Lightning droughts will be common with global warming – 04/17/2023 – Environment

Flash droughts, the kind that come on quickly and can devastate crops in a matter of weeks, are becoming more common and faster around the world, and human-caused climate change is one of the main reasons why, a new study has revealed. scientific.

As global warming continues, more abrupt dry spells could have serious consequences for people in wetlands whose livelihoods depend on rainfed agriculture. The study found that sudden droughts occurred more frequently than slower ones in some tropical areas such as India, Southeast Asia, sub-Saharan Africa and the Amazon basin.

But “even for slow droughts, the speed of onset has been increasing,” said Xing Yuan, a hydrologist at Nanjing University of Science and Information Technology in China and lead author of the new study, published Thursday in Science magazine.

In other words, droughts of all kinds are coming more quickly, overwhelming meteorologists’ ability to anticipate them and communities’ ability to cope.

The world has probably always experienced rapid-onset droughts, but only in the last two decades have they become a significant focus of scientific research. New data sources and advances in computer modeling have allowed scientists to focus on the complex physical processes behind them.

The concept also gained attention in 2012, after a severe drought hit the United States, devastating farmland and grasslands and causing more than $30 billion in losses, most of them in agriculture.

This type of rapid drought usually occurs when it’s hot and it should normally be raining, but there’s very little rain, said Andrew Hoell, a climate scientist at the National Oceanic and Atmospheric Administration (NOAA) who was not involved in the new research, but contributed to other studies on the subject.

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

This is why the wet tropics tend to experience more sudden droughts than slow ones. The wet seasons are usually wet enough to keep the land and vegetation moist. But when the rains fail unexpectedly, the equatorial heat can dry out the soil with devastating effects.

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 occur. But scientists have not determined whether sudden droughts and slow droughts are becoming more common at the same rate or whether there is a transition from one type to another.

Yuan and his colleagues analyzed data from computer models of soil moisture around the world between 1951 and 2014. They focused on drought episodes of 20 days or longer, excluding very short drought periods that don’t cause much damage.

Trends varied from place to place but, viewed globally, show a shift towards more frequent and rapid sudden droughts.

Yuan and his co-authors found that these trends were well captured in computer simulations that took into account both human-made emissions of heat-trapping gases and natural variations in the global climate, including volcanic eruptions and changes in solar radiation.

But the trends didn’t show up as clearly in simulations that only included natural variations. This suggests that human-induced climate change has played a role.

In the coming decades, even if global warming increases only relatively modestly, sudden droughts will become even more common and faster in nearly all regions of the globe, the study predicted.

Scientists still need to improve their understanding of what drives individual dry spells, Yuan said. Droughts involve heat and rain, but also local factors such as topography, vegetation and soil type. A better understanding of the interaction between these elements would help meteorologists to issue more timely warnings to water resource producers and managers.

“We’ve done a reasonable job in most places looking at what the weather will be like in the next few days, potentially a week,” said Justin Sheffield, professor of hydrology and remote sensing at the University of 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.”

Among them, he added, is where scientists’ forecasting skills need work. “Right now, I think we’re a long way off.”

Jordan I. Christian, a postdoctoral researcher in meteorology at the University of Oklahoma who was not involved in the new study, closely observed a sudden drought in Oklahoma and the southern plains of the United States last summer.

“The precipitation was good. The soil moisture was good. The vegetation was very green. It looked great,” he said. “Then two or three weeks later you see the ecosystem and the environment struggling. Honestly, it’s crazy to see that happen.”

_{Translated by Luiz Roberto M. Gonçalves}