Four
severe droughts
During the
last 30 years, Australia underwent 4 important droughts:
- In 1982 Eastern
Australia suffered an extensive drought, particularly in the southeast.
Extensive areas, including all of Victoria and southern New South Wales
have recorded low rainfall for the period of April 1982-February 1983.
This drought was also the cause of severe dust storms in north-western
Victoria and severe bushfires in the south east.
- A very severe
drought occurred in the second half of 1991 in the state of Queensland.
About three-quarters of the state recorded very low rainfall from March
to November 1991. It was the driest such period on record in parts of
the Darling Downs. The northern half of the state of New South Wales
was also seriously affected with about half this region affected by an
important deficit of precipitation during the same nine months.
- During 2002,
Australia experienced its worst drought since reliable records began in
1910. The average Australian rainfall for the spring, summer and autumn
2002 was the lowest ever recorded. The drought was concentrated in
eastern Australia especially in the Murray-Darling Basin (the nation’s
agricultural heartland). This drought has had a more severe impact than
any other drought since at least 1950, because the temperatures in 2002
have also been significantly higher than in other drought years. The
higher temperatures caused a marked increase in evaporation rates,
which sped up the loss of soil moisture and the drying of vegetation
and watercourses.
- Since November
2006, from the late-winter to mid-spring rainfalls had failed in the
state of South Australia. Across Victoria and the Murray-Darling Basin
the season was the second driest since 1900. New South Wales' rainfall
was boosted by above normal precipitation along the north coast of the
state; however the state average rainfall for the season is the third
driest since 1900. The situation has been worsened by very high
temperatures.
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Displacement
of lake Hume’s shore (New South Wales state) - Source
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The common thread
between these 4 events is that they occurred at the same
time as El Niņo. As we know, the term El Niņo refers to
a sequence of changes in circulations across the Pacific Ocean and
Indonesian archipelago when warming is particularly strong (on average
every three to eight years). One of the consequences of this phenomenon
in Australia is the occurrence of droughts. The physical causes of
drought during El Niņo events have their origins in the natural
fluctuations of the global climate system, which is an extremely
complex mix of different subsystems.
However, during
the last 50 years the Australian average surface temperature increased
by more than 0.7ēC. A one-degree average temperature
increase may appear to be a relatively small increase but it can have a
major impact on the severity of drought.
Higher temperatures lead to higher evaporation of water from the soil,
plants, lakes, and rivers. This places stress on water supplies and has
a detrimental impact on vegetation health and agricultural
productivity. Under normal conditions evaporation rates
in Australia are high, with almost 90% of
the precipitation that falls on the country returned
through evapotranspiration to the atmosphere. As a result of the higher
maximum temperatures, the evaporation rates in 2002 for
example were significantly higher. This warming trend
cannot be explained by natural climate variability and most of this
warming is likely due to the increase in greenhouse gases in the
atmosphere.
Since 1950, besides the droughts, the
trend is towards an increase of the average temperature and a decrease
of the rainfall mainly over Southern and Eastern Australia. The
situation is critical because the three most populated
states are concerned (Victoria, New South Wales and
Queensland) and no evidence shows that this trend will change in the
near future.
