Climate change is set to unleash a series of decades-long “megadroughts” this century, according to research to be published this week.
Experts warn the droughts could be even more severe than the prolonged water shortage currently afflicting California, where residents have resorted to stealing from fire hydrants amid mass crop failures and regular wildfires.
Megadroughts – which are generally defined as lasting 35 years or more – will become considerably more frequent as global warming increases temperatures and reduces rainfall in regions already susceptible, warns Cornell University’s Dr Toby Ault, the author of the new report.
Megadroughts are also likely to be hotter and last longer than in the past, he claimed. His peer-reviewed research – to be published in the American Meterological Society’s Journal of Climate – is the first to scientifically establish that climate change exacerbates the threat.
“We can now explicitly add megadroughts to the list of risks that are being intensified by climate change. Without climate change there would be a 5 to 15 per cent risk of a megadrought in the south-west of the US this century. With it, the probability jumps to between 20 per cent and 50 per cent, with the southernmost part of the country particularly at risk,” Dr Ault told The Independent.
The threat megadroughts pose is so great they could decimate the world’s economy and food supply, inflicting a humanitarian crisis, experts warned.
“Global warming will make droughts evermore severe and devastating in the future. The south-west of the US, southern Europe, much of Africa, India, Australia and much of Central and South America could all have a drought that lasts decades,” said Jonathan T Overpeck, an environmental scientist at the University of Arizona.
Megadroughts are defined more by their duration than their intensity. They have historically been associated with prolonged La Niña conditions, which create cooler than normal water temperatures in the tropical eastern Pacific Ocean. This reduces evaporation and, in turn, the amount of rainfall.
Megadroughts have occurred periodically around the world in the past few thousand years. In some cases they have caused civilisations to collapse, such as the ancient Puebloan native-American tribes in the south-west of the US – who abandoned their homes during a megadrought in the late 13th century – and the Khmer empire of Cambodia in the 14th century.
The fallout from future megadroughts will be even more severe because the global population is larger and the strain on water supplies is greater, warns Professor Park Williams of Columbia University in New York.
“Many of the already drought-prone parts of the planet will see megadroughts during this century that are far worse than anything those regions have seen in the past several thousand years at least.”
Prof Williams believes governments should pay some industry and communities to cut their water consumption.
While the UK is unlikely to suffer its own megadrought, Dr Overpeck warned that Britain could be hit by a megadrought elsewhere, especially in regions it relies on for food, or in zones prone to conflict.
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