CHAMPAIGN, Ill., 4/22/21: Farmland vegetation and grasses can affect both the frequency and extent of flash droughts, say scientists at the Illinois State Water Survey (ISWS), who hope to better understand the phenomenon and improve early warnings.
Flash droughts intensify quickly compared to normal droughts, magnifying the resulting economic and environmental effects. Typical droughts can take many months or years to reach peak intensity, whereas flash droughts can become severe within weeks.
In the past few years, scientists have begun examining flash droughts to learn more about the climatic, atmospheric, and environmental conditions that affect them.
“The flash drought is a new type of rapidly developing drought, and there is still a lack of consensus in its definition,” said ISWS climatologist Liang Chen. “Ever since the drought in the summer of 2012, flash droughts have received more attention from the scientific community, particularly because the impact on crop production is so much greater and stakeholders have much less time to prepare.”
The 2012 drought in the central U.S.—one of the most intense droughts on record—was later categorized as a flash drought because of how swiftly it developed. Soil moisture conditions that were normal in early June declined to what is considered exceptional drought just eight weeks later.
Chen and his colleagues studied the climatology of warm-season flash drought occurrence in the United States using data from 1979 to 2014 and experiments in a climate model. Findings showed that vegetation greening over the spring and summer months can significantly increase flash drought occurrence, particularly in the Great Plains and in the western U.S. The extent of flash droughts is also affected, but the duration is not.
A primary reason for the drought sensitivity to vegetation is the enhanced evapotranspiration that can deplete soil moisture with little effect on the health of vegetation until the soil moisture approaches the wilting point of plants. With evapotranspiration, water is transferred from the land to the atmosphere through evaporation from the soil and transpiration from plants.
Variable rainfall, leading to changes in soil moisture, also can potentially cause more flash drought events.
In the Midwest and in the eastern U.S., adequate rainfall and humidity typically provide enough moisture for vegetation and can offset reductions in soil moisture, so flash droughts are more sensitive to vegetation phenology in semi-arid and arid areas than in humid regions.
Climate projections show increasing drought conditions in large parts of the country, so there will likely be an increased risk of flash droughts in a warming climate, Chen said. Although irrigation is a potential option to decrease the risk of flash droughts, groundwater depletion in some areas of the country will likely pose challenges for meeting irrigation water demand.
The results of early studies such as this one can be influenced by the climate model used and the way that flash drought is defined. Chen and his colleagues plan to conduct more experiments to find more answers on how flash droughts develop in their future work.
This study was published in the Journal of Hydrometeorology. State Climatologist Trent Ford, also an author on this study, was interviewed for a previous story about flash drought.
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Media contacts: Liang Chen, liangch@illinois.edu
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