Low winter rainfall part of long-term pattern

Low winter rainfall part of long-term pattern


Weather
The Yass Valley is part of a number of areas with markedly lower than average winter rainfall this year, this photo from last week showing only a bare minimum of green pick for cattle even though it is already mid-July.

The Yass Valley is part of a number of areas with markedly lower than average winter rainfall this year, this photo from last week showing only a bare minimum of green pick for cattle even though it is already mid-July.

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This year's below average winter rainfall in eastern Australia is part of a drying pattern over winter over the past 20 years.

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THIS year's below average winter rainfall is part of a 20-year long trend towards lowe winter rainfall in the areas that depend on it most.

Data presented during a Bureau of Meteorology (BOM) climate seminar this week showed much of southern Australia has seen a massive reduction in cool season rainfall over the long term average for the period from 1998 to 2018.

Southern areas have a winter/spring dominant rainfall pattern and rely on rain from April to November to produce crops and pastures for livestock.

In contrast, tropical areas which have their dry season over the winter preiod have showed an increase in winter rain, albeit from a low base.

This year the trend has continued with large tracts of eastern Australia in particular well below average for winter rainfall.

Even the areas currently rated as in good condition in terms of cropping prospects are only at or slightly below the long term average for winter rainfall rather than markedly wetter.

David Jones, climatologist with the BOM, said part of the problem was that cold fronts were persistently slipping south into the southern ocean rather than delivering frontal rainfall to southern Australia.

Dr Jones was speaking as the BOM attempted to explain the factors behind the current dry spell.

He said the current dry snap was being compounded by higher than average daytime temperatures.

"It is not only a drought but a hot drought and that has implications for water demand."

He said the figures were not so noticeable in terms of overnight temperatures, but said this may be because of the high incidence of heavy frosts, caused by the clear conditions.

Apart from the headline rainfall and temperature figures, the BOM also presented sobering evaporation and NDVI (normalised difference vegetation index) figures, showing much higher evaporation rates and lower rates of ground cover than normal.

"We are very, very much below average in terms of vegetation," Dr Jones said.

He said realistically the next chance to beat the drought would come in the summer, saying that rainfall in the parched northern part of the Murray Darling Basin was generally low over the spring period and that climate indicators was that it was going to be dry over the spring.

"It is looking like being dry and heating up early for the northern spring so that means we are realistically looking towards tropical moisture coming down over the summer as the best chance in the short term to ease the drought."

The story Low winter rainfall part of long-term pattern first appeared on Farm Online.

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