Australia is the driest inhabited continent even though some areas have annual rainfall of over 1200 millimetres. Our climate is highly variable - across the continent generally, as well as from year-to-year. We must learn to live with drought!
A drought is a prolonged, abnormally dry period when there is not enough water for users' normal needs. Drought is not simply low rainfall; if it was, much of inland Australia would be in almost perpetual drought. Because people use water in so many different ways, there is no universal definition of drought.
Meteorologists monitor the extent and severity of drought in terms of rainfall deficiencies. Agriculturalists rate the impact on primary industries, hydrologists compare ground water levels, and sociologists define it on social expectations and perceptions.
During climate extremes, whether droughts or flooding rains, those on the land feel it most. Agriculture suffers first and most severely - yet eventually everyone feels the impact.
Drought disrupts cropping programs, reduces breeding stock, and threatens permanent erosion of the capital and resource base of farming enterprises. Declining productivity affects rural Australia and the national economy.
The risk of serious environmental damage, particularly through vegetation loss and soil erosion, has long term implications for the sustainability of our agricultural industries. Water quality suffers, and toxic algae outbreaks may occur; plants and animals are also threatened. Bushfires and duststorms often increase during dry times.
Australia has one of the most variable rainfall climates in the world. Over the long term we have about three good years and three bad years out of ten. These fluctuations have many causes, but the strongest is the climate phenomenon called the Southern Oscillation. This is a major air pressure shift between the Asian and east Pacific regions - its best-known extreme is El Niño.
In recent years, the Bureau of Meteorology's greater understanding of
El Niño has improved its ability to predict seasonal rainfall and
help authorities and individuals with early drought warnings.
More information: About El Niño and La Niña
Photograph courtesy of the Department of Foreign Affairs and Trade.
The Bureau's Drought Watch Service has been a key component of national drought management since 1965. It is based on a nationwide daily rainfall measuring network and established relationships between rainfall deficiency and the severity of recorded drought. Its rainfall information assists government, business and the rural community. It also helps to assess the current situation, providing early indication of the need for contingency action or drought relief. Since the implementation of Commonwealth Government 'National Drought Policy' initiatives in 1992, the Bureau has expanded its rainfall analysis services.
Using monthly rainfall analysis, areas suffering from rainfall deficiencies appear in the Drought Statement as well as the publication Monthly Drought Review. If the accumulated rainfall over three successive months was within the lowest 10 per cent on record, a Drought Watch is commenced and the region is highlighted. This initial dry period stretches to six months for arid regions. Consideration is also given to whether an area is usually dry at that time of the year. There are two rainfall deficiency categories:
A severe rainfall deficiency exists in a district when rainfall for three months or more is in the lowest 5 per cent of records (see graph below - orange section).
A serious deficiency lies in the next lowest 5 per cent i.e. lowest 5 per cent to 10 per cent of historical records for a three month or longer period (yellow section in graph below).
Allowing for seasonal conditions, the Drought Watch may continue for many months and ceases when plentiful rainfall returns. 'Plentiful' is defined as well above average rainfall for one month, or above-average rainfall over a three-month period.
The Drought Watch Service provides a consistent starting point for national drought alerts. Drought declarations take account of other factors in addition to rainfall and are the responsibility of the State Governments.
For Australian conditions, drought frequency is crucial. Research indicates that severe drought affects some part of Australia about once every 18 years. This does not indicate that severe drought regularly and predictably recurs every 18 years; intervals between severe droughts have varied from four to 38 years. We have long historical rainfall records to give a clearer picture of what is 'normal' for an area, and how much variation might be expected.
There is little chance that all Australia could be in drought at the same time. Some droughts are long-lived; some are short and intense, causing significant damage. Some can be localised while other parts of the country enjoy bountiful rain. Some regional droughts are not related to El Niño events, and are therefore harder to forecast. Examples of each of these types of drought are shown in the large picture below.
Meteorologists need up-to-date information on global climate patterns for early warning and monitoring of drought. Under the umbrella of the World Meteorological Organization (WMO), the Bureau participates in and contributes to international weather and climate watch programs. The WMO's new Climate Information and Prediction Services (CLIPS) project is designed to enable member nations to make the most of new abilities to monitor and predict seasonal climate variations.
|The effects of major drought|
|1864-66||All States affected except Tasmania.||1963-68||Widespread drought. Also longest drought in arid central Australia: 1958-67. The last two years saw a 40 per cent drop in wheat harvest, a loss of 20 million sheep, and a decrease in farm income of $300-500 million|
|1880-86||Southern and eastern States affected.|
|1895-1903||Sheep numbers halved and more than 40 per cent loss of cattle. Most devastating drought in terms of stock losses.|
|1911-16||Loss of 19 million sheep and 2 million cattle.||1972-73||Mainly in eastern Australia.|
|1918-20||Only parts of Western Australia free from drought.||1982-83||Total loss estimated in excess of $3000 million. Most intense drought in terms of vast areas affected.|
|1939-45||Loss of nearly 30 million sheep between 1942 and 1945.||1991-95||Average production by rural industries fell about 10 per cent, resulting in possible $5 billion cost to the Australian economy, $590 million drought relief provided by the Commonwealth Government between September 1992 and December 1995.|