Drought in the American West is becoming a persistent reality instead of a periodic emergency due to climate change, and a recent study found that an essential tool used to measure drought can’t keep up.
Every week since 1999, the U.S. Drought Monitor has published a new map showing drought conditions across the country, with five categories of drought severity depicted in shades of yellows, oranges and reds. Policymakers and elected leaders in Colorado and other states use the map to make critical decisions about water use, campfire bans, declarations of emergency and more.
And multiple federal agencies use the map to determine how much financial aid is filtered to ranchers and farmers in times of drought.
But what was once considered an exceptional, rare drought is no longer so rare, the study found.
An “exceptional drought” — the most severe category of drought, depicted in dark red — should occur in a region only 2% of the time, according to the monitor’s guidelines. But some areas of the western U.S. have been in exceptional drought 18% of the time, according to a study published this spring in AGU Advances, a scientific journal. An exceptional drought is also more harmful than it was when the monitor was founded more than two decades ago, the study states.
“What is the value to a decision-maker of a map that is just red all of the time?” said Justin Mankin, a professor at Dartmouth College and the study’s lead author. “It doesn’t help you triage resources.”
In Colorado, the severity, length and breadth of droughts can have substantial impacts on the state’s $47 billion agriculture industry. Swaths of the state are so often in drought that brief reprieves from dryness merit news stories — as in 2023, when the Drought Monitor declared the state drought-free for the first time since 2019.
But dryness has returned and nearly half of Colorado is now in drought or has near-drought conditions, according to the monitor’s most recent report.
Mankin and the other study authors explored two ways to better incorporate climate change into the monitor reports, but both have drawbacks.
Those in charge of the Drought Monitor — the National Drought Mitigation Center at the University of Nebraska-Lincoln, the National Oceanic and Atmospheric Administration and the U.S. Department of Agriculture — could create a new category for drought that is more severe than “exceptional drought.” Scientists have similarly proposed creating a new Category 6 for measuring hurricanes as they intensify due to climate change.
Another solution could be to adjust the data used as the “normal” baseline for the Drought Monitor so that it includes more recent drier years.
The Department of Agriculture last year updated its plant hardiness map to incorporate more recent data indicative of climate change. The map helps farmers and gardeners decide what and when to plant based on their location.
Making such a shift with the Drought Monitor, however, would mute the existence of climate change and would minimize impacts on people affected by aridification, Mankin said.
The Drought Monitor is a crucial tool, he said, and there will be no silver bullet or simple solution to adapt it to climate change. Instead, he said, “a constellation of fixes and investments” is needed.
