For as long as he can remember, Rob Sowby has heard people call Utah the second-driest state in the nation.
Over the years, that claim has become nearly inescapable, echoed by everyone from state departments, city governments and water conservancy districts to national news outlets without a clear citation for what data it’s based on.
As Sowby got older, it bothered him that he couldn’t figure out where this statistic originated.
“It seemed to be one of those things that if we say it enough, it becomes true,” he said. “I think that can be dangerous in some ways.”
Now a Brigham Young University civil engineering assistant professor focused on sustainable water supplies, he decided to get to the bottom of it. Using precipitation data, he found that Utah is actually the nation’s third-driest state, behind Nevada and Arizona.
The point of this research, he said, is not to discredit the people who have been calling Utah the second-driest state or the importance of water conservation. Rather, it’s a reminder that we should fact-check the assumptions we base our decisions on.
“We should be able to verify these things pretty easily before we act on them,” he said. “For some reason, we as Utahns [and] as stakeholders in the water community have not done so on this particular point.”
The surprising thing, he said, was that other researchers hadn’t tried to put this question to bed long ago, especially since the data that held the answer was so readily available.
Here’s how he did it.
In his research paper published in November in the Journal of Hydrologic Engineering, he sorted through 70 years of National Oceanic and Atmospheric Administration data. He specifically looked at historical precipitation averages over each 30-year period between 1951 and 2020, a common climatology standard known as a 30-year normal.
That long-term data, he said, captures the best picture of Utah’s dryness because each year can be vastly different — just look at the swing from extreme drought to record snowpack the state has experienced since 2022.
In the most recent period from 1991-2020, Utah received an average of 34.3 centimeters of precipitation per year. Nevada and Arizona got 25.9 and 29.6, respectively.
Using that same dataset, he also looked at how each state ranked on a year-by-year basis. Arizona was the second-driest state in 17 of those 30 years, while Utah ranked as the second-driest state just three times. Utah was also the state most likely to rank third-driest (10 times) or fourth-driest (14 times) during that period.
Given how long Utahns have been calling it the second-driest state, he said, it’ll likely be an uphill battle to get people to change. But his work is already getting results.
When Sowby worked with the Utah Division of Water Resources a few years ago on developing water conservation goals, he brought up his uncertainty about including language that Utah was the second-driest state. So the division did its own analysis and couldn’t find data to back up that claim or figure out where it originated.
Now, it’s moving away from that term in favor of calling Utah “one of the driest states” instead.
“At the end of the day, I think words matter, and trying to be accurate in our words is important,” Division Director Candice Hasenyager said. “So we have changed our own messaging and encourage others to do the same.”
Accuracy is especially critical in conversations about environmental issues because there will always be some people who may want to poke holes in the science, said Betsy Brunner, who specializes in environmental and science communication at Utah State University. So, even if it’s an honest mistake and a small difference, it could damage the message’s credibility.
“We do have to be very careful when we're doing this kind of work and we're trying to translate science.”
This challenge has become even harder in a world dominated by social media, she said. People are inundated with messages and most don’t have time to go around verifying the science of each piece of data they’re presented with.
“It's important to get these issues right because once misinformation is out there — even if it's accidental — it's really hard to take it back,” Brunner said.
There are so many aspects of the scientific world where we don’t have all the answers yet and can’t say things with certainty, Sowby said, so making sure we accurately convey the information that’s easy to confirm should be a priority. And he hopes this case study will serve as a cautionary tale the next time Utahns encounter a long-held assumption.
“It makes me wonder what else we are missing when it comes to checking important data on whatever kind of environmental issues that are coming our way.”
