Issued 7 January 2003

Rainfall deficiencies persist in east and south

December rainfall had little effect on the overall pattern of rainfall deficiencies, the Bureau of Meteorology announced today. Some areas, such as the Hunter Valley in NSW, received some relief with above average rainfall, but in other parts, such as western Queensland, the situation worsened following another month of below average rain. Falls early in 2003 have been well below that required to have any significant impact on the long-term rainfall deficiencies.

9-month rainfall deficiencies

For the nine-month period from April to December, serious to severe rainfall deficiencies cover more than half of Victoria and most of Queensland and New South Wales. Much of inland South Australia and central parts of the NT also remain affected, and some areas in the southwest of WA are experiencing rainfall deficits for the third successive year.

Areas of lowest on record totals for the April to December period, in a record dating back to 1900, cover extensive regions of central and far western Queensland, as well as being scattered across NSW.

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13-month rainfall deficiencies

For the thirteen-month period from December 2001 to December 2002,some additional areas around Cairns and Cooktown in far north Queensland, and along the coast from Mackay to Grafton have experienced serious to severe rainfall deficiencies.

The January to March period is the most likely three-month period for a significant change in Australiaís rainfall patterns at the end of an El Niño event. These changed rainfall patterns, which usually mark the beginning of the end of drought conditions, can take various forms ranging from a succession of moderately wetter than average months, to a widespread deluge that heralds several months of significantly above average rainfall.

It is impossible to say just how the current drought will end, but because it is so widespread the breakdown is unlikely to be uniform in either time or space. Furthermore, what constitutes drought-breaking rain is a matter of perspective. For example, an engineer managing water supply storages is likely to have different criteria for considering the drought broken, from those of a farmer or grazier.

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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 Commonwealth Department of Agriculture Fisheries and Forestry - Australia (AFFA) takes the lead on drought impact 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 Bureauís 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 extent of areas below the 10th percentile, as well as the mean Australian percentile ranking. The 9-month period from April to December is compared to the first nine months of previous Australian droughts with the results tabulated as follows:

Rank 9-month period %of Australia
below the 10th
percentile
Rank 9-month period Mean Australian
percentile value
1. Nov 1901 - July 1902 58.9 1. April - Dec 2002 13.2
2. April - Dec 2002 58.6 2. March - Nov 1994 15.7
3. March - Nov 1994 52.6 3. April - Dec 1972 17.1
4. March - Nov 1940 49.9 4. March - Nov 1940 18.6
5. July 1951 - Mar 1952 49.4 5. July 1951 - Mar 1952 19.4
6. April - Dec 1982 46.8 6. April - Dec 1967 21.3
7. April - Dec 1972 46.5 7. May 1928 - Jan 1929 21.6
8. Nov 1964 - July 1965 46.2 8. April - Dec 1982 21.6
9. June 1925 - Feb 1926 45.7 9. Nov 1964 - July 1965 21.7
10. April - Dec 1967 45.0 10. Nov 1901 - July 1902 21.8

So in an Australia-wide sense, the current drought is among the worst on record, as far as relatively short-duration events are concerned, being remarkable for both its spatial extent of rainfall deficiencies, and average level of "dryness". Even outside of the rainfall deficient areas, the past nine months were mainly drier than average with very few regions experiencing average or above average totals.

However, itís also true that relatively few regions have registered record low rainfall totals. This contrasts with 1901/02 when almost all of NSW and over half of Queensland had record low rainfall. The national mean percentile (above) for 1901/02 though, also takes into account above average rainfall over WA.

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