How Large Is Your Dust Storm?
On September 23, 2009 our colleagues at FEWW posted the following on their blog:
FEWW entry summarized a phenomenal dust storm which had started a day earlier ( September 22), sweeping across Australia’s eastern states of New South Wales (NSW) and Queensland (Qld), reaching Sydney, the country’s largest city, and Brisbane.
The dust plume measured about 500 kilometres wide and at least 1,000 km long, covering dozens of communities, towns and cities in both states.
Recently, they posted details of another dust storm
They have now asked EDRO Moderators the following questions:
‘How much dust would it take, and under what circumstances could it make Sydney uninhabitable?’
Desertification of farmlands, villages and small communities have been commonly occurring throughout history. In recent times, countries like China have experienced accelerated rates of desertification. Up to 3 million km² of land in China have already desertified. The country’s annual desertification rates have more than doubled to 3,400 km² since the 1970s (1,560 km²) and have increased by 62 percent compared with the 1980s (2,100 km²). Thousands of villages have been lost to encroaching deserts.
According to a report by the Secretariat of the United Nations Convention to Combat Desertification (UNCCD), “some 24,000 villages, 1,400 kilometres of railway lines, 30,000 kilometres of highways, and 50,000 kilometres of canals and waterways are subject to constant threats of desertification.”
“Dust-laden blasts have buried villages before blowing into cities and suffocating urban residents.”
Historic examples are abound about large cities in Africa, Asia, Near and middle East that were lost to desert.
Chilean town of Chaitén is one of the latest examples of a town lost to [human-enhanced] natural phenomena, namely lahar caused by volcanic ash deposits, and other pyroclastic materials.
Well, Could it Happen to Sydney, Australia?
The short answer is yes!
Given copious supplies of dust [or sand,] sufficiently strong winds, as well as extremes of climatic and atmospheric conditions conducive to precipitating large amounts of airborne dust on the ground, dust storms could bury any village, town or city in their path and make them partially or completely uninhabitable.
Under the said conditions, one or more dust storms blowing within a critical period of time, with wind forces lasting long enough to deposit significantly large amounts of dust over a critically large portion of the city could trigger a partial or total collapse of Sydney [or other cities in eastern Australia.]
How Much Dust?
Australia’s CSIRO estimated that the September 22-24 storm carried a record-breaking 16 million tons of dust from the deserts in the heart of Australia [The Lake Eyre Basin was reportedly the main region, where the dust came from.] Interestingly enough, the media boasted how the benevolent storms had dumped a million tons of iron-rich topsoil from Australia’s outback into the Tasman Sea and Pacific Ocean.
Most of the dust spread over a vast area precipitating on the continental Australia, Indian ocean to the west, and Tasman Sea to the east, reaching as far as the North Island, New Zealand.
EDRO Team designed a basic model and, using the available data, ran a few dozen simulations. The simulations showed that the amount of dust needed to ‘bury’ central Sydney [an area about 100 km²,] so as to make the entire city mostly uninhabitable, would be about 10-12 times the dust blown off in the Septemeber 22-24 dust storm.
- The simulations were based on optimally extreme climatic and atmospheric conditions conducive to precipitating large amounts of airborne dust in a relatively small area.
- Dust diameters of (i) less than 60 micrometer, and (ii) 62 – 65 micrometer, were used in the simulations.
- The maximum air particle concentration levels reached over 45,000 micrograms/m³ of air.
- As the air particle concentration levels rose above about 25,000 micrograms/m³ of air, the number of casualties dramatically increased.