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The southwest will be drier over the next century than any time in the past millennium

The southwest will be drier over the next century than any time in the past millennium

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The driest part of the US may see more drought risk in the next century than it faced in the previous thousand years, according to a new report published today in Science Advances. Led by NASA climate scientist Benjamin Cook, the team tracked three different drought indices for the American southwest and central plains over the past thousand years. The team then compared the historical record to climate projections of the next century. The result was a bleak forecast. Under current projections, the next hundred years are set to be significantly drier for the region than any other period on record.

"The dry are getting drier."

There will be a little less rain for arid regions like the southwest and central plains over the next 100 years, but most of the changes will come from warmer temperatures leading to more evaporation and drier soil, according to the models used in the study. Adding the expected changes together, the scientists found stronger drought conditions than anything the region has seen in the past millennium even during the 200-year dry spell between 1100 and 1300. The study didn't control for human factors, however, which could potentially render the region even drier if water use from habitation and agriculture continues to grow.

The study is based on 17 projections from the CMIP5 climate model, an internationally managed collection climate projection that dates back to 2011. There are a number of more recent models outside the CMIP5, but University of Illinois climate scientist Donald Wuebbles says other models are likely to produce similar results. "One of the things that they find in essentially all the models is, the wet are getting wetter and the dry are getting drier," says Wuebbles, who didn’t participate in the study. "It's really not too shocking that you would get a strong trend in droughts."

NASA’s Cook hopes further research will unlock more regional detail within the southwest and central plains, but the most urgent work will have more to do with time than geography. "The big question is when these areas will start to transition to these much drier conditions," Cook says. "Will the transition be apparent in 20 years? 30 years? 40 years?"