For 11 of the last 14 years, most of the American west has faced drought conditions. Although California’s drought gets the most attention, recent droughts have stretched as far east as Texas and Oklahoma. According to new research, however, the worst is yet to come.

During the second half of the 20th century, the US Southwest and Great Plains can expect drought conditions worse than anything seen in 1,000 years. These will even surpass the decades long “megadroughts” that have impacted the region in the past. This includes the 13th century drought that some believe caused the decline of the Anasazi or Ancient Pueblo Peoples in the Colorado Plateau, according to a study published this week.

Other recent studies have suggested that the Southwest could be dry due to global warming, but this is the first to say that it will be worse than any recent historic droughts in the region.

“We are the first to do this kind of quantitative comparison between the projections and the distant past, and the story is a bit bleak. Even when selecting for the worst megadrought-dominated period, the 21st century projections make the megadroughts seem like quaint walks through the Garden of Eden,” said Jason E. Smerdon in a statement.

Smerdon is a climate scientist at the Lamont-Doherty Earth Observatory, part of the Earth Institute at Columbia University and a co-author of the paper “Unprecedented 21st-Century Drought Risk in the American Southwest and Central Plains,” which will appear in the inaugural edition of the journal Science Advances.

“The surprising thing to us was really how consistent the response was over these regions, nearly regardless of what model we used or what soil moisture metric we looked at. It all showed this really, really significant drying,” said lead author Benjamin I. Cook of the NASA Goddard Institute for Space Studies and the Lamont-Doherty Earth Observatory.

Many western states have already imposed water use restrictions as aquifers are being drained at unsustainable levels. Lake Mead and Lake Powell, both significant water sources in the area are at historic low points and this year’s snow pack in the Sierras at less than a quarter of normal levels.

Last year Northern California shut off the flow of water to the south, forcing Central Valley farmers to leave hundreds of thousands of acres unplanted.

“Changes in precipitation, temperature and drought, and the consequences it has for our society–which is critically dependent on our freshwater resources for food, electricity and industry–are likely to be the most immediate climate impacts we experience as a result of greenhouse gas emissions,” said Kevin Anchukaitis, a climate researcher at the Woods Hole Oceanographic Institution.

For the study, researchers used data from the North American Drought Atlas to represent past climate. The atlas was developed from an extensive study of tree rings conducted by Lamont-Doherty scientist Edward Cook. It contains drought history over the last 2,005 years based on tens of thousands of samples from the United States, Mexico and Canada.

The atlas data was combined with two soil moisture measurements and a version of the Palmer Drought Severity Index, which measures precipitation, evaporation and transportation of water. The data was then applied to 17 different climate models using two different scenarios. The first assumed that greenhouse gas emissions would continue on their current trajectory, the second assumed that emission levels would be moderated.

Most of these measures drew the same conclusions.

“The results … are extremely unfavorable for the continuation of agricultural and water resource management as they are currently practiced in the Great Plains and southwestern United States,” said David Stahle, professor in the Department of Geosciences at the University of Arkansas and director of the Tree-Ring Laboratory there.

Despite the historic drought conditions, the west coast may be one of the most habitable areas in the second half of the century. This year a $1 billion water desalination plant is expected to open in Carlsbad California. It is expected to produce 54 million gallons of fresh water daily. With several more such projects the west coast could have enough water, even if it is expensive.

By contrast, according to the 2014 National Climate Assessment most of the United States will face severe conditions including flooding from rising oceans, severe storms causing flooding followed by heat waves and drought and other issues. With desalinized water the West coast might at least be spared the impact of severe storms and flooding.