Droughts have an insidious reputation, often building gradually over several dry seasons. Flash droughts are a lesser known phenomenon in which intensely dry conditions develop in as little as 2 weeks, wreaking havoc on crops and water supplies. A new study is shedding light on how scientists can more effectively monitor and predict these quickly evolving phenomena, which are projected to become more frequent with climate change.
Flash droughts were first recognized in 2002, but “we don’t know much about how they develop because few studies have focused specifically on short-term events,” said lead author Angeline Pendergrass, an atmospheric scientist at the National Center for Atmospheric Research in Boulder, Colo.
In the new study, published in Nature Climate Change, Pendergrass and colleagues define flash droughts as sudden onset events that create severely dry conditions in about 2–6 weeks. If these events occur during the peak of the growing season, they can kill off crops over large areas, as happened across the midwestern United States in 2012.
The conditions leading up to a flash drought are still being quantified, but decreased rainfall, above-average temperatures, and low soil moisture all play a role, with many flash droughts triggered by heat waves following a dry period. Like regular droughts, flash droughts can strike anywhere, although arid and semiarid environments are especially susceptible because soils there often have low moisture levels year-round, Pendergrass said.
More work is needed to elucidate a myriad of other factors that may also contribute to flash droughts, she said, including the atmospheric and meteorological conditions that lead to decreased rainfall patterns, how the land surface responds to warmer temperatures, and the balance between water absorption and runoff in capturing the rain that does fall on a parched landscape.
Adapting Early-Warning Systems
Drought early-warning systems are already in place across the United States, said Donald Wilhite, a drought management specialist at the University of Nebraska–Lincoln, but these systems will need to be adapted to be able to predict droughts that evolve over short time frames. Wilhite was not involved in the new study.
“A comprehensive early-warning system is not just about tracking precipitation and temperature,” he said. “You also need to monitor soil moisture conditions, streamflow, water stress, and reservoir levels.”
Currently, these variables tend to be monitored on a weekly basis, with some factors updating more or less often, Pendergrass said. “We need to increase the frequency with which monitoring products are being updated so we can better capture these quickly moving flash drought events,” she said. “[It] will take time, money, and people to accomplish that, but it’s possible.”
Both droughts and flash droughts are expected to occur more frequently and with more severity in the future, Wilhite said. “With climate change, temperatures are escalating, increasing water stress over large areas of the planet. We’re seeing droughts run the gamut from weeks to multiple years, affecting entire continents. It’s a hugely dynamic phenomenon.”
The new study, authored by 22 people in fields ranging from atmospheric science to agricultural management, shows that flash droughts are becoming a more mainstream area of study, Wilhite said. “The authorship on this study is a good sign that flash droughts are being widely recognized by the scientific community. It’s a very impressive cross-disciplinary collaboration, and that’s what’s needed to better understand these quickly moving drought events.”
—Mary Caperton Morton (@theblondecoyote), Science Writer