Climate Change and the Phoenix Dust Cloud

Hotter temps could set the stage for more — but the science is complex

On July 5, a massive dust cloud, or haboob, swept across Phoenix, Arizona, brought by the North American monsoon. (Photo: Greg Gorman/Flickr)

By Alyson Kenward

On Tuesday night, a massive dust storm rolled into Phoenix, Arizona knocking out power in much of the city, reducing visibility to nearly zero, and grounding flights overnight. Photos of the 100-mile wide dust cloud swallowing the city circulated yesterday, and the event looked practically apocalyptic. In fact, if the photos weren’t in color, and there weren’t YouTube videos of the dust storm, I would have thought I was looking at old-timey images from the 1930’s dust bowl. Now, a couple days later, lingering dust in the air has triggered allergy-like symptoms for many people.

This isn’t the worst dust storm Phoenix has endured, mind you; not by a long shot. This kind of immense dust cloud, known as a haboob, can stir up in the Southwest during North America’s monsoon season, and Phoenix can see several of these each year. According to Wunderblog’s Jeff Masters, last night’s storm was brought on by:

…a large complex of thunderstorms known as a mesoscale convective system (MCS) that developed to the east of Phoenix. As the outflow from the MCS hit the ground, large quantities of sand and dust became suspended in the air by 50-60 mph winds.

Tuesday’s intense monsoon thunderstorm drove heavy winds down across the dry land, and whipped it up into a dust cloud that pushed ahead of rain that accompanied the storm.

If you’re like me, you might not know much about the North American monsoon, but the Climate Assessment for the Southwest (CLIMAS) has a helpful website on the subject. With help from a couple of scientists at the University of Arizona, the site tackles the tricky question of how climate change might impact the monsoon, which brings beneficial rains to the region.

As Chris Castro and Dave Gutzler write, there is still a lot of uncertainty about how the monsoon might change, if at all, because “the current generation of global climate models doesn’t come close to any consensus as to what the expectation is for a changed monsoon.” In the past 100 years, there hasn’t been a detectable change in how variable the monsoon can be. However, they warn, warmer climates tend to reinforce the monsoon. As global temperatures increase with increasing greenhouse gas emissions, scientists predict the American Southwest will see a corresponding rise in temperatures, by 4-10°F, in the coming decades.

A more prominent monsoon might sound inviting for the region, where 20-50 percent of average rainfall comes during the stormy summer months. The extra rainfall replenishes reservoirs and moistens farmers’ fields temporarily during an otherwise hot, dry season. The intense thunderstorms can also cause flash floods in some areas, ignite wildfires in others, and, as we saw the other day, stir up massive dust clouds that drive ahead of the rain.

As for the dust, new research suggests increasing temperatures in the Southwest (and specifically along the Colorado Plateau) could create more dust in the region. Hotter average temperatures mean the region could become even drier than it is already, making it harder for perennial grasses and plants to thrive. Without these grasses to keep the soil intact, it’s a lot easier for wind to pick the dust up off the ground. Even though the monsoons bring rainfall that can tamp some of the dust down, clouds like the one that formed on Tuesday stir up ahead of the rain, so drier ground in general could still contribute to these monstrous haboobs.

In general, scientists predict that the entire Southwest is going to get drier over the next century, which means that, on average, annual precipitation will be lower than it is today. That doesn’t mean, however, that the monsoon season could become more prominent and bring more rainfall during the summer — there just isn’t any consensus yet on how much the summer rain will offset the overall trend towards warmer and drier conditions.

A version of this post also appears at Climate Central, a content partner of Climate Watch.

  • Jim Pettit

    Good evening. I’ve been trying to find information about the size of this week’s dust storm in comparison with the many others Phoenix has dealt with, but I’m having a difficult time.

    The Phoenix NWS page about the storm (http://www.wrh.noaa.gov/psr/pns/2011/July/DustStorm.php) says, “While records of most widespread, most intense, largest, etc., dust storms are not kept, NWS meteorologists that have worked in Phoenix for almost 30 years have said this was one of the most significant dust storms they have experienced.”

    Meanwhile, your article states, “This isn’t the worst dust storm Phoenix has endured, mind you; not by a long shot”. Do you indeed have information on previous dust storms, and if so, can you please post them?

  • Alyson

    Jim,

    I gathered information on previous dust storms by checking the National Climatic Data Center’s Storm Event Data base (http://www4.ncdc.noaa.gov/cgi-win/wwcgi.dll?wwEvent~Storms) and by reading through news reports of previous dust storms. It does appear to be the case, however, that there aren’t thorough records kept on these types of dust storms; though the NCDC database has some details about storms since 1994, I have seen similar statements like the one you highlight from the new NWS page that says this is one of the worst people can recall.

    By a different measure of severity, several other dust storms over the past decade left people killed or severely injured (in accidents related to the poor visibility), including ones on August 11, 2004 and May 8, 2007. To my knowledge no deaths have been reported in relation to Tuesday’s dust storm.

  • Julie Jones

    Hello – Earth to Sky!!! Was there chem trail/geoeongineering/aerosol spraying going on before the dust clouds happened???? People better start connecting the dots to weather modification/sky pollution and what the unintended consequenses are – on the ground, in the sky… everywhere. see geoengineeringwatch.org and californiaskywatch.com for info — plus You Tube has thousands of photos of grid lines of spray – internationally.

  • http://firefoxgoogle lisa

    MY friend’s mother was killed by this storm in Phoenix. She was 76. Her air conditioning went out and she cooked to death in her trailer. How many other people were killed by this storm? Why was there no attempt to move vulnerable out of harm’s way because of the heat wave and no air conditioning combination? Are there no cooling stations in Phoenix? Are there any laws in place abut authorities helping elderly people in extreme weather conditions in Phoenix? Thank you