The American Southwest may be headed for a “megadrought,” an arid period longer than any in recent memory.
A megadrought is the name for a decades-long dry spell. Researchers have known since 1998 that megadroughts can occur in the region. Under normal conditions, dry periods of several decades or more come once or twice in a millennium, but the changing climate has made the danger much more imminent. Now, a new study has determined there is a 50 percent chance that a drought as long as 35 years will occur in the next century. And the chances of another decade-long drought are as high as 80 percent.
In order to understand the conditions that lead to these rare multi-decade dry periods, researchers went into the field to study the traces that ancient weather patterns leave behind. “You go up into the mountains and these beautiful places where moisture limits growth to take samples,” Dr. Toby Ault, lead researcher of the study, tells Popular Science.
In dry places, plants grow slower and the gaps between their annual tree rings are shorter. By matching up modern tree rings with ancient wood -- such as beams from pre-Columbian Native American desert dwellings -- researchers can track annual moisture patterns going back centuries. That’s an important part of how they know the Southwest has been through megadroughts before, as well as how often they've happened.
Plus, climate models have long predicted the Southwest will lose water as the Earth warms, and the prolonged drying period predicted for the coming years looks eerily similar to the periods that preceded the sustained dry periods of the past.
“This pretty robust feature of climate change models loads the dice toward droughts and megadroughts,” Ault says.
Decade-long droughts came about once a century in the pre-climate change world. Today, California and Arizona are parched. An ongoing 15-year drought is sucking dry the region’s reservoirs and drying out its forests, leading to a range of problems, including immediate concerns about water shortages in Tucson, Phoenix, and even Las Vegas.
There is some uncertainty as to the relationship between the region’s current struggles and climate change, but this drought points to what the whole Southwest may have to deal with if droughts become more widespread and longer-lasting. A megadrought could include New Mexico and Texas, and last as long as 35 years.
However, Ault says a megadrought in our lifetimes would not have to mean devastation for the American Southwest.
“Some of our best evidence of droughts comes from tree rings,” he points out. “That means some trees grew during dry periods. A megadrought doesn’t spell death and destruction for all creatures. Less water does not mean no water.”
Ault says he hopes his findings will encourage state and local water conservation groups to deal with the danger of water scarcity becoming the norm. Advances in water conservation and management have prevented the current Arizona drought from becoming as bad as the Dust Bowl, a shorter dry spell that devastated American plains agriculture during the Great Depression in the 1930s.
“As long as we accept that we are a clever and adaptable species -- and I think all evidence points to us being a clever and adaptable species -- we can mange this,” he says.