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“Flash droughts” are increasingly common

“Flash droughts” are increasingly common

Rapidly forming droughts are happening more often and faster in many parts of the world due to climate change, a new study has found. These “flash droughts” replace more typical droughts that are slower, more difficult to predict and cope with, which could make their management more difficult.

Most major droughts have tended to occur on seasonal or annual time scales, resulting from the variability of large-scale climate models like El Niño (SN: 02/13/23). But over the past six decades or so, there has been a transition to no more droughts that form in just a few weeks with little warning in most countries around the world, researchers report in the April 14 Science.

“This finding has massive implications for ecosystem conservation and agricultural management,” says Christine O’Connell, an ecosystem ecologist at Macalester College in St. Paul, Minnesota, who was not involved in the study. “Will some plant species be less able to survive a flash drought trend? What would this mean for biodiversity or the amount of carbon stored in an ecosystem? »

Some sudden droughts turn into seasonal droughts, but even those that don’t can cause significant damage to agriculture and contribute to other extreme weather events such as wildfires and heat waves. In the summer of 2012, a sudden severe drought across the United States caused over $30 billion in damage. Many affected areas went from normal conditions to extreme drought within a month, and no climate model had predicted this.

Previous research has suggested that flash droughts are on the rise in some areas. But it was unclear whether they were replacing slower-onset droughts, meaning generally slow-onset droughts happened more quickly, or whether fast- and slow-onset droughts grew in tandem.

To find out, Xing Yuan, a hydrologist at Nanjing University of Information Science and Technology in China, and his colleagues analyzed soil moisture data from around the world from 1951 to 2014. They distinguished between flash and slow subseasonal droughts by exploring the rate at which soils dried during the initial period of drought onset, then calculated the frequency of each occurrence and the geographic spread.

The speed of onset of drought on subseasonal scales has increased across much of the world, the team found. And the ratio of fast to slow droughts has increased in more than 74% of the regions of the world defined by the Intergovernmental Panel on Climate Change’s special report on extreme events. Certain regions such as South Australia, North and East Asia, the Sahara, Europe and the west coast of South America have been the most affected.

By comparing climate models that included or omitted factors such as greenhouse gases, the researchers found that human-induced climate change exerts a major influence on global trends. These patterns intensify under higher emission scenarios, and the speed of onset of droughts also increases.

The climatic anomalies, such as heat waves, that cause these flash droughts are more extreme than those that cause seasonal or interannual droughts, leading to severe droughts in a shorter time, Yuan says.

As with most droughts, a period of low rainfall remains the main driver of flash droughts. But excessive evapotranspiration — water moving into the atmosphere from soil and plants — plays a key role in driving these droughts by rapidly drying out soils, the analysis found. Flash droughts occur two to three times more often in humid regions such as northwestern North America, Europe and southern China than elsewhere, according to the study.

As the world continues to warm, causing more evapotranspiration and less precipitation, the frequency of flash droughts is expected to continue to increase, researchers say.

The study is “very important because we’re living in it right now,” says Mark Svoboda, a climatologist at the University of Nebraska-Lincoln, who coined the term “flash droughts” 20 years ago but was not involved in the study. the new research. “We now have more data to confirm my hunch that the interaction of drought with winds, evapotranspiration and heat waves in particular could really lead to rapid onset drought.”

Predicting flash droughts is difficult because current monitoring systems often cannot capture their occurrence on short enough time scales. “We need to improve these systems,” Yuan says, exploring the mechanisms behind flash droughts and improving simulations, perhaps with the help of artificial intelligence.

To deal with these droughts, it’s not enough to have a better set of tools, says Svoboda, but also a different mindset. “It’s human nature not to deal with drought until you’re there. Instead, we advocate that drought be addressed proactively rather than reactively.

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