Issued 1 November 2002

Rainfall deficiencies worsen following dry October

The Bureau of Meteorology announced today that the area of the country experiencing severe rainfall deficiencies has expanded as a result of a very dry October. Nearly half of Australia recorded October falls within the lowest 10% of records with much of NSW registering record low totals. Also recording their driest October on record were parts of the Upper North and Northeast districts in South Australia, as well as scattered patches through southern and central Queensland.

7-month rainfall deficiencies

For the seven-month period from April to October, serious to severe rainfall deficiencies cover about 70% of the country, the most notable exceptions being western Tasmania and northwest WA where average to above average falls occurred. Some parts of the southwest of WA are affected for the third successive year. The deficiencies in northern areas of Australia are not as significant as those further south as the April to October period is largely in the seasonally dry time of year, although early wet season falls have been very poor.

Pockets of lowest on record totals for the April to October period, in a record dating back to 1900, are scattered across the country. Some of the more noteworthy areas include regions in southern WA and a strip through eastern NSW from Wollongong to Tamworth.

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11-month rainfall deficiencies

For the eleven-month period from December to October, some additional areas around Cairns and Cooktown in far north Queensland, and along the coast from Mackay to Grafton have experienced rainfall deficiencies. There are also some patches between Longreach and Rockhampton that appear on the longer period, and deficiencies are slightly more extensive in southwest Victoria and southeast SA as well.

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Comparisons with other dry spells

A frequently asked question is "how does the current drought compare with other notable ones from the past?" It should be noted that the Federal Department of Agriculture Fisheries and Forestry - Australia (AFFA) takes the lead on drought issues at the national level, and official drought declarations are the responsibility of the State and Territory Governments. The Bureau of Meteorology advises AFFA on all aspects of climate conditions.

The Bureau's National Climate Centre monitors Australian rainfall patterns on a range of time-scales from days to years, including analyses of rainfall deficiency that form the basis for statements like those above. To reiterate, rainfall is said to be deficient if it is within the lowest 10% of historical totals (decile range 1 or below the 10th percentile) for the period in question (3 months or longer).

The National Climate Centre has analysed the historical rainfall record back to 1900 looking at both the national coverage of areas below the 10th percentile, as well as the mean Australian percentile ranking. The current period from April to October (7-months) is compared to the first seven months of previous Australian droughts with the results tabulated as follows:

Rank 7-month period %of Australia
below the 10th
Rank 7-month period Mean Australian
percentile value
1. April - Oct 2002 68.3 1. April - Oct 2002 10.1
2. April - Oct 1946 61.9 2. April - Oct 1946 15.4
3. Nov 1901 - May 1902 56.4 3. March - Sept 1994 16.4
4. March - Sept 1994 55.2 4. April - Oct 1982 18.8
5. April - Oct 1982 53.2 5. May - Nov 1928 19.0
6. Nov 1964 - May 1965 49.1 6. Nov 1964 - May 1965 19.2
7. April - Oct 1967 45.0 7. Sept 1963 - Mar 1964 22.1
8. Sept 1963 - Mar 1964 41.2 8. April - Oct 1967 22.6
9. March - Sept 1940 40.8 9. March - Sept 1940 22.7
10. May - Nov 1929 38.3 10. Nov 1901 - May 1902 23.5

So in an Australia-wide sense, the current period is remarkable for its spatial extent of rainfall deficiencies, and average level of "dryness". Even outside of the rainfall deficient areas, the past seven months were mainly drier than average with very few regions experiencing average or above average totals.

On regional scales the rankings are somewhat different. For example, if the analysis is confined to the Murray-Darling Basin (MDB) the most severe first seven months of drought occurred in 1901/02. During that time 99.3% of the basin recorded serious or severe rainfall deficiencies, and the mean percentile ranking was an arid 0.7. Over the MDB the current period ranks 4th for both spatial coverage and mean percentile.

Furthermore, most of the previous droughts had durations longer than seven months, so ultimately it will only be at the conclusion of the current event that its true historical context can be calculated.