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1301.0 - Year Book Australia, 2004  
Previous ISSUE Released at 11:30 AM (CANBERRA TIME) 27/02/2004   
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Contents >> Environment >> Drought

Severe drought conditions have been experienced throughout much of Australia recently. Defining exactly when droughts begin and end is a difficult task. One problem is that droughts are defined and measured in different ways. Because of this, this section focuses on rainfall deficiencies as the primary indicator of drought and uses 1 July 2002 to 30 June 2003 as the reference period.

Defining and measuring drought

Drought is a term that has no universal definition. While the Bureau of Meteorology (BOM) defines drought as a 'prolonged, abnormally dry period when there is not enough water for users normal needs', it is not simply an acute shortage of water (BOM 2003a).

Drought is defined and measured, in various ways by different users, for different purposes. To meteorologists, drought is defined by rainfall deficiencies over extended periods of time. For example, BOM measures rainfall over time and produces maps that show areas considered to be suffering from serious or severe rainfall deficiencies.

Drought can also be defined by its impacts on primary industries, in particular agriculture. This can be illustrated by the evaluation process of Drought Exceptional Circumstances (DEC), which forms part of the National Drought Policy (NDP), a joint Commonwealth and state government initiative. The DEC evaluation process involves the integration of climatic, agricultural production and economic data from a range of government agencies to assess the severity and impact of drought on farm businesses and families, to determine if government assistance is required.

Scientists (e.g. hydrologists, soil scientists and botanists) define and measure drought in terms of changes and impacts on surface and groundwater levels, soil moisture and plant growth. Social scientists can define drought in terms of social expectations, perceptions and impacts on rural communities.

Rainfall deficiencies

The Australian climate of 2002 was characterised by dry and warm conditions. It was the fourth driest year on record, while maximum temperatures across the continent were the warmest on record (BOM 2003b). Droughts and higher than average temperatures are often linked (Jones & Trewin 2000).

The rainfall deficiency map produced by BOM (map 24.30) illustrates the areas and severity of rainfall deficits over the period July 2002 to June 2003. According to BOM, an area is determined to be suffering from a serious rainfall deficiency when rainfall is between the lowest 5 and 10% recorded rainfall for the period in question. Severe rainfall deficiency is when rainfall is among the lowest 5% for the period in question. Rainfall deficiency maps produced by BOM also show areas where rainfall is the lowest on record for the time period. This map shows how severe rainfall deficiencies occurred over most of eastern Australia during the period July 2002 to June 2003, with many areas experiencing the driest periods on record.

24.30 RAINFALL DEFICIENCY- 2002-03
Map - 24.30 Rainfall deficiency - 2002-03

Source: BOM 2003c.

All states and territories were affected by rainfall deficiencies in the approach to the 2002-03 year. By December 2002, serious to severe rainfall deficiencies covered more than half of Victoria, and much of Queensland and New South Wales. Inland South Australia and central Northern Territory were also affected by rainfall deficiencies, while areas in the south-west of Western Australia were experiencing rainfall deficits for the third successive year (BOM 2003d).

While widespread above average rainfalls were recorded in February 2003 and temporarily relieved many areas suffering from rainfall deficiencies, by March serious to severe rainfall deficits occurred from far north Queensland through to most of New South Wales (including the Australian Capital Territory) and Victoria, and east South Australia (BOM 2003e). Parts of Tasmania, Western Australia and Northern Territory were also affected by rainfall deficits. Below average Autumn rainfalls exacerbated the dry conditions across the country. By June 2003, longer term serious to severe rainfall deficiencies continued across most of eastern Australia, parts of central Australia and Western Australia.

It is difficult to compare this drought, of which part has occurred during 2002-03, to other droughts in Australia on record until this event is considered concluded. However, analysis by BOM suggests that this drought is among the worst on record in terms of short to medium duration drought events both for the spatial extent of rainfall deficiencies and the average level of dryness (BOM 2003f).

Drought declared and exceptional circumstance areas

At the national level, the Bureau of Rural Sciences (BRS) produced maps of declared Drought Exceptional Circumstances (DEC) areas, that reflect an integrated evaluation of drought involving physical, economic and social indicators (map 24.31). These maps are used to direct Australian Government assistance to areas determined to be affected by drought. However, drought declaration in Australia is primarily the responsibility of state governments, who take into account a variety of factors including rainfall deficiencies in determining an area drought affected. For example, during 2002-03 both New South Wales and Queensland had significant areas of land declared drought affected by their respective state governments. In July 2003 the entire state of New South Wales and almost two-thirds of Queensland was declared to be in drought.

24.31 EXCEPTIONAL CIRCUMSTANCES(EC) BOUNDARIES - June 2003

Map - 24.31 Exceptional Circumstances (EC) Boundaries - June 2003
Source: BRS 2003.

Water storage levels and water restrictions

One of the measurable impacts of drought is a reduction in water storage levels. Changes in water storage levels can lead to the introduction of water restrictions, which limit the volume and way users can utilise water, especially in urban settlements.

Substantial decreases in water storage levels were experienced in eastern Australia over 2002-03. Graph 24.32 shows the changes that occurred in the water storage capacity of Melbourne Water reservoirs in the period August 2002 to June 2003. The declining volume of water in the storages of Melbourne are typical of those of in many parts of eastern Australia.

Graph - 24.32 Melbourne water storages levels, By month


As a result of low levels of water in storage, water restrictions were introduced in most capital cities around Australia during 2002-03. These water restrictions varied from voluntary reductions of water use to mandatory restrictions of use. Sydney, Melbourne, Perth, Hobart and Canberra all experienced water restrictions during 2002-03. Restrictions were introduced in Adelaide from July 2003. Brisbane had permanent restrictions on the times residents were able to use sprinklers. The only capital city not affected by water restrictions during 2002-03 was Darwin. Water restrictions were also introduced in rural areas and farmers in drought affected regions had their water allocations greatly reduced in the 2002-03 irrigation season.

Economic impact of drought in 2002-03

Drought can have a significant impact on the economy, in particular through the decline of agricultural production. Based on forecasts by the Australian Bureau of Agriculture and Resource Economics (ABARE), the ABS has estimated the impact of drought on gross domestic product (GDP) growth.

The latest estimates by the ABS suggest that the direct effect of the current drought on agricultural production has had a downward impact on GDP growth of 1.0 percentage point between 2001-02 and 2002-03 (see Impact of the drought on Australian production in 2002-03 - National accounts). Gross value added at basic prices for the agriculture industry fell by 28.5% in 2002-03 compared with the level in the preceding year.

Drought can also have indirect effects on the economy which are not quantified in this analysis. These indirect effects can include negative impacts of falling agricultural production on downstream industries, particularly transport, wholesale trade and industries involved in the manufacturing of products from agricultural outputs. Any reduction in the inputs of these industries can also lead to a reduction in the production of other Australian industries. In addition, any reduction in agricultural income can lead to a fall in expenditure by farmers and others who draw an income from these industries.

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