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Dust storms are being made worse by Australia's drought. Here's how they work

By Yara Murray-Atfield and Christopher Testa, Friday November 22, 2019 - 15:23 EDT

As Victoria sweltered through a , the regional hub of Mildura was blanketed in dust, turning the centre of the city orange.

While dust storms are regular occurrences for people living in the centre of Australia, a "double whammy" drought and weather patterns this year means they're happening more.

Dust storms need four key ingredients

For dust storms to form, the soil needs to be dry and exposed.

Then you need strong winds that can pick up the soil and carry it across long distances. Just how powerful the wind needs to be depends on the size of the dust particles, but the minimum speed is about 30 kilometres per hour.

The storms are more likely to form if there's an unstable atmosphere that can lift the dust into the air.

Bureau of Meteorology (BOM) forecaster Jonathan How says a classic example of an unstable atmosphere occurs ahead of a trough or a cold front, where air is rising, or before thunderstorms.

And the dust is likely to stay in the air and travel if there are dry conditions.

Mr How says if the atmosphere is moist, there's a greater chance of seeing the dust particles condense into clouds or rain — or the dust could join together and become too heavy to be carried by the wind.

If the conditions are right, Mr How says the storms can move across the country for "hundreds, if not thousands, of kilometres".

That's what happened with the 2009 dust storm that saw dust travel from South Australia right across the east coast of the country, blanketing Sydney in red and orange dust — .

Drought is making those conditions worse

With much of the country gripped by drought, , causing more and more dust to be picked up by wind.

In Central Gippsland in Victoria's east, by damaging drought-affected paddocks, contaminating feed and water and distressing animals.

And Mildura resident Sara White has told the ABC while the city is used to dust storms, it feels different now: "If you talk to any of the locals, everyone is saying the same thing — they've never known the frequency of dust that we're getting at the moment."

Mr How says lots of vegetation is drying out, which means there are more dusty and dry conditions in central parts of Australia "and even parts of Australia where we wouldn't normally see these kinds of conditions".

He says the dry conditions mean there are a lot more "source regions" where dust storms can form, meaning there's a "much larger pool of dust available".

It's not being helped by other weather patterns

Dust storms tend to peak in Spring, because of cold fronts moving across dry parts of the country's centre.

Mr How says we're currently experiencing a "double whammy" because of a weather pattern known as the Southern Annular Mode.

At the moment, we're in what's called a Negative Southern Annular Mode, which means we're seeing cold fronts further north, causing stronger winds to blow over the interior of the country where dust is more easily picked up.

The best place to go when they hit is inside

Health authorities warn the people who are most vulnerable during a dust storm are young children, the elderly, people with heart disease and people with respiratory conditions like asthma, bronchitis and emphysema.

Victoria's health department says prolonged exposure to airborne dust can lead to chronic breathing and lung problems, and possibly heart disease.

That's on top of — even to people hundreds of kilometres away from fires — to lungs and hearts.

Experts warn the best thing to do is stay indoors, avoid vigorous exercise and where possible, keep the dust out by closing doors and windows and using well-maintained air conditioning.

Mildura GP Philip Webster says anyone who has ever experienced asthma or hay fever symptoms needs to be prepared for dusty conditions, even if they aren't frequent sufferers.

"The other thing to remember is the risk doesn't stop as the sun sets but can persist in the night as the earth cools and the inversion of the atmosphere happens, so don't think you're safe just because it's dark."

Dr Webster said Thursday's day-long dusty haze was a "one-off event" during his five years of practising in Mildura.

But while major cities can monitor the quality of the air, many regional towns and cities like Mildura don't have the infrastructure in place to see just how bad the air quality is, which has some residents worried about what the storms could contain.

Environment Protection Authority Victoria's chief environmental scientist Andrea Hinwood says testing of soils has found low concentrations of pesticides.

But Dr Hinwood cautions "that's not to say those chemicals are not present in the dust" and warned the best option was to stay out of the storms where possible.



© ABC 2019

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