Living Land

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Long-term drought in southern Australia

David Jones and Alex Evans, Australian Bureau of Meteorology

ustralia is the driest inhabited continent with

strong rainfall variability from year to year. Annual

mean rainfall averaged across the continent is 465

mm, but this has varied between a low of 314 mm during

1902 (an El Niño event) to 760 mm during 1974 (a La

Niña event). While rainfall is not strongly correlated from

year to year, a number of multi-year drought events have

occurred of varying spatial and temporal duration and

intensity including the federation drought (1896-1902),

Second World War drought (1937-1945) and more

recently the millennium drought (1997-2010).

Each of the multi-year drought episodes resulted in severe soci-

etal and economic impacts, with the loss of life through wildfires

and heatwaves. The first two of these multi-year droughts were

widespread in impact affecting the bulk of continental Australia,

whereas the millennium drought mostly impacted southern

Australia. While an estimate of the full cost of the millennium

drought is not available, extremely low rainfall during 2006 saw

the loss of an estimated $A7 billion in agricultural production

alone. Devastating wildfires occurred during the summer of

2002/03, 2006/07 and 2009 in forests which were tinder dry due

to drought and heat. The Black Saturday bushfires of 7 February

2009 resulted in 173 deaths and at least $A4.4billion in property

damage across south-east Australia, being one of the costliest

disasters in the country’s history.

While drought is an episodic feature of the Australian

climate, the most recent drought highlights a confluence of

climate variability (drought) and climate change (changing

aridity) and raises the question of how to define and manage

drought in a changing climate.

The millennium drought affected most of southern Australia

with particularly severe conditions experienced in the more

densely populated and cultivated south-east and south-west

regions. A feature of the millennium drought was the especially

marked decline of cool season rainfall in the south with little

reduction in the warm season rainfall in the south and excessive

summer rainfall in the tropical north. The cool season is the

main agricultural period across southern Australia. This meant

that irrigated agriculture reliant on winter inflows into dams

was badly affected across the south, as was winter grain produc-

tion in the southern cropping regions of Australia (annual grain

production is near 40 million tons). Impacts on ecosystems and

urban water supplies dependent on cool season replenishment

were also significant. In striking contrast northern Australia,

a region of low population density and lower intensity agri-

culture, saw above-average to record-high rainfall during the

summer half of the year.

The effect of below-average rainfall during the cool season

was accumulative in southern Australia, leading to increas-

ing hydrological impacts which compounded over the years.

This saw a long-term drying of vegetation and a drawdown

of surface and ground water resources. For example, in

Melbourne (a city of more than 4 million people) urban water

storages dropped from almost full in October 1996 (97.5 per

cent) to only one-third full by June 2010 (33 per cent). Water

supplies for this city would have been emptied at the peak

of the drought were it not for water restrictions and price

increases applied to water use in response to the drought

which curtailed consumption.

With the millennium drought affecting all major capital cities

across southern Australia, large-scale urban water projects were

commissioned, including the construction of desalination

plants in Perth, Adelaide, Melbourne, Sydney and Brisbane with

a total cost of more than $A10 billion. The trigger for supple-

mental water supplies was a lack of confidence in the past as a

Rainfall deciles for the peak of the millennium

drought, calculated from national rainfall data

from 1900 to the present

Source: Australian Bureau of Meteorology

Above Average

Average

Very Much Above Average

Highest on Record

Lowest on Record

Very Much Below Average

Below Average

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