Written By: Tu-Uyen Tran
Fargo Forum
Nov. 14, 2018
FARGO — On a drive west from Fargo, a motorist can see the scenery outside the window change and not just from flat plains to rolling hills, but the roadside plants and farms change, too.
This is because there is a divide running through North Dakota and the rest of the Great Plains that separates the arid West from the humid East.
Scientists say the divide is gradually moving east and picking up speed as the global climate changes with repercussions for man and nature.
Richard Seager, a Columbia University climatologist who led research on this shifting line, said wheat will displace corn as soil gets drier, some areas will only be suitable as ranch land and farms will need to get bigger to endure the financial stress of droughts.
Fargo-Moorhead won’t soon be part of the arid West, he said, but, by century’s end, it will likely be in a transition zone between East and West that will be drier than the present.
He advocated for better planning to be ready for that change.
While the federal government seems to deny the reality of climate change, he said he’s been “modestly encouraged” to see that state and local officials in the Great Plains have begun such planning.
Old observation
The arid-humid divide was first observed by 19th century explorer and scientist John Wesley Powell, who pegged it at the 100th meridian, a line of longitude running from pole to pole. For a westbound motorist on Interstate 94, that’s about 4 miles past the exit to Steele.
Seager said he came across Powell’s work while studying droughts in the West. He said Powell had urged the federal government to change its settlement policies to something more suitable for an arid climate but was ignored.
Nature, however, had the last word anyway, and Seager and his team found that patterns of settlement and farming largely reflect the climate reality. Other than along the coast, population density drops quickly west of the divide. Farms get bigger. Wheat, which tolerates dry conditions better than corn, dominates and so does grassland for grazing cattle; the exception is where farmers tap into aquifers.
Some of this happened naturally as settlers adjusted to local conditions. But there was also the man-made disaster of the Dust Bowl, in which over-farming by desperate farmers led to massive erosion. There were many small farms before the Dust Bowl and fewer but larger farms afterwards as small farmers went bankrupt.
A massive federal response was required to slow down the erosion.
“You do see when you look at the history of the Plains that there was a big adjustment that occurred as a response to the Dust Bowl,” Seager said. “It would be good if those adjustments could happen in a more anticipatory way rather than responding to environmental emergency.”
Shifting lines
When Seager and his team looked at 40 years of climate data to see whether Powell’s observations have some scientific validity, they found that the line where the arid climate begins is roughly the 98th meridian. This is defined as an area where soil moisture from precipitation is less than the ability of the atmosphere to take that moisture back, which is to say, there’s a “moisture deficit.”
He said Powell probably knew the line was at 98 degrees westward but, because he was trying to influence politicians, decided 100 was a more appealing round number.
The reason Seager and his team believe the line exists is because of an abrupt change in precipitation. The East is kept moist by winds from the Gulf of Mexico and, in the winter, the North Atlantic also. The West is dried out by dry winds coming over the Rockies and, in summer, by dry winds from the southwestern deserts also.
Seager said the divide is projected to move east in part because the southwest is expected to get even drier with less winter and spring precipitation. Globally, rising temperatures mean the air will hold more moisture than before, so more moisture will evaporate from the soil, he said.
The divide actually varies a bit, according to the data. In North Dakota, it’s at about 99.5 degrees westward, or just west of the Crystal Springs exit on I-94. Farther south, it’s 98 degrees. And it shifts back and forth with wet and dry years, a more pronounced phenomenon here in the northern end of the Great Plains. But, on average, it’s shifting east, according to Seager’s study.
Using a combination of 20 global climate models, his team projected that by 2099, the line in North Dakota will have shifted to 98.5 degrees, about 47 miles. On I-94, that’s roughly where the Spiritwood exit is. Jamestown will then be in the same arid climate as Bismarck.
East of the line is a transition zone where there is neither a moisture deficit or surplus, and that zone extends many miles to the east before the humid climate of the East begins.
Fargo-Moorhead, with its humid climate, is currently part of the East but will have moved into the transition zone by 2099. The line where the humid climate ends will have moved from 98 degrees, where the main Valley City exit is on I-94, to 96.5 degrees, at the western edge of Buffalo River State Park on U.S. Highway 10 in Minnesota.
To see what the future holds, Seager said to look west where the transition zone is now. “You’d expect soil moisture to decline. You’d expect water stress on vegetation, whether it’s natural or crops, to increase,” he said. “You might find that growing corn becomes less possible, and you would have to shift it towards wheat. Or you might find that your land becomes more suitable for ranching than it does for crop cultivation.”