With more persistent and severe droughts in the Western United States, experts who rely on a national tool that measures a region’s aridness to determine drought policy say there needs to be changes to accurately reflect the trend of a drying climate.
The U.S. Drought Monitor, developed by the U.S. Department of Agriculture and used for nearly 25 years, measures dryness through multiple factors, including precipitation, ground and reservoir water levels, soil moisture and snowpack.
A nationwide map labels drought conditions from low to high severity each week, with shades of yellow, orange and red to show how dry a region is.
A recent study led by Justin Mankin, a professor at Dartmouth College, was published in the scientific journal Advancing Earth and Space Sciences saying that the monitor’s classification of “exceptional drought” — the most severe category shown in dark red on the maps — occurs too frequently to be useful.
According to the monitor’s guidelines, it should only occur less than 2% of the time to be an effective data point, but the study found some areas of the western U.S. – especially in Colorado – have seen that dark red color 18% of the time.
“California is one of the places where the amount of time spent in severe drought has exceeded the guidelines for the drought monitor,” Mankin said, adding that the monitoring of drought is being undermined by climate change. “The drought classes are benchmarks of how likely precipitation decline is and how likely soil moisture will decline. You have a situation where severe drought is increasing and the climate is trending toward drier conditions.”
While Southern California and the state aren’t in drought conditions now – recent rainfall and a healthy snowpack in the Sierra Nevada have made the state wetter recently – it wasn’t long ago that its residents were asked to conserve water. With constant fluctuations, experts aren’t sure what the area’s conditions could be in 12 months.
David Feldman, a professor of urban planning and public policy at UC Irvine and director of the interdisciplinary Water UCI center, agrees the state and Southern California have seen an increase in severe drought ranges since the monitor was introduced and wonders what might be done to make the tool more relevant.
“What do you do if you’re consistently in a state of severity? How do you deploy resources? Maybe we need another category like ‘ultra-severe,’” he said.
Or, he suggested the existing categories need to be refined to reflect current conditions – not those that were the baseline when the monitor was first deployed more than two decades ago.
“We do know the variability of the drought has varied,” he said. “Feast or famine seems to be our reality in the West.”
Local fire agencies look to the drought monitor when assessing conditions and use the information to help inform preparedness and responses. Making sure it gives an accurate reflection is important, said Orange County Fire Authority Chief Brian Fennessy.
“It makes sense to me that (it could be) revised to account for previous (excessive) droughts, ” said Fennessy, who believes this season could see massive wildfires. “From a fuels perspective, after all those years of consecutive drought in Southern California, a lot of the vegetation died and is not coming back. Add two years of above-average precipitation, and now the dead vegetation is mixed in with and covered by the new growth.”
Though the drought monitor says Southern California isn’t in a drought and the amount of green is deceiving, he’s preparing for fires that could grow large very quickly, he said. “As a result, we have added all three helicopters to our vegetation fire response.”
While the state uses the drought monitor to inform policy, it also began collecting local water supply and demand assessments from water districts to help provide information about potential shortages, said Fiona Sanchez, director of water resources with the Irvine Ranch Water Distirct. “The more complete picture better informs the state’s response and helps minimize unnecessary restrictions on customers.”
Mankin and the other study authors explored ways to better incorporate climate change into the monitor reports, but found 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.”
Think of it like the Category 6 scientists have similarly proposed creating for measuring hurricanes as they intensify due to climate change.
But Mankin said adding another category to reflect an even more extreme drought doesn’t solve the issue.
“There are a few reasons why I don’t think adding a ‘more exceptional’ drought class, defined in a similar way to the other drought classes, would solve the issue,” he said. “There is a hard cap to how bad a drought can get. You can’t have less than zero water. This is distinct from other weather and climate features like hurricanes or tornadoes. The winds associated with a hurricane do not have a hard cap; they can always get stronger, so an additional class for a hurricane or tornado makes sense. It’s not the case for a drought.”
He suggested using something that reflects the new normal might be more useful. But updating the baseline of “normal” against which droughts are assessed, that would say that places have drier climates now, and thus droughts would be systematically downgraded relative to the past.
“A hard conversation needs to happen about how we should understand monitoring droughts,” Mankin said. “How should the tool be amended to inform emergency management? You can’t put triage to the greatest effect when everyone is in an emergency.”
Mankin said California will continue to see swings between wet and dry conditions. And that will require officials to balance managing both standing water in the streets and a multi-year drought, he said.
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“There needs to be a set of resources for drought and long-term water management,” he said. “How do we amend the drought monitor to be effective as a decision tool while also recognizing that droughts are trending from climate change? You can’t manage the impact of climate change in the way we are measuring climate abnormalities.”
Brad Pugh, a meteorologist with NOAA, is a drought monitor author, which means he helps create the weekly maps.
While he knows of Mankin’s research, he said he believes the monitor, as it is currently working, is accurate and a good indicator of drought conditions nationally. He also believes keeping a longer historical baseline intact is critical as an indicator of climates.
He said if the baseline were tweaked and therefore reflected a shorter period, it wouldn’t include some of the historically severe droughts of the 1930s and 1950s.
But he said he understands that managing the dryness in the West is difficult and that, as a scientist, he is open to more research.
“If you look at the time sequence for the U.S. Drought Monitor, people think California has been in a drought for two decades,” he said. “That’s just not true.”
Denver Post Staff Writer Elise Schmelzer contributed to this story.