Next four years expected to be wetter than usual

Press, 24 July 1987, Page 13

Next four years expected to be wetter than usual

The meteorologist who predicted the low rainfall which caused regionally disastrous droughts between 1982 and 1986 expects the next four years to be wetter than usual.

One or two years could be very wet, Mr Alaric Tomlinson, of the New Zealand Meteorological Office, wrote in the latest issue of “Soil and Water” magazine. In 1980, Mr Tomlinson suggested New Zealand could expect generally dry weather from 1983 to 1986.

His forecast was based on a statistical analysis of rainfall records since 1900 from 20 sites throughout New Zealand. Mr Tomlinson said the predictions largely came true, although a year earlier than he expected. The year 1982 recorded only 87 per cent of aver-

age rainfall across the country. “Apart from 1982, an extremely dry year, the four years 1982-85 were all below average,” he said.

“Such a nationally persistent rim of dry years has only occurred twice previously this century — once from 1911 to 1915 and, once from 1930 to 1934.”

It was not equally dry over the whole country but some areas, notably eastern parts from Hawke’s Bay to Canterbury, suffered quite badly. It may be possible to use the same type of analysis to forecast rainfall in specific regions and individual years where adequate records exist, Mr Tomlinson said. “The local area prediction would be whether next year’s rainfall is

likely to be above or below the median value.”

The prediction could expect a success rate of 60 to 80 per cent, similar to the accuracy of conventional one to three-day forecasts of the likelihood of rain. Mr Tomlinson said that since 1980 research in a number of countries has led to definite opinions on what is creating the patterns of rainfall observed in New Zealand and other countries.

A major influence is the southern oscillation, which is a see-sawing of atmospheric pressure between two centres of activity, one in the central South Pacific Ocean and the other in the eastern Indian Ocean.

Changing weather patterns are also attributed to sunspot and lunar cycles.