In the late 1800s, geologist and explorer John Wesley Powell first described a clear boundary running longitudinally through North America along the 100th meridian west that visibly separated the humid eastern part of the continent from the more arid western plains. Now, 140 years later, scientists have confirmed that such a sharp climatic boundary exists and that it is slowly shifting east due to climate change — a change that scientists say could have significant implications on farming in the region.

The new research, published in a pair of studies in the journal Earth Interactions late last month, found the divide is created by three factors: the Rocky Mountains stopping moisture from the Pacific Ocean reaching farther inland, Atlantic winter storms bringing moisture to the eastern half of the U.S., and moisture from the Gulf of Mexico moving north and curving eastward during the summer months. The only other clear, straight divide between humid and arid areas on the globe is the one separating the Sahara Desert from the rest of Africa, climate scientist Richard Seager of Columbia University, lead author of the new papers, said in a statement.

Seager and his colleagues wanted to study the boundary as an example of “psychogeography” — how environmental conditions affect human decisions. “Powell talked eloquently about the 100th meridian, and this concept of a boundary line has stayed with us down to the current day,” said Seager. “We wanted to ask whether there really is such a divide, and whether it’s influenced human settlement.”

The divide cuts through eastern Mexico, Texas, Oklahoma, Kansas, Nebraska, the Dakotas, and the Canadian province of Manitoba. West of the 100th meridian, population density declines and development is sparse, and farms are larger and primarily depend on arid-resistant crops like wheat. To the more humid east, more people and infrastructure exist. Farms are smaller and 70 percent of the harvested crop is moisture-loving corn.

Studying rainfall and temperature data since 1980, Seager and his colleagues found this climatic boundary has already shifted east about 140 miles so that it now sits closer to the 98th meridian. And it will continue to move east as warming global temperatures increase evaporation from the soil and change precipitation patterns, they concluded.

According to a press release by Columbia University’s Earth Institute, “Seager predicts that as drying progresses, farms further and further east will have to consolidate and become larger in order to remain viable. Unless farmers turn to irrigation or otherwise adapt, they will have to turn from corn to wheat or some other more suitable crop. Large expanses of cropland may fail altogether, and have to be converted to western-style grazing range. Water supplies could become a problem for urban areas.”