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Statement on Drought for the 12-month
period ending 30th April 2007
Short Term Relief but Long Term Drought Persists
With the demise of the 2006 El Niño event, 2007 has seen a general
improvement in rainfall across Australia. Above average rainfall has
been widespread across southern Australia for the four month period
January to April 2007, with near to average rainfall across much of
the Murray Darling Basin. April saw particularly good falls across
southern Western Australia much of South Australia, and parts of
western Victoria and New South Wales. While follow-up falls are clearly
needed, this rainfall will provide short term relief to many
agricultural systems.
History shows that the breakdown of past El Niño droughts has usually
been associated with a shift to above-normal rainfall across much of
eastern Australia. For example, of the 20 past El Niño-related
droughts in the Murray-Darling Basin, in all 20 cases, a period
of sustained above-normal rainfall occurred no later than the following
winter (June-August). In 60% of cases this had occurred by the February-April
period, whilst in the remaining 40% of cases it was later than that, most
commonly in the May-July period. There is no historical precedent in 107
years of records for dry conditions to continue unbroken through the winter
following an El Niño event.
An important consideration in the recovery from this drought event
is the different rate at which systems respond to drought. At the
current time, many catchments in eastern Australia are excessively
dry from a very protracted period of below average rainfall and
above average temperatures. This means that it will take above
average rainfall just to produce average runoff, and very considerable
rainfall to make a material difference to water storages.
Long Term Deficiencies Remain in parts of Southwestern and Eastern Australia
Above average rainfall during April in Western Australia to the north
of Carnarvon and to the south of Perth, eased areas of lowest on record
rainfall for the period, but
severe deficiencies
still remain. In contrast below average rainfall for April in the area
around Melbourne and in northern Tasmania caused an expansion of an area
of lowest on record rainfall. Dry conditions were eased in parts of
southern South Australia, which received above average rainfall for
the month, but for the past twelve months, rainfall deficiencies
remain evident in western WA. southeastern South Australia and in a
band stretching across much of the region from Tasmania to southeast
Queensland.
For the 12-month period from May 2006 to
April 2007, there were serious to severe rainfall deficiencies over
southern and eastern Australia in a broad arc extending across
southeastern SA, much of Victoria, much of southeastern NSW west of
the Great Divide, and a large part of southeast Queensland. Northern
and eastern parts of Tasmania were also affected as was WA west of a
line from around Exmouth to Bremer Bay in the south. Record low 12-month
falls were recorded between Dalby and Goondiwindi in southern Queensland,
along much of WA’s southwest coast and Tasmania’s north coast, and in a
large area around Melbourne.
The worst of the long-term deficiencies are likely to remain for some
time. For them to be removed by the end of July, for example,
falls over the next three months would need to be in the highest
10% of the historical record in many areas, especially in Victoria and
southeast Queensland.
In comparison with the situation for the twelve months to March, areas
of lowest rainfall on record shrank parts of western WA, particularly
around Carnarvon and expanded in southern Victoria around Melbourne.
The deficiencies discussed above have occurred against a backdrop of
multi-year rainfall deficits that have severely stressed water supplies
in the east and southwest of the country.
Rainfall
deficiency maps for standard periods out to three years are
available.
Note: The terms used to describe rainfall in these
Drought Statements have the following meanings -
Serious deficiency
- rainfalls in the lowest 10% of historical totals,
but not in the lowest 5%
Severe deficiency
- rainfalls in the lowest 5% of historical totals
Lowest on record
- lowest since at least 1900 when the data analysed begin
Very much below average
- rainfalls in the lowest 10% of historical totals
Below average
- rainfalls in the lowest 30% of historical totals,
but not in the lowest 10%
Average
- rainfalls in the middle 40% of historical totals
Above average
- rainfalls in the highest 30% of historical totals,
but not in the highest 10%
Very much above average
- rainfalls in the highest 10% of historical totals
For more information regarding this rainfall
deficiencies statement, please contact the following
climate meteorologists in the National Climate Centre:
David Jones on (03) 9669 4085
Blair Trewin on (03) 9669 4623
External Sites Relating to Drought
The Bureau of Meteorology does not make formal drought declarations
as these are done by either the relevant State Governments or by the
Australian Government. The Australian Government Program is called
Exceptional Circumstances
and it is administered by the Federal Department of Agriculture,
Fisheries and Forestry (DAFF). General information about Australian
Government drought assistance is available at
http://www.daff.gov.au/droughtassist.
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