U.S. DOE researchers identify new way to predict droughts

Computed “flash droughts” as a proxy for global warming

Argonne National Laboratory researchers have developed a new method to assess the likelihood of extreme drought conditions in several different regions of the United States over the remainder of the 21st Century.

Based on highly detailed regional climate models, the method shows droughts are likely to be exacerbated by global warming -- and especially likely in regions like the Midwest, Northwestern U.S. and California’s Central Valley.

The projected worsening of droughts … is likely to have significant consequences in terms of crop loss, wildfires, and demand for water resources,” said Rao Kotamarthi, an Argonne environmental scientist and author of the study.

Researchers believe the new technique can help identify “flash drought” events that have a quick onset period that could be as short as few weeks.

Kotamarthi explained that unlike conventional droughts resulting from a “prolonged lack of precipitation, flash droughts occur because of high temperatures and extremely high evaporation rates.”

Since precipitation deficit alone may not identify a drought, researchers used a new measure called vapor pressure deficit (VPD), which is calculated based on a combination of temperature and relative humidity. It’s the difference between the air’s capacity to hold water vapor when saturated and the total amount of water vapor available.

“An extended period of higher-than-average VPD can mean that a drought is occurring,” said Brandi Gamelin, Argonne environmental scientist. “We’re primarily look(ing) at the effect of temperature and future temperature changes on drought” because hotter air typically has a higher VPD than colder air.

Gamelin added, “…The warmer the air temperature, the more water vapor it can hold, which can draw moisture out of the surface, drying it out.”

Current drought monitoring indices rely on weekly or monthly data, typically represent lagging indicators of actual droughts.

In contrast, the Argonne-produced Standardized VPD Drought Index (SVDI) uses daily data, making it more useful in identifying flash droughts.

Read the paper, “Projected U.S. drought extremes through the Twenty-First Century with vapor pressure deficit,” based on the study which appeared in Scientific Reports.

The research was funded by a strategic partnership project with AT&T. The researchers used computing resources provided by the Argonne Leadership Computing Facility (ALCF), Argonne’s Laboratory Computing Resource Center, and the National Energy Research Scientific Computing Center (NERSC) at Lawrence Berkeley National Laboratory. The ALCF and NERSC are DOE Office of Science user facilities.

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