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The Hon Dr Sharman Stone
Parliamentary Secretary to the Minister for the Environment and Heritage
Federal Member for Murray
In reply to concerns about the data coverage of rainfalls in the Mallee Wimmera, Dr Sharman Stone, Parliamentary Secretary with responsibility for the Bureau of Meteorology said today that the Bureau's rain gauge network across the country included over 6500 stations, with an average spacing of 40kms.
''In the Wimmera Mallee the Bureau's network included some 130 stations, with an average spacing of some 24 kms. This is clearly above the national average of coverage,'' Dr Stone said.
Obviously in areas of high rainfall variability between and within a season, individual stations will pick up different rain falls that may have resulted from patchy thunderstorm activity. These falls are then averaged for a district or region.
Rainfall averages in a district also varied according to factors such as elevation and the aspect of the site. For example long-term average annual rainfall at Horsham (Polkemmett) is 450mm, based on a 128 year record. At Longeronong the average is only 419mm, based on 105 years of record.
''The Bureau's analysis techniques take such variations into account,'' Dr Stone said.
Dr Stone also paid tribute to the Wimmera-Mallee rainfall readers.
''Some families have been taking daily readings for over a century. There are over 6000 volunteers across Australia. Anyone who wishes to join these great volunteers is always welcome to contact the Bureau,'' Dr Stone said.
Given it can be days or sometimes even over a week between the first and last rainfall records coming into the Bureau, the final rainfall average for a district or region may be refined a number of times as new records are added.
''I can also understand some of the confusion about the concept of a one in twenty year drought,'' Dr Stone said.
''Some people think this means the worst drought in the last twenty years (ie since 1982-3). In fact, the one in twenty year comparison is derived from the Bureau of Meteorology taking all of an area's rainfall figures dating back to first record taking, which is usually over 100 years, and ranking the yearly totals.
The lowest five years of rainfall are then identified, and referred to as years of 'severe' rainfall deficiency. Given these five years are roughly twenty per cent of the total record, any year that is as least as bad as any of these severely deficient five years is referred to as a 1 in 20 year phenomena.
The rainfall data collected by the Bureau of Meteorology are distributed widely, including to the Bureau of Rural Sciences. They then use the rainfall data as a factor in monitoring drought conditions, and making comparisons for recommendations about such things as which area is eligible for Interim EC measures.
Dr Stone said she understood only too well the frustrations and despair of those facing failed seasons. The combination of higher temperatures have meant that what little rain did fall was quickly evaporated.
Fortunately the Federal Government has committed an unprecedented level of support, including the declaration of Interim Exceptional Circumstances Support to much of the inland Eastern Australia, Dr Stone said.
The Bureau of Meteorology's daily, weekly and monthly maps are available on its website at www.bom.gov.au
Andrew Cox, Office of Dr Stone, 0408 057 226, or (03) 5821 5371
Kevin O'Loughlin, BOM, (03) 9669 4217