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Sept 23 (Reuters) - A dust storm swept across eastern Australia and blanketed Sydney on Wednesday, disrupting transport, placing health authorities on alert for widespread respiratory illness and stripping thousands of tonnes of topsoil off Australia's main farmlands.
Following are answers to questions about the storm.
WHAT CAUSED THE DUST STORM?
During winter in Australia low pressure storms are generated in the Indian and Southern Oceans, whipping up huge seas and creating severe cold fronts which sweep across southern and eastern Australia. A severe thunderstorm with 100 km per hour (60 miles per hour) plus winds formed in South Australia state on Monday and began whipping up dust from drought-hit outback lands. As vegetation gets dried off the topsoil is loosened, and it easily blows away. As the dust storm travelled into the eastern seaboard state of New South Wales, one of the worst hit by drought, it grew in size and by Wednesday morning was affecting most of NSW, the fifth biggest state or territory representing 10 percent of the island continent, and had descended on Sydney like a thick blanket.
IS THE DUST STORM LINKED TO CLIMATE CHANGE?
Weather scientists are reluctant to directly link climate change with extreme weather events such as storms and droughts, saying these fluctuate according to atmospheric conditions, but green groups link the two in their calls for action to fight climate change.
Dust storms in Australia, the world's driest inhabited continent with a vast desert-like outback interior, are not uncommon. Central and eastern Australia is a major global source of atmospheric dust, say weather experts. But dust storms are usually restricted to the inland of Australia. Occasionally, during widespread drought they can affect coastal areas. Australia is battling one of its worst droughts and weather officials say an El Nino is slowly developing in the Pacific which will mean drier conditions for Australia's eastern states.
Before the Sydney dust storm, one of the most spectacular storms swept across Melbourne in February 1983, late in the severe El Nino drought of 1982/83. The extended dry period of the 1930s and 1940s generated many severe dust storms, culminating in the summer of 1944/45 when on several occasions dust in Adelaide was so thick that street lighting had to be turned on. Satellite images showed a 2002 dust storm, about 1,500 km (930 miles) long by 400 km (250 miles) wide and 2.5 km (1.5 miles) high, stretching across New South Wales and Queensland states.
WHAT IS THE ECONOMIC AND ENVIRONMENTAL IMPACT OF DUST STORMS?
While dust storms may cause temporary disruptions to towns and cities, by far the worst effect is the stripping of topsoil from Australia's farmlands. In the late 1970s and early 1980s severe drought in Australia saw dust storms strip millions of dollars worth of topsoil, causing massive crop and stock losses, according to the country's Emergency Management Authority. Crop analysts say the current dust storm is unlikely to have an immediate impact on wheat crops which are already struggling with dry conditions. Harvesting starts next month in NSW, the country's second largest grain producing state. Australian Crop Forecasters estimates the NSW wheat crop will be down by about one million tonnes to around 6.5 million tonnes.
WILL THERE BE MORE DUST STORMS?
Australian weather officials are warning of another severe storm to sweep across the southern and eastern parts of the country on Thursday and Friday. Australia's main farmlands are located in the eastern part of the country. The next storm could again whip up a dust storm, cause damage with gale-force winds and send temperatures plummeting and dump snow on Australia's alpine region. If El Nino weather conditions continue in the western Pacific then Australia's dry conditions and then more dust storms can be expected, but whether they remain confined to inland or outback regions or sweep across farmlands and reach more populated centres remains unknown. (Reporting by Michael Perry; Editing by Dean Yates)
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