Dividing line: The past, present and future of the 100th Meridian

[NeoGreen]

https://www.earthmagazine.org/article/dividing-line-past-present-and-future-100th-meridian


The 100th meridian runs from pole to pole, 100 degrees longitude west of the prime meridian in Greenwich, England. It cuts through six U.S. states, forming a partial boundary between Oklahoma and Texas. Powell identified this line as marking the point where the average annual rainfall dropped from 61 centimeters on the eastern edge to 46 centimeters at the western edge. New research shows a sharp aridity gradient still exists, but it’s moved east a bit, closer to the 98th meridian. Climate models predict it will move farther eastward in coming decades. Credit: National Atlas, modified by K. Cantner, AGI

Dividing line: The past, present and future of the 100th Meridian
By Harvey Leifert

In 1878, without benefit of the Landsat program, GPS or Google, and just a decade after the creation of the National Weather Service, John Wesley Powell first advanced the idea that the climatic boundary between the United States’ humid East and arid West lay along a line “about midway in the Great Plains” — almost exactly 100 degrees longitude west of the prime meridian in Greenwich, England. This line, the 100th meridian, runs from pole to pole and cuts through six U.S. states, forming a partial boundary between Oklahoma and Texas. The 100th meridian also corresponds roughly to the 600-meter elevation contour as the land rises from the Great Plains toward the Rockies.

In his 1878 “Report on the Lands of the Arid Region of the United States,” Powell identified the “arid region” as the land west of the 51-centimeter-per-year rainfall line, which closely tracked the 100th meridian. This amount of rainfall per year is about the minimum that permits farming without irrigation, and it also greatly influences the types of crops that can be grown. The line Powell noted as dividing the arid and humid sections of the continent has become known as the “effective” 100th meridian.

Powell’s original goal in describing the effective 100th meridian as a dividing line was to persuade the federal government to bear in mind the greater aridity when planning for settlement and development in the western territories, which would be very different than in the moisture-rich east. He created a map that he presented to the House of Representatives in 1890, delineating western watersheds. He proposed that each one be designated a “commonwealth” for the purpose of regulating its water usage, which would remain under federal control without regard to state lines. Although Powell had by then been named second director of the U.S. Geological Survey, owing to his knowledge of the geological makeup of North America, he did not succeed with his proposal.

The Great Plains are well known for their sweeping grasslands, which, to the east, eventually turn into great farms, and, to the west, give way to deserts and mountains. Credit: ©iStockphoto.com/Danielrao.

[hatrack]

1. Topeka becomes Hays, Kansas City becomes Topeka, and so on . . .

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[mountain grammy]

2. Fascinating.