Today’s Top Science Headline: “100th Meridian” –Arid Dry Climate of Western U.S. Shifting Eastward




“People have lived in these regions for millennia, and we’ve developed over time different ways to deal with droughts when they do occur,” says Benjamin Cook, a climate scientist at NASA Goddard Institute for Space Studies. “The only potential losing prospect is just to pretend that this is not going to be an issue.”

Geologist and explorer John Wesley Powell was the first scientist known to have conceptualized the east/west climate divide in the mid–19th century. Soon it became known as the “100th meridian”—for the longitude with which it roughly coincided—and took on a sort of mythic status in the country’s lore, continues Shannon Hall in today's Scientific American.


More than a century later it caught the attention of Richard Seager, a climate scientist at Columbia University’s Lamont–Doherty Earth Observatory, when he chanced upon a world map of population density. On it he noticed a sharp drop west of the 100th meridian: The sprawl of homes, commercial facilities and roads starts to vanish along with the vegetation. Even seen from space, the city lights of the east quickly fade into darkness west of the line. Seager wanted to know more about how the humid/arid divide might have influenced the stark population falloff.




First, he and his colleagues set out to decipher if the line was a true physical entity, because it had yet to be analyzed with modern scientific data sets. The team found the boundary was clearly defined in drought and precipitation patterns as well as in measurements of soil moisture and vegetation, according to the Earth Interactions research. “What I like about the paper is that it keys in on what has become myth—but shows it to be fact,” says Martin Hoerling, a meteorologist at the National Oceanic and Atmospheric Administration who was not involved in the study.

The modern data also helped Seager and his colleagues understand why the line exists. Powell had correctly noted the western plains are dry in part because they lie in the rain shadow of the Rocky Mountains, which block moisture sweeping in from the Pacific Ocean. Seager’s team found the line is also reinforced by Atlantic winter storms and by summer moisture moving northeast from the Gulf of Mexico.

Continue reading…


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