As the world heats up, droughts are accelerating, study finds

Flash droughts, those that come on quickly and can devastate crops in weeks, are becoming more common and growing faster around the world, and human-caused climate change is a major reason, according to a news report. scientific studies.

As global warming continues, more severe droughts could have serious consequences for people in humid regions whose livelihoods depend on rain-fed agriculture. The study found that flash droughts occur more often than slower droughts in certain tropical regions such as India, Southeast Asia, sub-Saharan Africa and the Amazon Basin.

But “even for slow droughts, the speed of onset has increased,” said Xing Yuan, a hydrologist at Nanjing University of Information Science and Technology in China and lead author of the new study, which was published Thursday in Science. In other words, droughts of all kinds are coming faster, straining the ability of forecasters to anticipate them and the ability of communities to cope with them.

The world has probably always had rapid-onset droughts, but only in the past two decades have they become a major focus of scientific research. New data sources and advances in computer modeling have allowed scientists to focus on the complex physical processes that underlie them. The concept also caught the eye in 2012 after a severe drought loaded across the United States, ravaging agricultural fields and pastures and causing more $30 billion in lossesmost in agriculture.

Typically, this type of rapid drying occurs when it’s warm and normally rains, but very little, said Andrew Hoell, a National Oceanic and Atmospheric Administration climatologist who was not involved in the new research. but has contributed to other studies on the subject.

Under such circumstances, the ground could already be wet from previous rain or snow, Dr Hoell said. So when precipitation suddenly stops, hot, sunny and windy conditions can cause large amounts of water to evaporate quickly.

This is why the humid tropics tend to experience more flash droughts than slow droughts. The rainy seasons here are usually rainy enough to keep the land and vegetation moist. But when the rains fail unexpectedly, the equatorial heat can dry out the ground with devastating effect.

As the burning of fossil fuels warms the planet, droughts of all kinds are becoming more likely in many places, simply because more evaporation can take place. But scientists had not determined whether flash droughts and slow droughts were becoming more common at the same rate, or whether there was a transition from one type to the other.

Dr Yuan and his colleagues looked at computer model data on soil moisture around the world between 1951 and 2014. They focused on drought spells lasting 20 days or longer, to rule out drought periods that were too short. to cause a lot of damage.

The trends vary from place to place, but when viewed globally they show a shift towards more frequent and faster flash droughts. Dr. Yuan and his co-authors found that these trends were well captured in computer simulations that accounted for both anthropogenic emissions of heat-trapping gases and natural variations in global climate, including volcanic eruptions and changes in solar radiation. But the trends didn’t show up as clearly in the simulations that only included natural variations. This suggests that human-induced climate change has been a factor.

In the decades to come, even if global warming increases only relatively modestlyflash droughts will become even more frequent and faster in almost all regions of the globe, the study predicts.

Scientists still need to improve their understanding of what drives individual drought periods, Dr Yuan said. Droughts involve heat and precipitation, but also local factors such as topography, vegetation and soil type. A better understanding of how these elements interact would help forecasters issue more timely warnings to producers and water managers.

“We are doing a reasonable job in most places looking at the weather over the next two days, potentially up to a week,” said Justin Sheffield, professor of hydrology and remote sensing at the University. from Southampton in England. and another author of the new study. “And we do a reasonable job of saying something about what happens over the seasons.”

In between, he said, is where scientists’ forecasting skills need to be worked on. “At the moment, I think we are way off the mark.”

Jordan I. Christian, a postdoctoral researcher in meteorology at the University of Oklahoma who was not involved in the new study, had a front row seat to a sudden severe drought in Oklahoma and the Southern Plains l last summer.

“The rainfall was good. Soil moisture was good. The vegetation was very green. It looks awesome,” he said. “And then, two or three weeks later, you just see the ecosystem and the environment struggling. Honestly, it’s really crazy to see that happen.

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