Carbon emissions up risk of US megadroughts: NASA

Continued increases in human-produced greenhouse gas emissions drives up the risk of severe droughts in some US regions, according to a new NASA study.
Droughts in the US Southwest and Central Plains during the last half of this century could be drier and longer than than drought conditions seen in those regions in the last 1,000 years, researchers said.
The study, published in the journal Science Advances, is based on projections from several climate models, including one sponsored by NASA.
"Natural droughts like the 1930s Dust Bowl and the current drought in the Southwest have historically lasted maybe a decade or a little less," said Ben Cook, climate scientist at NASA's Goddard Institute for Space Studies, and lead author of the study.

"What these results are saying is we're going to get a drought similar to those events, but it is probably going to last at least 30 to 35 years," said Cook.
According to Cook, the current likelihood of a megadrought, a drought lasting more than three decades, is 12 per cent.

If greenhouse gas emissions stop increasing in the mid-21st century, Cook and his colleagues project the likelihood of megadrought to reach more than 60 per cent.
However, if greenhouse gas emissions continue to increase along current trajectories throughout the 21st century, there is an 80 per cent likelihood of a decades-long megadrought in the Southwest and Central Plains between the years 2050 and 2099.

The scientists analysed a drought severity index and two soil moisture data sets from 17 climate models that were run for both emissions scenarios.
The high emissions scenario projects the equivalent of an atmospheric carbon dioxide concentration of 1,370 parts per million (ppm) by 2100, while the moderate emissions scenario projects the equivalent of 650 ppm by 2100. Currently, the atmosphere contains 400 ppm of CO2.
In the Southwest, climate change would likely cause reduced rainfall and increased temperatures that will evaporate more water from the soil.
In the Central Plains, drying would largely be caused by the same temperature-driven increase in evaporation.