A car approaches a dust storm near Winslow, Arizona, in April 2011. In drought years, low vegetation cover and disturbance to soil surfaces leads to more dust storms.

Dust storms that rolled across the Arizona desert July 21-22, 2012, effectively blinded motorists, knocked out electricity for thousands of people and grounded airline flights.

The weekend storms, 50 miles wide and up to 10,000 feet high, were followed by additional storm warnings into the following week. Like the storms that passed through Phoenix in July and October 2011, they carried large quantities of airborne particulates and caused considerable property damage and potential harm to human health.

But what is causing these storms?

USGS and partner research shows that there are many causes of dust storms. Two contributing factors are low vegetation cover and disturbance to soil surfaces.

Vegetation contributes to ecological integrity. The presence of plants reduces soil erosion and dust storms, because it keeps the soil intact, reduces wind momentum, and traps moving soil particles (See Figure 1). In spaces between the plants, many undisturbed desert soils are naturally armored by hardened physical and biological crusts.

Low vegetation cover can especially be a problem in drought years in abandoned agricultural fields, which are generally dominated by annual plants. This means that the consequences of dust storms, including motor vehicle crashes, are high in a drought year and low in years with more precipitation (See Figure 2).

Figure 1: The presence of plants reduces soil erosion and dust storms because it keeps the soil intact, reduces wind momentum, and traps moving soil particles. Intact soil surfaces, which may include soil crusts, can also reduce the risk of dust storms.

Similarly, in places where land-use activities destroy or reduce soil crusts and weaken soil stability, experts know to assume higher dust storm activity than in places where soils are left undisturbed.

Future climate scenarios predict that drought conditions will worsen, and therefore more dust storms are likely.

Nevertheless, site restoration and reduced disturbance can mitigate some of the factors that promote dust emission. The USGS and land managers are working together to better understand the causes and sources of dust storm activity in the southwestern United States.

Figure 2: The number of motor vehicle crashes caused by dust storms in Arizona has generally been lower when the annual precipitation has been higher. In a changing climate, climate scenarios predict more drought, which will likely mean more dust storms. But site restoration and reduced disturbance can mitigate some factors that promote dust emissions.