Two weeks ago, on July 5, a large dust storm moved through the Phoenix area. Hundreds of photographers captured it—there was no lack of images on YouTube —and dozens of others speculated on what it might mean, beyond the obvious delayed flights, coated streets and buildings, and coughing residents. Some claimed they saw UFOs in the cloud (later identified as a news helicopter and a Southwest Airlines jet coming in for a landing at Sky Harbor Airport just ahead of the storm). Just as people refer to “100-year rain events,” some are calling this a “100-year dust storm.”
According to the National Weather Service, the storm was approximately 100 miles wide and roughly a mile high, and it traveled three to six times farther than the typical dust storm, moving about 150 miles. Although it was larger than most, it was started by fairly mundane weather conditions: a thunderstorm to the south of Phoenix produced downdrafts that picked up sand and soil. This is the time of year for storms in the Southwest desert, and there was nothing particularly remarkable about the atmospheric conditions that led to the dust cloud. However, the drier-than-usual conditions—Arizona is experiencing a modest drought—caused more dust to be picked up than would ordinarily have been the case.
Government scientists do expect the Southwestern US to become drier, and we know from experience that periodic droughts do result in more dust storms. One possible repercussion might be debates over responsibility: the places where dust originates and the places where it falls can be far enough apart that any dust control measures people undertake—or don’t—in a particular area are likely to benefit—or harm, or at least annoy—their neighbors more than themselves.