island, flows were above normal in Hawke’s Bay and Wairarapa. In the South Island, flows were above normal in coastal Southland, but very low in most other places.
Percentage of average June streamflows for rivers monitored in national and regional networks. The contributing catchment area above each monitoring location is shaded.
Low South Canterbury and Otago moisture
Soil moisture levels in parts of South Canterbury and Otago remained lower than normal in June, following low June rainfalls in the region. Elsewhere in the country, soils were mostly at field capacity or above, and unusually wet in Hawke’s Bay and Kaikoura.
Water balance in the pasture root zone for an average soil type where the available water capacity is taken to be 150 mm.