Lightning droughts, which can occur quickly and devastate crops within weeks, are becoming more common and accelerating around the world, and human-caused climate change is one of the main reasons, a new scientific study has found.
As global warming continues, more abrupt droughts could have serious consequences for people in wet regions whose livelihoods depend on rain-fed agriculture. The study found that flash droughts were more common than slower droughts in parts of tropical areas such as India, Southeast Asia, sub-Saharan Africa and the Amazon Basin.
But “even with 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 in Science on Thursday. In other words, droughts of all kinds are coming faster and faster, straining forecasters’ ability to anticipate them and communities’ ability to deal with them.
The world has probably always experienced rapid-onset droughts, but it’s only in the last decade or two that they’ve become a significant focus of scientific research. New sources of data and advances in computer modeling have enabled scientists to study the complex physical processes behind them. The concept also attracted attention in 2012 after a heavy dry season raised in the United States, devastate fields and pastures and caused by $30 billion lossmost of them in agriculture.
Generally, this type of rapid drying occurs when it’s warm and rain would normally fall, but very little, said Andrew Hoell, a climate scientist at the National Oceanic and Atmospheric Administration, who wasn’t involved with the new research but contributed has other studies on the subject.
In such circumstances, the ground could already be wet from previous rain or snow, said Dr. hell. So when precipitation suddenly stops, hot, sunny, and windy conditions can cause large amounts of water to evaporate quickly.
Because of this, the humid tropics tend to experience more flash droughts than slow ones. The rainy seasons there are usually rainy enough to keep the land and vegetation wet. But when the rain fails unexpectedly, the equatorial heat can dry out the soil to devastating effect.
As the burning of fossil fuels warms the planet, droughts of all kinds become more likely in many places simply because more evaporation can take place. But the scientists hadn’t determined whether both flash droughts and slow droughts were increasing at the same rate, or whether there was a transition from one type to the other.
dr Yuan and his colleagues examined computer model data on soil moisture around the world between 1951 and 2014. They focused on drought episodes lasting 20 days or longer to rule out droughts that were too short to cause major damage.
Trends have varied from location to location, but 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 man-made emissions of heat-trapping gases and natural variations in global climate, including volcanic eruptions and changes in solar radiation. But the trends didn’t appear as clearly in simulations that included only the natural fluctuations. This suggests that human-caused climate change was a factor.
In the coming decades, even if Global warming is increasing only relatively moderatelyThe study predicted that lightning droughts will occur more frequently and faster in almost all regions of the world.
Scientists still need to better understand what drives individual dry spells, said Dr. Yuan. 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 warn producers and water managers more timely.
“We’re doing a good job in most places looking at what the weather is going to be like over the next few days, possibly up to a week,” said Justin Sheffield, a professor of hydrology and remote sensing at the University of Southampton in England and a another author of the new study. “And we’re doing a reasonable job of saying something about what’s happening across the seasons.”
In between, he said, scientists’ forecasting skills need to be improved. “Right now I think we’re far away.”
Jordan I. Christian, a postdoctoral fellow in meteorology at the University of Oklahoma who was not involved in the new study, got a front row seat to a severe flash drought in Oklahoma and the Southern Plains last summer.
“The rainfall was good. Soil moisture was good. The vegetation was very green. It looks great,” he said. “And then, two or three weeks later, you just see the ecosystem and the environment struggling. Honestly, it’s just crazy to see that.”
