Photos and video of the haboob that ate Phoenix on July 5 went viral on the Internet. News stories worldwide predicted a hotter, drier, dustier future for the "Southwest Dust Bowl."
The "haboob" - an Arabic term for a violent, giant dust storm - was indeed biblical in its proportions. It was more than a mile high and at least 100 miles across, moving at 40 mph across a swath of Arizona that stretched from the Pima County line to the Colorado River in La Paz County, 250 miles away.
It was followed by five other dust storms, none quite as big, but big enough to alarm scientists and public health officials.
Don Gabrielson, director of air quality for Pinal County - source of much of the dust that blows through Phoenix each summer - said this summer has him rethinking previous assumptions.
"I thought I had a handle on this," he said. "But after this month, I don't think I do."
Nobody has a handle on Arizona's dust storms. The usual reaction to haboobs is to call them unstoppable acts of God, like earthquakes, blizzards and hurricanes, and to throw out the off-the-chart readings they trigger on air-pollution monitors.
Scientists who study "Aeolian transport" say more research is needed but two things are clear: We have contributed to the problem, and it is going to get worse.
How did the Epic haboob happen?
On July 5, a line of thunderstorms collapsed along the Pima/Pinal county line. Rain-cooled air plummeted and fanned out at speeds up to 60 mph.
A big arc of wind followed the path of least resistance down through the wide valley of the lower Santa Cruz River, picking up dust as it went, becoming the monster dust-laden storm front that pummeled the Valley of the Sun.
How rare are they?
Dust storms happen all the time, particularly in the huge bowl between Tucson and Phoenix, where the terrain is fairly flat and dust sources are plentiful. The one on July 5 was bigger than any recent one, but probably not the biggest one ever. Phoenix was even dustier before it was paved over, scientists say.
This year, though, was a corker. The Phoenix metro area has been hit with six major dust storms, two of them - on July 5 and July 18 - were giants in the "haboob" category, said Ken Waters, meteorologist with the National Weather Service in Phoenix. The region has an average of three or so major dust storms a year, he said.
Where does the dust come from?
That's a simple question with a complicated answer.
It's easy to point fingers at the farmers, but these huge monsoon dust storms are too big to have a single source and they came during a summer of high commodity prices.
Most of Pinal County was planted in alfalfa, wheat and cotton and at the peak of irrigation, said Ron Rayner of the A Tumbling T Ranch in Buckeye. "Virtually every field that had water available was being farmed," he said. "On our farm, I guarantee you there is not one acre of cropland that added to it," Rayner said.
Truth is, we don't know where all the dust comes from. Some is already in the air. In summer, when the wind blows in from the south and the rains have not yet dampened the terrain, our storms pick up dust in northern Mexico.
But when a storm starts north of Tucson and hits Phoenix, Pinal County's degraded bowl is the likely contributor. Name your poison: vast acreages of tilled land, grazed desert, feedlots, land cleared for subdivisions, silty washes and river bottoms, dirt roads, ATV trails, sand-and-gravel operations.
This year, you can blame the drought. Arizona has been drying out for 13 years and this past winter saw little rain. The annual grasses never grew, leaving more exposed desert. The dust storm may have been biblical, said University of Arizona climatologist Mike Crimmins, but "the winter was epic" in its lack of rain.
The economy played a role with the wind rolling over cleared, partially developed subdivisions.
The storm rolled over vast stretches of public lands managed by the state Land Department and the Bureau of Land Management. They are riddled with wildcat trails and roads and leases for grazing, though this spring there was not enough forage for cattle.
How does Tucson escape such things?
It doesn't. Pima County had a pretty good dust storm this summer, but it came in the night on Aug. 27, triggering air pollution readings more than 10 times normal for a brief time and leaving a hazy landscape the next morning. Our saving grace here is that we usually get rain when we get thunderstorms. "We get a nice crusted surface on our deserts because of that," said Sarah Walters, meteorologist with Pima County Air Quality District.
The Phoenix area gets about half Pima County's monsoon rain. It and Pinal County had received only traces when the dust storms hit.
Will it get worse?
The prediction for next summer is dreadful - a repeat of this year's La Niña winter that kept annual grasses from growing.
When the equatorial waters of the Pacific Ocean cool, the storm track pushes north. Last year, that meant scant rainfall, followed by record wildfires and those dust storms.
In the future, we'll have the usual mix of wet and dry winters but the overall trend is drier and hotter. That could trigger the die-off of plant communities, more exposed desert surface and more dust, concludes a recent study by scientists with the U.S. Geological Survey and UCLA.
Lead author Seth Monson, a USGS ecologist, said ground cover impedes the growth of dust storms because it keeps dust from getting airborne, disrupts the wind pattern and traps dust.
What does it mean when we say the Southwest is the next Dust Bowl?
Scientists say we shouldn't conjure up images from the '30s when wind blew away the deeply tilled topsoil of Oklahoma and Texas during a six-year drought. Even the man whose 1997 article predicted a Dust Bowl Southwest, Richard Seagar of Columbia University, backpedals a bit when you ask him.
Farming practices are better than they were in the Depression era, and we don't have a lot of soil to begin with, Seagar said. But the prediction for the Southwest is worsening conditions as temperatures increase and precipitation decreases.
Why should we care?
Dust is unhealthy. The particles can lodge in our lungs, leading to disease. It is especially harmful for those with asthma and other pulmonary diseases.
Dust clouds, particularly those blowing off mine tailings, can contain toxins and the winds can pick up the mold spores of valley fever.
Dr. John Galgiani is watching closely for a spike in valley fever cases following this summer's events. After the July 5 haboob, Galgiani, director of the Valley Fever Center for Excellence at the UA, projected an additional 3,600 cases in the Phoenix area.
That spike hasn't appeared but there is usually a gap of up to two months between infection and reporting.
What can be done?
We can regulate agricultural practices, manage public lands better, pave roads, limit grazing, and pursue a host of other strategies.
Monson, of the USGS, said land management is key. Overgrazing not only removes vegetation that keeps dust from blowing, it also breaks the desert's natural crust, the one defense left when the vegetation is gone.
Pinal County is being forced to come to grips with its dust problems. It is being declared a non-attainment area for particulate air pollution by the EPA and has to devise a plan to reduce emissions.
But when a big wind blows across a dry desert, there is no way around a big dust storm, haboob, whatever you want to call it.
These truly are "exceptional events," in the parlance of the regulators. They can sand-blast through the protective desert crust and they leave behind a layer of fine particles that contribute to the next storms, said Eric Massey, air quality director for the Arizona Department of Environmental Quality.
Massey said state meteorologists can predict winter dust events and have begun dispatching inspectors to problem areas to head off their occurrence. Farmers and other potential dust-generating sources can use the information to wet down fields or hold off on tilling operations, he said.
Summer dust storms are difficult to predict, he said: Nobody saw that July 5 storm coming.
On StarNet: See more photos of this summer's dust storms at azstarnet.com/gallery
Contact reporter Tom Beal at email@example.com or 573-4158