Climate warming looks set to plunge the American Southwest into decades-long drought by the end of the century.

Credit: Rick Wilking/Reuters

Such 'megadroughts' have hit the region (Lake Powell on the Colorado River, pictured) during the past millennium. To calculate how changes in temperature, rainfall and soil moisture will affect the likelihood of such events, Toby Ault of Cornell University in Ithaca, New York, and his colleagues ran simulations using climate models and two greenhouse-gas emission scenarios.

If emissions continue to rise unabated, the projected increase in regional mean temperature alone will boost the risk of a megadrought to 70–99% by 2100, depending on whether precipitation increases moderately, stays the same or decreases. If warming remains below 2 °C compared to temperatures seen in the second half of the twentieth century, that risk falls to less than 66%.

Sci. Adv. 2, e1600873 (2016)