Longer, drier droughts may be ahead for the Southwest and Central Plains if greenhouse gas emissions continue unabated, according to study released this month that included NASA-sponsored projections.
The longer droughts could be similar to drought experienced in the 1930s and current drought in the Midwest, but it will be as much as 30 to 35 years long, as opposed to lasting a decade or less, according to Ben Cook, climate scientist at NASA's Goddard Institute for Space Studies.
Currently likelihood of a megadrought is about 12%, though if greenhouse gas emissions continue along on current trajectories, the likelihood of a megadrought in the Southwest and Central Plains increases to 80% between 2050 and 2099.
The research supporting these conclusions was published in the journal Science Advances. It included analysis of a drought severity index and two soil moisture data sets from 17 climate models that were run on both current emissions trajectories and the premise that emissions could stop increasing by the mid-21st century.
The study said in the Southwest and Plains, climate change could cause reduced rainfall and higher temperatures, evaporating more water from the soil.
Until this study, much of the previous research included analysis of only one drought indicator and results from fewer climate models, NASA's Ben Cook said, making this a more robust drought projection than any previously published.
This study also is the first to compare future drought projections directly to drought records from the last 1,000 years.
"We can't really understand the full variability and the full dynamics of drought over western North America by focusing only on the last century or so," Cook said. "We have to go to the paleoclimate record, looking at these much longer timescales, when much more extreme and extensive drought events happened, to really come up with an appreciation for the full potential drought dynamics in the system."
Scientists used historical drought data to establish moisture conditions of years past. Natural observations, like tree rings, were also used – species like oak and bristle cone pines grow more in wet years, leaving wider rings, and vice versa for drought years.
The scientists were interested in megadroughts that took place between 1100 and 1300 in North America. These medieval-period droughts, on a year-to-year basis, were no worse than droughts seen in the recent past. But they lasted, in some cases, 30 to 50 years.
When these past megadroughts are compared side-by-side with computer model projections of the 21st century, both the moderate and business-as-usual emissions scenarios are drier, and the risk of droughts lasting 30 years or longer increases significantly.