Dust storms have created havoc in the US city of Phoenix this summer. No sooner have residents and local businesses in the nation’s sixth largest city cleaned up after one storm than another biblical wave of choking dust has swept over the city and its suburbs.
The most powerful storm rolled across Phoenix on July 5. An awesome mile high wall of dust closed the airport, cut off power for 10,000 people and covered everything in its path with a carpet of dust.
At its height, there was near-zero visibility and winds of up to 110 kilometres per hour, according to the US National Weather Service. The storm travelled 240 kilometres in total, with the dust reaching 1,800 metres in altitude, and its leading edge stretched for almost 160 kilometres.
The Phoenix metro area was revisited by another 1,200 metre high dust storm on July 18 and then incredibly, the same thing happened twice again in August.
Phoenix is used to dust storms – but the severity and frequency of events this year has been unusual. Why? lloyds.com spoke to dust storm scientist Thomas E. Gill, Ph.D., Associate Professor of Geological Sciences and Environmental Science & Engineering at the University of Texas at El Paso.
Why has Phoenix been hit so badly this summer with dust storms?
The storms that have hit Phoenix this summer are a specific kind of dust storm, called a "haboob" (from the Arabic, just like the word monsoon). They’re caused by a band of strong winds spreading away from a thunderstorm picking up sand and dust. When these strong winds from the storms hit loose desert soil, they pick up sand and dust which spreads out as a dramatic front ahead of the storm.
These storms and winds are actually a regular phenomenon here in the Southwest USA (Arizona, New Mexico, Texas) every summer, so that in itself is not unusual. There have been more-than-typical (and dramatic) amounts of dust with these storms, however, due to the extreme drought which the region has been experiencing. That’s caused the desert soil to be extremely dry and didn't allow for enough vegetation to grow to hold down the soil from the wind.
Is there generally a return to the Dust Bowl conditions of the ‘30s in the US?
The Dust Bowl years of the 1930s were caused by a combination of both natural and human phenomena. The extreme drought, coupled with a lack of understanding of proper land use practices in the semi-arid southern Great Plains – combined with an economic depression that caused many farmers to abandon or not have the resources to take care of their land – came together to form a "perfect storm" causing the Dust Bowl catastrophe.
Since then, soil conservation practices have been implemented, and farmers have learned how to manage the land better. So, when a drought arguably as bad as the one during the Dust Bowl years hit in the 1950s, times were tough but a return to Dust Bowl extreme conditions was averted.
The region is again experiencing a severe drought, and conditions are difficult, but due to these improved understandings a new Dust Bowl has so far been averted.
However, the climate record shows that south-western North America could experience a drought far more intense and lasting far longer than any experienced since widespread farming of that land began. If that were to happen once more, the results could again be disastrous.
What does the future hold: is there a climate change link here?
Climate change will certainly have an impact: the climate models predict that many areas will get wetter, but some areas will get drier.
The data I've seen for model predictions of climate in the south-west USA are mixed. Most predict a warmer and wetter climate, but others predict a warmer and drier climate – in which case, it would be a dustier climate.
Climate models predict that the world as a whole is in for more extreme events, which will likely mean more dust storms (if only from perhaps having more strong wind storms, which of course are an ingredient for dust).
Dust isn’t always associated with drought, either. While it’s true in most regions dust is associated with drought, some regions actually experience more dust following wet periods. That’s because the storms and floods loosen and carry sediment and leave it exposed over larger areas of the ground when the water finally recedes, making it available for the wind to pick up.
What's the wider global picture? We hear drought and water scarcity are growing problems around the world. Does it follow that other regions around the world will suffer dust storms more often?
Drought, water scarcity, and water availability are growing problems around the world. Some of the world's biggest dust-related disasters have been associated with the extraction of water from desert lakes – such as the Aral Sea in the former Soviet Union, and Owens Lake in California – leaving dried-up lakebeds exposed to the wind.
A number of areas across the globe are clearly at risk of similar dust problems as water becomes a more limited resource.
Does more dust in the atmosphere have knock-on effects?
There is interplay between dust and climate. Climate changes can result in changed dust levels, but dust itself can impact the climate. Aerosols (airborne particles, including dust, as well as smoke and smog) impact the global climate by absorbing solar energy and acting as miniature chemical reaction vessels in the sky.
Yet their exact role in global climate change is not yet thoroughly understood. Depending on the size and the composition of the particle, aerosols could promote either cooling or warming, so a change in dust levels could, itself, modulate climate changes in different ways.
What are the risks to people associated with dust?
The risks from dust not only include the obvious hazards to infrastructure, transportation and fouling of water supplies – but also human health.
Several diseases, such as coccidioidomycosis ("valley fever"), can be spread by dust storms. And even if it does not carry pathogens or toxic compounds along with it, dust itself can cause health problems, especially if the dust particles are fine enough to be inhaled deep into the respiratory tract.
For example, research we have recently completed in El Paso shows that people – children especially – are much more likely to be hospitalized for asthma or acute bronchitis after dust storms (as compared to non-dusty days).
