Issued 4 February 2003
Rainfall deficiencies intensify
Widespread dry conditions throughout eastern Australia in January intensified rainfall deficiencies, the Bureau of Meteorology announced today. Furthermore, the situation was exacerbated by continuing well above average temperatures. One area that did experience relief was around the Gulf of Carpentaria, particularly in the NT, where heavy monsoonal rain ended periods of rainfall deficiencies.
10-month rainfall deficiencies
For the ten-month period from April to January, serious to severe rainfall deficiencies covered the vast majority of Queensland, NSW and Victoria, more than half of South Australia, much of the southern NT, significant areas in southwest WA and the far east of Tasmania. A large area through central Queensland and northern NSW has had record low rainfall for the April to January period, with records dating from 1900.
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14-month rainfall deficiencies
For the fourteen-month period from December 2001 to January 2003, some additional areas between Cooktown and Townsville in far north Queensland, and in the southeast of the State from Rockhampton to the NSW border have also experienced serious to severe rainfall deficiencies.
The period to the end of March remains the most likely time for a significant change in Australia’s rainfall patterns. This relates to the end of the current El Nino event, which is now showing clear signs of decay. 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 not possible for the Bureau to say just how or when this current period of rainfall deficiencies will end, but because they are so widespread, the breakdown is unlikely to be uniform in either space or time. Furthermore, different industries are impacted by different lengths of periods of rainfall deficiencies and for example, it may take water supply storages longer to recover from a period of rainfall deficiency than a farming or grazing activity.
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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 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 extent of areas below the 10th percentile, as well as the mean Australian percentile ranking. The 10-month period from April to January is compared to all ten-month periods of previous Australian droughts with the results tabulated below. Note that for long droughts with multiple overlapping 10-month periods, only the most intense period is shown in the table.
| Rank | 10-month period | % of Australia below the 10th percentile |
Rank | 10-month period | Mean Australian percentile value |
|---|---|---|---|---|---|
| 1. | Nov 1901 - Aug 1902 | 61.2 | 1. | May 1982 - Feb 1983 | 16.2 |
| 2. | May 1982 - Feb 1983 | 60.3 | 2. | March - Dec 1940 | 17.5 |
| 3. | Apr 2002 - Jan 2003 | 53.8 | 3. | March - Dec 1994 | 18.3 |
| 4. | Feb - Nov 1940 | 51.0 | 4. | Feb - Nov 1902 | 18.9 |
| 5. | July 1951 - Apr 1952 | 45.2 | 5. | Apr 2002 - Jan 2003 | 19.0 |
| 6. | May 1928 - Feb 1929 | 45.0 | 6. | Apr 1946 - Jan 1947 | 19.2 |
| 7. | Apr 1946 - Jan 1947 | 45.0 | 7. | March - Dec 1938 | 19.7 |
| 8. | Oct 1964 - July 1965 | 43.6 | 8. | July 1951 - Apr 1952 | 20.9 |
| 9. | March - Dec 1994 | 42.1 | 9. | Apr 1928 - Jan 1929 | 22.2 |
| 10. | March - Dec 1918 | 39.9 | 10. | Nov 1969 - Aug 1970 | 22.5 |
So in an Australia-wide sense, the current drought is among the worst on record, as far as relatively short to medium-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 ten months were mainly drier than average with very few regions experiencing average or above average totals. The main exception is around the southern Gulf of Carpentaria where recent very heavy rain has produced the wettest April to January period on record!
Ultimately it will only be at the conclusion of the current event that its true historical context can be calculated.
