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Introduction

The Australian continent is subject to a wide diversity of climatic and environmental conditions, which can cause significant amounts of damage. Of all the natural hazards to plague the continent, drought, or a period of rainfall that does not provide for the needs of users, is the most financially costly. Over the years, the financial losses incurred by drought have been significant. Total losses caused by the severe 1982-1983 drought, for example, were estimated by the Australian Government to exceed $3 billion. Australia's history has been dominated by periods of extreme dryness, particularly in rural regions located far from well-watered coastal areas. See image 1

What is drought?

A drought is a long period of time in which the water available from rainfall and stored water is not enough to provide for the needs of users. It is not simply an acute shortage of water. This definition, for the purposes of clarity, provides a basic outline of what constitutes drought. It is widely recognised amongst meteorologists (people who study weather conditions), however, that drought cannot be defined in a precise manner, as water is used in many different ways. In a technical sense, the term 'drought' can be applied in three ways, meteorological, hydrological and agricultural.

A meteorological drought is simply a prolonged period of below-average precipitation. It does not take into account the needs of users or the amount of stored water. A hydrological drought occurs when water reserves available in sources such as lakes, dams, aquifers and reservoirs, fall below the statistical average. Droughts of this nature can prevail even with substantial periods of precipitation, such as when increased water usage diminishes reserves. In recent years, periods of low rainfall coupled with expanding populations in major cities and towns have forced many populations to deal with hydrological drought. An agricultural drought arises when there is insufficient moisture for average crop production. In conjunction with low periods of rainfall, drought can be intensified in rural regions through poor soil quality and inefficient agricultural techniques.

There is little chance that the entire continent would suffer from drought at the same time. Some regions can be afflicted by severe drought, while other districts enjoy bountiful rain. Some droughts are short-lived, while others extend over a number of years.

Why is Australia prone to drought?

Australia is an extremely dry continent. This is because of a variety of factors. There is a persistent high pressure system located above central Australia. Cool water currents off the coast of Western Australia prevent rainfall in that part of the continent. Australia is also a very flat continent, which leads to reduced orographic rainfall. (Refer Topic 2, Chapter 1)

A phenomenon responsible for rainfall variability in Australia is the El Niño Southern Oscillation system (ENSO). El Niño is an abnormal warming of surface ocean waters in the eastern tropical Pacific, occurring every three to seven years. This causes ocean currents near Australia to be cooler, which supports the creation of high pressure systems. On the Australian continent, El Niño events are associated with increased probability of drier conditions. Some of Australia's most devastating droughts have occurred during El Niño periods, including the 1914-1915 Drought, the severe 1982-1983 Drought, and the long El Niño Drought of 1991-1995. Droughts, however, do not always occur during El Niño years. Some develop independently of this global force, however, such as the drought which began on 1 June 1979 and lasted until December 1980.

In contrast to El Niño, La Nina is an anomaly in which there are unusually cold sea surface temperatures in the eastern tropical Pacific. La Nina occurs approximately half as often as El Niño and is related to an increased probability of wetter conditions in Australia. The Southern Oscillation reflects the seasonal or monthly fluctuations in the air pressure difference between Tahiti and Darwin. In recent years, an understanding of the ENSO system has allowed meteorologists to predict seasonal rainfall and give advanced warning to authorities and individuals.

Effects of drought

Drought impacts upon the lives of all Australians, even those who reside in areas far from drought-affected regions. The impact of major droughts can often have dire economic implications, particularly for the agricultural farming community. In order for agriculture to be successful, a baseline amount of water is needed. When a drought occurs, this baseline cannot be met. Livestock and crops die, leading to reduced output and a loss of earnings for farmers. Some of the industries directly affected by drought include beef, grain, cotton, dairy, sugar, other food products and wool. See image 2

When rural regions suffer from drought, a number of primary agricultural industries can be adversely affected, which in turn hinders the economy as a whole. In other words, the economic effects of drought are not only felt by farmers. They can cascade into other areas in an indirect manner. If there were a drought-produced shortage of wheat in Australia, for example, food prices in cities would rise. See image 3

Drought does not only kill crops and livestock, it can also degrade the land. As topsoil becomes very dry, it is easily influenced by wind erosion. This can lead to the land becoming infertile, which decreases crop and livestock outputs once the drought is over. See image 4

Drought in Australia can also directly affect people living in cities. The Warragamba Dam, which accounts for 80 percent of the water supplied to the Sydney region, for example, fell from 76 percent capacity in January 2002 to 42 percent by January 2005. As a result of this problem, a number of measures have been employed to restrict the amount of water used by the public, including limiting the times available to water gardens and lawns, banning the use of sprinklers and prohibiting the hosing of all hard surfaces, including motor vehicles.


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