Weather Made Lewis and Clark's Trek Successful

If Meriwether Lewis and William Clark had set off on their historic expedition across what is now the northwestern United States a few years earlier, or a couple of years later, the dream of then-President Thomas Jefferson might have turned into a nightmare.

The success of that venture contributed to the expansion of the West, based largely on glowing reports of lush, fertile regions where wildlife was abundant. But according to new research, Lewis and Clark were extraordinarily lucky.

Unbeknownst to them, they had hit a narrow "window of opportunity" which created favorable images of the normally arid regions of the inland Northwest, according to geographer Paul A. Knapp of Georgia State University in Atlanta. The expedition, from 1804 to 1806, was sandwiched between two major droughts that could have left the explorers stranded and starving in a tragedy that could have had a profound impact on the young nation.

The explorers "traveled through the American Northwest during a climatically favorable period after one of the most severe droughts within the past several centuries, and they concluded their travel two years before the onset of another major drought," Knapp says in a report on his research in the current issue of the Bulletin of the American Meteorological Society.

Drought Avoided

Knapp has spent years studying tree rings in his native state of Oregon, in the area traversed by the Lewis and Clark expedition. Tree rings provide a reliable record of past climate because narrow rings show little growth and thus little moisture. Using his own records, and others collected by tree ring laboratories, Knapp became fascinated with a drought that struck in 1800.

"I call that the Lewis and Clark drought because it follows their path," he says. He began asking himself what it would have been like if the expedition had tried to cross that area in 1800 instead of 1805.

It could have been a really bad scene.

"There's no doubt they would have had a much more difficult time," he says. The expedition would have taken much longer because rivers would have been lower, thus forcing them to carry their boats over long stretches of parched land. And wild animals needed to feed the members of the expedition would have been much more scarce because of a lack of vegetation, and the result of that could have been disastrous. As it was, members of the party complained of nearly starving to death even under unusually favorable conditions.

Knapp says they were lucky because conditions could have been much worse, although they had no way of knowing that. Even Jefferson, who one historian has described as "probably the best-informed meteorologist in the United States" at the time, was dead wrong in what he thought the inland Pacific Northwest was like.

It was thought that the western part of the country was a mirror image of the east, looking a lot like Virginia, Knapp says. But that's way off the mark. Although the Pacific coast is rainy and lush, most of the region east of the Cascades is very arid and prone to droughts.

Jefferson, like many other scholars, believed the two coasts were connected by an inland waterway that could become a highway for western expansion. Lewis and Clark never found that, but they did find vast regions across the Great Plains and the far West that appeared lush and fertile, fueling Jefferson's dreams of creating vast farmlands to feed a growing nation.

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