The U.S. Southwest and Central Plains regions are likely to be scorched by a decades-long "megadrought" in the second half of this century if climate change continues unabated, scientists from NASA and Cornell and Columbia universities have warned.

In a study published by the journal Science Advances this week, the researchers forecast that future drought risk in the area is likely to exceed even the driest conditions experienced during extensive Medieval-era periods that have been dubbed "megadroughts."

There is an 80 per cent chance of an extended drought between 2050 and 2099 unless aggressive steps are taken to mitigate the impacts of climate change, the article predicted.

"Ultimately, the consistency of our results suggests an exceptionally high risk of a multidecadal megadrought ... (and) a level of aridity exceeding even the persistent megadroughts that characterized the Medieval era," the scientists wrote.

The researchers said their results point to a remarkably drier future, one that presents a substantial challenge and "falls far outside the contemporary experience of natural and human systems in Western North America."

Future droughts will occur in a significantly warmer world, the study added, and conditions are likely to be a major added stress on both natural ecosystems and agriculture. (Rich Pedroncelli/ Associated Press)

They said the number of people living in the U.S. Southwest and Central Plains, and the volume of water they need, had increased rapidly over recent decades and that these trends are expected to continue for years to come.

Future droughts will occur in a significantly warmer world, the study added, and conditions are likely to be a major added stress on both natural ecosystems and agriculture.

It said recent years have seen the widespread depletion of nonrenewable groundwater reservoirs.

"Combined with the likelihood of a much drier future and increased demand, the loss of groundwater and higher temperatures will likely exacerbate the impacts of future droughts, presenting a major adaptation challenge," it said.