New research from Virginia Tech has identified an atmospheric shift that can rapidly trigger “flash droughts” in Puerto Rico, offering insight that could support earlier warning systems and preparedness.
The study, published in Geophysical Research Letters, examines how drought conditions on the island can develop within days rather than weeks or months.
Flash drought can take hold in as little as five to 10 days, leaving limited time for response. This can disrupt agriculture, water supplies and ecosystems, increasing the risk of crop losses and water shortages.
Researchers identified a key change in atmospheric behavior as the trigger. The process involves a shift from rising air, which supports cloud formation and rainfall, to sinking air, which suppresses precipitation.
“When air is rising, it helps clouds form and brings rainfall,” said Craig Ramseyer, associate professor in the Department of Geography at Virginia Tech. “But when that motion suddenly switches and the air starts sinking, it shuts that process down very quickly.”
As air begins to sink, it warms and dries the atmosphere, breaks up clouds and allows more sunlight to reach the surface. This accelerates moisture loss from soil and can quickly lead to drought conditions.
“It’s really like a switch gets flipped in the atmosphere,” Ramseyer said. “You go from conditions that support rainfall to conditions that actively dry things out, and that can happen on the order of just a few days.”
The findings reflect observations from farmers and water managers in Puerto Rico, who have reported rapid transitions from wet to dry conditions. In some cases, these shifts have led to water rationing and pressure on agricultural production.
“Stakeholders have been telling us for a while that these rapid changes are possible,” Ramseyer said. “This research shows that they are correct and helps explain why.”
By identifying this atmospheric “switch”, researchers say it may be possible to detect early signals of flash drought before impacts become severe.
“If we can identify these signals in advance, there’s potential to give communities a heads-up before drought conditions fully develop,” Ramseyer said.
While flash droughts have been widely studied in the continental USA, where they typically develop over longer periods, the study highlights how tropical regions can experience much faster onset due to stronger atmospheric dynamics and solar intensity.
The researchers say similar conditions may exist across the Caribbean and other tropical regions, suggesting broader applications for forecasting and water management.
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