Has the monsoon changed over time?

Talk to people who’ve lived in Arizona more than 10 years and many of them will say they think our monsoon weather has changed over the years. Is it another indication of climate change?

Interviewing a sampling of long-time Valley residents produces a variety of opinions. Some think the monsoon used to be wetter years ago. Some say the storms don’t reach the center of the city as often as they had before.

ASU climatologist Randy Cerveny, Ph.D., has watched the monsoon for two decades. When asked if climate change is affecting monsoon, he said, “It may, but we can't detect it.” That’s because weather experts are still trying to figure out all the “causative mechanisms” of our monsoon. “We're finding out new things pretty much each and every year.”

Cerveny said it does appear that patterns of heaviest rainfall have changed over the years, referring to a study by state climatologist Nancy Selover, Ph.D. Cerveny has looked at some of the rainfall maps produced by the study, “and we do see shifts from decade to decade as to which parts of the valley get the most rain, but it doesn't appear to be linked to anything that we can put a finger on.”

Maps of monsoon rainfall since 1990

One change in the monsoon that Cerveny has noticed: dust storms don't get into center of city as much as they did 20 years ago. But he attributes that to urban development that has covered agricultural land around the Valley, so dusty fields are farther away.